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

Sulfation of hesperetin, naringenin and apigenin by the human cytosolic sulfotransferases: a comprehensive analysis

Previous studies have revealed sulfation as a major pathway for the metabolism of hesperetin, naringenin and apigenin. The current study was designed to identify the human cytosolic sulfotransferase (SULT) enzyme(s) capable of sulfating these flavonoid compounds. Of the thirteen human SULTs, six (1A1, 1A2, 1A3, 1B2, 1C4, 1E1) displayed significant sulfating activity toward hesperetin, five (1A1, 1A2, 1A3, 1B2, 1C4) displayed sulfating activity towards naringenin, and four (1A1, 1A2, 1A3, 1C4) showed sulfating activity towards apigenin. Of the four human organ specimens tested, liver and intestine cytosols displayed much higher hesperetin-, naringenin- and apigenin-sulfating activity than lung and kidney cytosols. Moreover, sulfation of hesperetin, naringenin and apigenin was shown to take place in HepG2 human hepatoma cells and Caco-2 human colon adenocarcinoma cells under cultured conditions. Taken together, these results provided a biochemical basis underlying the metabolism of hesperetin, naringenin and apigenin through sulfation in humans.[Formula: see text].

Polypharmacology or Promiscuity? Structural Interactions of Resveratrol With Its Bandwagon of Targets

Resveratrol (3, 4', 5-trihydroxy-trans-stilbene) is a natural phytoalexin found in grapes and has long been thought to be the answer to the "French Paradox." There is no shortage of preclinical and clinical studies investigating the broad therapeutic activity of resveratrol. However, in spite of many comprehensive reviews published on the bioactivity of resveratrol, there has yet to be a report focused on the variety and complexity of its structural binding properties, and its multi-targeted role. An improved understanding of disease mechanisms at the systems level has enabled targeted polypharmacology to mature into a rational drug discovery approach. Unlike traditional hit-to-lead campaigns that typically optimize activity and selectivity for a single target, polypharmacological drugs aim to selectively target multiple proteins, while avoiding critical off target interactions. This strategy bears promise of improved efficacy and reduced clinical attrition. This review seeks to investigate whether the bioactivity of resveratrol is due to a polypharmacological effect or promiscuity of the phenolic small molecule by examining the modes of binding with its diverse collection of protein targets. We focused on annotated targets, identified via the ChEMBL database, and matched these targets to a representative structure deposited in the Protein Data Bank (PDB), as crystal structures are most informative in understanding modes of binding at the atomic level. We discuss the structural aspects of resveratrol itself that permits binding to multiple proteins in various signaling pathways. Furthermore, we suggest that resveratrol's bioactivity is a result of scaffold promiscuity rather than polypharmacology, and the variety of binding modes across targets display little similarity in the pattern of target interaction.

Effects of Human Sulfotransferase 2A1 Genetic Polymorphisms 3 on the Sulfation of Tibolone

BACKGROUND AND OBJECTIVES

Previous studies have demonstrated the metabolism of tibolone through sulfation, with the cytosolic sulfotransferase (SULT) SULT2A1 as the major responsible enzyme. The current study aimed to investigate how SULT2A1 genetic polymorphisms may affect the dehydroepiandrosterone (DHEA)- and tibolone-sulfating activity of SULT2A1.

METHODS

Site-directed mutagenesis was employed to generate cDNAs encoding ten different SULT2A1 allozymes. Recombinant SULT2A1 allozymes were expressed in BL21 E. coli cells, and purified using glutathione-sepharose affinity chromatography. An established sulfotransferase assay was used to analyze DHEA- and tibolone-sulfating activity of the purified SULT2A1 allozymes.

RESULTS

The nine human SULT2A1 allozymes plus the wild-type SULT2A1 were found to display differential sulfating activity toward DHEA and tibolone. Kinetic analysis revealed that different SULT2A1 allozymes exhibited differential substrate affinity and catalytic efficiency toward the two substrates tested.

CONCLUSION

The results obtained provided useful information concerning the differential metabolism of tibolone through sulfation in individuals with different SULT2A1 genotypes.

The Clock Protein Bmal1 Regulates Circadian Expression and Activity of Sulfotransferase 1a1 in Mice

Sulfotransferase 1a1 (Sult1a1) is a phase II enzyme that contributes extensively to metabolism and detoxification of various drugs and chemicals. Here we aimed to investigate a potential role of the clock protein Bmal1 (brain and muscle Arnt-like protein-1) in circadian regulation of Sult1a1 in mice. The regulatory effects of Bmal1 on Sult1a1 were assessed both in vivo (using Bmal1- deficient mice) and in vitro (using both normal and serum-shocked Hepa-1c1c7 cells). The relative mRNA and protein levels of Sult1a1 in the cells or mouse livers were measured by RT-qPCR and Western blotting, respectively. Sulfation activities of two Sult1a1 substrates (i.e., p-nitrophenol and galangin) were determined using mouse liver S9 fractions. Transcriptional regulation of Sult1a1 by Bmal1 was investigated using luciferase reporter, electrophoretic mobility shift (EMSA), and chromatin immunoprecipitation (ChIP) assays. We first showed that hepatic Sult1a1 was rhythmically expressed at both mRNA and protein levels (higher expressions during the night than the daytime). Consistently, the liver sulfation activities toward two Sult1a1 substrates were circadian time dependent with a higher activity at ZT14 than at ZT2. Furthermore, deletion of Bmal1 in mice blunted the circadian rhythmicity of hepatic Sult1a1 (with reduced expression levels). Likewise, Bmal1 positively regulated Sult1a1 expression in conventionally cultured Hepa-1c1c7 cells, and Bmal1 knockdown blunted expression rhythmicity of Sult1a1 in serum-shocked Hepa-1c1c7 cells. A combination of promoter analysis, EMSA and ChIP assays revealed that Bmal1 stimulated Sult1a1 transcription through its specific binding to the-571- to -554-bp region (an E-box element) in the promoter. In conclusion, Bmal1 activated the transcription of Sult1a1 and controlled circadian expression and activity of the enzyme.

The sulfoconjugation of androstenone and dehydroepiandrosterone by human and porcine sulfotransferase enzymes

Porcine sulfotransferase 2A1 (pSULT2A1) is a key enzyme involved in the testicular and hepatic sulfoconjugation of steroids such as dehydroepiandrosterone (DHEA) and potentially androstenone. This latter steroid is a major cause of boar taint, which is an unpleasant off-odour and off-flavour in pork from male pigs. Sulfotransferase 2B1 (pSULT2B1) may also be important, although no direct evidence exists for its involvement in sulfoconjugation of steroids. The purpose of this study was to investigate the sulfoconjugation activity of human and porcine sulfotransferases towards DHEA and androstenone. pcDNA 3.1 vectors expressing porcine (p) SULT2A1, pSULT2B1, human (h) SULT2A1, hSULT2B1a, and hSULT2B1b enzymes were transfected into human embryonic kidney cells. Transfected cells were then incubated with either androstenone or dehydroepiandrosterone (DHEA) in both time-course and enzyme kinetics studies. The production of sulfonates of androstenone metabolites and DHEA sulfonate increased over time for all enzymes with the exception of pSULT2B1. Enzyme kinetics analysis showed that androstenone and DHEA were poor substrates for the human orthologs, hSULT2B1a and hSULT2B1b. Human and porcine SULT2A1 showed substantially different substrate affinities for androstenone (K_m 5.8 ± 0.6 µM and 74.1 ± 15.9 µM, respectively) and DHEA (K_m 9.4 ± 2.5 µM and 3.3 ± 1.9 µM, respectively). However, these enzymes did show relatively similar sulfonation efficiencies for DHEA (V_max/K_m 50.5 and 72.9 for hSULT2A1 and pSULT2A1, respectively). These results highlight the species differences in sulfonation activity and provide direct evidence, for the first time, suggesting that pSULT2B1 is not involved in sulfonation of either androstenone metabolites or DHEA.

