Sulfation of "estrogenic" alkylphenols and 17beta-estradiol by human platelet phenol sulfotransferases

Association of SULT1A2 rs1059491 with obesity and dyslipidaemia in southern Chinese adults

In the sulfotransferase (SULT) superfamily, members of the SULT1 family mainly catalyse the sulfonation reaction of phenolic compounds, which is involved in the phase II metabolic detoxification process and plays a key role in endocrine homeostasis. A coding variant rs1059491 in the SULT1A2 gene has been reported to be associated with childhood obesity. This study aimed to investigate the association of rs1059491 with the risk of obesity and cardiometabolic abnormalities in adults. This case‒control study included 226 normal weight, 168 overweight and 72 obese adults who underwent a health examination in Taizhou, China. Genotyping of rs1059491 was performed by Sanger sequencing in exon 7 of the SULT1A2 coding region. Chi-squared tests, one-way ANOVA, and logistic regression models were applied. The minor allele frequencies of rs1059491 in the overweight combined with obesity and control groups were 0.0292 and 0.0686, respectively. No differences in weight and body mass index were detected between the TT genotype and GT + GG genotype under the dominant model, but the levels of serum triglycerides were significantly lower in G-allele carriers than in non-G-allele carriers (1.02 (0.74-1.32) vs. 1.35 (0.83-2.13) mmol/L, P = 0.011). The GT + GG genotype of rs1059491 versus the TT genotype reduced the risk of overweight and obesity by 54% (OR 0.46, 95% CI 0.22-0.96, P = 0.037) after adjusting for sex and age. Similar results were observed for hypertriglyceridaemia (OR 0.25, 95% CI 0.08-0.74, P = 0.013) and dyslipidaemia (OR 0.37, 95% CI 0.17-0.83, P = 0.015). However, these associations disappeared after correction for multiple tests. This study revealed that the coding variant rs1059491 is nominally associated with a decreased risk of obesity and dyslipidaemia in southern Chinese adults. The findings will be validated in larger studies including more detailed information on genetic background, lifestyle and weight change with age.

Computational Analysis of Chemical Space of Natural Compounds Interacting with Sulfotransferases

The aim of this study was to investigate the chemical space and interactions of natural compounds with sulfotransferases (SULTs) using ligand- and structure-based in silico methods. An in-house library of natural ligands (hormones, neurotransmitters, plant-derived compounds and their metabolites) reported to interact with SULTs was created. Their chemical structures and properties were compared to those of compounds of non-natural (synthetic) origin, known to interact with SULTs. The natural ligands interacting with SULTs were further compared to other natural products for which interactions with SULTs were not known. Various descriptors of the molecular structures were calculated and analyzed. Statistical methods (ANOVA, PCA, and clustering) were used to explore the chemical space of the studied compounds. Similarity search between the compounds in the different groups was performed with the ROCS software. The interactions with SULTs were additionally analyzed by docking into different experimental and modeled conformations of SULT1A1. Natural products with potentially strong interactions with SULTs were outlined. Our results contribute to a better understanding of chemical space and interactions of natural compounds with SULT enzymes and help to outline new potential ligands of these enzymes.

Multigenerational reproduction and developmental toxicity, and HPG axis gene expression study on environmentally-relevant concentrations of nonylphenol in zebrafish

Nonylphenol (NP) is a toxic xenobiotic compound, which is persistent in the aquatic environment and is extremely toxic to aquatic organisms. Although the exact molecular mechanisms of its toxic effect are well understood, the multigenerational reproduction and multigenerational - gene expression changes caused by NP still remain unclear. The following work investigated the effect of NP on four consecutive generations of zebrafish by examining their growth and several reproductive parameters, the degree of gonad damage, and the expression of related reproduction related genes. The results showed that high concentrations (20 and 200 μg·L^-1) of NP could decrease growth and induce gonad damage in zebrafish. In addition, gnrh2 and gnrh3 genes were up-regulated, and fshβ and lhβ genes were downregulated in the hypothalamus in male zebrafish; while in female fish, the fshβ and lhβ were upregulated in P and F1 generations, and then down-regulated in the F2 generation. Meanwhile, the cyp19a1a gene was downregulated in the gonad of male fish, while the genes of fshr, lhr and esr showed a downward trend in females. Compared to P generation, F2 generation was more tolerant to higher NP concentrations (20 and 200 μg·L^-1), as was also more sensitive to lower concentrations of NP (2 μg·L^-1). Consequently, stress and damage caused by environmentally-relevant concentrations of aquatic pollutants in a vertebrate model were measured and predicted. Prevention and control measures can be actively and effectively proposed, which might be transversal to other exposed organisms, including humans. After several generations, typical transgenerational genetic phenomena might occur, which should be addressed by further studies.

[Effects of Shoutai pills on immune function and oxidative stress in pregnant rats with di(2-ethylhexyl) phthalate exposure]

OBJECTIVE

To investigate the effects of Shoutai pills (a traditional Chinese medicinal preparation) on immune functions and oxidative stress in pregnant rats exposed to di(2-ethylhexyl) phthalate (DEHP).

METHODS

Thirty-six mature female SD rats were randomly divided into 3 groups (n=12). After pregnancy was confirmed, the rats were given 10 mL/kg corn oil +10 mL/kg saline (control group), 500 mg/kg DEHP+10 mL/kg saline (model group), and 500 mg/kg DEHP+10 mL/kg Shoutai pills (treatment group). At 19 days of gestation, the rats were sacrificed and the fetal rats were weighed and the numbers of live and stillborn fetal rats were recorded. Serum levels of interleukin-6 (IL-6), interleukin-2 (IL-2), tumor necrosis factor-ɑ (TNF-ɑ), estradiol (E2) and progesterone (P) levels were detected. The appearance, color and quality of the placenta in each group were recorded, and the placental tissues were examined pathologically. The total antioxidant capacity (T-AOC), superoxide dismutase (SOD), glutathione peroxidase (GSH- Px), catalase (CAT), reactive oxygen species (ROS) and malondialdehyde (MDA) in the placental tissues were measured.

