Biomedical subjects

M W Coughtrie

Publications and source records attributed to M W Coughtrie.

At least 19 recordsLinked to original sources

PubMed2001

Influence of culture system and medium enrichment on sulfotransferase and sulfatase expression in male rat hepatocyte cultures.

The expression of sulfotransferase and steroid sulfatase was studied in rat liver using the most promising culture models of hepatocytes, including monolayer culture with a pyruvate (30 mM) enriched medium, co-culture with rat epithelial cells from primitive biliary origin and collagengel sandwich culture. In the latter, addition of dexamethasone (1 microM) to the medium was examined. Phenol sulfotransferase enzymes (SULT1) were studied by measuring activities towards 4-methylphenol and estradiol, hydroxysteroid sulfotransferase (SULT2A) activity was determined towards dehydroepiandrosterone (DHEA). Microsomal steroid sulfatase activity was measured towards estrone sulfate. Western blot analysis was carried out using polyclonal antibodies raised against rat phenol sulfotransferase SULT1A1 (ASTIV), estrogen sulfotransferase SULT1E1 (EST) and hydroxysteroid sulfotransferase (HST). SULT2A activity towards DHEA was maintained at a high level during the whole culture time. In the co-culture it even reached the level of freshly isolated cells. Addition of pyruvate had no positive effect on the activity measured in monolayer cultures. High SULT1A1 activity towards 4-methylphenol was found in the co-culture system. In the monolayer culture, the activity initially decreased with 35% but was then kept at a constant level, while in the sandwich culture low activities were measured. For dexamethasone, an inducing effect on the various SULT activities could not be detected. Independently of the culture model used, the SULT1E1 activity towards estradiol decreased to 20% and 5% of the initial activity after four and seven days of culture, respectively. Microsomal steroid sulfatase activity was best maintained in collagengel sandwich cultures. During the first four days in culture it retained 73% of the initial activity, afterwards it decreased to 40% of the activity found in freshly isolated hepatocytes, irrespective of the culture conditions. High expectations exist for collagengel sandwich cultures, however, in our study the results were rather disappointing. Monolayer is a suitable culture model for short-term purposes. For long-term in vitro biotransformation studies, co-culture is preferred but is rather complex.

Albumins↗

PubMed2001

The antihyperglycemic effect of estrone sulfate in genetically obese-diabetic (ob/ob) mice is associated with reduced hepatic glucose-6-phosphatase.

Excessive glucose production by the liver contributes significantly to diabetic hyperglycemia. The enzyme system glucose-6-phosphatase plays a key role in regulating hepatic glucose production and therefore its inhibition is a potential therapeutic target for the correction of hyperglycemia. It has previously been shown that sulfated steroids, such as estrone sulfate and dehydroepiandrosterone sulfate, inhibit the glucose-6-phosphatase system in vitro, principally through inhibition of endoplasmic reticulum glucose-6-phosphate transport. We report here that in the obese/diabetic ob/ob mouse model, orally administered estrone sulfate reduces the abnormally elevated hepatic glucose-6-phosphatase enzyme activity and enzyme protein levels that are characteristic in the ob/ob mouse, and that this reduction is associated with normalization of blood glucose levels. Other sulfated and non-sulfated steroids also reduced, to a lesser extent, glucose-6-phosphatase enzyme activity - with the exception of dehydroepiandrosterone sulfate, which had no apparent effect on this system in ob/ob mice. Estrone sulfate is therefore an effective antihyperglycemic agent in ob/ob mice, and the glucose-6-phosphatase system can be successfully targeted for the therapeutic management of hyperglycemia in this animal model of non-insulin-dependent diabetes mellitus.

Aging↗

PubMed2001

Phenol sulphotransferase SULT1A1*1 genotype is associated with reduced risk of colorectal cancer.