Molecular and functional analysis of PmCHST1b in nacre formation of Pinctada fucata martensii

Keratan sulfate possesses considerable amounts of negatively charged sulfonic acid groups and participates in biomineralization. In the present study, we investigated characteristics and functions of a CHST1 gene identified from the pearl oyster Pinctada fucata martensii (PmCHST1b) which participated in the synthesis of keratan sulfate. PmCHST1b amino acid sequence carried a typical sulfotransferase-3 domain (sulfotransfer-3 domain) and belonged to membrane-associated sulfotransferases. Homologous analysis of CHST1 from different species showed the conserved motif (5' PSB motif and 3' PB motif) which interacted with 3'-phosphoadenosine-5'-phosphosulfate (PAPS). Structure analysis of sulfotransferase domain indicted that PmCHST1b showed the conserved catalytic structure character and the relationships presented in the phylogenetic tree conformed to that of traditional taxonomy. Expression pattern of PmCHST1b in different tissues and development stages showed that PmCHST1b widely expressed in all the detected tissues and development stages and showed the highest expression level in the central zone of mantle (MC). PmCHST1b expressed highly in the trochophore, D-stage larvae and spat which corresponded to prodissoconch and dissoconch shell formation, respectively. RNA interference (RNAi) successfully inhibited expression level of PmCHST1b in MC (P<0.05), and sulfate polymer content in the extrapallial fluid significantly reduced (P<0.05). Crystallization of shell nacre became irregular. Results above indicated that PmCHST1b may affect nacre formation by participating in synthesis of keratan sulfate in extrapallial fluid. This study provided fundamental materials for further research on the role of sulfotransferases and keratan sulfate in nacre formation.

Sterol Sulfates and Sulfotransferases in Marine Diatoms

Sterol sulfates are widely occurring molecules in marine organisms. Their importance has been so far underestimated although many of these compounds are crucial mediators of physiological and ecological functions in other organisms. Biosynthesis of sterol sulfates is controlled by cytosolic sulfotransferases (SULTs), a varied family of enzymes that catalyze the transfer of a sulfo residue (-SO₃H) from the universal donor 3'-phosphoadenosine-5'-phosphosulfate to the hydroxyl function at C-3 of the steroid skeleton. The absence of molecular tools has been the main impediment to the development of a biosynthetic study of this class of compounds in marine organisms. In fact, there is very limited information about these enzymes in marine environments. SULT activity has, however, been reported in several marine species, and, recently, the production of sterol sulfates has been linked to the control of growth in marine diatoms. In this chapter, we describe methods for the study of sterol sulfates in this lineage of marine microalgae. The main aim is to provide the tools useful to deal with the biosynthesis and regulation of these compounds and to circumvent the bottleneck of the lack of molecular information. The protocols have been designed for marine diatoms, but most of the procedures can be used for other marine organisms.

Occurrence of sulfonated steroids and ovarian expression of steroid sulfatase and SULT1E1 in cyclic cows

Historically sulfonated steroids were primarily considered as inactive metabolites destined for elimination. However, more recently they have been increasingly recognized as precursors for the production of bioactive steroids in target tissues and as functional molecules without preceding hydrolysis. In order to comprehensively characterize their occurrence in cyclic cows and their formation and hydrolysis in bovine ovarian steroidogenesis, ovaries from cyclic cows were screened for the expression of oestrogen sulfotransferase (SULTE1) and steroid sulfatase (STS) by Western blot and immunohistochemistry. Moreover, a broad spectrum of 13 sulfonated steroids was measured applying liquid chromatography-tandem mass spectrometry (LC-MS/MS) in blood samples collected from three cycling heifers during defined stages of the ovarian cycle and in fluid obtained from ovarian follicles of different size. SULT1E1 was undetectable in ovarian tissues. For STS only a weak immunostaining was found predominantly in granulosa cells of larger follicles. However, no specific band occurred in Western blot. In blood, concentrations of all sulfonated steroids investigated were below the limit of quantification (LOQ). In follicular fluid, only cholesterol sulfate was measured in considerable concentrations (328.3 ± 63.8 ng/ml). However, the role of cholesterol sulfate in bovine follicular steroidogenesis remains unclear as concentrations were obviously unrelated to follicular size. The remaining sulfonated steroids investigated were undetectable or only slightly exceeded LOQ in a minor proportion of samples. The results are clearly contrary to a role of sulfonated steroids as important precursors, intermediates or products of bovine ovarian steroidogenesis.

The critical role of His48 in mouse cytosolic sulfotransferase SULT2A8 for the 7α-hydroxyl sulfation of bile acids

Members of the cytosolic sulfotransferase (SULT) SULT2A subfamily are known to be critically involved in the homeostasis of steroids and bile acids. SULT2A8, a 7α-hydroxyl bile acid-preferring mouse SULT, has been identified as the major enzyme responsible for the mouse-specific 7-O-sulfation of bile acids. Interestingly, SULT2A8 lacks a conservative catalytic His residue at position 99th. The catalytic mechanism underlying the SULT2A8-mediated 7-O-sulfation of bile acids thus remained unclear. In this study, we performed a mutational analysis in order to gain insight into this yet-unresolved issue. Results obtained revealed two amino acid residues, His48 and Leu99, that are unique to the mouse SULT2A8, but not other SULTs, are essential for its 7-O-sulfating activity toward bile acids. These findings suggested that substitutions of two amino acids, which might have occurred during the evolution of the mouse SULT2A8 gene, endowed mouse SULT2A8 the capacity to catalyze the 7-O-sulfation of bile acids.

Identification of Galeterone and Abiraterone as Inhibitors of Dehydroepiandrosterone Sulfonation Catalyzed by Human Hepatic Cytosol, SULT2A1, SULT2B1b, and SULT1E1

Galeterone and abiraterone acetate are antiandrogens developed for the treatment of metastatic castration-resistant prostate cancer. In the present study, we investigated the effect of these drugs on dehydroepiandrosterone (DHEA) sulfonation catalyzed by human liver and intestinal cytosols and human recombinant sulfotransferase enzymes (SULT2A1, SULT2B1b, and SULT2E1) and compared their effects to those of other antiandrogens (cyproterone acetate, spironolactone, and danazol). Each of these chemicals (10 μM) inhibited DHEA sulfonation catalyzed by human liver and intestinal cytosols. Enzyme kinetic analysis showed that galeterone and abiraterone acetate inhibited human liver cytosolic DHEA sulfonation with apparent Ki values at submicromolar concentrations, whereas cyproterone acetate, spironolactone, and danazol inhibited it with apparent Ki values at low micromolar concentrations. The temporal pattern of abiraterone formation and abiraterone acetate depletion suggested that the metabolite abiraterone, not the parent drug abiraterone acetate, was responsible for the inhibition of DHEA sulfonation in incubations containing human liver cytosol and abiraterone acetate. Consistent with this proposal, similar apparent Ki values were obtained, regardless of whether abiraterone or abiraterone acetate was added to the enzymatic incubation. Abiraterone was more effective than abiraterone acetate in inhibiting DHEA sulfonation when catalyzed by human recombinant SULT2A1 or SULT2B1b. In conclusion, galeterone and abiraterone are novel inhibitors of DHEA sulfonation, as determined in enzymatic incubations containing human tissue cytosol (liver or intestinal) or human recombinant SULT enzyme (SULT2A1, SULT2B1b, or SULT1E1). Our findings on galeterone and abiraterone may have implications in drug-drug interactions and biosynthesis of steroid hormones.