RESULTS

Compared with the control group, the rats with DEHP exposure showed slow weight gain in the middle and late gestation period and significantly lower fetal weight (P < 0.05) with lowered serum levels of IL-2, IL-6 and TNF-ɑ, increased estradiol level (P < 0.05), decreased placental T-AOC, GSH-Px, SOD and CAT levels, and increased ROS and MDA levels (P < 0.01). Compared with the model group, the rats treated with Shoutai pills had significantly increased weight gain in mid and late pregnancy and greater fetal weight (P < 0.05) with significantly increased serum IL-2 and IL-6 levels, decreased estradiol level (P < 0.05), slightly increased TNF-ɑ expression (P> 0.05), increased placenta T-AOC, GSH- Px and CAT levels, decreased MDA level (P < 0.05), and slightly increased SOD and decreased ROS levels (P>0.05). No significant difference was found in progesterone levels among the groups (P>0.05). HE staining showed that the trophoblast in the placental tissue sponge in the model group was loose and irregular with numerous vacuoles. In the treatment group, the structure of the placenta remained intact with clearly visible labyrinth zone, sponge trophoblast and giant cell trophoblast, and the cell distribution in each layer was better than that in the model group.

CONCLUSIONS

Shoutai pills can regulate the immune function of DEHP-exposed pregnant rats possibly by antagonizing the estrogenlike effect of DEHP and regulating serum immune factors; Shoutai pills can also reduce placental tissue damage and improve pregnancy outcome by correcting DEHP-induced imbalance of oxidative stress in the placental tissues.

Adipose Tissue Gene Expression Associations Reveal Hundreds of Candidate Genes for Cardiometabolic Traits

Genome-wide association studies (GWASs) have identified thousands of genetic loci associated with cardiometabolic traits including type 2 diabetes (T2D), lipid levels, body fat distribution, and adiposity, although most causal genes remain unknown. We used subcutaneous adipose tissue RNA-seq data from 434 Finnish men from the METSIM study to identify 9,687 primary and 2,785 secondary cis-expression quantitative trait loci (eQTL; <1 Mb from TSS, FDR < 1%). Compared to primary eQTL signals, secondary eQTL signals were located further from transcription start sites, had smaller effect sizes, and were less enriched in adipose tissue regulatory elements compared to primary signals. Among 2,843 cardiometabolic GWAS signals, 262 colocalized by LD and conditional analysis with 318 transcripts as primary and conditionally distinct secondary cis-eQTLs, including some across ancestries. Of cardiometabolic traits examined for adipose tissue eQTL colocalizations, waist-hip ratio (WHR) and circulating lipid traits had the highest percentage of colocalized eQTLs (15% and 14%, respectively). Among alleles associated with increased cardiometabolic GWAS risk, approximately half (53%) were associated with decreased gene expression level. Mediation analyses of colocalized genes and cardiometabolic traits within the 434 individuals provided further evidence that gene expression influences variant-trait associations. These results identify hundreds of candidate genes that may act in adipose tissue to influence cardiometabolic traits.

Sulfotransferase 4A1 Increases Its Expression in Mouse Neurons as They Mature

Cytosolic sulfotransferases (SULTs) catalyze sulfation and play essential roles in detoxification of xenobiotics as well as inactivation of endobiotics. SULT4A1, which was originally isolated as a brain-specific sulfotransferase, is the most highly conserved isoform among SULTs in vertebrates. Here, expression of SULT4A1 was examined neuron enriched and neuron-glia mixed cells derived from mouse embryo brains at day 14 gestation and mixed glia from 2-day-old neonate brains. Western blots showed an increase of SULT4A1 expression as neurons maturated. Reverse-transcription polymerase chain reaction and agarose gel analysis found two different forms (variant and wild type) of SULT4A1 mRNA in neurons; the level of wild type correlated with the protein level of SULT4A1. SULT1E1 was not expressed in mouse brains, neuron-enriched cells, or mixed glia cells. SULT1A1 protein was only detected in adult brains. Immunofluorescence staining of neuron-glia mixed cells confirmed selective expression of SULT4A1 in neurons, including dopaminergic neurons, but not in either astrocytes or microglia. Thus, SULT4A1 is a neuron-specific sulfotransferase and may play a role in neuronal development.

Identification of Human Sulfotransferases Involved in Lorcaserin N-Sulfamate Formation

Lorcaserin [(R)-8-chloro-1-methyl-2,3,4,5-tetrahydro-1H-3-benzazepine] hydrochloride hemihydrate, a selective serotonin 5-hydroxytryptamine (5-HT) 5-HT(2C) receptor agonist, is approved by the U.S. Food and Drug Administration for chronic weight management. Lorcaserin is primarily cleared by metabolism, which involves multiple enzyme systems with various metabolic pathways in humans. The major circulating metabolite is lorcaserin N-sulfamate. Both human liver and renal cytosols catalyze the formation of lorcaserin N-sulfamate, where the liver cytosol showed a higher catalytic efficiency than renal cytosol. Human sulfotransferases (SULTs) SULT1A1, SULT1A2, SULT1E1, and SULT2A1 are involved in the formation of lorcaserin N-sulfamate. The catalytic efficiency of these SULTs for lorcaserin N-sulfamate formation is widely variable, and among the SULT isoforms SULT1A1 was the most efficient. The order of intrinsic clearance for lorcaserin N-sulfamate is SULT1A1 > SULT2A1 > SULT1A2 > SULT1E1. Inhibitory effects of lorcaserin N-sulfamate on major human cytochrome P450 (P450) enzymes were not observed or minimal. Lorcaserin N-sulfamate binds to human plasma protein with high affinity (i.e., >99%). Thus, despite being the major circulating metabolite, the level of free lorcaserin N-sulfamate would be minimal at a lorcaserin therapeutic dose and unlikely be sufficient to cause drug-drug interactions. Considering its formation kinetic parameters, high plasma protein binding affinity, minimal P450 inhibition or induction potential, and stability, the potential for metabolic drug-drug interaction or toxicological effects of lorcaserin N-sulfamate is remote in a normal patient population.

Fine Mapping of a GWAS-Derived Obesity Candidate Region on Chromosome 16p11.2

INTRODUCTION

Large-scale genome-wide association studies (GWASs) have identified 97 chromosomal loci associated with increased body mass index in population-based studies on adults. One of these SNPs, rs7359397, tags a large region (approx. 1MB) with high linkage disequilibrium (r2>0.7), which comprises five genes (SH2B1, APOBR, sulfotransferases: SULT1A1 and SULT1A2, TUFM). We had previously described a rare mutation in SH2B1 solely identified in extremely obese individuals but not in lean controls.

