A proposed nomenclature system for the cytosolic sulfotransferase (SULT) superfamily

Transformation of zearalenone to zearalenone-sulfate by Aspergillus spp

The primary goal of this research was to assess the biotransformation of zearalenone (ZEA), an oestrogenic mycotoxin, into ZEA-sulfate by some Aspergillus section Nigri isolates. A. niger isolates were shown to be able to convert ZEA after 72 h of incubation at different ZEA concentrations (5 to 150 µg/ml). The product formula corresponding to ZEA-sulfate was determined by accurate mass measurement. This conjugate was shown to be less oestrogenic than ZEA using a MCF-7 proliferation assay. This study demonstrated that A. niger has the ability to transform ZEA over a broad range of ZEA concentrations (5 to 150 µg/ml) and that sulfonation could lead to a less toxic compound. These results are significant as little is known about the ability of fungi, and especially A. niger, to detoxify ZEA by sulfonation. This study could lead to a way of detoxifying feed naturally contaminated with mycotoxins.

Characterization of iodothyronine sulfotransferase activity in the cytosol of Rana catesbeiana tadpole tissues

We have investigated the sulfation of thyroid hormones (THs) in the cytosol from Rana catesbeiana tadpole tissues. Sulfation of 3,3',5-triiodothyronine (T(3)) by the liver cytosol, which was dependent on protein amount, incubation time, and temperature, suggested the presence of TH sulfotransferases (SULTs) in the liver. The apparent Michaelis-Menten constant (K(m)) of the liver cytosol was 0.22 microM for T(3), and the apparent maximum velocity (V(max)) of the liver cytosol was 7.65 pmol/min/mg protein for T(3). Iodothyronine sulfating activity in the liver cytosol was increased in tadpoles at premetamorphic (stages IX-X) and metamorphic climax (stage XX) stages, and in adult frogs. The substrate preference of iodothyronine sulfation for the liver cytosol from tadpoles (stage X) was: 3,3',5'-triiodothyronine>T(3)>3,3',5,5'-tetraiodothyroacetic acid>3,3',5-triiodothyroacetic acid, T(4), 3-iodothyronine>3,5-diiodothyronine. Several halogenated phenols were potent inhibitors (IC(50)=0.15-0.21 microM). The substrate preference for T(3) was gradually lost by the onset of metamorphic climax stages. These enzymatic characteristics of iodothyronine sulfation in the liver cytosol from tadpoles resembled those of mammalian phenol SULTs, except that the tadpole cytosol had a higher affinity (one or two orders of magnitude) for T(3) than mammalian SULTs. These results suggested that an enzyme homologous to mammalian phenol SULT (SULT1) may be involved in TH metabolism in tadpoles.

Phase II metabolism of hesperetin by individual UDP-glucuronosyltransferases and sulfotransferases and rat and human tissue samples

Phase II metabolism by UDP-glucuronosyltransferases (UGTs) and sulfotransferases (SULTs) is the predominant metabolic pathway during the first-pass metabolism of hesperetin (4'-methoxy-3',5,7-trihydroxyflavanone). In the present study, we have determined the kinetics for glucuronidation and sulfonation of hesperetin by 12 individual UGT and 12 individual SULT enzymes as well as by human or rat small intestinal, colonic, and hepatic microsomal and cytosolic fractions. Results demonstrate that hesperetin is conjugated at positions 7 and 3' and that major enzyme-specific differences in kinetics and regioselectivity for the UGT and SULT catalyzed conjugations exist. UGT1A9, UGT1A1, UGT1A7, UGT1A8, and UGT1A3 are the major enzymes catalyzing hesperetin glucuronidation, the latter only producing 7-O-glucuronide, whereas UGT1A7 produced mainly 3'-O-glucuronide. Furthermore, UGT1A6 and UGT2B4 only produce hesperetin 7-O-glucuronide, whereas UGT1A1, UGT1A8, UGT1A9, UGT1A10, UGT2B7, and UGT2B15 conjugate both positions. SULT1A2 and SULT1A1 catalyze preferably and most efficiently the formation of hesperetin 3'-O-sulfate, and SULT1C4 catalyzes preferably and most efficiently the formation of hesperetin 7-O-sulfate. Based on expression levels SULT1A3 and SULT1B1 also will probably play a role in the sulfo-conjugation of hesperetin in vivo. The results help to explain discrepancies in metabolite patterns determined in tissues or systems with different expression of UGTs and SULTs, e.g., hepatic and intestinal fractions or Caco-2 cells. The incubations with rat and human tissue samples support an important role for intestinal cells during first-pass metabolism in the formation of hesperetin 3'-O-glucuronide and 7-O-glucuronide, which appear to be the major hesperetin metabolites found in vivo.

Recent advances on the action of estrogens and progestogens in normal and pathological human endometrium

Hormonal control in the development of the normal endometrium is of the utmost importance. It is well established that the two main hormones involved in this process are estradiol and progesterone, which are also implicated in the pathological conditions concerning endometriosis and endometrial carcinoma. There are two types of endometrial carcinoma: type I which represents 80%–90% is hormone-dependent, whereas the remainder is type II and is hormone-independent. The endometrial tissue contains all the enzymatic systems in the formation and transformation of the various hormones, including aromatases, sulfatases, sulfotransferases, hydroxysteroid dehydrogenases, hydroxylases, and glucuronidases. It is interesting to note that increased sulfatase activity is correlated with severity of endometriosis. An increased sulfatase/sulfotransferase ratio represents a poor prognosis in patients with endometrial carcinoma. Treatment with hormone replacement therapy (estrogens+progestogens), as well as with tibolone, is most effective in protecting this tissue by climacteric alterations, owing to the significant decrease of ovarian hormones. In conclusion, enzymatic control can open appealing perspectives to protect this organ from possible pathological alterations.

In vitro and in vivo conjugation of dietary hydroxycinnamic acids by UDP-glucuronosyltransferases and sulfotransferases in humans

Hydroxycinnamic acids are a class of phenolic antioxidants found widely in dietary plants. Their biotransformation in the human organism primarily involves Phase II conjugation reactions. In this study, activities of UDP-glucuronosyltransferases (UGTs) and sulfotransferases (SULTs) towards major dietary hydroxycinnamic acids (caffeic, dihydrocaffeic, dihydroferulic, ferulic and isoferulic acids) were investigated. Conjugate formation was evaluated using human liver and intestinal S9 homogenates, and in vitro characterization was carried out using recombinant human UGTs and SULTs. Analysis of the kinetics of hydroxycinnamic acid conjugation in human S9 homogenates revealed that intrinsic clearance (V(max)/K(m)) is much greater for sulfation than for glucuronidation. Assessment of activity using a panel of recombinant human SULTs showed that SULT1A1 is most active in the sulfation of caffeic, dihydrocaffeic and isoferulic acids, while SULT1E1 is most active in the sulfation of ferulic and dihydroferulic acids. Only isoferulic acid was significantly glucuronidated by human liver S9 homogenates, explained by the high activity of liver-specific UGT1A9. Studies on the kinetics of active SULTs and UGTs demonstrated a markedly lower K(m) for SULTs. To further corroborate our findings, we carried out an intervention study in healthy humans to determine the hydroxycinnamic acid conjugates in urine after consumption of hydroxycinnamate-rich coffee (200 ml). Analysis showed that sulfates are the main conjugates in urine, with the exception of isoferulic acid, which is mainly glucuronidated. These data suggest that sulfates are the predominant hydroxycinnamic acid conjugates in humans, and that SULT mediated sulfation is a major factor determining the bioavailability of hydroxycinnamic acids in vivo.