Sulphation is an important detoxification pathway for numerous xenobiotics; however, it also plays an important role in the metabolism and bioactivation of many dietary and environmental mutagens, including heterocyclic amines implicated in the pathogenesis of colorectal and other cancers. A major sulphotransferase (SULT) enzyme in humans, SULT1A1, is polymorphic with the most common variant allele, SULT1A1*2, occurring at a frequency of about 32% in the Caucasian population. This allele codes for an allozyme with low enzyme activity and stability compared to the wild-type (SULT1A1*1) enzyme, and therefore SULT1A1 genotype may influence susceptibility to mutagenicity following exposure to heterocyclic amines and other environmental toxins. Previously, a significant association of SULT1A1*1 genotype with old age has been observed, suggesting a 'chemoprotective' role for the high-activity phenotype. Here we have compared the frequencies of the most common SULT1A1 alleles in 226 colorectal cancer patients and 293 previously described control patients. We also assessed whether SULT1A1 genotype was related to various clinical parameters in the patient group, including Duke's classification, differentiation, site, nodal involvement and survival. There was no significant difference in allele frequency between the control and cancer patient populations, nor was there a significant association with any of the clinical parameters studied. However, when the age-related difference in allele frequency was considered, a significantly reduced risk of colorectal cancer (odds ratio = 0.47; 95% confidence interval = 0.27-0.83; P = 0.009), was associated with homozygosity for SULT1A1*1 in subjects under the age of 80 years. These results suggest that the high activity SULT1A1*1 allozyme protects against dietary and/or environmental chemicals involved in the pathogenesis of colorectal cancer.

Adolescent↗

PubMed2001

Thyroid hormone metabolism and the developing human lung.

Thyroid hormones are involved in the regulation of fetal lung development, and maturation is accelerated in animal models by antepartum exposure to raised concentrations of the receptor-active thyroid hormone triiodothyronine and glucocorticoids. It is essential that the nature of the regulation of the spatial and temporal metabolism of iodothyronines in the human fetus and infant is known before effective therapies can be developed to modify human lung maturation. Thyroid hormone bioavailability to the human fetus is regulated in part by enzymatic deiodination and reversible sulfation of iodothyronines, with contributions from other factors such as fetomaternal and fetoamniotic hormone transfers, fetal thyroid gland production, and the activities of plasma membrane transporters mediating uptake of iodothyronines from plasma into tissues.

Arylsulfatases↗

PubMed2001

Differential expression of sulfotransferase enzymes involved in thyroid hormone metabolism during human placental development.

Thyroid hormone is essential for normal human development, and disruption of thyroid hormone homeostasis at critical developmental stages can result in severe and often long-term effects on crucial organs such as the brain and lungs. Numerous factors control the bioavailability of receptor active thyroid hormone T(3). Sulfation, catalyzed by sulfotransferase enzymes (SULTs), is an important pathway of thyroid hormone metabolism by which T(4) is irreversibly converted to inactive reverse T(3) rather than active T(3). The human fetus and neonate have high levels of circulating sulfated iodothyronines, although the source of these is not clear. The placenta forms the link between the fetus and its mother and is involved in transfer of thyroid hormone early in pregnancy, although its capacity for sulfation is unknown. We therefore examined expression of the SULTs involved in iodothyronine metabolism during human placental development. SULT activity was measured in human placental cotyledon and membranes (amnion, chorion, and decidua basalis) from 13-42 wk of gestation, and Western blot analysis was employed to verify enzyme activity data. Phenol and catecholamine sulfotransferases were expressed at the highest levels and were generally higher in the villous than membranous tissues. SULT1A1 activity showed significant correlation with sulfation of 3,3'-T(2), suggesting that this enzyme is primarily responsible for placental T(2) sulfation. Estrogen sulfotransferase was present at extremely low levels during early pregnancy, although in mid- and late gestation increased expression in the (predominantly maternal-derived) decidual component of the placenta was observed. Hydroxysteroid sulfotransferase, T(3), reverse T(3), and T(4) SULT activities were also low in all tissues examined, and expression of SULTs 1B1 and 1C2 were essentially undetectable by Western blot analysis. The results highlight a tissue-specific regulation of SULT expression during placental development, demonstrate very low sulfation of iodothyronines suggesting that the placenta is not a major source of circulating sulfated iodothyronines in the fetus.