METHODS

The coding regions of the genes APOBR, SULT1A1, SULT1A2, and TUFM were screened for mutations (dHPLC, SSCP, Sanger re-sequencing) in 95 extremely obese children and adolescents. Detected non-synonymous variants were genotyped (TaqMan SNP Genotyping, MALDI TOF, PCR-RFLP) in independent large study groups (up to 3,210 extremely obese/overweight cases, 485 lean controls and 615 obesity trios). In silico tools were used for the prediction of potential functional effects of detected variants.

RESULTS

Except for TUFM we detected non-synonymous variants in all screened genes. Two polymorphisms rs180743 (APOBR p.Pro428Ala) and rs3833080 (APOBR p.Gly369_Asp370del9) showed nominal association to (extreme) obesity (uncorrected p = 0.003 and p = 0.002, respectively). In silico analyses predicted a functional implication for rs180743 (APOBR p.Pro428Ala). Both APOBR variants are located in the repetitive region with unknown function.

CONCLUSION

Variants in APOBR contributed as strongly as variants in SH2B1 to the association with extreme obesity in the chromosomal region chr16p11.2. In silico analyses implied no functional effect of several of the detected variants. Further in vitro or in vivo analyses on the functional implications of the obesity associated variants are warranted.

Single nucleotide polymorphisms in SULT1A1 and SULT1A2 in a Korean population

SULT1A1 and SULT1A2 are encoded on the same chromatid, and exhibit a 96% amino acid similarity. To screen for genetic variants in these two closely related genes, SULT1A1 and SULT1A2 were directly sequenced in 50 healthy Koreans. A total of 30 variations were identified in SULT1A1: eight in exons, thirteen in introns, and nine in the 5'-untranslated region. With regard to SULT1A2, 21 variants were identified, comprising seven in exons, five in introns, and nine in the 5'-untranslated region. Among these 51 variations, one in SULT1A1 and eight in SULT1A2 were previously unidentified, which include three coding variants (SULT1A2 R37Q, 110G>A; SULT1A2 G50S, 148G>A; SULT1A2 F286L, 3819C>A) and one null allele (SULT1A2 E217Stop, 3542G>T). Two LD blocks, major haplotype structures, and 7 haplotype-tagging SNPs were determined together for SULT1A1 and SULT1A2 as a single set. Frequencies of common functional variants were compared among ethnic groups. Since these two SULT enzymes are on the same chromatid in a parallel direction with overlapping substrate specificities, a combined analysis using LD and haplotype-tagging single-nucleotide polymorphisms (SNPs) will facilitate understanding of the variations in the sulfation reactions of a wide range of substrates, as compared with analysis of individual genes.

Effects of environmental relevant doses of pollutants from offshore oil production on Atlantic cod (Gadus morhua)

The release of produced water (PW), a by-product of offshore oil production, has increased in Norwegian waters in recent years. Alkylphenols (AP), a major component of PW, have been shown to have endocrine disrupting effects on several fish species. In the present study, four groups of female Atlantic cod (Gadus morhua) were orally exposed for 20 weeks to two different concentrations of a mixture of C4-C7 APs, PW or 17beta-estradiol. The transcriptional responses in the liver of Atlantic female cod were studied using a custom-made cDNA microarray. The largest transcriptional effects were seen in cod exposed to the lowest dose of APs. Several biological processes such as glycolysis, apoptosis and the general stress response were affected by exposure to APs. In addition, genes coding for the detoxification enzymes CYP1A and sulfotransferase 2 were up-regulated in the low exposure group. Significant reduction in gonadosomatic index (GSI) and the concentration of plasma vitellogenin were seen in both AP and 17beta-estradiol exposed cod. Exposure to PW had little effect on GSI and the regulation of stress responsive genes. The findings indicate that chronic exposure to low levels of APs may cause a stress response and delayed maturation in female cod.

Determination and residual characteristic of alkylphenols in household food detergents of Taiwan

The non-ionic surfactants are mostly composed of alkylphenols for the ingredients of synthetic food detergents. Due to the ability to mimic hormones, it has been noticed that the exposures of alkylphenols might cause a variety of adverse effects. To assess the associate risks from possible exposures, concentrations of alkylphenols, including 4-nonylphenol (4-NP), technical nonylphenol isomers (t-NP(S)), and 4-tert-octylphenol (4-t-OP), in household food detergents of Taiwan were determined. Gas chromatography with mass spectrometer (GC/MS) was used to analyze alkylphenols in samples. The Taguchi experimental design was utilized to study the possible factors that might affect the residual characteristics of alkylphenols from detergents on dishware and fruits. By the analysis of variance, the orders of importance of different parameters were determined. The results showed that the concentrations of alkylphenols in food detergents ranged from 1.71 x 10(-5) to 2.13 x 10(-3) (APs/detergent, mgg(-1)). For residual characteristics, the cleaning temperature was found to be the only significant factor that will affect the 4-t-OP left on the dishware, while the concentrations of detergents used will affect the left of t-NPs and 4-NP on dishware as well. On the other hand, the varieties of fruits, the concentrations of detergents, and the concentrations of alkylphenols were found to have significant effects for the t-NPs left on fruits. As for the exposure assessments, the maximum dose of APs exposures from the use of household food detergents in Taiwan was also estimated in the study.

Long-term study of urinary bisphenol A in elementary school children

OBJECTIVES

Due to its industrial application and frequent use as a coating material for food containers, bisphenol A (4,4'-isopropylidenediphenol, BPA) is present in abundance in our environment. Data on intake levels of BPA are limited in preadolescent children in Japan. This study was designed to help us better understand the current state of BPA exposure in children in Japan.

METHODS

We followed first graders (n = 104) attending school in a Tokyo suburb from 1998 until the sixth grade (2003), during which time we collected a total of three morning urine samples. Urinary BPA was analyzed using high-performance liquid chromatography isotope-dilution tandem mass spectrometry.

RESULTS

Ninety-four children were followed for 5 years. Median urinary BPA level was 2.66 ng/mg creatinine (CRE) (range 0.9-38.9) at first grade (1998), 1.52 ng/mg CRE (0.4-11.8) at third grade (2000), and 0.66 ng/mg CRE (0.2-8.5) at sixth grade (2003), showing a significant decrease in urinary BPA levels over a 5-year follow-up study (p < 0.001). No significant difference was seen between boys and girls at each grade.

CONCLUSIONS

Urinary levels of BPA were relatively low throughout the study period; however, as the study progressed, we observed a significant decline in levels, the reason behind which is not yet clear.