Aldo-keto reductase (AKR) superfamily: genomics and annotation

Aldo-keto reductases (AKRs) are phase I metabolising enzymes that catalyse the reduced nicotinamide adenine dinucleotide (phosphate) (NAD(P)H)-dependent reduction of carbonyl groups to yield primary and secondary alcohols on a wide range of substrates, including aliphatic and aromatic aldehydes and ketones, ketoprostaglan-dins, ketosteroids and xenobiotics. In so doing they functionalise the carbonyl group for conjugation (phase II enzyme reactions). Although functionally diverse, AKRs form a protein superfamily based on their high sequence identity and common protein fold, the (α/(β)₈-barrel structure. Well over 150 AKR enzymes, from diverse organisms, have been annotated so far and given systematic names according to a nomenclature that is based on multiple protein sequence alignment and degree of identity. Annotation of non-vertebrate AKRs at the National Center for Biotechnology Information or Vertebrate Genome Annotation (vega) database does not often include the systematic nomenclature name, so the most comprehensive overview of all annotated AKRs is found on the AKR website (http://www.med.upenn.edu/akr/). This site also hosts links to more detailed and specialised information (eg on crystal structures, gene expression and single nucleotide polymorphisms [SNPs]). The protein-based AKR nomenclature allows unambiguous identification of a given enzyme but does not reflect the wealth of genomic and transcriptomic variation that exists in the various databases. In this context, identification of putative new AKRs and their distinction from pseudogenes are challenging. This review provides a short summary of the characteristic features of AKR biochemistry and structure that have been reviewed in great detail elsewhere, and focuses mainly on nomenclature and database entries of human AKRs that so far have not been subject to systematic annotation. Recent developments in the annotation of SNP and transcript variance in AKRs are also summarised.

Quantitative evaluation of the expression and activity of five major sulfotransferases (SULTs) in human tissues: the SULT "pie"

Expression levels of the major human sulfotransferases (SULTs) involved in xenobiotic detoxification in a range of human tissues (i.e., SULT "pies") are not available in a form allowing comparison between tissues and individuals. Here we have determined, by quantitative immunoblotting, expression levels for the five principal human SULTs-SULT1A1, SULT1A3/4, SULT1B1, SULT1E1, and SULT2A1-and determined the kinetic properties toward probe substrates, where available, for these enzymes in cytosol samples from a bank of adult human liver, small intestine, kidney, and lung. We produced new isoform-selective antibodies against SULT1B1 and SULT2A1, which were used alongside antibodies against SULT1A3 and SULT1A1 previously produced in our laboratory or available commercially (SULT1E1). Expression levels were derived using purified recombinant enzymes to construct standard curves for each individual isoform and immunoblot. Substantial intertissue and interindividual differences in expression were observed. SULT1A1 was the major enzyme (>50% of total, range 420-4900 ng/mg cytosol protein) in the liver, followed by SULT2A1, SULT1B1, and SULT1E1. SULT1A3 was completely absent from this tissue. In contrast, the small intestine contained the largest overall amount of SULT of any of the tissues, with SULT1B1 the major enzyme (36%), closely followed by SULT1A3 (31%), and SULT1A1, SULT1E1, and SULT2A1 more minor forms (19, 8, and 6% of total, respectively). The kidney and lung contained low levels of SULT. We provide a unique data set that will add value to the study of the role and contribution of sulfation to drug and xenobiotic metabolism in humans.

Caco-2 cell monolayers as a tool to study simultaneous phase II metabolism and metabolite efflux of indomethacin, paracetamol and 1-naphthol

The human intestinal cell line, Caco-2, was used to study compounds - indomethacin, paracetamol and 1-naphthol - that undergo intestinal phase II metabolism followed by apical and/or basolateral efflux of the metabolites and/or parent compounds. The interplay was studied during permeability experiments across fully differentiated Caco-2 cell monolayers. The parent compounds and their glucuronide and/or sulfate metabolites were detected by LC-MS/MS. Conjugation of the model compounds and effluxes of their metabolites were observed. The efflux of indomethacin glucuronide was apical, but complementary basolateral efflux was observed at the highest indomethacin concentration (500 microM), probably due to apical saturation. Paracetamol glucuronide was not formed in these experiments, but apical and basolateral effluxes of paracetamol sulfate were observed. A typical bell-shaped inhibition curve was observed for the formation of 1-naphthol glucuronides, indicating substrate or product inhibition of the UGT enzyme(s) at higher 1-naphthol concentrations (200 microM and 500 microM). Based on these results, the fully differentiated Caco-2 cell monolayers can be applied as a platform for qualitative in vitro studies, where phase II metabolism and efflux activities are ongoing simultaneously.

On the similar spatial arrangement of active site residues in PAPS-dependent and phenolic sulfate-utilizing sulfotransferases

Mammalian sulfotransferases (STs) utilize exclusively the sulfuryl group donor 3'-phosphoadenosine 5'-phosphosulfate (PAPS) to catalyze the sulfurylation reactions based on a sequential transfer mechanism. In contrast, the commensal intestinal bacterial arylsulfate sulfotransferases (ASSTs) do not use PAPS as the sulfuryl group donor, but instead catalyze sulfuryl transfer from phenolic sulfate to a phenol via a Ping-Pong mechanism. Interestingly, structural comparison revealed a similar spatial arrangement of the active site residues as well as the cognate substrates in mouse ST (mSULT1D1) and Escherichia coli CFT073 ASST, despite that their overall structures bear no discernible relationship. These observations suggest that the active sites of PAPS-dependent SULT1D1 and phenolic sulfate-utilizing ASST represent an example of convergent evolution.

Cytosolic Aryl sulfotransferase 4A1 interacts with the peptidyl prolyl cis-trans isomerase Pin1

Sulfonation by cytosolic sulfotransferases plays an important role in the metabolism of both endogenous and exogenous compounds. Sulfotransferase 4A1 (SULT4A1) is a novel sulfotransferase found primarily in neurons in the brain. It is highly conserved between species, but no substantial enzyme activity has been identified for the protein. Consequently, little is known about the role of this enzyme in the brain. We performed a yeast two-hybrid screen of a human brain library to isolate potential SULT4A1-interacting proteins that might identify the role or regulation of the sulfotransferase in humans. The screen isolated the peptidyl-prolyl cis-trans isomerase Pin1. Its interaction with SULT4A1 was confirmed by coimmunoprecipitation studies in HeLa cells and by in vitro pull-down of expressed proteins. Moreover, Pin1 binding was dependent on phosphorylation of the SULT4A1 protein. Pin1 destabilized SULT4A1, decreasing its half-life from more than 8 h to approximately 4.5 h. This effect was dependent on the isomerase activity of Pin1 and was inhibited by okadaic acid, suggesting a role for the phosphatase PP2A. Pin1-mediated SULT4A1 degradation did not involve the proteosomes or macroautophagy, but it was inhibited by the calpain antagonists N-acetyl-Leu-Leu-Nle-CHO and Z-Val-Phe-CHO. Finally, Pin1 binding was mapped to two threonine-proline motifs (Thr(8) and Thr(11)) that are not present in any of the other human cytosolic sulfotransferases. Our findings suggest that SULT4A1 is subject to post-translational modification that alters its stability in the cell. These modifications may also be important for enzyme activity, which explains why specific substrates for SULT4A1 have not yet been identified.