Female↗

PubMed2001

Sulfation of thyroid hormone and dopamine during human development: ontogeny of phenol sulfotransferases and arylsulfatase in liver, lung, and brain.

Sulfation is an important mechanism for regulating the biological activity of numerous hormones and neurotransmitters in man. Here we have investigated the ontogeny of sulfotransferases (SULT) and sulfatase (ARS) involved in the metabolism of thyroid hormone and dopamine. SULT1A1 enzyme activity was lower in postnatal liver and lung than in fetal tissues. Hepatic SULT1A3 (dopamine) was expressed at high levels early in development, but decreased substantially in late fetal/early neonatal liver and was essentially absent from the adult liver. In lung, significant SULT1A3 activity was observed in the fetus, but neonatal levels were considerably lower. In brain, the highest activity was observed in the choroid plexus for SULT1A1, with low and widespread activity for both SULT1A1 and SULT1A3 in other brain regions. SULT activity with 3,3'-diiodothyronine (3,3'-T(2)) as substrate was measured in all tissues and correlated significantly with SULT1A1 activity (4-nitrophenol), suggesting that SULT1A1 is primarily responsible for the sulfation of this iodothyronine. The developmental expression of SULT1A3 and SULT1A1 in liver and brain was confirmed by immunoblot, and immunohistochemistry of developing liver showed substantial expression of these proteins in hemopoietic cells in fetal liver. We also detected low activity for the hydrolysis of 3,3'-T(2) sulfate by ARS, although there was less distinction between fetal and neonatal samples than with SULT activities. We have therefore shown that the developing fetus has substantial sulfation capacity. Sulfation may therefore play a major role in the homeostasis of hormones and other endogenous compounds as well as in detoxification in the fetus, particularly as other conjugating enzyme systems, such as the UDP-glucuronosyltransferases, are not expressed at significant levels until the neonatal period.

Aging↗

PubMed2001

Interactions between dietary chemicals and human sulfotransferases-molecular mechanisms and clinical significance.

Sulfation plays a major role in the detoxication of xenobiotics as well as in modulating the biological activity of numerous important endogenous chemicals. In contrast to this "chemical defense" function, sulfation is also a key step in the bioactivation of a host of pro-mutagens and pro-carcinogens. These reactions are catalyzed by an expanding family of sulfotransferase (SULT) enzymes, which transfer a sulfuryl moiety from the universal donor 3'-phosphoadenosine 5'-phosphosulfate. Here, we discuss current knowledge of the human sulfotransferase enzyme family, of which at least 11 members have been identified to date, including regulation of expression by endogenous compounds and xenobiotics as well as the molecular basis of polymorphisms in members of the SULT1A (phenol sulfotransferase) family. We also present new data on the inhibition of SULT1A enzymes by dietary chemicals, showing that compounds to which we are exposed regularly, such as epigallocatechin gallate and epicatechin gallate are extremely potent inhibitors of phenol sulfotransferases (K(i) in the nanomolar range for SULT1A1). We found that the mechanism of inhibition by these chemicals varied depending on the individual isoform involved, showing uncompetitive inhibition of SULT1A1 whereas with SULT1A2 and -1A3 they demonstrated mixed type inhibition. Thus, genetic-environmental interactions may play an important role in modulating sulfotransferase activity and in determining individual response to chemicals metabolized by these important enzymes.

Biotransformation↗

PubMed2000

Sulfotransferases: genetics and role in toxicology.

The mammalian xenobiotic-metabolizing sulfotransferases are cytosolic enzymes, which form a gene superfamily (SULT). Ten distinct human SULT forms are known. Two SULT forms represent splice variants, the other forms are encoded by separate genes. Common functional polymorphisms of the transcribed region are known for two of the forms. We have expressed 16 separate rat and human SULTs as well as some of their allelic variants, in Salmonella typhimurium TA1538 and/or V79 cells, which are target cells of commonly used mutagenicity assays. The expressed SULTs activated numerous compounds to mutagens in both assay systems. However, some promutagens were activated by only one or several of the human SULTs. Pronounced differences in promutagen activation were also detected between orthologous rat and human SULTs, and between allelic variants of human SULTs.