Pilot survey monitoring pharmaceuticals and related compounds in a sewage treatment plant located on the Mediterranean coast

A one-year monitoring study was performed to evaluate the occurrence, persistence and fate of a group of 14 organic compounds in a sewage treatment plant (STP) located in the south of Spain. These results are part of a more extensive study, financed by the Spanish Ministry of Research with the aim to evaluate the traceability of new pollutants on the Mediterranean coast and to determine the removal efficiency of sewage treatment plants (STP) for these pollutants. The compounds which have been analyzed include pharmaceuticals of various therapeutic categories (ibuprofen, acetaminophen, dipyrone, diclofenac, carbamazepine and codeine), pesticides (chlorfenvinfos and permethrin), caffeine, triclosan, bisphenol A and three of their more relevant metabolites (1,7-dimethylxanthine, carbamazepine 10,11-epoxide and 2,7/2,8-dichlorodibenzo-p-dioxin). An SPE/GC-MS multi-residue analytical method was developed and validated to facilitate simultaneous determination of these compounds in both influent and effluent wastewater. The method provided mean recoveries higher than 75%, with the exception of 2,7/2,8-dichlorodibenzo-p-dioxin, dipyrone and permethrin which exhibited recoveries lower than 22%. The overall variability of the method was below 14%. The method detection limit (LOD) was between 1 and 100 ng l(-1) and precision, which was calculated as relative standard deviation (RSD), ranged from 1.8% to 11.2%. The application of the proposed method has allowed the identification of all the target compounds at mean concentrations which ranged from 0.12 to 134 microg l(-1) in the influent and from 0.09 to 18.0 microg l(-1) in the effluent. The removal efficiencies of the STP for these compounds varied from 20% (carbamazepine) to 99% (acetaminophen), but in all cases resulted insufficient in order to avoid their presence in treated water and subsequently in the environment.

Development and validation of a fluorescence HPLC-based screening assay for inhibition of human estrogen sulfotransferase

Human estrogen sulfotransferase (SULT1E1) is involved in the regulation of 17beta-estradiol responsiveness and is believed to protect peripheral tissues from excessive estrogenic effects. Several assays already have been developed to investigate the inhibitory effect of endocrine-disrupting compounds (EDCs) on SULT1E1. However, most of these assays make use of the radiolabeled cofactor [(35)S]3'-phosphoadenosine 5'-phosphosulfate (PAPS) or radiolabeled substrate [(3)H]estradiol. In this article, we describe the development and validation of an assay for the inhibition of human SULT1E1 that is rapid and simple and that uses the nonradioactive and noncarcinogenic 1-hydroxypyrene. A gradient HPLC separation of 15 min using a C18-RP column was developed to detect 1-hydroxypyrene and its metabolite pyrene 1-sulfate fluorescently. Time- and protein-dependent formation of pyrene 1-sulfate was investigated, and enzyme kinetics was determined (K(m)=6.4+/-0.8 nM and V(max)=158+/-19 pmol/min/microg SULT1E1). At higher 1-hydroxypyrene concentrations, the assay displayed non-Michaelis-Menten kinetics involving substrate inhibition. IC(50) values have been determined for eight known SULT1E1 inhibitors or competing substrates (17beta-estradiol, 17alpha-estradiol, genistein, 17alpha-ethynylestradiol, estrone, diethylstilbestrol, estriol, and hexestrol) and two previously unknown SULT1E1 inhibitors (zearalenone and dienestrol). The method was demonstrated to be easy, feasible, and highly reproducible for SULT1E1 screening assay inhibition studies.

Sulfotransferase activities towards xenobiotics and estradiol in two marine fish species (Mullus barbatus and Lepidorhombus boscii): characterization and inhibition by endocrine disrupters

We have characterized hepatic phenol sulfotransferase (SULT) activities in two benthic fish species, Mullus barbatus and Lepidorhombus boscii, using p-nitrophenol, dopamine, 17beta-estradiol, 4-nonylphenol, and 1-naphthol as substrates. High affinity sulfation of 17beta-estradiol was observed in both species (Km=28-75 nM), suggesting the presence of a specific estrogen sulfotransferase that catalyzes the formation of estradiol-3 sulfate. Among the tested compounds, 1-naphthol was the most effective substrate for sulfation, with Vmax/Km ratios several hundred-fold higher than the other substrates examined. Both species sulfated the tested compounds, but only M. barbatus was able to sulfate dopamine. We also tested the inhibitory effects of common marine pollutants with estrogenic (4-nonylphenol) and androgenic (tributyltin, triphenyltin) properties on p-nitrophenol and 17beta-estradiol SULT activities. 4-Nonylphenol and triphenyltin inhibited sulfation of both substrates at micromolar concentrations in both species. However, tributyltin was only effective against SULTs from L. boscii, again at micromolar concentrations. The data indicate that M. barbatus and L. boscii are able to sulfate a range of xenobiotics and endogenous compounds, and inhibition of these activities by environmental pollutants may contribute to the known toxic effects of these compounds.

The immune system as a target for environmental chemicals: Xenoestrogens and other compounds

The immune system in higher organisms is under integrated control and has the capacity to rapidly respond to the environment. Recently, there has been a significant increase in the prevalence of allergic diseases. Environmental factors likely play a major role in the explosion of allergy. Although the "hygiene hypothesis" may explain the increase in allergic diseases which are prone to T helper 2 (Th2) immune responses, recent findings highlight the possible involvement of environmental xenobiotic chemicals which can modulate normal immune function. Interestingly, several reports suggest that the prevalence of systemic lupus erythematosus, a Th2-type autoimmune disease, is also increasing, although the development of high-sensitivity immunological tests may be a possible cause. The increased prevalence of autoimmune disease in women, the sexual dimorphism of the immune response, and the immunomodulatory effects of sex steroids, have focused attention on the role of chemicals which influence sex steroids in the development of immune diseases. Moreover, recent reports indicate that some environmental chemicals can work on nuclear hormone receptors, other than sex hormone receptors, and modulate immune reactions. This review focuses on the impact of environmental chemicals on immune system function and pathogenesis of immune diseases, including allergy and autoimmune diseases.