Molecular cloning, expression and characterization of a novel mouse SULT6 cytosolic sulfotransferase

By searching the mouse EST database, we identified a novel mouse cytosolic sulfotransferase (SULT) cDNA (RIKEN cDNA 2410078J06). Sequence analysis revealed that this new SULT belongs to the cytosolic SULT6 gene family. The recombinant form of this newly identified SULT, designated SULT6B1, was expressed using the pGEX-4T-1 glutathione S-transferase fusion system and purified from transformed BL21 Escherichia coli cells. Purified mouse SULT6B1 exhibited sulfonating activity toward thyroxine and bithionol among a variety of endogenous and xenobiotic compounds tested as substrates. pH optimum of purified mouse SULT6B1 was determined to be 8.0. Tissue-specific expression of mouse and human SULT6B1 was examined by RT-PCR. While human SULT6B1 was specifically expressed in kidney and testis, mouse SULT6B1 was detected in brain, heart, kidney, thymus, lung, liver and testis. Further studies are needed in order to clarify the role of SULT6B1 in the metabolism of thyroxine and possibly some xenobiotics in mouse.

Impact of gut microbiota on intestinal and hepatic levels of phase 2 xenobiotic-metabolizing enzymes in the rat

Using immunoblotting, we compared levels of phase 2 enzymes in liver, small intestine, cecum, and colon of germ-free and control rats (reassociated with rat intestinal microbiota). In addition, colonic levels were studied after association with human intestinal microbiota. The glutathione transferases (GSTs) studied, gastrointestinal glutathione peroxidase (GPX2), both epoxide hydrolases (EPHXs), and N-acetyltransferase (NAT) 1, were detected in all tissues. GPX2 and GSTP1 were highest in large bowel; the other enzymes of this group were highest in liver. NAT2 was found in the large bowel but not in the liver or small bowel. Sulfotransferases (SULTs) were detected in liver but were absent in small intestine; two forms were present at moderate levels in the large intestine. Strong gender-dependent differences were observed for several enzymes in liver but not in gut. Colonic levels in germ-free animals differed from those in control animals (* indicates statistical significance) for GSTA1/2 (4.0*- and 5.0*-fold in males and females, respectively), GSTA4 (1.5*/1.9*-fold), GSTM1 (1.1/1.5*-fold), EPHX1 (3.5*/2.4*-fold), EPHX2 (1.4/2.1*-fold), SULT1B1 (0.4*/0.6*-fold), SULT1C2 (1.3/1.6*-fold), and NAT2 (1.4/1.5*-fold). Smaller effects were observed when rats were colonized with human, compared with rat, intestinal bacteria. Cecal enzyme levels in germ-free rats were changed similarly to those in colon. No effects were seen in small intestine. In liver, SULT1A1, SULT1C1, and SULT1C2 were elevated in germ-free animals of both genders (1.5- to 2.6-fold); hepatic EPHX2 was elevated 1.6-fold in females. In conclusion, intestinal microbiota can affect levels of xenobiotic-metabolizing enzymes in large intestine and liver, but the effects observed were moderate compared with tissue-dependent expression differences.

An unusually small dimer interface is observed in all available crystal structures of cytosolic sulfotransferases

Cytosolic sulfotransferases catalyze the sulfonation of hormones, metabolites, and xenobiotics. Many of these proteins have been shown to form homodimers and heterodimers. An unusually small dimer interface was previously identified by Petrotchenko et al. (FEBS Lett 2001;490:39-43) by cross-linking, protease digestion, and mass spectrometry and verified by site-directed mutagenesis. Analysis of the crystal packing interfaces in all 28 available crystal structures consisting of 17 crystal forms shows that this interface occurs in all of them. With a small number of exceptions, the publicly available databases of biological assemblies contain either monomers or incorrect dimers. Even crystal structures of mouse SULT1E1, which is a monomer in solution, contain the common dimeric interface, although distorted and missing two important salt bridges.

Expression and localization of cytosolic sulfotransferase (SULT) 1A1 and SULT1A3 in normal human brain

Cytosolic sulfotransferases (SULTs) are a family of Phase II drug-metabolizing enzymes that catalyze the transfer of a sulfonate group from 3'-phosphoadenosine 5'-phosphosulfate to endogenous and xenobiotic compounds. Several SULT isoform messages have been detected in the human brain; however, protein expression patterns have not been characterized. Immunoblot analysis of the SULT1A1 and 1A3 isoforms was carried out with cytosolic fractions isolated from superior temporal gyrus, hippocampus, cerebellum, occipital pole, frontal pole, and temporal pole regions of normal adult human brains. SULT1A1 expression was highest in cytosolic fractions isolated from cerebellum, occipital, and frontal lobes, whereas, SULT1A3 expression was highest in cytosol from superior temporal gyrus, hippocampus, and temporal lobe. SULT1A1 and SULT1A3 immunoreactivities were found in both neurons and glial cells by immunohistochemical analysis in all brain regions studied. SULT1A1 is known to catalyze the metabolism of small phenols, whereas SULT1A3 sulfates catecholamine neurotransmitters. Because SULT1A1 and 1A3 have distinct substrate specificities, the differences in expression pattern and cellular localization of the SULT1A isoforms are probably associated with the distribution and function of their selective substrates in the different brain regions.

Sulfation of o-demethyl apixaban: enzyme identification and species comparison

Apixaban, a potent and highly selective factor Xa inhibitor, is currently under development for treatment of arterial and venous thrombotic diseases. The O-demethyl apixaban sulfate is a major circulating metabolite in humans but circulates at lower concentrations relative to parent in animals. The aim of this study was to identify the sulfotransferases (SULTs) responsible for the sulfation reaction. Apixaban undergoes O-demethylation catalyzed by cytochrome P450 enzymes to O-demethyl apixaban, and then is conjugated by SULTs to form O-demethyl apixaban sulfate. Of the five human cDNA-expressed SULTs tested, SULT1A1 and SULT1A2 exhibited significant levels of catalytic activity for formation of O-demethyl apixaban sulfate, and SULT1A3, SULT1E1, and SULT2A1 showed much lower catalytic activities. In human liver S9, quercetin, a highly selective inhibitor of SULT1A1 and SULT1E1, inhibited O-demethyl apixaban sulfate formation by 99%; 2,6-dichloro-4-nitrophenol, another inhibitor of SULT1A1, also inhibited this reaction by >90%; estrone, a competitive inhibitor for SULT1E1, had no effect on this reaction. The comparable K(m) values for formation of O-demethyl apixaban sulfate were 41.4 microM (human liver S9), 36.8 microM (SULT1A1), and 70.8 microM (SULT1A2). Because of the high level of expression of SULT1A1 in liver and its higher level of catalytic activity for formation of O-demethyl apixaban sulfate, SULT1A1 might play a major role in humans for formation of O-demethyl apixaban sulfate. O-Demethyl apixaban was also investigated in liver S9 of mice, rats, rabbits, dogs, monkeys, and humans. The results indicated that liver S9 samples from dogs, monkeys, and humans had higher activities for formation of O-demethyl apixaban sulfate than those of mice, rats, and rabbits.