Animals↗

PubMed2000

Expression and activity of dehydroepiandrosterone sulfotransferase in human gastric mucosa.

Dehydroepiandrosterone sulfotransferase (DHEA-ST) is a key enzyme in the formation of Dehydroepiandrosterone sulfate (DHEAS) and is thought to be involved in the conversion of various substances such as bile acids and cholesterol. The existence of DHEA-ST in the small intestine in addition to the adrenal gland and liver in adult humans was recently reported. As the sulfotransferases can act on toxic or potentially toxic substances to reduce their biological activity, we attempted to clarify the significance of DHEA-ST in gastrointestinal tract. We examined surgically resected human stomach for the presence of DHEA-ST and attempted to determine its possible biological significance. DHEA-ST activity ranged widely from 6 to 84 pmoles/mg protein/90 min in 7 cases. Immunoblotting revealed one single band of a 35-kDa protein corresponding to the moleculr weight of DHEA-ST. Both DHEA-ST immunoreactivity and mRNA hybridization signals were localized in parietal cells of the gastric glands. The results of our present study demonstrated that the sulfation of DHEA by DHEA-ST occurs in the gastric glands. The localization of DHEA-ST in parietal cells suggests that this enzyme is correlated to mucosal function in the human stomach in addition to detoxification of exogenous substances.

Adult↗

PubMed2000

Human phenol sulfotransferases hP-PST and hM-PST activate propane 2-nitronate to a genotoxicant.

The industrial solvent 2-nitropropane (2-NP) is a genotoxic hepatocarcinogen in rats. The genotoxicity of the compound in rats has been attributed to sulfotransferase-mediated formation of DNA-reactive nitrenium ions from the anionic form of 2-NP, propane 2-nitronate (P2N). Whether human sulfotransferases are capable of activating P2N is unknown. In the present study we have addressed this question by investigating the genotoxicity of P2N in various V79-derived cell lines engineered for expression of individual forms of human sulfotransferases, the phenol-sulfating and the monoamine-sulfating phenol sulfotransferases (hP-PST and hM-PST) and the human hydroxysteroid sulfotransferase (hHST). Genotoxicity was assessed by measuring the induction of DNA repair synthesis and by analyzing the formation of DNA modifications. P2N induced repair synthesis in V79-hP-PST and V79-hM-PST cells, whereas induction of repair synthesis in V79-hHST cells was negligible. P2N also resulted in the formation of 8-aminodeoxyguanosine and increased the level of 8-oxodeoxyguanosine in V79-hP-PST cells, but not in the parental V79-MZ cells, which do not show any sulfotransferase activity. Acetone oxime, the tautomeric form of the first reduction product of 2-NP, 2-nitrosopropane, was inactive in all cell lines. The results show that the human phenol sulfotransferases P-PST and M-PST are capable of metabolically activating P2N (P-PST >> M-PST) and that the underlying mechanism is apparently identical to that resulting in the activation of P2N in rat liver, where 2-NP causes carcinomas. These results support the notion that 2-NP should be regarded as a potential human carcinogen.

8-Hydroxy-2'-Deoxyguanosine↗

PubMed2000

Potent inhibition of estrogen sulfotransferase by hydroxylated PCB metabolites: a novel pathway explaining the estrogenic activity of PCBs.

Polychlorinated biphenyls (PCBs) are persistent environmental pollutants which exert a variety of toxic effects in animals, including disturbances of sexual development and reproductive function. The estrogenic effects of PCBs may be mediated in part by hydroxylated PCB metabolites (PCB-OHs), but the mechanisms by which they are brought about are not understood. PCBs as well as PCB-Hs show low affinities for both alpha and beta estrogen receptor isoforms. In the present study we demonstrate that various environmentally relevant PCB-OHs are extremely potent inhibitors of human estrogen sulfotransferase, strongly suggesting that they indirectly induce estrogenic activity by increasing estradiol bioavailability in target tissues.