Identification of genetic networks involved in the cell injury accompanying endoplasmic reticulum stress induced by bisphenol A in testicular Sertoli cells

To identify detailed mechanisms by which bisphenol A (BPA), an endocrine-disrupting chemical, induces cell injury in mouse testicular Sertoli TTE3 cells, we performed genome-wide microarray and computational gene network analyses. BPA (200muM) significantly decreased cell viability and simultaneously induced an increase in mRNA levels of HSPA5 and DDIT3, endoplasmic reticulum (ER) stress marker genes. Of the 22,690 probe sets analyzed, BPA down-regulated 661 probe sets and up-regulated 604 probe sets by >2.0-fold. Hierarchical cluster analysis demonstrated nine gene clusters. In decreased gene clusters, two significant genetic networks were associated with cell growth and proliferation and the cell cycle. In increased gene clusters, two significant genetic networks including many basic-region leucine zipper transcription factors were associated with cell death and DNA replication, recombination, and repair. The present results will provide additional novel insights into the detailed molecular mechanisms of cell injury accompanying ER stress induced by BPA in Sertoli cells.

Sperm motility in the Pacific oyster (Crassostrea gigas) is affected by nonylphenol

Nonylphenol, a widespread aquatic pollutant with endocrine-disrupting potential has been found to affect sperm motility in the Pacific oyster, Crassostrea gigas (Thunberg). This marine invertebrate, a global aquaculture species, was exposed to nonylphenol at concentrations of 1 and 100 microg l(-1) for a duration of 72 h during the period of gametogenesis. Growth was monitored at regular intervals until sexual maturity when sperm motility was assessed. The growth rate of C. gigas remained unaffected by exposure to nonylphenol during gametogenesis. However, the number of individuals with motile sperm was significantly reduced.

Non-genomic effects of endocrine disrupters: inhibition of estrogen sulfotransferase by phenols and chlorinated phenols

Phenols are used world-wide and their presence in the environment is a cause of increasing concern. Despite evidence to suggest that, in general, they bind poorly to estrogen receptors, they are suspected of being endocrine disrupters. Here, we show that 2, x-substituted phenols are potent inhibitors of estrogen sulfotransferase with IC(50) values at low- or sub-micromolar levels. Our results demonstrate a potential non-genomic mechanism of action for these compounds and suggest that, where viable alternatives exist, both phenols substituted in the 2-position and their metabolic precursors should be avoided.

Comparative study of the estrogenic responses of mirror carp (Cyprinus carpio) exposed to treated municipal sewage effluent (Lisbon) during two periods in different seasons

To assess the estrogenic potency of the treated domestic sewage effluent from a sewage treatment plant (STP) located in Lisbon (Chelas), 60 mirror carp (Cyprinus carpio) were exposed to different concentrations of the sewage effluent (0%, 25%, 50% and 100%) for two periods of 28 days in two different seasons (winter/spring). Vitellogenin induction in males was used as a biomarker of exposure to xenoestrogens. At the end of the experiment, blood samples were taken for vitellogenin analysis and the fish were sacrificed and dissected. Gonad samples were taken for histological evaluation of the sewage effects. The results showed an increase in vitellogenin induction in exposed fish, both males and females, depending on the different dilutions of the sewage effluent. In comparison with controls, the gonadosomatic index decreased significantly (P < 0.05) in fish exposed to 100% treated effluent. Although statistically not significant, the hepatosomatic index (HSI) was high in all exposed fish. Histological abnormalities in fish gonads were evaluated and related to the different percentages of sewage effluent. Seasonal variations found in estrogenic responses were attributed to weather influences on sewage dilution.

Sulfotransferase 2A1 forms estradiol-17-sulfate and celecoxib switches the dominant product from estradiol-3-sulfate to estradiol-17-sulfate

Using recombinant sulfotransferases (SULTs) expressed in E. coli, beta-estradiol (E2) sulfonation was examined to determine which SULT enzyme is responsible for producing E2-17-sulfate (E2-17-S). SULTs 1A1*1, 1A1*2, 1A3, 1E1 and 2A1 all sulfated E2 to varying extents. No activity was observed with SULT1B1. Among the SULTs studied, SULT2A1 produced primarily E2-3-sulfate (E2-3-S), but also some E2-17-S and trace amounts of E2 disulfate. SULT2A1 had a K(m) value of 1.52 microM for formation of E2-3-S and 2.95 microM for formation of E2-17-S. SULT2A1 had the highest V(max) of 493 pmol/min/mg protein for formation of E2-3-S, which was 8.8- and 47-fold higher than the maximal rates of formation of E2-17-S and E2 disulfate, respectively. SULT2A1 formed E2-3-S more efficiently. However, when celecoxib (0-160 microM) was included in the incubation with either SULT2A1 or human liver cytosol, sulfonation switched from E2-3-S to E2-17-S in a concentration-dependent manner. The ratio of E2-17-S/E2-3-S went up to 15 with SULT2A1, and was saturated at 1 with human liver cytosol. In both cases, more E2-17-S was formed, with the unreacted E2 remained unchanged, suggesting celecoxib probably bound to a separate effector site to cause a conformational change in SULT2A1, which favored production of E2-17-S. The ability of celecoxib to alter the position of sulfonation of E2 may in part explain its success in the experimental prevention and treatment of breast cancer.

Common genetic polymorphisms in the 5'-flanking region of the SULT1A1 gene: haplotypes and their association with platelet enzymatic activity

SULT1A1 is a phase II detoxification enzyme involved in the biotransformation of a wide variety of endogenous and exogenous phenolic compounds. Human platelet SULT1A1 enzymatic activity shows marked inter-individual variability and a common coding polymorphism, SULT1A1*1/*2, has been described that accounts for a proportion of this variability. We examined the 5'-flanking region of the SULT1A1 gene to determine if genetic variability in this portion of the gene influenced enzymatic activity. Direct sequencing revealed five common genetic polymorphisms (-624G>C, -396G>A, -358A>C, -341C>G and -294T>C) that were present at different allele frequencies in Caucasian, African-American and Chinese groups. Platelet SULT1A1 enzymatic activity was significantly correlated with individual promoter region polymorphisms and the associations were different between African-Americans and Caucasians. Haplotypes were constructed and platelet enzymatic activity according to haplotype was examined. The haplotypes were also significantly correlated with activity; haplotypes GAACT and GGACT (accounting for 13% and 5% of inter-individual variability in platelet activity, respectively) were important in Caucasians while haplotypes GAACC, GAACT and GGACC (accounting for 8%, 5% and 4% of variability) were significantly associated with activity in African-Americans. The coding region polymorphism, SULT1A1*1/*2 was in linkage disequilibrium with the promoter region polymorphisms and showed no effect on activity when examined in the context of the 5'-flanking region polymorphisms. These studies indicate that variation in the promoter region of the SULT1A1 gene exerts a significant influence on enzymatic activity.