Snapshot of a Michaelis complex in a sulfuryl transfer reaction: Crystal structure of a mouse sulfotransferase, mSULT1D1, complexed with donor substrate and accepter substrate

We report the crystal structure of mouse sulfotransferase, mSULT1D1, complexed with donor substrate 3'-phosphoadenosine 5'-phosphosulfate and accepter substrate p-nitrophenol. The structure is the first report of the native Michaelis complex of sulfotransferase. In the structure, three proposed catalytic residues (Lys48, Lys106, and His108) were in proper positions for engaging in the sulfuryl transfer reaction. The data strongly support that the sulfuryl transfer reaction proceeds through an S(N)2-like in-line displacement mechanism.

Estrogen sulfotransferases in breast and endometrial cancers

Estrogen sulfotransferase is significantly more active in the normal breast cell (e.g., Human 7) than in the cancer cell (e.g., MCF-7). The data suggest that in breast cancer sulfoconjugated activity is carried out by another enzyme, the SULT1A, which acts at high concentration of the substrates. In breast cancer cells sulfotransferase (SULT) activity can be stimulated by various progestins: medrogestone, promegestone, and nomegestrol acetate, as well as by tibolone and its metabolites. SULT activities can also be controlled by other substances including phytoestrogens, celecoxib, flavonoids (e.g., quercetin, resveratrol), and isoflavones. SULT expression was localized in breast cancer cells, which can be stimulated by promegestone and correlated with the increase of the enzyme activity. The estrogen sulfotransferase (SULT1E1), which acts at nanomolar concentration of estradiol, can inactivate most of this hormone present in the normal breast; however, in the breast cancer cells, the sulfotransferase denoted as SULT1A1 is mainly present, and this acts at micromolar concentrations of E(2). A correlation was postulated among breast cancer cell proliferation, the effect of various progestins, and sulfotransferase stimulation. In conclusion, it is suggested that factors involved in the stimulation of the estrogen sulfotransferases could provide new possibilities for the treatment of patients with hormone-dependent breast and endometrial cancers.

Sulfotransferase gene copy number variation: pharmacogenetics and function

Pharmacogenetics is the study of the role of inheritance in variation to drug response. Drug response phenotypes can vary from adverse drug reactions at one end of the spectrum to equally serious lack of the desired effect of drug therapy at the other. Many of the current important examples of pharmacogenetics involve inherited variation in drug metabolism. Sulfate conjugation catalyzed by cytosolic sulfotransferase (SULT) enzymes, particularly SULT1A1, is a major pathway for drug metabolism in humans. Pharmacogenetic studies of SULT1A1 began over a quarter of a century ago and have advanced from biochemical genetic experiments to include cDNA and gene cloning, gene resequencing, and functional studies of the effects of single nucleotide polymorphisms (SNPs). SNP genotyping, in turn, led to the discovery of functionally important copy number variations (CNVs) in the SULT1A1 gene. This review will briefly describe the evolution of our understanding of SULT1A1 pharmacogenetics and CNV, as well as challenges involved in utilizing both SNP and CNV data in an attempt to predict SULT1A1 function. SULT1A1 represents one example of the potential importance of CNV for the evolving disciplines of pharmacogenetics and pharmacogenomics.

Regulation of hepatic sulfotransferase (SULT) 1E1 expression and effects on estrogenic activity in cystic fibrosis (CF)

Cystic fibrosis (CF) is a major genetic disease in Caucasians affecting 1 in 2500 newborns. Hepatobiliary pathology is a major cause of morbidity and mortality in CF second only to pulmonary disease. SULT1E1 activity is significantly elevated, generally 20-30-fold, in hepatocytes of mouse models of CF. SULT1E1 is responsible for the inactivation of beta-estradiol (E2) at physiological concentrations via conjugation with sulfonate. The increase in SULT1E1 activity results in the alteration of E2-regulated protein expression in CF mouse liver. To investigate the mechanism by which the absence of CFTR in human cholangiocytes induces SULT1E1 expression in hepatocytes, a membrane-separated human MMNK-1 cholangiocyte and human HepG2 hepatocyte co-culture system was developed. The cystic fibrosis transmembrane conductance regulator (CFTR) is expressed in bile duct cholangiocytes but not hepatocytes, whereas SULT1E1 is expressed in hepatocytes but not cholangiocytes. CFTR expression in MMNK-1 cells was inhibited with siRNA by >90% as determined by immunoblot and immunohistochemical analysis. Control and CFTR-siRNA-MMNK-1 cells were co-cultured with HepG2 cells in a Transwell membrane-separated system. After 8h of co-culture, HepG2 cells were removed from exposure to MMNK-1 cells and placed in fresh medium. After 24-48h, expression of SULT1E1 and selected E2-regulated proteins was analyzed in the HepG2 cells. Results demonstrated that SULT1E1 message and activity were selectively induced in HepG2 cells co-cultured with CFTR-deficient MMNK-1 cells. The expression of E2-regulated proteins (IGF-1, GST-P1 and carbonic anhydrase II) was also altered in response to decreased E2 levels. Thus, the loss of CFTR activity in cholangiocytes stimulates the expression of SULT1E1 in hepatocytes by a paracrine mechanism. SULT1E1 expression in HepG2 cells is inducible by sterol mediated liver-X-receptor (LXR) activation although not by progestins that induce SULT1E1 in the endometrium. SULT1E1 induction in the human cholangiocyte/hepatocyte co-culture system is consistent with and supports the results observed in CF mice. The changes in hepatocyte gene expression affect liver biochemistry and may facilitate the development of CF liver disease.

Sulfotransferases, sulfatases and formylglycine-generating enzymes: a sulfation fascination

Sulfotransferases and sulfatases are the major enzymes responsible for sulfate transfer processes. The past two years have seen the elucidation of new functions for these enzymes, and a great progression in their structural characterization, which confirms that these two types of enzymes possess a highly conserved fold. For catalytic activity, sulfatases must contain a formylglycine residue, which is generated by various formylglycine-generating enzymes. Mechanistic and structural details have recently been obtained for a group of cofactor-independent formylglycine-generating enzymes termed FGEs. Finally, an increasing light has been cast upon the mechanism of sulfatase inactivation by a group of clinically important agents, the aryl sulfamates.