Biological Availability↗

PubMed1999

X-ray crystal structure of human dopamine sulfotransferase, SULT1A3. Molecular modeling and quantitative structure-activity relationship analysis demonstrate a molecular basis for sulfotransferase substrate specificity.

Humans are one of the few species that produce large amounts of catecholamine sulfates, and they have evolved a specific sulfotransferase, SULT1A3 (M-PST), to catalyze the formation of these conjugates. An orthologous protein has yet to be found in other species. To further our understanding of the molecular basis for the unique substrate selectivity of this enzyme, we have solved the crystal structure of human SULT1A3, complexed with 3'-phosphoadenosine 5'-phosphate (PAP), at 2.5 A resolution and carried out quantitative structure-activity relationship (QSAR) analysis with a series of phenols and catechols. SULT1A3 adopts a similar fold to mouse estrogen sulfotransferase, with a central five-stranded beta-sheet surrounded by alpha-helices. SULT1A3 is a dimer in solution but crystallized with a monomer in the asymmetric unit of the cell, although dimer interfaces were formed by interaction across crystallographic 2-fold axes. QSAR analysis revealed that the enzyme is highly selective for catechols, and catecholamines in particular, and that hydrogen bonding groups and lipophilicity (cLogD) strongly influenced K(m). We also investigated further the role of Glu(146) in SULT1A3 using site-directed mutagenesis and showed that it plays a key role not only in defining selectivity for dopamine but also in preventing many phenolic xenobiotics from binding to the enzyme.

Alanine↗

PubMed1999

Estradiol formation by human osteoblasts via multiple pathways: relation with osteoblast function.

The importance of estrogens in bone metabolism is illustrated by the accelerated bone loss and increase in osteoporotic fractures associated with postmenopausal estrogen deficiency. In this study, the expression and activity of the enzymes involved in estrogen metabolism in human osteoblastic cells were investigated in relation to differentiation of these cells. PCR reactions using mRNA from an in vitro differentiating human cell line (SV-HFO) were performed to assess mRNA expression of the enzymes aromatase, different subtypes of 17beta-hydroxysteroid dehydrogenase (17beta-HSD), and steroid sulfatase. Aromatase, sulfatase, and 17beta-HSD type 2 and 4 were found to be expressed throughout differentiation. Expression of 17beta-HSD type 3, however, was relatively weak, except for early time points in differentiation. Type 1 17beta-HSD expression was not detected. Aromatase activity decreased during differentiation, as was demonstrated by the conversion of androstenedione (A) and testosterone (T) into estrone (E(1)) and estradiol (E(2)), respectively. The 17beta-HSD isozymes catalysing a reductive reaction convert androstenedione and estrone into testosterone and estradiol, respectively. Their activity declined with differentiation. Analysis of 17beta-HSD activity indicated both oxidative (E(2) to E(1); T to A) and reductive (E(1) to E(2); A to T) metabolism at all stages of osteoblast differentiation. Both activities declined as cells moved toward a differentiating mineralizing phenotype. However, the oxidative reaction was increasingly in favor of the reductive reaction at all times during differentiation. Sulfatase activity, as demonstrated by the conversion of estrone-sulfate into estrone, was constant during differentiation. In conclusion, we have demonstrated that all enzymes necessary for estrogen metabolism are expressed and biologically active in differentiating human osteoblasts. The activity of aromatase and 17beta-HSD was found to be dependent on the stage of cell differentiation. In addition, human osteoblasts effectively convert estradiol into estrone. The efficacy of osteoblasts to synthesize estradiol may determine the ultimate change in rate of bone turnover after menopause, as well as the development of osteoporosis. Moreover, the enzymes involved in the metabolism of estradiol may form a target for intervention.

17-Hydroxysteroid Dehydrogenases↗

PubMed1999

Activation of propane 2-nitronate to a genotoxicant in V79-derived cell lines engineered for the expression of rat hepatic sulfotransferases.