A robust protocol for directed aryl sulfotransferase evolution toward the carbohydrate building block GlcNAc

Bacterial aryl sulfotransferases (AST) utilize p-nitrophenylsulfate (pNPS) as a phenolic donor to sulfurylate typically a phenolic acceptor. Interest in aryl sulfotransferases is growing because of their broad variety of acceptors and cost-effective sulfuryl-donors. For instance, aryl sulfotransferase A (ASTA) from Desulfitobacterium hafniense was recently reported to sulfurylate d-glucose. In this study, a directed evolution protocol was developed and validated for aryl sulfotransferase B (ASTB). Thereby the well-known pNPS quantification system was advanced to operate efficiently as a continuous screening system in 96-well MTP format with a true coefficient of variation of 14.3%. A random mutagenesis library (SeSaM library) of ASTB was screened (1,760 clones) to improve sulfurylation of the carbohydrate building block N-acetylglucosamine (GlcNAc). The beneficial variant ASTB-V1 (Val579Asp) showed an up to 3.4-fold increased specific activity toward GlcNAc when compared to ASTB-WT. HPLC- and MS-analysis confirmed ASTB-V1's increased GlcNAc monosulfurylation (2.4-fold increased product formation) representing the validation of the first successful directed evolution round of an AST for a saccharide substrate.

Human Cytosolic Sulphotransferase SULT1C3: genomic analysis and functional characterization of splice variant SULT1C3a and SULT1C3d

The cytosolic sulphotransferase SULT1C3 remained the most poorly understood human SULT. The SULT1C3 gene has been shown to contain alternative exons 7 and 8, raising the question concerning their evolutionary origin and implying the generation of multiple SULT1C3 variants. Two SULT1C3 splice variants, SULT1C3a and SULT1C3d, were investigated to verify the impact of alternative C-terminal sequences on their sulphating activity. Sequence homology and gene location analyses were performed to verify the orthology of the SULT1C3 gene. The SULT1C3 gene appears to be present only in humans and other primates, but alternative exons 7b and 8b share high degrees of homology with corresponding regions of rodent SULT1C1 genes, implying their evolutionary origin being from a defunct human SULT1C1 gene. Purified recombinant SULT1C3a and SULT1C3d were analyzed for sulphating activities toward a variety of endogenous and xenobiotic compounds. While SULT1C3a displayed weaker activities and strict substrate specificity toward hydroxyl-chlorinated biphenyls, SULT1C3d exhibited broader substrate specificity toward bile acids and thyroid hormones as well as hydroxyl-chlorinated biphenyls. Molecular docking simulation suggested that Tyr249 and Met257 may play an important role in substrate recognition by SULT1C3d. Alternative splicing of exons 7 and 8 sequences resulted in differential catalytic properties of SULT1C3 variants.

Δ4-3-ketosteroids as a new class of substrates for the cytosolic sulfotransferases

Cytosolic sulfotransferase (SULT)-mediated sulfation is generally known to involve the transfer of a sulfonate group from the active sulfate, 3'-phosphoadenosine 5'-phosphosulfate (PAPS), to a hydroxyl group or an amino group of a substrate compound. We report here that human SULT2A1, in addition to being able to sulfate dehydroepiandrosterone (DHEA) and other hydroxysteroids, could also catalyze the sulfation of Δ⁴-3-ketosteroids, which carry no hydroxyl groups in their chemical structure. Among a panel of Δ⁴-3-ketosteroids tested as substrates, 4-androstene-3,17-dione and progesterone were found to be sulfated by SULT2A1. Mass spectrometry analysis and structural modeling supported a reaction mechanism which involves the isomerization of Δ⁴-3-ketosteroids from the keto form to an enol form, prior to being subjected to sulfation. Results derived from this study suggested a potential role of SULT2A1 as a Δ⁴-3-ketosteroid sulfotransferase in steroid metabolism.

Tetrahydrobiopterin regulates monoamine neurotransmitter sulfonation

Monoamine neurotransmitters are among the hundreds of signaling small molecules whose target interactions are switched "on" and "off" via transfer of the sulfuryl-moiety (-SO3) from PAPS (3'-phosphoadenosine 5'-phosphosulfate) to the hydroxyls and amines of their scaffolds. These transfer reactions are catalyzed by a small family of broad-specificity enzymes-the human cytosolic sulfotransferases (SULTs). The first structure of a SULT allosteric-binding site (that of SULT1A1) has recently come to light. The site is conserved among SULT1 family members and is promiscuous-it binds catechins, a naturally occurring family of flavanols. Here, the catechin-binding site of SULT1A3, which sulfonates monoamine neurotransmitters, is modeled on that of 1A1 and used to screen in silico for endogenous metabolite 1A3 allosteres. Screening predicted a single high-affinity allostere, tetrahydrobiopterin (THB), an essential cofactor in monoamine neurotransmitter biosynthesis. THB is shown to bind and inhibit SULT1A3 with high affinity, 23 (±2) nM, and to bind weakly, if at all, to the four other major SULTs found in brain and liver. The structure of the THB-bound binding site is determined and confirms that THB binds the catechin site. A structural comparison of SULT1A3 with SULT1A1 (its immediate evolutionary progenitor) reveals how SULT1A3 acquired high affinity for THB and that the majority of residue changes needed to transform 1A1 into 1A3 are clustered at the allosteric and active sites. Finally, sequence records reveal that the coevolution of these sites played an essential role in the evolution of simian neurotransmitter metabolism.

Implications of sulfotransferase activity in interindividual variability in drug response: clinical perspective on current knowledge

The interindividual variability in drug response is a major issue in clinical practice and in drug development. Sulfoconjugation is an important Phase II reaction catalyzed by cytosolic sulfotransferases (SULTs), playing a major role in homeostatic functions, xenobiotic detoxification, and carcinogen bioactivation. SULT display wide interindividual variability, explained only partially by genetic variation, suggesting that other non-genetic, epigenetic, and environmental influences could be major determinants of variability in SULT activity. This review focuses on the factors known to influence SULT variability in expression and activity and the available evidence regarding the impact of SULT variability on drug response.