Are all EDC effects mediated via steroid hormone receptors?

Despite the surge of interest in the endocrine disruption field, there is still no globally accepted definition of the term. There is a great political will to test chemicals to determine whether they have endocrine disrupting potential. This is a huge task and the US Environmental Protection Agency has taken the lead by setting up an Endocrine Disruptor Screening and Testing Advisory Committee (EDSTAC), which with international co-operation, will ultimately deliver a validated testing strategy to detect endocrine disrupting chemicals (EDCs) in humans and wildlife. One of the major developments will be the use of high throughput pre-screening (HTPS) methods that will detect binding to steroid receptor hormones, although many other testing methods will be employed. This paper describes two mechanisms of EDC action that are not mediated via steroid receptors; firstly, the suppression of fetal testosterone synthesis in rodents by in utero exposure to phthalates; and secondly, the ability of several chemicals to interfere with steroid metabolism by inhibiting estrogen sulfotransferases. These examples will be discussed with reference to pertinent human disorders, which have been associated with exposure to EDCs. Issues and questions about how scientists and regulators can deal with these types of chemicals or potential mechanisms in a risk assessment paradigm are raised.

Effects of endocrine disrupters on sex steroid synthesis and metabolism pathways in fish

The interactions of estrogenic (nonylphenol, dicofol, atrazine), androgenic (organotins, phthalates, fenarimol) and anti-androgenic compounds (vinclozolin, diuron, p,p'-DDE) with key enzymatic activities involved in both synthesis and metabolism of sex hormones was investigated. Carp testicular microsomes incubated in the presence of androstenedione and different xenobiotics evidenced higher sensitivity of 5alpha-reductase activity than 17beta-hydroxysteroid dehydrogenase activity towards those chemicals. Dicofol, organotins and phthalates were among the most effective inhibitors. In contrast, ovarian synthesis of maturation-inducing hormones (20alpha- and 20beta-hydroxysteroid dehydrogenase activities) were enhanced by nonylphenol, dicofol, fenarimol and p,p'-DDE. Metabolic clearance pathways of hormones were also affected. Fenarimol, nonylphenol and triphenyltin inhibited the glucuronidation of testosterone and estradiol at concentrations as low as 10, 50 and 100 microM, respectively. Triphenyltin, tributyltin and nonylphenol were also inhibitors of estradiol sulfation with IC(50) values of 17, 18 and 41 microM. Overall, the data indicates the interaction of selected chemicals with key enzymatic pathways involved in both synthesis and metabolism of sex hormones. This interference might be one of the underlying mechanisms for the reported hormonal disrupting properties of the tested compounds, and might finally affect physiological processes such as gamete growth and maturation.

Analysis of endocrine disrupting alkylphenols, chlorophenols and bisphenol-A using hollow fiber-protected liquid-phase microextraction coupled with injection port-derivatization gas chromatography–mass spectrometry

Liquid-phase microextraction (LPME) coupled with gas chromatography-mass spectrometry were used to determine alkylphenols (APs), chlorophenols (CPs) and bisphenol-A (BPA) in aqueous samples. APs, CPs and BPA are highly polar compounds and need to be derivatized before analysis by GC-MS. In this work, they were derivatized in the GC injection port with bis(trimethylsilyl)trifluoroacetamide (BSTFA). The analytes were extracted directly from 5 ml of sample solution using 5 microl of organic solvent though a porous polypropylene hollow fiber. The hollow fiber, filled with an immiscible organic solvent (ca. 5 microl), was immersed in the sample solution which was stirred during the 30-min extraction. An aliquot (2 microl) of the extract and 2 microl of BSTFA were then consecutively injected into the GC injection port. Extraction parameters such as extraction time, pH of sample, concentration of salt added, and stirring rate were optimised. The proposed LPME provided a good average enrichment factor of up to 162-fold, reproducibility ranging from 5.9 to 13.9% (n = 4), and good linearity (r2 = 0.995) for spiked water samples. The limits of detection (LODs) ranged between 0.005 and 0.015 microgl(-1) (S/N = 3) using GC-MS with selective ion monitoring and limits of quantification were in the range of 0.012-0.026 microg l(-1). A comparative study was performed between LPME, headspace solid-phase microextraction (HS-SPME) and liquid-liquid extraction (LLE). The results obtained suggested that hollow fiber LPME was a rapid, simple and efficient technique for APs, CPs and BPA, and provided a good alternative to SPME and LLE. Finally, the proposed method was applied to monitor Singapore coastal water samples.

Distribution characteristics of nonylphenols in the artificial Lake Shihwa, and surrounding creeks in Korea

Nonylphenols were determined from the water, suspended particle, and sediment samples taken from the Lake Shihwa in Korea and its surrounding creeks flowing through municipal and industrial areas, and into the lake. The nonylphenols were detected at the concentration ranges of 0.0-41.3 microg/l, 0.0-116.6 and 0.3-31.7 mg/kg in water, suspended particle and sediment samples respectively. The contamination levels of nonylphenols were increased along the down stream. Considerably high levels of nonylphenols were found at the industrial area compared to the municipal area. No remarkable differences were found between the isomer patterns of nonylphenols for the sample matrices of each sampling site, i.e. water, suspended solids and sediment. Strong correlations between water and sediment with 10(5.2) of the mean partition coefficient (Koc ) were observed. These indicate that most of nonylphenols came from industrial wastewater at high level. It is thought that the water quality of the Lake Shihwa is affected greatly by industrial environments surrounding.

Nonylphenol enhances apoptosis induced by serum deprivation in PC12 cells

Although nonylphenol is well known as an endocrine disrupting chemical, there is little information concerning biological effect of nonylphenol. In this study, we investigated effect of nonylphenol on apoptosis induced by serum deprivation in PC12 cells using TUNEL and DNA fragmentation assays. In addition, changes in contents of proapoptotic factors, Bad and Bax, and antiapoptotic factor, Bcl-2, and enzyme activity of caspase-3 were studied. Below 100 ng/ml of nonylphenol increased TUNEL signals, DNA fragmentation and content of proapoptotic factor, Bad as compared to those by serum deprivation without nonylphenol. Furthermore, addition of nonylphenol enhanced caspase-3 activity and Z-VAD, caspase-3 inhibitor, diminished such effect. These results indicated that below 100 ng/ml of nonylphenol enhanced apoptosis induced by serum deprivation via caspase-3 activation in PC12 cell.