2-Nitropropane (2-NP) is a genotoxic hepatocarcinogen in rats. The genotoxicity of the compound has been attributed to a sulfotransferase-mediated formation of DNA-reactive species from the anionic form of 2-NP, propane 2-nitronate (P2N). Several observations have suggested that sulfotransferases (SULTs) 1A1 and/or 1C1 may be important in the activation of P2N to a genotoxicant in rat liver, but a definite proof is lacking. In order to identify the sulfotransferase(s) of rat liver that are capable of activating P2N, we have investigated the genotoxicity of P2N in various V79-derived cell lines engineered for expression of individual forms of rat hepatic sulfotransferases. Genotoxicity was assessed by measuring the induction of DNA repair synthesis. 1-Hydroxymethylpyrene (HMP), which is metabolically activated by most sulfotransferases, served as a positive control. Neither P2N nor HMP induced DNA repair in the parental V79-MZ cells, which do not show any sulfotransferase activity. P2N was also inactive in V79-rHSTa and V79-rHST20 cells, which express specific hydroxysteroid sulfotransferases. By contrast, a clear and concentration-dependent induction of repair synthesis by P2N was observed in V79-rPST-IV and V79-rST1C1 cells, which express rat SULT1A1 and SULT1C1, respectively. HMP was genotoxic in all sulfotransferase-expressing cell lines. Acetone oxime (AO), the tautomeric form of the first reduction product of 2-NP, 2-nitrosopropane, was inactive in all cell lines. The results corroborate the essential role of sulfotransferases in the metabolic activation of P2N to genotoxic products and identify two rat sulfotransferases which are capable of catalyzing the activation step.

Animals↗

PubMed1999

Phenol sulphotransferase SULT1A1 polymorphism: molecular diagnosis and allele frequencies in Caucasian and African populations.

Sulphation, catalysed by members of the sulphotransferase (SULT) enzyme family, is an important component of the body's chemical defence mechanism, but also acts to bioactivate mutagens such as hydroxylated aryl and heterocyclic amines. A major human sulphotransferase, SULT1A1 (P-PST), metabolizes and/or bioactivates many drugs, iodothyronines and hydroxylated aromatic amines. The enzyme activity varies widely within the population and is under genetic control. We have developed an assay detecting a G-->A transition in SULT1A1 that causes an Arg213-->His substitution associated with low SULT activity and altered enzyme properties, and have used it to assess the SULT1A1 genotype in Caucasian (n=293) and African (Nigerian, n=52) populations. We show that the mutant SULT1A1*2 allele is present at frequencies of 0.321 and 0.269 in the Caucasian and African populations respectively. We also demonstrate a significant age-related difference in SULT1A1 genotype within our Caucasian population, with increasing incidence of SULT1A1*1 homozygosity and decreasing incidence of SULT1A1*2 homozygosity with increasing age, indicating a potential association of SULT1A1*1 allozyme(s) with protection against cell and/or tissue damage during aging.

Adolescent↗

PubMed1999

Kinetic properties of human dopamine sulfotransferase (SULT1A3) expressed in prokaryotic and eukaryotic systems: comparison with the recombinant enzyme purified from Escherichia coli.

Sulfation, catalyzed by members of the sulfotransferase enzyme family, is a major metabolic pathway which modulates the biological activity of numerous endogenous and xenobiotic chemicals. A number of these enzymes have been expressed in prokaryotic and eukaryotic systems to produce protein for biochemical and physical characterization. However, the effective use of heterologous expression systems to produce recombinant enzymes for such purposes depends upon the expressed protein faithfully representing the "native" protein. For human sulfotransferases, little attention has been paid to this despite the widespread use of recombinant enzymes. Here we have validated a number of heterologous expression systems for producing the human dopamine-metabolizing sulfotransferase SULT1A3, including Escherichia coli, Saccharomyces cerevisiae, COS-7, and V79 cells, by comparison of Km values of the recombinant enzyme in cell extracts with enzyme present in human platelets and with recombinant enzyme purified to homogeneity following E. coli expression. This is the first report of heterologous expression of a cytosolic sulfotransferase in yeast. Expression of SULT1A3 was achieved in all cell types, and the Km for dopamine under the conditions applied was approximately 1 microM in all heterologous systems studied, which compared favorably with the value determined with human platelets. We also determined the subunit and native molecular weights of the purified recombinant enzyme by SDS-PAGE, electrospray ionization mass spectrometry, dynamic light scattering, and sedimentation analysis. The enzyme purified following expression in E. coli existed as a homodimer with Mr approximately 68,000 as determined by light scattering and sedimentation analysis. Mass spectrometry revealed two species with experimentally determined masses of 34,272 and 34,348 which correspond to the native protein with either one or two 2-mercaptoethanol adducts. We conclude that the enzyme expressed in prokaryotic and eukaryotic heterologous systems, and also purified from E. coli, equates to that which is found in human tissue preparations.