A reappraisal of the 6-O-desmethylnaproxen-sulfating activity of the human cytosolic sulfotransferases

In this study, we aimed to obtain a comprehensive account of the human cytosolic sulfotransferases (SULTs) that are capable of sulfating 6-O-desmethylnaproxen (O-DMN), a major metabolite of naproxen. Of the 13 known human SULTs tested, 7 (SULT1A1, SULT1A2, SULT1A3, SULT1B1, SULT1C2, SULT1C4, and SULT1E1) displayed O-DMN-sulfating activity, when analyzed using an elevated substrate concentration (500 μmol·L−1) together with 14 μmol·L−1 of the sulfate donor, 3′-phosphoadenosine-5′-phosphosulfate (PAPS). At 10 μmol·L−1 O-DMN concentration, however, only SULT1A1 and SULT1A3 displayed detectable activity, with the former being nearly 2 orders of magnitude more active than the latter. A pH-dependence study indicated that SULT1A1 exhibited a broad pH optimum spanning pH 5.5–7. Kinetic parameters of the sulfation of O-DMN by SULT1A1 were determined. The production and release of sulfated O-DMN was demonstrated using cultured human HepG2 hepatoma cells and Caco-2 colon carcinoma cells. Moreover, assays using human organ specimens revealed that the O-DMN-sulfating activities present in the cytosols of liver and small intestine (at 502.5 and 497.2 pmol·min−1·(mg protein)−1, respectively) were much higher than those detected for the cytosols of lung and kidney. Taken together, these results provided relevant information concerning the sulfation of O-DMN both in vitro and in vivo.

Identification and characterization of a novel PPARα-regulated and 7α-hydroxyl bile acid-preferring cytosolic sulfotransferase mL-STL (Sult2a8)

PPARα has been known to play a pivotal role in orchestrating lipid, glucose, and amino acid metabolism via transcriptional regulation of its target gene expression during energy deprivation. Recent evidence has also suggested that PPARα is involved in bile acid metabolism, but how PPARα modulates the homeostasis of bile acids during fasting is still not clear. In a mechanistic study aiming to dissect the spectrum of PPARα target genes involved in metabolic response to fasting, we identified a novel mouse gene (herein named mL-STL for mouse liver-sulfotransferase-like) that shared extensive homology with the Sult2a subfamily of a superfamily of cytosolic sulfotransferases, implying its potential function in sulfonation. The mL-STL gene expressed predominantly in liver in fed state, but PPARα was required to sustain its expression during fasting, suggesting a critical role of PPARα in regulating the mL-STL-mediated sulfonation during fasting. Functional studies using recombinant His-tagged mL-STL protein revealed its narrow sulfonating activities toward 7α-hydroxyl primary bile acids, including cholic acid, chenodeoxycholic acid, and α-muricholic acid, and thus suggesting that mL-STL may be the major hepatic bile acid sulfonating enzyme in mice. Together, these studies identified a novel PPARα-dependent gene and uncovered a new role of PPARα as being an essential regulator in bile acid biotransformation via sulfonation during fasting.

Influence of testosterone on phase II metabolism and availability of soy isoflavones in male Wistar rats

Genistein and daidzein are the main isoflavones in soy. Their potential beneficial or adverse effects in males like the prevention of prostate cancer or the impact on reproductive functions are controversially discussed. Major determinants of their bioactivity are the absorption and biotransformation of isoflavones. In this study, we focused on the influence of testosterone on plasma availability and phase II metabolism of isoflavones. Male Wistar rats, receiving an isoflavones rich diet, were randomized into three groups: Two groups were orchiectomized (ORX) at postnatal day (PND) 80 and treated for 11 days with testosterone propionate (TP) (ORX TP group) or a vehicle (ORX group) after a 7 days lasting hormonal decline. The third group served as control and remained intact. Rats were sacrificed at PND 98. ORX rats had reduced isoflavones plasma levels. Differently regulated mRNA expressions of transporters relevant for transport of phase II metabolites in liver and kidney may be responsible for this reduction, more precisely Slc10a1 and Slc21a1 in kidney as well as Slc22a8 in liver. While main phase II metabolites in intact rats were disulfates and sulfoglucuronides, the amount of sulfate conjugates was significantly diminished by ORX. In accordance with that, mRNA expression of different sulfotransferases was reduced in liver by ORX. The observed effects could be almost restored by TP treatment. In conclusion, testosterone, and likely further androgens, has a huge impact on phase II metabolism and availability of isoflavones by influencing the expression of different sulfotransferases and transporters.

Expression, purification and characterization of human cytosolic sulfotransferase (SULT) 1C4

Human cytosolic sulfotransferase 1C4 (hSULT1C4) is a dimeric Phase II drug-metabolizing enzyme primarily expressed in the developing fetus. SULTs facilitate the transfer of a hydrophilic sulfonate moiety from 3'-phosphoadenosine-5'-phosphosulfate (PAPS) onto an acceptor substrate altering the substrate's biological activity and increasing the compound's water solubility. While several of the hSULTs' endogenous and xenobiotic substrates have been identified, the physiological function of hSULT1C4 remains unknown. The fetal expression of hSULT1C4 leads to the hypothesis that the function of this enzyme may be to regulate metabolic and hormonal signaling molecules, such as estrogenic compounds, that may be generated or consumed by the mother during fetal development. Human SULT1C4 has previously been shown to sulfonate estrogenic compounds, such as catechol estrogens; therefore, this study focused on the expression and purification of hSULT1C4 in order to further characterize this enzyme's sulfonation of estrogenic compounds. Molecular modeling of the enzyme's native properties helped to establish a novel purification protocol for hSULT1C4. The optimal activity assay conditions for hSULT1C4 were determined to be pH 7.4 at 37°C for up to 10 min. Kinetic analysis revealed the enzyme's reduced affinity for PAPS compared to PAP. Human SULT1C4 sulfonated all the estrogenic compounds tested, including dietary flavonoids and environmental estrogens; however, the enzyme has a higher affinity for sulfonation of flavonoids. These results suggest hSULT1C4 could be metabolizing and regulating hormone signaling pathways during human fetal development.

Regioselective production of sulfated polyphenols using human cytosolic sulfotransferase-expressing Escherichia coli cells

Dietary polyphenols present in fruits and vegetables have been reported to manifest beneficial health effects on humans. Polyphenol metabolites including their sulfated derivatives have been shown to be biologically active. Primarily due to the difficulty in preparing regiospecific sulfated polyphenols for detailed investigations, the exact functions of sulfated polyphenols, however, remain unclear. The current study aimed to develop a procedure for the regioselective production of sulfated polyphenols using Escherichia coli cells expressing human cytosolic sulfotransferases (SULTs). Two regioisomers of sulfated genistein were produced by E. coli cells expressing human SULT1A3, SULT1C4, or SULT1E1, and purified using Diaion HP20 resin, followed by high pressure liquid chromatography (HPLC). Structural analysis using mass spectrometry (MS) and nuclear magnetic resonance (NMR) revealed that E. coli cells expressing SULT1A3 preferentially produced genistein 4'-sulfate, whereas E. coli cells expressing SULT1C4 preferentially produced genistein 7-sulfate. To improve the bioproductivity, the effects of several factors including the concentrations of glucose and SO₄^2-, and growth temperature were investigated. The bioproduction procedure established in this study will be valuable for the production of regioselective sulfated polyphenols for use in future studies on their biological functions.