Characterization and ontogenic study of novel steroid-sulfating SULT3 sulfotransferases from zebrafish

In vertebrates, sulfation as catalyzed by members of the cytosolic sulfotransferase (SULT) family has been suggested to be involved in the homeostasis of steroids. To establish the zebrafish as a model for investigating how sulfation functions to regulate steroid metabolism during the developmental process, we have embarked on the identification of steroid-sulfating SULTs in zebrafish. By searching the GenBank database, we identified two putative cytosolic SULT sequences from zebrafish, designated SULT3 ST1 and ST2. The recombinant proteins of these two zebrafish SULT3 STs were expressed in and purified from BL21 (DE3) cells transformed with the pGEX-2TK expression vector harboring SULT3 ST1 or ST2 cDNA. Upon enzymatic characterization, purified SULT3 ST1 displayed the strongest sulfating activity toward 17beta-estradiol among the endogenous substrates tested, while SULT3 ST2 exhibited substrate specificity toward hydroxysteroids, particularly dehydroepiandrosterone (DHEA). The pH-dependence and kinetic constants of these two enzymes with 17beta-estradiol and DHEA were determined. A developmental expression study revealed distinct patterns of the expression of SULT3 ST1 and ST2 during embryonic development and throughout the larval stage onto maturity. Collectively, these results imply that these two steroid-sulfating SULT3 STs may play differential roles in the metabolism and regulation of steroids during zebrafish development and in adulthood.

PhRMA white paper on ADME pharmacogenomics

Pharmacogenomic (PGx) research on the absorption, distribution, metabolism, and excretion (ADME) properties of drugs has begun to have impact for both drug development and utilization. To provide a cross-industry perspective on the utility of ADME PGx, the Pharmaceutical Research and Manufacturers of America (PhRMA) conducted a survey of major pharmaceutical companies on their PGx practices and applications during 2003-2005. This white paper summarizes and interprets the results of the survey, highlights the contributions and applications of PGx by industrial scientists as reflected by original research publications, and discusses changes in drug labels that improve drug utilization by inclusion of PGx information. In addition, the paper includes a brief review on the clinically relevant genetic variants of drug-metabolizing enzymes and transporters most relevant to the pharmaceutical industry.

The ontogeny of drug metabolism enzymes and implications for adverse drug events

Profound changes in drug metabolizing enzyme (DME) expression occurs during development that impacts the risk of adverse drug events in the fetus and child. A review of our current knowledge suggests individual hepatic DME ontogeny can be categorized into one of three groups. Some enzymes, e.g., CYP3A7, are expressed at their highest level during the first trimester and either remain at high concentrations or decrease during gestation, but are silenced or expressed at low levels within one to two years after birth. SULT1A1 is an example of the second group of DME. These enzymes are expressed at relatively constant levels throughout gestation and minimal changes are observed postnatally. ADH1C is typical of the third DME group that are not expressed or are expressed at low levels in the fetus, usually during the second or third trimester. Substantial increases in enzyme levels are observed within the first one to two years after birth. Combined with our knowledge of other physiological factors during early life stages, knowledge regarding DME ontogeny has permitted the development of robust physiological based pharmacokinetic models and an improved capability to predict drug disposition in pediatric patients. This review will provide an overview of DME developmental expression patterns and discuss some implications of the data with regards to drug therapy. Common themes emerging from our current knowledge also will be discussed. Finally, the review will highlight gaps in knowledge that will be important to advance this field.

Cloning, expression, and characterization of cytosolic sulfotransferase isozymes from Drosophila melanogaster

We have identified four cytosolic sulfotransferase (SULT) homologs in the genome database of Drosophila melanogaster, and have designated these genes dmST1-4. Each of these four isozymes was subsequently classified into a different and novel gene family, as determined by the low amino acid sequence homology (less than 40%) between them, and also toward their vertebrate homologs. The transcripts for these four SULT homologs were detectable at all developmental stages in D. melanogaster. In addition, three of these isozymes, the exception being dmST2, were successfully expressed and purified in Escherichia coli. These recombinant dmST1, 3, and 4 products showed high sulfating activity toward phenolic compounds such as vanillin and 4-nitrophenol, but showed no activity toward typical endogenous substrates such as tyramine and serotonin. DmST4 and dmST3 showed the lowest and highest K(m) values for 3'-phosphoadenosine-5'-phosphosulfate (PAPS) respectively. DmST4 also showed low but not negligible activity toward 20-hydroxyecdysone.

Sulfotransferase forms expressed in human intestinal Caco-2 and TC7 cells at varying stages of differentiation and role in benzo[a]pyrene metabolism

The Caco-2 cell line and its subclone TC7 are frequently used for studying human intestinal transport and metabolism of xenobiotics. We have investigated the expression of soluble sulfotransferases (SULT) in parental Caco-2 and TC7 cells by immunoblotting. SULT1A1, SULT1A2, SULT1A3, SULT1B1, SULT1C1, SULT1C2, and SULT2A1 were expressed in both cell lines. SULT2B1a, SULT2B1b, and SULT4A1 were absent. SULT1E1 protein was found in TC7 but not in Caco-2 cells. Other differences in SULT between the cell lines were minor. More important was the influence of differentiation. Expression of the various SULT forms was low or not detectable in cultures just reaching confluence but then increased strongly. Likewise, the rate of sulfation of the model substrate 3-hydroxybenzo[a]pyrene was increased with increasing culture duration. Benzo[a]pyrene-1-sulfate and -3-sulfate were formed in both cell lines when benzo[a]pyrene was used as a substrate. A further metabolite, 3-hydroxybenzo[a]pyrene-glucuronide, was detected in TC7 but not in parental Caco-2 cells. Cytochrome P450 inducers enhanced the conversion of benzo[a]pyrene to these metabolites without altering mRNA levels of major phenol-conjugating SULT forms (SULT1A1, SULT1A3, and SULT1B1). Overall, differentiated Caco-2 and TC7 cells are rich sources of SULT, as is human intestinal mucosa. The SULT pattern is most similar to that found in small intestine, although levels of SULT1A1 and SULT1B1 are lower, and those of SULT1C1 are higher in Caco-2 and TC7 cells than previously found in intestinal samples. The differentiation-dependent expression of SULT in the cultured cells reflects the in vivo situation, where SULT expression is focused to differentiated enterocytes.

Expressed sequence tags from cynomolgus monkey (Macaca fascicularis) liver: a systematic identification of drug-metabolizing enzymes

The liver, a major organ for drug metabolism, is physiologically similar between monkeys and humans. However, the paucity of identified genes has hampered a deep understanding of drug metabolism in monkeys. To provide such a genetic resource, 28655 expressed sequence tags (ESTs) were generated from a cynomolgus monkey liver full-length enriched cDNA library, which contained 23 unique ESTs homologous to human drug-metabolizing enzymes. Our comparative genomics approach identified nine lineage-specific candidate ESTs, including three drug-metabolizing enzymes, which could be important for understanding the physiological differences between monkeys and humans.