Active site mutations and substrate inhibition in human sulfotransferase 1A1 and 1A3

Human SULT1A1 is primarily responsible for sulfonation of xenobiotics, including the activation of promutagens, and it has been implicated in several forms of cancer. Human SULT1A3 has been shown to be the major sulfotransferase that sulfonates dopamine. These two enzymes shares 93% amino acid sequence identity and have distinct but overlapping substrate preferences. The resolution of the crystal structures of these two enzymes has enabled us to elucidate the mechanisms controlling their substrate preferences and inhibition. The presence of two p-nitrophenol (pNP) molecules in the crystal structure of SULT1A1 was postulated to explain cooperativity at low and inhibition at high substrate concentrations, respectively. In SULT1A1, substrate inhibition occurs with pNP as the substrate but not with dopamine. For SULT1A3, substrate inhibition is found for dopamine but not with pNP. We investigated how substrate inhibition occurs in these two enzymes using molecular modeling, site-directed mutagenesis, and kinetic analysis. The results show that residue Phe-247 of SULT1A1, which interacts with both p-nitrophenol molecules in the active site, is important for substrate inhibition. Mutation of phenylalanine to leucine at this position in SULT1A1 results in substrate inhibition by dopamine. We also propose, based on modeling and kinetic studies, that substrate inhibition by dopamine in SULT1A3 is caused by binding of two dopamine molecules in the active site.

Alkylphenol endocrine disrupters inhibit IP3-sensitive Ca2+ channels

We have investigated the influence of alkylphenol endocrine disrupters and the synthetic estrogen diethylstilbestrol (DES) on inositol-1,4,5-trisphosphate (IP(3))-sensitive Ca(2+) channels from porcine cerebellum and rat testicular membranes. All alkylphenols and DES inhibited the extent of IP(3)-induced Ca(2+) release (IICR) from both cerebellar and testicular microsomes. 4-n-nonylphenol was the most potent compound tested (IC(50), 8 microM). Inhibition of IICR was directly related to the length and hydrophobicity of the alkylphenol side chain. None of the alkylphenols or DES appeared to influence the concentration dependence of IICR nor did they have a significant effect on [3H]IP(3) binding to the membranes. An investigation of the effects of nonylphenol on the transient kinetics of IICR showed that it inhibited the rate constants for both the fast and the slow phases of IICR and also the extent of Ca(2+) release. These results illustrate another mechanism by which these environmental pollutants can disrupt endocrine function without the involvement of estrogen receptors.

cDNA microarray analysis reveals chop-10 plays a key role in Sertoli cell injury induced by bisphenol A

We examined the time course of changes in gene expression in detail using cDNA microarray analysis of mouse Sertoli TTE3 cells treated with bisphenol A (BPA). A subtoxic dose of BPA (200 microM) transiently increased intracellular Ca(2+) concentration and time-dependently induced an increase in mRNA level of 78-kDa glucose-regulated protein, indicating that BPA induces endoplasmic reticulum stress. Of the 865 genes analyzed, 31 genes showed increased levels of expression. TaqMan analysis confirmed that the mRNA levels of chop-10, fra-2, c-myc, and ornithine decarboxylase were increased, and showed that chop-10 is the most sensitive gene. The expression level of chop-10 protein and cell injury induced by BPA were significantly reduced in stable TTE3 cells overexpressing full-length chop-10 antisense RNA. We conclude that chop-10 plays a key role in Sertoli cell injury induced by BPA.

Tamoxifen induction of aryl sulfotransferase and hydroxysteroid sulfotransferase in male and female rat liver and intestine

The antiestrogenic drug tamoxifen (TAM) is widely used in the treatment of breast cancer. Species-specific mutagenic and carcinogenic potentialities have been reported and have raised concerns. Sulfotransferases (STs) are important phase II drug-metabolizing enzymes. STs are involved in the sulfation processes of some TAM metabolites (i.e., alpha-hydroxy tamoxifen and 4-hydroxy tamoxifen). Regulation of drug-metabolizing enzymes is important for the understanding of drug metabolism and detoxification. Studies on ST induction are limited. In the present investigation, protein and mRNA expression of aryl sulfotransferase (AST-IV) and hydroxysteroid sulfotransferase (STa) have been studied in liver and intestine of male and female Sprague-Dawley rats after TAM treatment with either 6.8 or 68 mg/kg/day for 1 or 2 weeks. Enzyme assay and Western blot methods were used for protein level determination; reverse transcription-polymerase chain reaction method was used for mRNA level determination. Here, for the first time, we have demonstrated that AST-IV and STa could be induced in intestine by tamoxifen. Furthermore, intestinal inductions were found to be much greater than the inductions found in the liver, suggesting a distinct potentiality of intestinal cells in TAM metabolism. The impact of induction and regulation of intestinal STs on TAM metabolism with respect to its toxicity has yet to be studied. The role of STs induction and relevant TAM metabolism is discussed in the context of organ- and species-specific variable carcinogenic manifestations.

Environmental endocrine disrupters dysregulate estrogen metabolism and Ca2+ homeostasis in fish and mammals via receptor-independent mechanisms

Xenoestrogen endocrine disrupters (EDs) in the environment are thought to be responsible for a number of examples of sexual dysfunction that have recently been reported in several species. There is growing concern that these compounds may also cause abnormalities of the male reproductive tract and reduced spermatogenesis in man. Whilst some effects of EDs may be receptor-mediated, there is growing evidence that these compounds can exert potent effects in vivo by directly interacting with cellular enzyme targets. Here we report on, and review, the effects of alkylphenols and other EDs on two such enzymes: (1) sulfotransferases, which convert active estrogenic steroids to inactive steroid sulfates; and (2) Ca(2+)-ATPases, which are responsible for maintaining low, physiological, intracellular Ca(2+) concentrations. These enzymes are potently inhibited by EDs in both fish and mammalian species. The increased concentrations of active estrogens and the likely cytotoxic effects of elevated concentrations of intracellular Ca(2+) arising from these effects may underlie some of the endocrine disrupting potential of these widespread industrial pollutants.