The structure of the catechin-binding site of human sulfotransferase 1A1

We are just beginning to understand the allosteric regulation of the human cytosolic sulfotransferase (SULTs) family-13 disease-relevant enzymes that regulate the activities of hundreds, if not thousands, of signaling small molecules. SULT1A1, the predominant isoform in adult liver, harbors two noninteracting allosteric sites, each of which binds a different molecular family: the catechins (naturally occurring flavonols) and nonsteroidal antiinflammatory drugs (NSAIDs). Here, we present the structure of an SULT allosteric binding site-the catechin-binding site of SULT1A1 bound to epigallocatechin gallate (EGCG). The allosteric pocket resides in a dynamic region of the protein that enables EGCG to control opening and closure of the enzyme's active-site cap. Furthermore, the structure offers a molecular explanation for the isozyme specificity of EGCG, which is corroborated experimentally. The binding-site structure was obtained without X-ray crystallography or multidimensional NMR. Instead, a SULT1A1 apoprotein structure was used to guide positioning of a small number of spin-labeled single-Cys mutants that coat the entire enzyme surface with a paramagnetic field of sufficient strength to determine its contribution to the bound ligand's transverse (T₂) relaxation from its 1D solution spectrum. EGCG protons were mapped to the protein surface by triangulation using the T₂ values to calculate their distances to a trio of spin-labeled Cys mutants. The final structure was obtained using distance-constrained molecular dynamics docking. This approach, which is readily extensible to other systems, is applicable over a wide range of ligand affinities, requires little protein, avoids the need for isotopically labeled protein, and has no protein molecular weight limitations.

Transcriptional Regulation of Human Cytosolic Sulfotransferase 1C3 by Peroxisome Proliferator-Activated Receptor γ in LS180 Human Colorectal Adenocarcinoma Cells

Cytosolic sulfotransferase 1C3 (SULT1C3) is the least characterized of the three human SULT1C subfamily members. Originally identified as an orphan SULT by computational analysis of the human genome, we recently reported that SULT1C3 is expressed in human intestine and LS180 colorectal adenocarcinoma cells and is upregulated by agonists of peroxisome proliferator-activated receptor (PPAR) α and γ To determine the mechanism responsible for PPAR-mediated upregulation, we prepared reporter plasmids containing fragments of the SULT1C3 5'-flanking region. During initial attempts to amplify a 2.8-kb fragment from different sources of human genomic DNA, a 1.9-kb fragment was sometimes coamplified with the expected 2.8-kb fragment. Comparison of the 1.9-kb fragment sequence to the published SULT1C3 5'-flanking sequence revealed an 863-nt deletion (nt -146 to -1008 relative to the transcription start site). Transfection analysis in LS180 cells demonstrated that PPARα, δ, and γ agonist treatments induced luciferase expression from a reporter plasmid containing the 2.8-kb but not the 1.9-kb fragment. The PPAR agonists also activated a 1-kb reporter containing the 863-nt deletion region. Computational analysis identified three peroxisome proliferator response elements (PPREs) within the 863-nt region and serial deletions and site-directed mutations indicated that the most distal PPRE (at nt -769) was essential for obtaining PPAR-mediated transcriptional activation. Although agonists of all three PPARs could activate SULT1C3 transcription, RNA interference analysis indicated the predominance of PPARγ These data demonstrate that the PPARγ regulatory network includes SULT1C3 and imply that this enzyme contributes to the control of such PPARγ-regulated intestinal processes as growth, differentiation, and metabolism.

Updated perspectives on the cytosolic sulfotransferases (SULTs) and SULT-mediated sulfation

The cytosolic sulfotransferases (SULTs) are Phase II detoxifying enzymes that mediate the sulfate conjugation of numerous xenobiotic molecules. While the research on the SULTs has lagged behind the research on Phase I cytochrome P-450 enzymes and other Phase II conjugating enzymes, it has gained more momentum in recent years. This review aims to summarize information obtained in several fronts of the research on the SULTs, including the range of the SULTs in different life forms, concerted actions of the SULTs and other Phase II enzymes, insights into the structure-function relationships of the SULTs, regulation of SULT expression and activity, developmental expression of SULTs, as well as the use of a zebrafish model for studying the developmental pharmacology/toxicology.

Arylsulfatase B Mediates the Sulfonation-Transport Interplay in Human Embryonic Kidney 293 Cells Overexpressing Sulfotransferase 1A3

Elucidating the intricate relationships between metabolic and transport pathways contributes to improved predictions of in vivo drug disposition and drug-drug interactions. Here we reported that inhibited excretion of conjugative metabolites [i.e., hesperetin 3'-O-sulfate (H3'S) and hesperetin 7-O-sulfate (H7S)] by MK-571 led to reduced metabolism of hesperetin (a maximal 78% reduction) in human embryonic kidney 293 cells overexpressing sulfotransferase 1A3 (named SULT293 cells). The strong dependence of cellular sulfonation on the efflux transport of generated sulfated metabolites revealed an interplay of sulfonation metabolism with efflux transport (or sulfonation-transport interplay). Polymerase chain reaction (PCR) and Western blot analyses demonstrated that SULT293 cells expressed multiple sulfatases such as arylsulfatase A (ARSA), ARSB, and ARSC. Of these three desulfonation enzymes, only ARSB showed significant activities toward hesperetin sulfates. The intrinsic clearance values for the hydrolysis of H3'S and H7S were estimated at 0.6 and 0.5 μl/h/mg, respectively. Furthermore, knockdown of ARSB attenuated the regulatory effect of efflux transporter on cellular sulfonation, whereas overexpression of ABSB enhanced the transporter effect. Taken together, the results indicated that ARSB mediated the sulfonation-transport interplay in SULT293 cells.

Sulfate conjugation of daphnetin by the human cytosolic sulfotransferases

ETHNOPHARMACOLOGICAL RELEVANCE

In Turkey, daphnetin-containing Daphne oleoides is used as a folk medicine for treating rheumatic pain and lumbago. A daphnetin-containing traditional Chinese medicine tablet, named Zushima-Pian, is available in China for treating rheumatoid arthritis. The present study aimed to investigate the metabolism of daphnetin through sulfation in cultured human cells and to identify the human cytosolic sulfotransferase(s) (SULT(s)) that is(are) capable of mediating the sulfation of daphnetin.

MATERIALS AND METHODS

Cultured HepG2 human hepatoma cells and Caco-2 human colon carcinoma cells were labeled with [(35)S]sulfate in the presence of different concentrations of daphnetin. Thirteen known human SULTs, previously expressed and purified, as well as cytosols of human kidney, liver, lung, and small intestine, were examined for daphnetin-sulfating activity using an established sulfotransferase assay.

RESULTS

[(35)S]sulfated daphnetin was found to be generated and released by HepG2 cells and Caco-2 cells labeled with [(35)S] sulfate in the presence of daphnetin. Among the 13 known human SULTs, SULT1A1, SULT1A2, SULT1A3, SULT1B1, and SULT1C4 displayed significant sulfating activity toward daphnetin. Of the four human organ samples later tested, small intestine and liver cytosols displayed considerably higher daphnetin-sulfating activity than those of lung and kidney.

CONCLUSION

The results derived from the present study showed unequivocally that daphnetin could be sulfated in cultured human cells and by purified human SULT enzymes as well as human organ cytosols. The information obtained provided a basis for further studies on the metabolism of daphnetin through sulfation in vivo.