Sulfotransferase 4A1

In this review, we highlight the physical and enzymatic properties of the novel human sulfotransferase, SULT4A1. The gene is most highly expressed in selective regions of the brain, although work to date has failed to identify any specific endogenous substrate for the enzyme. SULT4A1 shares low homology with other human sulfotransferases. Nevertheless, it is highly conserved between species. Despite the low homology, it is structurally very similar to other cytosolic sulfotransferases with a conserved substrate binding domain, dimerization site and partial cofactor binding sites. However, the catalytic cavity is much smaller, and it has been suggested that the cofactor may not be accommodated within it. A recent link between variability in the 5'UTR of the SULT4A1 gene and schizophrenia has heightened interest in the endogenous function of the enzyme and its possible role in human disease.

Pregnenolone sulfate in the brain: a controversial neurosteroid

Pregnenolone sulfate (PREGS) has been shown, either at high nanomolar or at micromolar concentrations, to increase neuronal activity by inhibiting GABAergic and by stimulating glutamatergic neurotransmission. PREGS is also a potent modulator of sigma type 1 (sigma1) receptors. It has been proposed that these actions of PREGS underlie its neuropharmacological effects, and in particular its influence on memory processes. On the other hand, the PREGS-mediated increase in neuronal excitability may become dangerous under particular conditions, for example in the case of excitotoxic stress or convulsions. However, the physiopathological significance of these observations has recently been put into question by the failure to detect significant levels of PREGS within the brain and plasma of rats and mice, either by direct analytical methods based on liquid chromatography/mass spectrometry (LC/MS) or enzyme linked immunosorbent assay (ELISA) with specific antibodies against PREGS, or by indirect gas chromatography/mass spectrometry (GC/MS) analysis with improved sample workup. These recent results have not come to the attention of a large number of neurobiologists interested in steroid sulfates. However, although available direct analytical methods have failed to detect levels of PREGS above 0.1-0.3 ng/g in brain tissue, it may be premature to completely exclude the local formation of biologically active PREGS within specific and limited compartments of the nervous system. In contrast to the situation in rodents, significant levels of sulfated 3beta-hydroxysteroids have been measured in human plasma and brain. Previous indirect measures of steroid sulfates by radioimmunoassays (RIA) or GC/MS had detected elevated levels of PREGS in rodent brain. The discrepancies between the results of different assay procedures have revealed the danger of indirect analysis of steroid sulfates. Indeed, PREGS must be solvolyzed/hydrolyzed prior to RIA or GC/MS analysis, and it is the released, unconjugated PREG which is then quantified. Extreme caution needs to be exercised during the preparation of samples for RIA or GC/MS analysis, because the fraction presumed to contain only steroid sulfates can be contaminated by nonpolar components from which PREG is generated by the solvolysis/hydrolysis/derivatization reactions.

Induction of human sulfotransferase 1A3 (SULT1A3) by glucocorticoids

Sulfotransferases (SULTs) play an important role in the detoxification and bioactivation of endogenous compounds and xenobiotics. Studies on rat sulfotransferases had shown that SULT genes, like cytochrome P450 genes, can be regulated by ligands that bind nuclear receptors. For human SULT genes, the regulation of human SULT2A1 expression is currently the best characterized. In this study, we systematically examined the regulation of human SULT1A genes by glucocorticoids. Treatment of the human hepatocellular carcinoma derived HepG2 cells with 10(-7) M dexamethasone did not affect the SULT1A1 activity toward p-nitrophenol. In contrast, SULT1A3 activity toward dopamine was significantly induced. Transient transfection of the SULT1A3 5'-flanking region/luciferase reporter construct showed that SULT1A3 was responsive to dexamethasone and prednisolone in a concentration-dependent manner with maximal induction at 10(-7) M dexamethasone or 1 microM prednisolone. In addition, induction by dexamethasone was dependent on the level of expression of the glucocorticoid receptor. Analysis of the 5'-flanking region led to the identification of a putative glucocorticoid response element at position (-1211 to -1193) upstream of the transcription start site and deletion or mutation of this element resulted in a loss of response. In summary, the data from this study shows that the human SULT1A3 gene is inducible by glucocorticoids through a glucocorticoid receptor-mediated mechanism and the glucocorticoid response element at position (-1211 to -1193) is necessary for this induction.

Comparison of 2-aminophenol and 4-nitrophenol as in vitro probe substrates for the major human hepatic sulfotransferase, SULT1A1, demonstrates improved selectivity with 2-aminophenol

Sulfation, catalysed by members of the cytosolic sulfotransferase (SULT) enzyme family, is important in xenobiotic detoxification and in the biosynthesis and homeostasis of many hormones and neurotransmitters. The major human phenol sulfotransferase SULT1A1 plays a key role in chemical defence, is widely expressed in the body and is subject to a common polymorphism that results in reduced protein levels. Study of these enzymes in vitro requires robust probe substrates, and we have previously shown measurement of activity with the widely used SULT1A1 substrate, 4-nitrophenol, does not accurately reflect protein expression. Additionally, the high degree of substrate inhibition observed with this compound further reduces its value as a probe for SULT1A1. Here we show that 2-aminophenol is a more suitable probe substrate for quantifying SULT1A1 activity in human liver. This compound is sulfated at a high rate (V(max) with purified recombinant SULT1A1=121nmol/(minmg) and shows strong affinity for the enzyme (K(m) with purified recombinant SULT1A1=9microM) and, importantly, is a very poor substrate for the other major SULT1 enzyme expressed in liver, SULT1B1 (with V(max) and K(m) values of 17nmol/(minmg) and 114microM, respectively). Experiments with purified recombinant human SULTs and a panel of 28 human liver cytosols demonstrated that 2-aminophenol shows limited substrate inhibition with SULT1A1, and V(max) values measured in liver cytosols correlated strongly with SULT1A1 enzyme protein levels measured by a quantitative immunoblot method. We therefore suggest that 2-aminophenol is a suitable substrate to use for quantifying SULT1A1 enzyme activity.

Identification and localization of soluble sulfotransferases in the human gastrointestinal tract

Soluble SULTs (sulfotransferases) are important in the regulation of messenger molecules and the elimination of xenobiotics. However, sulfo-conjugation of various substrates can also lead to the formation of reactive metabolites that may induce cancer and cause other damage. The aim of the present study was to identify the SULT forms expressed in the human gastrointestinal tract, especially the colon and rectum (common sites for cancer), and to determine their cellular localization. Normal colonic or rectal tissue, resected with tumours, was obtained from 39 subjects. For comparison, we additionally studied one to four samples from stomach, jejunum, ileum, cecum and liver. SULTs were detected by immunoblotting, immunohistochemistry and measurement of enzyme activities. SULT1A1, 1A3 and 1B1 were found in all parts of the gastrointestinal tract, often exceeding levels in liver (where these forms were present at high, undetectable and low levels respectively). They were predominantly localized in differentiated enterocytes. SULT1E1 and 2A1 were only detected in liver, jejunum, ileum and cecum. SULT1C1 was readily found in stomach, but was negligible elsewhere. SULT1A2 was present at low levels in individual samples. The remaining forms were not detected with the limitation that only high levels could be recognized with the antisera used. In conclusion, SULTs are abundant in the gastrointestinal tract of man. We suspect that they are involved in the presystemic elimination of bioactive food-borne components, including aglycones released by gut microbiota, as well as the bioactivation of some procarcinogens.