Human gastrointestinal sulfotransferases: identification and distribution

Sulfotransferases (STs) catalyze the sulfation of many structurally diverse molecules. Enzymatic assays and Western blots have been used to identify and characterize STs in the human gastrointestinal tract. Sulfation activities for 2-naphthol, dopamine, estradiol, and dehydroepiandrosterone (DHEA) from 23 donors were measured in cytosol prepared from stomach, duodenum, segments of small intestine, and colon and were compared to levels in human liver cytosol. Stomach and colon had low 2-naphthol and dopamine sulfation activities and almost no estradiol and DHEA sulfation activity. For all four substrates, small intestine has higher activities than both stomach and colon. Human small intestine 2-naphthol sulfation specific activity is approximately half that of human liver. Human small intestine dopamine sulfation activity is three times as high as that of human liver. While estrogen sulfation activity is about the same for both human intestine and human liver, human liver DHEA sulfation activity is about five times as high as that of human small intestine. The distribution of ST activities along the length of the small intestine was very different among different donors. Some donors had higher activity in the proximal segments of the small intestine, whereas other donors had higher activity in the distal segments of the small intestine. Our results also demonstrated high variation of small intestine sulfation activities compared with human liver activities among different donors. The Western blot results agreed with the enzymatic assay results. These results suggest that xenobiotics may regulate human small intestinal STs.

DNA microarray analysis of differentially expressed genes responsive to bisphenol A, an alkylphenol derivative, in an in vitro mouse Sertoli cell model

To identify genes elicited by bisphenol A (BPA) in Sertoli cells, we carried out a microarray analysis of TTE3 cells (a mouse Sertoli cell line) treated with BPA. BPA (100, 200 and 400 microM) induced cell death concentration-dependently, with levels being 25%, 33% and 96%, respectively. Of the 1,081 genes analyzed, 3 genes showed decreased levels of expression while the remaining 10 genes showed increased levels in the cells treated with a subtoxic dose of BPA (200 microM). The expressions of six genes were confirmed by the TaqMan assay. These findings suggest that DNA microarray analysis is a useful tool for investigating the molecular mechanisms of the toxic effects of BPA in testicular cells.

Sulfation of Environmental Estrogens by Cytosolic Human Sulfotransferases

It is known that in humans taking soy food, the phytoestrogens, daidzein (DZ) and genistein (GS), exist as sulfates and glucuronides in the plasma and are excreted as conjugates in urine. To investigate which human sulfotransferase (SULT) isoforms participate in the sulfation of these phytoestrogens, the four major cytosolic SULTs, SULT1A1, SULT1A3, SULT1E1, and SULT2A1, occurring in the human liver were bacterially expressed as His-tagged proteins and chromatographically purified to homogeneity in the presence of Tween 20 and glycerol as highly efficient agents for stabilizing the recombinant enzymes. All the SULTs showed sulfating activity toward both DZ and GS. However, k(cat)/K(m) values observed indicated that these phytoestrogens were sulfated predominantly by SULT1A1 and SULT1E1 with K(m) values of 0.3 and 0.7 microM for GS and 1.9 and 3.4 microM for DZ, respectively. DZ and GS strongly inhibited the sulfation of the endogenous substrate, beta-estradiol, by SULT1E1 in a non-competitive manner with K(i) values of 14 and 7 microM, respectively, suggesting that these phytoestrogens might affect tissue levels of beta-estradiol in the human. The phenolic endocrine-disrupting chemicals, bisphenol A (BPA), 4-n-nonylphenol (NP), and 4-t-octylphenol (t-OP), were used as substrates to investigate the possible participation of human SULTs in their metabolism for excretion. High k(cat)/K(m) values were observed for the sulfation of BPA by SULT1A1, NP by SULT1A1 and SULT1E1, and t-OP by SULT1E1 and SULT2A1.

Estrogenic alkylphenols induce cell death by inhibiting testis endoplasmic reticulum Ca(2+) pumps

Industrial alkylphenols in the environment may act as "xenoestrogens" to disrupt testicular development and decrease male fertility. Amongst possible targets for these compounds are testicular Sertoli cells, which nurture the developing sperm cells. We demonstrate that SERCA 2 and 3 Ca(2+) pumps are relatively abundant in rat testis microsomal membranes, and also in Sertoli, myoid, and TM4 cells (a Sertoli cell line). A number of estrogenic alkylphenols such as nonylphenol, octylphenol, bisphenol A, and butylated hydroxytoluene all inhibit testicular Ca(2+) ATPase in the low micromolar concentration range. These agents also mobilize intracellular Ca(2+) in intact TM4 cells in a manner consistent with the inhibition of ER Ca(2+) pumps. Alkylphenols dramatically decrease the viability of TM4 cells, an effect that is reversed by either a caspase inhibitor or by BAPTA, and is therefore consistent with Ca(2+)-dependent cell death via apoptosis. We postulate that alkylphenols disrupt testicular development by inhibiting ER Ca(2+) pumps, thus disturbing testicular Ca(2+) homeostasis.

Identification of novel metabolites of the xenoestrogen 4-tert-octylphenol in primary rat hepatocytes

A number of environmental pollutants, including 4-tert-alkylphenols, can mimic the actions of endogenous steroids and have the potential to disrupt the endocrine function in humans and animals. The biotransformation of a 4-tert-alkylphenol in isolated rat hepatocytes was studied in order to determine the possible fate and activity of these xenoestrogens in higher vertebrates. Hepatocytes were incubated with 30 microM 4-(1',1',3', 3'-tetramethylbutyl)[U-(14)C]phenol (4-tert-octylphenol; t-OP) for up to 60 min. Radiolabelled metabolites were detected by radio-HPLC and the structures determined by gas chromatography-mass spectrometry (GC-MS) analysis of the conjugated or aglycone products. After a 15 min incubation, over 97% of t-OP was metabolised to a complex mixture of metabolites. The initial metabolites formed were identified as products of hydroxylation of the aromatic ring to form catechols and methylated catechols, as well as glucuronide conjugates of the catechol metabolites or parent phenol. These products were further metabolised by hydroxylation of the alkyl chain followed by glucuronide conjugation of the alkoxy group. The conjugated metabolites of t-OP are unlikely to retain estrogen receptor activity, however t-OP is metabolised by some pathways that are similar to that of estrogen catabolism, namely by ortho-hydroxylation to form catechols, methylation by catechol O-methyltransferases and ring conjugation by uridine diphosphoglucuronosyl transferases. Further investigations are needed to determine whether 4-tert-alkylphenols can alter circulating sex steroid profiles by acting as substrates of enzymes determining estrogen metabolism and excretion.