Isozyme Specific Allosteric Regulation of Human Sulfotransferase 1A1

The human cytosolic sulfotransferases (SULTs) comprise a 13-member enzyme family that regulates the activities of hundreds, perhaps thousands, of signaling small molecules via regiospecific transfer of the sulfuryl moiety (-SO3) from PAPS (3'-phosphoadenosine 5'-phosphosulfate) to the hydroxyls and amines of acceptors. Signaling molecules regulated by sulfonation include numerous steroid and thyroid hormones, epinephrine, serotonin, and dopamine. SULT1A1, a major phase II metabolism SULT isoform, is found at a high concentration in liver and has recently been show to harbor two allosteric binding sites, each of which binds a separate and complex class of compounds: the catechins (naturally occurring polyphenols) and nonsteroidal anti-inflammatory drugs. Among catechins, epigallocatechin gallate (EGCG) displays high affinity and specificity for SULT1A1. The allosteric network associated with either site has yet to be defined. Here, using equilibrium binding and pre-steady state studies, the network is shown to involve 14 distinct complexes. ECGG binds both the allosteric site and, relatively weakly, the active site of SULT1A1. It is not a SULT1A1 substrate but is sulfonated by SULT2A1. EGCG binds 17-fold more tightly when the active-site cap of the enzyme is closed by the binding of the nucleotide. When nucleotide is saturating, EGCG binds in two phases. In the first, it binds to the cap-open conformer; in the second, it traps the cap in the closed configuration. Cap closure encapsulates the nucleotide, preventing its release; hence, the EGCG-induced cap stabilization slows nucleotide release, inhibiting turnover. Finally, a comprehensive quantitative model of the network is presented.

Transcriptomic Analysis of Differentially Expressed Genes During Larval Development of Rapana venosa by Digital Gene Expression Profiling

During the life cycle of shellfish, larval development, especially metamorphosis, has a vital influence on the dynamics, distribution, and recruitment of natural populations, as well as seed breeding. Rapana venosa, a carnivorous gastropod, is an important commercial shellfish in China, and is an ecological invader in the United States, Argentina, and France. However, information about the mechanism of its early development is still limited, because research in this area has long suffered from a lack of genomic resources. In this study, 15 digital gene expression (DGE) libraries from five developmental stages of R. venosa were constructed and sequenced on the IIIumina Hi-Sequation 2500 platform. Bioinformaticsanalysis identified numerous differentially and specifically expressed genes, which revealed that genes associated with growth, nervous system, digestive system, immune system, and apoptosis participate in important developmental processes. The functional analysis of differentially expressed genes was further implemented by gene ontology, and Kyoto encyclopedia of genes and genomes enrichment. DGE profiling provided a general picture of the transcriptomic activities during the early development of R. venosa, which may provide interesting hints for further study. Our data represent the first comparative transcriptomic information available for the early development of R. venosa, which is a prerequisite for a better understanding of the physiological traits controlling development.

Modulation of GABAA receptors by neurosteroids. A new concept to improve cognitive and motor alterations in hepatic encephalopathy

Hepatic encephalopathy (HE) is a complex neuropsychiatric syndrome affecting patients with liver diseases, mainly those with liver cirrhosis. The mildest form of HE is minimal HE (MHE), with mild cognitive impairment, attention deficit, psychomotor slowing and impaired visuo-motor and bimanual coordination. MHE may progress to clinical HE with worsening of the neurological alterations which may lead to reduced consciousness and, in the worse cases, may progress to coma and death. HE affects several million people in the world and is a serious health, social and economic problem. There are no specific treatments for the neurological alterations in HE. The mechanisms underlying the cognitive and motor alterations in HE are beginning to be clarified in animal models. These studies have allowed to design and test in animal models of HE new therapeutic approaches which have successfully restored cognitive and motor function in rats with HE. In this article we review the evidences showing that.

Function and organization of the human cytosolic sulfotransferase (SULT) family

The sulfuryl transfer reaction is of fundamental biological importance. One of the most important manifestations of this process are the reactions catalyzed by members of the cytosolic sulfotransferase (SULT) superfamily. These enzymes transfer the sulfuryl moiety from the universal donor PAPS (3'-phosphoadenosine 5'-phosphosulfate) to a wide variety of substrates with hydroxyl- or amino-groups. Normally a detoxification reaction this facilitates the elimination of a multitude of xenobiotics, although for some molecules sulfation is a bioactivation step. In addition, sulfation plays a key role in endocrine and other signalling pathways since many steroids, sterols, thyroid hormones and catecholamines exist primarily as sulfate conjugates in humans. This article summarizes much of our current knowledge of the organization and function of the human cytosolic sulfotransferases and highlights some of the important interspecies differences that have implications for, among other things, drug development and chemical safety analysis.

Use of genetically manipulated Salmonella typhimurium strains to evaluate the role of human sulfotransferases in the bioactivation of nitro- and aminotoluenes

Various nitro- and aminotoluenes demonstrated carcinogenic activity in rodent studies, but were inactive or weakly active in conventional in vitro mutagenicity assays. Standard in vitro tests do not take into account activation by certain classes of enzymes. This is true in particular for sulfotransferases (SULTs). These enzymes may convert aromatic hydroxylamines and benzylic alcohols, two major classes of phase-I metabolites of nitro- and aminotoluenes, to reactive esters. Here it is shown that expression of certain human SULTs in Salmonella typhimurium TA1538 or TA100 strongly enhanced the mutagenicity of various nitrotoluenes and nitro- and amino-substituted benzyl alcohols. Human SULT1A1, SULT1A2, and SULT1C2 showed the strongest activation. The observation that some nitrotoluenes as well as some aminobenzyl alcohols were activated by SULTs in the absence of cytochromes P450 implies that mutagenic sulfuric esters were formed at both the exocyclic nitrogen and the benzylic carbon, respectively. Nitroreductase deficiency (using strain YG7131 instead of TA1538 for SULT1A1 expression) did not affect the SULT-dependent mutagenicity of 1-hydroxymethylpyrene (containing no nitro group), moderately enhanced that of 2-amino-4-nitrobenzyl alcohol, and drastically attenuated the effects of nitrobenzyl alcohols without other substituents. The last finding suggests that either activation occurred at the hydroxylamino group formed by nitroreductase or the nitro group (having a strong -M effect) had to be reduced to an electron-donating substituent to enhance the reactivity of the benzylic sulfuric esters. The results pointed to an important role of SULTs in the genotoxicity of nitrotoluenes and alkylated anilines. Activation occurs at nitrogen functions as well as benzylic positions.

The influence of the SULT1A status - wild-type, knockout or humanized - on the DNA adduct formation by methyleugenol in extrahepatic tissues of mice

Methyleugenol, present in herbs and spices, has demonstrated carcinogenic activity in the liver and, to a lesser extent, in extrahepatic tissues of rats and mice. It forms DNA adducts after hydroxylation and sulphation. As previously reported, hepatic DNA adduct formation by methyleugenol in mice is strongly affected by their sulphotransferase (SULT) 1A status. Now, we analysed the adduct formation in extrahepatic tissues. The time course of the adduct levels was determined in transgenic (tg) mice, expressing human SULT1A1/2, after oral administration of methyleugenol (50 mg per kg body mass). Nearly maximal adduct levels were observed 6 h after treatment. They followed the order: liver > caecum > kidney > colon > stomach > small intestine > lung > spleen. We then selected liver, caecum, kidney and stomach for the main study, in which four mouse lines [wild-type (wt), Sult1a1-knockout (ko), tg, and humanized (ko-tg)] were treated with methyleugenol at varying dose levels. In the liver, caecum and kidney, adduct formation was nearly completely dependent on the expression of SULT1A enzymes. In the liver, human SULT1A1/2 led to higher adduct levels than mouse Sult1a1, and the effects of both enzymes were approximately additive. In the caecum, human SULT1A1/2 and mouse Sult1a1 were nearly equally effective, again with additive effects in tg mice. In the kidney, only human SULT1A1/2 played a role: no adducts were detected in wt and ko mice even at the highest dose tested and the adduct levels were similar in tg and ko-tg mice. In the stomach, adduct formation was unaffected by the SULT1A status.