Regioselective sulfonation of dopamine by SULT1A3 in vitro provides a molecular explanation for the preponderance of dopamine-3-O-sulfate in human blood circulation

SULT1A3 is an enzyme that catalyzes the sulfonation of many endogenous and exogenous phenols and catechols. The most important endogenous substrate is dopamine (DA), which is often used as a probe substrate for SULT1A3. We developed a new method for analyzing the SULT1A3 reaction products by high-performance liquid chromatography (HPLC) with electrochemical detection. The sulfonate donor 3'-phosphoadenosine-5'-phosphosulfate (PAPS), DA and the two dopamine sulfates, DA-3-O-sulfate and DA-4-O-sulfate, can be separated within 3 min. This enables quantitation of the sulfates without radioactive PAPS or the precipitation of unreacted PAPS. Both sulfates were synthesized as reference substances and characterized by (1)H and (13)C nuclear magnetic resonance (NMR), mass spectrometry (MS) and tandem mass spectrometry (MS/MS). The purity of the dopamine sulfates was estimated by HPLC using a diode array detector. We determined the enzyme kinetic parameters for formation of DA-3-O-sulfate and DA-4-O-sulfate using purified recombinant human SULT1A3. The reactions followed Michaelis-Menten kinetics up to 50 microM DA concentration, and strong substrate inhibition was observed at higher concentrations. The apparent K(m) values for sulfonation at both hydroxy groups were similar (2.21+/-0.764 and 2.59+/-1.06 microM for DA-4-O-sulfate and DA-3-O-sulfate, respectively), but the V(max) was approximately six times higher for the formation of the 3-O-sulfate (344+/-139 nmol/min/mg protein) than the 4-O-sulfate (45.4+/-16.5 nmol/min/mg protein). These results are in accordance with the observation that DA-3-O-sulfate is more abundant in human blood than DA-4-O-sulfate and that in the crystal structure of SULT1A3 with dopamine bound to the active site, the 3-hydroxy group is aligned to form hydrogen bonds with catalytic residues of the enzyme.

Structural and chemical profiling of the human cytosolic sulfotransferases

The human cytosolic sulfotransfases (hSULTs) comprise a family of 12 phase II enzymes involved in the metabolism of drugs and hormones, the bioactivation of carcinogens, and the detoxification of xenobiotics. Knowledge of the structural and mechanistic basis of substrate specificity and activity is crucial for understanding steroid and hormone metabolism, drug sensitivity, pharmacogenomics, and response to environmental toxins. We have determined the crystal structures of five hSULTs for which structural information was lacking, and screened nine of the 12 hSULTs for binding and activity toward a panel of potential substrates and inhibitors, revealing unique "chemical fingerprints" for each protein. The family-wide analysis of the screening and structural data provides a comprehensive, high-level view of the determinants of substrate binding, the mechanisms of inhibition by substrates and environmental toxins, and the functions of the orphan family members SULT1C3 and SULT4A1. Evidence is provided for structural "priming" of the enzyme active site by cofactor binding, which influences the spectrum of small molecules that can bind to each enzyme. The data help explain substrate promiscuity in this family and, at the same time, reveal new similarities between hSULT family members that were previously unrecognized by sequence or structure comparison alone.

Molecular and biochemical characterization of two brassinosteroid sulfotransferases from Arabidopsis, AtST4a (At2g14920) and AtST1 (At2g03760)

Mammalian sulfotransferases (EC 2.8.2) are involved in many important facets of steroid hormone activity and metabolism. In this study, Arabidopsis AtST4a and AtST1 were identified and characterized as brassinosteroid sulfotransferases that appear to be involved in different aspects of hormone regulation. The two proteins share 44% identity in amino acid sequence, and belong to different plant sulfotransferase families. AtST4a was specific for biologically active end products of the brassinosteroid pathway. The enzyme sulfated brassinosteroids with diverse side-chain structures, including 24-epibrassinosteroids and the naturally occurring (22R, 23R)-28-homobrassinosteroids. AtST4a belongs to a small subfamily of sulfotransferases having two other members, AtST4b and -c. Among the three recombinant enzymes, only AtST4a was catalytically active with brassinosteroids. Transcript expression of AtST4 subfamily members was largely specific to the root. AtST4b- and -c transcript levels were induced by treatment with trans-zeatin, while AtST4a was repressed under the same conditions, supporting a divergent function of AtST4a. Co-regulation of AtST4b and -c correlated with their location in tandem on chromosome 1. AtST1 was stereospecific for 24-epibrassinosteroids, with a substrate preference for the metabolic precursor 24-epicathasterone, and exhibited catalytic activity with hydroxysteroids and estrogens. To gain more insight into this dual activity with plant and mammalian steroids, enzymatic activities of human steroid sulfotransferases toward brassinosteroids were characterized. The dehydroepiandrosterone sulfotransferase SULT2A1 displayed catalytic activity with a selected set of 24-epibrassinolide precursors, including 24-epicathasterone, with specific activities comparable to that measured for the endogenous substrate dehydroepiandrosterone. The comparable activity profiles of AtST1 and SULT2A1 suggest a similar architecture of the acceptor-binding site between the two enzymes, and may potentially reflect a common ability to conjugate certain xenobiotics.

Pharmacokinetic Drug Interactions Involving 17??-Ethinylestradiol

17alpha-Ethinylestradiol (EE) is widely used as the estrogenic component of oral contraceptives (OC). In vitro and in vivo metabolism studies indicate that EE is extensively metabolised, primarily via intestinal sulfation and hepatic oxidation, glucuronidation and sulfation. Cytochrome P450 (CYP)3A4-mediated EE 2-hydroxylation is the major pathway of oxidative metabolism of EE. For some time it has been known that inducers of drug-metabolising enzymes (such as the CYP3A4 inducer rifampicin [rifampin]) can lead to breakthrough bleeding and contraceptive failure. Conversely, inhibitors of drug-metabolising enzymes can give rise to elevated EE plasma concentrations and increased risks of vascular disease and hypertension. In vitro studies have also shown that EE inhibits a number of human CYP enzymes, such as CYP2C19, CYP3A4 and CYP2B6. Consequently, there are numerous reports in the literature describing EE-containing OC formulations as perpetrators of pharmacokinetic drug interactions. Because EE may participate in multiple pharmacokinetic drug interactions as either a victim or perpetrator, pharmaceutical companies routinely conduct clinical drug interaction studies with EE-containing OCs when evaluating new chemical entities in development. It is therefore critical to understand the mechanisms underlying these drug interactions. Such an understanding can enable the interpretation of clinical data and lead to a greater appreciation of the profile of the drug by physicians, clinicians and regulators. This article summarises what is known of the drug-metabolising enzymes and transporters governing the metabolism, disposition and excretion of EE. An effort is made to relate this information to known clinical drug-drug interactions. The inhibition and induction of drug-metabolising enzymes by EE is also reviewed.