IN CONCLUSION

(i) the SULT1A enzymes only affected adduct formation in those tissues in which they are highly expressed (mouse Sult1a1 in the liver and caecum, but not in the kidney and stomach; human SULT1A1/2 in the liver, caecum and kidney, not in the stomach of tg mice and humans), indicating a dominating role of local bioactivation; (ii) the additivity of the effects of both enzymes in the liver and caecum implies that the enzyme level was limiting in the adduct formation; (iii) SULT1A forms dominated the activation of methyleugenol in several tissues, but non-Sult1a1 forms or SULT-independent mechanisms were involved in its adduct formation in the stomach.

Design and Interpretation of Human Sulfotransferase 1A1 Assays

The human sulfotransferases (SULTs) regulate the activities of hundreds, if not thousands, of small molecule metabolites via transfer of the sulfuryl-moiety (-SO3) from the nucleotide donor, 3'-phosphoadenosine 5'-phosphosulfate (PAPS) to the hydroxyls and amines of the recipients. Our understanding of the molecular basis of SULT catalysis has expanded considerably in recent years. The basic kinetic mechanism of these enzymes, previously thought to be ordered, has been redefined as random for SULT2A1, a representative member of the superfamily. An active-site cap whose structure and dynamics are highly responsive to nucleotides was discovered and shown to be critical in determining SULT selectivity, a topic of longstanding interest to the field. We now realize that a given SULT can operate in two specificity modes-broad and narrow-depending on the disposition of the cap. More recent work has revealed that the caps of the SULT1A1 are controlled by homotropic allosteric interactions between PAPS molecules bound at the dimer's active sites. These interactions cause the catalytic efficiency of SULT1A1 to vary in a substrate-dependent fashion by as much as two orders of magnitude over a range of PAPS concentrations that spans those found in human tissues. SULT catalysis is further complicated by the fact that these enzymes are frequently inhibited by their substrates. This review provides an overview of the mechanistic features of SULT1A1 that are important for the design and interpretation of SULT1A1 assays.

Gender-Dependent Pharmacokinetics of Veratramine in Rats: In Vivo and In Vitro Evidence

Veratramine, a major alkaloid from Veratrum nigrum L., has distinct anti-tumor and anti-hypertension effects. Our previous study indicated that veratramine had severe toxicity toward male rats. In order to elucidate the underling mechanism, in vivo pharmacokinetic experiments and in vitro mechanistic studies have been conducted. Veratramine was administrated to male and female rats intravenously via the jugular vein at a dose of 50 μg/kg or orally via gavage at 20 mg/kg. As a result, significant pharmacokinetic differences were observed between male and female rats after oral administration with much lower concentrations of veratramine and 7-hydroxyl-veratramine and higher concentrations of veratramine-3-O-sulfate found in the plasma and urine of female rats. The absolute bioavailability of veratramine was 0.9% in female rats and 22.5% in male rats. Further experiments of veratramine on Caco-2 cell monolayer model and in vitro incubation with GI content or rat intestinal subcellular fractions demonstrated that its efficient passive diffusion mediated absorption with minimal intestinal metabolism, suggesting no gender-related difference during its absorption process. When veratramine was incubated with male or female rat liver microsomes/cytosols, significant male-predominant formation of 7-hydroxyl-veratramine and female-predominant formation of veratramine-3-O-sulfate were observed. In conclusion, the significant gender-dependent hepatic metabolism of veratramine could be the major contributor to its gender-dependent pharmacokinetics.

Sulfation of benzyl alcohol by the human cytosolic sulfotransferases (SULTs): a systematic analysis

The aim of the present study was to identify human cytosolic sulfotransferases (SULTs) that are capable of sulfating benzyl alcohol and to examine whether benzyl alcohol sulfation may occur in cultured human cells as well as in human organ homogenates. A systematic analysis revealed that of the 13 known human SULTs, SULT1A1 SULT1A2, SULTA3, and SULT1B1 are capable of mediating the sulfation of benzyl alcohol. The kinetic parameters of SULT1A1 that showed the strongest benzyl alcohol-sulfating activity were determined. HepG2 human hepatoma cells were used to demonstrate the generation and release of sulfated benzyl alcohol under the metabolic settings. Moreover, the cytosol or S9 fractions of human liver, lung, kidney and small intestine were examined to verify the presence of benzyl alcohol sulfating activity in vivo. Copyright © 2015 John Wiley & Sons, Ltd.

Transcriptional Regulation of Cytosolic Sulfotransferase 1C2 by Intermediates of the Cholesterol Biosynthetic Pathway in Primary Cultured Rat Hepatocytes

Cytosolic sulfotransferase 1C2 (SULT1C2) is expressed in the kidney, stomach, and liver of rats; however, the mechanisms regulating expression of this enzyme are not known. We evaluated transcriptional regulation of SULT1C2 by mevalonate (MVA)-derived intermediates in primary cultured rat hepatocytes using several cholesterol synthesis inhibitors. Blocking production of mevalonate with the 3-hydroxy-3-methylglutaryl-CoA reductase inhibitor pravastatin (30 μM), reduced SULT1C2 mRNA content by ∼40% whereas the squalene synthase inhibitor squalestatin (SQ1, 0.1 μM), which causes accumulation of nonsterol isoprenoids, increased mRNA content by 4-fold. Treatment with MVA (10 mM) strongly induced SULT1C2 mRNA by 12-fold, and this effect was blocked by inhibiting squalene epoxidase but not by more distal cholesterol inhibitors, indicating the effects of MVA are mediated by postsqualene metabolites. Using rapid amplification of cDNA ends (RACE), we characterized the 5' end of SULT1C2 mRNA and used this information to generate constructs for promoter analysis. SQ1 and MVA increased reporter activity by ∼1.6- and 3-fold, respectively, from a construct beginning 49 base pairs (bp) upstream from the longest 5'-RACE product (-3140:-49). Sequence deletions from this construct revealed a hepatocyte nuclear factor 1 (HNF1) element (-2558), and mutation of this element reduced basal (75%) and MVA-induced (30%) reporter activity and attenuated promoter activation following overexpression of HNF1α or 1β. However, the effects of SQ1 were localized to a more proximal promoter region (-281:-49). Collectively, our findings demonstrate that cholesterol biosynthetic intermediates influence SULT1C2 expression in rat primary hepatocytes. Further, HNF1 appears to play an important role in mediating basal and MVA-induced SULT1C2 transcription.