Human cytosolic sulfotransferase 2B1: isoform expression, tissue specificity and subcellular localization

Sulfation is an important Phase II conjugation reaction involved in the synthesis and metabolism of steroids in humans. Two different isoforms (2B1a and 2B1b) are encoded by the sulfotransferase (SULT) 2B1 gene utilizing different start sites of transcription resulting in the incorporation of different first exons. SULT2B1a and SULT2B1b are 350 and 365 amino acids in length, respectively, and the last 342 aa are identical. Message for both SULT2B1 isoforms is present in human tissues although SULT2B1b message is generally more abundant. However, to date only SULT2B1b protein has been detected in human tissues or cell lines. SULT2B1b is localized in the cytosol and/or nuclei of human cells. A unique 3'-extension of SULT2B1b is required for nuclear localization in human BeWo placental choriocarcinoma cells. Nuclear localization is stimulated by forskolin treatment in BeWo cells and serine phosphorylation has been identified in the 3'-extension. SULT2B1b is selective for the sulfation of 3beta-hydroxysteroids such as dehydroepiandrosterone and pregnenolone, and may also have a role in cholesterol sulfation in human skin. The substrate specificity, nuclear localization, and tissue localization of SULT2B1b suggest a role in regulating the responsiveness of cells to adrenal androgens via their direct inactivation or by preventing their conversion to more potent androgens and estrogens.

Sulfation of the isoflavones genistein and daidzein in human and rat liver and gastrointestinal tract

Phytoestrogens, in particular the isoflavone aglycones genistein and daidzein, are thought to be the bioactive components of soy. Like estrogens, isoflavones can be sulfur-conjugated. However, although isoflavones in the serum are found largely in the form of glucuronide and sulfur conjugates following soy consumption, little is known regarding the relative contributions of sulfotransferases in the liver and small intestine to isoflavone sulfation. Since the sulfates may be deconjugated in target tissues, circulating isoflavone sulfates may act as a source of tissue aglycones. In the current study genistein and daidzein sulfotransferase activities were measured in cytosol from human and rat liver and gastrointestinal tract. Isoflavone sulfation in the human gastrointestinal (GI) tract was correlated with activities towards substrates for previously characterized human sulfotransferases. Western blots of human cytosols were also conducted using antisera towards human sulfotransferases SULT1E1 and SULT2A1. Whereas rat liver was almost fourfold more active than small intestine in sulfation of genistein, in the human, activities in the two tissues were comparable. In contrast, intestinal sulfation of daidzein was comparable to hepatic sulfation in the rat and significantly greater in the human. Genistein and daidzein sulfation occurred throughout the human GI tract, but with a different distribution and different interindividual variability. Whereas genistein sulfation in the human GI tract correlated significantly with sulfation of the prototypical human phenolic sulfotransferase SULT1A family substrate 2-naphthol (r2 = 0.71), daidzein sulfotransferase activity did not correlate with activities towards any prototypical sulfotransferase substrate or with genistein sulfation. Our results suggest that metabolism in the human GI tract has an important role in the generation of potentially bioactive isoflavone sulfates and a major role for the human phenolic sulfotransferase SULT1A family in metabolism of genistein in the gut. However, human intestinal daidzein sulfation appears to be catalyzed by a separate enzyme.

Identification of novel hydroxysteroid-sulfating cytosolic SULTs, SULT2 ST2 and SULT2 ST3, from zebrafish: Cloning, expression, characterization, and developmental expression

By searching the expressed sequence tag database, two zebrafish cDNAs encoding putative cytosolic sulfotransferases (SULTs) were identified. Sequence analysis indicated that these two zebrafish SULTs belong to the cytosolic SULT2 gene family. The recombinant form of these two novel zebrafish SULTs, designated SULT2 ST2 and SULT2 ST3, were expressed using the pGEX-2TK glutathione S-transferase (GST) gene fusion system and purified from transformed BL21 (DE3) Escherichia coli cells. Purified GST-fusion protein form of SULT2 ST2 and SULT2 ST3 exhibited strong sulfating activities toward dehydroepiandrosterone (DHEA) and corticosterone, respectively, among various endogenous compounds tested as substrates. Both enzymes displayed pH optima at approximately 6.5. Kinetic constants of the two enzymes, as well as the GST-fusion protein form of the previously identified SULT2 ST1, with DHEA and corticosterone as substrates were determined. Developmental stage-dependent expression experiments revealed distinct patterns of expression of SULT2 ST2 and SULT2 ST3, as well as the previously identified SULT2 ST1, during embryonic development and throughout the larval stage onto maturity.

Xenobiotic- and vitamin D-responsive induction of the steroid/bile acid-sulfotransferase Sult2A1 in young and old mice: the role of a gene enhancer in the liver chromatin

The xenobiotic-activated nuclear receptors PXR (pregnane X receptor) and CAR (constitutive androstane receptor) and the vitamin D(3)-activated nuclear receptor VDR regulate steroid and xenobiotic metabolism by inducing the phase I cytochrome P450 monooxygenases, phase II conjugating transferases, and the phase III transporters, which mediate the efflux of water-soluble lipid metabolites from cells. Metabolic stress due to the deviant expression of steroid- and xenobiotic-metabolizing enzymes is known to have severe health consequences including accelerated aging, and increased expression of these enzymes is associated with extended longevity [Gachon, F, Olela, FF, Schaad, O, Descombes, P and Schibler, U, 2006. The circadian PAR-domain basic leucine zipper transcription factors DBP, TEF, and HLF modulate basal and inducible xenobiotic detoxification. 4, 25-36.; McElwee, JJ, Schuster, E, Blanc, E, Thomas, JH and Gems, D, 2004. Shared Transcriptional Signature in Caenorhabditis elegans Dauer Larvae and Long-lived daf-2 Mutants Implicates Detoxification System in Longevity Assurance. J. Biol. Chem., 279, 44533-43.]. Information on the similarities and dissimilarities in drug metabolism between the young and old, as may be uncovered by studying aging regulation of the genes relevant to steroid and xenobiotic metabolism, is likely to have clinical significance. In this report, we examined the VDR- and PXR-mediated gene induction of the phase II sulfotransferase Sult2A1 in the livers of 4-month- and 20-month-old mice. Sult2A1 converts bile acids, steroids and a number of drugs to the corresponding sulfated metabolites, which are readily eliminated from the body due to increased water solubility. In RT-PCR assay, aging did not change the induction of Sult2A1 mRNAs by the hormonally active vitamin D(3) and the catatoxic synthetic steroid PCN (pregnenolone-16alpha-carbonitrile). Chromatin immunoprecipitation (ChIP) from liver nuclei showed that aging had no effect on the activity of an IR0 enhancer in the Sult2A1 chromatin to recruit VDR, RXR-alpha (retinoid X receptor) and PXR in mice injected with D(3) or PCN. Thus, mice in late life are as competent as those in early life in responding to the hormonal and xenobiotic signaling for Sult2A1 induction. This is the first report describing the role of aging in the functional response of an enhancer in the liver chromatin to the nuclear receptor-dependent signaling.