Targeting the expression of glutathione- and sulfate-dependent detoxification enzymes in HepG2 cells by oxygen in minimal and amino acid enriched medium

Cancer cells exhibit specific metabolism allowing them to survive and proliferate in various oxygen conditions and nutrients' availability. Hepatocytes are highly active metabolically and thus very sensitive to hypoxia. The purpose of the study was to investigate the effect of oxygen on the expression of phase II detoxification enzymes in hepatocellular carcinoma cells (HepG2) cultured in minimal and rich media (with nonessential amino acids and GSH). The cells were cultured at 1% hypoxia, 10% tissue normoxia, and 21% atmospheric normoxia. The total cell count was determined by trypan blue exclusion dye and the expression on mRNA level by RT-PCR. The result indicated that the expression of glutathione-dependent enzymes (GSTA, M, P, and GPX2) was sensitive to oxygen and medium type. At 1% hypoxia the enzyme expression (with the exception of GSTA) was higher in minimal compared to rich medium, whereas at 10% normoxia it was higher in the rich medium. The expression was oxygen-dependent in both types of medium. Among phenol sulfotransferase SULT1A1 was not sensitive to studied factors, whereas the expression of SULT1A3 was depended on oxygen only in minimal medium. It can be concluded that in HepG2 cells, the detoxification by conjugation with glutathione and, to a lower extent with sulfate, may be affected by hypoxia and/or limited nutrients' availability. Besides, because the data obtained at 10% oxygen significantly differ from those at 21%, the comparative studies on hypoxia should be performed in relation to 10% but not 21% oxygen.

Multidrug Resistance-Associated Protein 4 (MRP4/ABCC4) Controls Efflux Transport of Hesperetin Sulfates in Sulfotransferase 1A3-Overexpressing Human Embryonic Kidney 293 Cells

Sulfonation is an important metabolic pathway for hesperetin. However, the mechanisms for the cellular disposition of hesperetin and its sulfate metabolites are not fully established. In this study, disposition of hesperetin via the sulfonation pathway was investigated using human embryonic kidney (HEK) 293 cells overexpressing sulfotransferase 1A3. Two monosulfates, hesperetin-3'-O-sulfate (H-3'-S) and hesperetin-7-O-sulfate (H-7-S), were rapidly generated and excreted into the extracellular compartment upon incubation of the cells with hesperetin. Regiospecific sulfonation of hesperetin by the cell lysate followed the substrate inhibition kinetics (Vmax = 0.66 nmol/min per mg, Km = 12.9 μM, and Ksi= 58.1 μM for H-3'-S; Vmax = 0.29 nmol/min per mg, Km = 14.8 μM, and Ksi= 49.1 μM for H-7-S). The pan-multidrug resistance-associated protein (MRP) inhibitor MK-571 at 20 μM essentially abolished cellular excretion of both H-3'-S and H-7-S (the excretion activities were only 6% of the control), whereas the breast cancer resistance protein-selective inhibitor Ko143 had no effects on sulfate excretion. In addition, knockdown of MRP4 led to a substantial reduction (>47.1%; P < 0.01) in sulfate excretion. Further, H-3'-S and H-7-S were good substrates for transport by MRP4 according to the vesicular transport assay. Moreover, sulfonation of hesperetin and excretion of its metabolites were well characterized by a two-compartment pharmacokinetic model that integrated drug uptake and sulfonation with MRP4-mediated sulfate excretion. In conclusion, the exporter MRP4 controlled efflux transport of hesperetin sulfates in HEK293 cells. Due to significant expression in various organs/tissues (including the liver and kidney), MRP4 should be a determining factor for the elimination and body distribution of hesperetin sulfates.

Effects of 2,2',4,4'-tetrabromodiphenyl ether (BDE47) on the enzymes of phase I (CYP2B1/2) and phase II (SULT1A and COMT) metabolism, and differences in the action of parent BDE-47 and its hydroxylated metabolites, 5-OH-BDE-47 and 6-OH-BDE47, on steroid secretion by luteal cells

In this study we determined the effects of BDE-47 on the expression and activity of phase I (CYP2B1/2) and phase II (SULT1A and COMT) enzymes, and assessed the actions of BDE-47 and its metabolites on luteal steroidogenesis. Luteal cells collected during early (ELP), middle (MLP) and late (LLP) luteal phase were exposed to BDE-47 (0.5, 25, and 50ng/ml) or metabolites (2.5, 5 and 25ng/ml). BDE-47 decreased CYP2B1/2 activity and expression but had no effect on SULT1A or COMT. BDE-47 exerted a stimulatory action on estrogen secretion in MLP and an inhibitory in LLP, but had no effect on progesterone secretion. 5-OH-BDE-47 and 6-OH-BDE-47 decreased progesterone, but had no effect on estrogen secretion.

CONCLUSIONS

The inhibitory effect of BDE-47 on CYP2B1/2 suggests the possibility of BDE-47 accumulation in the corpus luteum; by affecting steroid secretion and steroidogenesis enzymes, BDE-47 and its metabolites can be responsible for shortening luteal phase.

Transcriptomic profiling of male European eel (Anguilla anguilla) livers at sexual maturity

The European eel Anguilla anguilla has a complex life cycle that includes freshwater, seawater and morphologically distinct stages as well as two extreme long distance migrations. Eels do not feed as they migrate across the Atlantic to the Sargasso Sea but nevertheless reach sexual maturity before spawning. It is not yet clear how existing energy stores are used to reach the appropriate developmental state for reproduction. Since the liver is involved in energy metabolism, protein biosynthesis and endocrine regulation it is expected to play a key role in the regulation of reproductive development. We therefore used microarrays to identify genes that may be involved in this process. Using this approach, we identified 231 genes that were expressed at higher and 111 genes that were expressed at lower levels in sexually mature compared with immature males. The up-regulated set includes genes involved in lipid metabolism, fatty acid synthesis and transport, mitochondrial function, steroid transport and bile acid metabolism. Several genes with putative enzyme functions were also expressed at higher levels at sexual maturity while genes involved in immune system processes and protein biosynthesis tended to be down-regulated at this stage. By using a high-throughput approach, we have identified a subset of genes that may be linked with the mobilization of energy stores for sexual maturation and migration. These results contribute to an improved understanding of eel reproductive biology and provide insight into the role of the liver in other teleosts with a long distance spawning migrations.

Activity Suppression Behavior Phenotype in SULT4A1 Frameshift Mutant Zebrafish

Since its identification in 2000, sulfotransferase (SULT) 4A1 has presented an enigma to the field of cytosolic SULT biology. SULT4A1 is exclusively expressed in neural tissue, is highly conserved, and has been identified in every vertebrate studied to date. Despite this singular level of conservation, no substrate or function for SULT4A1 has been identified. Previous studies demonstrated that SULT4A1 does not bind the obligate sulfate donor, 3'-phosphoadenosine-5'-phosphosulfate, yet SULT4A1 is classified as a SULT superfamily member based on sequence and structural similarities to the other SULTs. In this study, transcription activator-like effector nucleases were used to generate heritable mutations in the SULT4A1 gene of zebrafish. The mutation (SULT4A1(Δ8)) consists of an 8-nucleotide deletion within the second exon of the gene, resulting in a frameshift mutation and premature stop codon after 132 AA. During early adulthood, casual observations were made that mutant zebrafish were exhibiting excessively sedentary behavior during the day. These observations were inconsistent with published reports on activity in zebrafish that are largely diurnal organisms and are highly active during the day. Thus, a decrease in activity during the day represents an abnormal behavior and warranted further systematic analysis. EthoVision video tracking software was used to monitor activity levels in wild-type (WT) and SULT4A1(Δ8/Δ8) fish over 48 hours of a normal light/dark cycle. SULT4A1(Δ8/Δ8) fish were shown to exhibit increased inactivity bout length and frequency as well as a general decrease in daytime activity levels when compared with their WT counterparts.