Amino Acid Sequence↗

PubMed1999

Regulation of sulphotransferase expression in the endometrium during the menstrual cycle, by oral contraceptives and during early pregnancy.

The endometrium plays a key role in reproduction, and this function is tightly regulated by endogenous and xenobiotic steroids. Sulphation, catalysed by members of the sulphotransferase (SULT) enzyme family, is a major deactivating mechanism for steroid hormones and we have investigated the expression and regulation in vivo of SULT in the human endometrium. In the normal cycling endometrium, expression of the phenol sulphotransferases SULT1A1 and SULT1A3 and the oestrogen sulphotransferase SULT1E1 were observed, with SULT1A1 and SULT1E1 expression being higher in the luteal phase than in the follicular phase. No expression of the hydroxysteroid sulphotransferase SULT2A1 was detected at any time in the endometrium. In endometrium from women taking the combined oral contraceptive pill (OCP), SULT1E1 expression was virtually absent, and SULT1A1 expression was substantially reduced. Similarly, in early pregnancy (i.e. first trimester) endometrium, SULT1E1 expression was absent, although SULT1A1 and SULT1A3 expression were unaffected. Our results with normal endometrium support in-vitro data showing that SULT1E1 expression is regulated by progesterone. However, the data obtained from OCP and early pregnancy endometrium suggest that factors other than the concentration of circulating progesterone are involved in the regulation of the expression of this important enzyme in the endometrium.

Adult↗

PubMed1999

Characterization of human iodothyronine sulfotransferases.

Sulfation is an important pathway of thyroid hormone metabolism that facilitates the degradation of the hormone by the type I iodothyronine deiodinase, but little is known about which human sulfotransferase isoenzymes are involved. We have investigated the sulfation of the prohormone T4, the active hormone T3, and the metabolites rT3 and 3,3'-diiodothyronine (3,3'-T2) by human liver and kidney cytosol as well as by recombinant human SULT1A1 and SULT1A3, previously known as phenol-preferring and monoamine-preferring phenol sulfotransferase, respectively. In all cases, the substrate preference was 3,3'-T2 >> rT3 > T3 > T4. The apparent Km values of 3,3'-T2 and T3 [at 50 micromol/L 3'-phosphoadenosine-5'-phosphosulfate (PAPS)] were 1.02 and 54.9 micromol/L for liver cytosol, 0.64 and 27.8 micromol/L for kidney cytosol, 0.14 and 29.1 micromol/L for SULT1A1, and 33 and 112 micromol/L for SULT1A3, respectively. The apparent Km of PAPS (at 0.1 micromol/L 3,3'-T2) was 6.0 micromol/L for liver cytosol, 9.0 micromol/L for kidney cytosol, 0.65 micromol/L for SULT1A1, and 2.7 micromol/L for SULT1A3. The sulfation of 3,3'-T2 was inhibited by the other iodothyronines in a concentration-dependent manner. The inhibition profiles of the 3,3'-T2 sulfotransferase activities of liver and kidney cytosol obtained by addition of 10 micromol/L of the various analogs were better correlated with the inhibition profile of SULT1A1 than with that of SULT1A3. These results indicate similar substrate specificities for iodothyronine sulfation by native human liver and kidney sulfotransferases and recombinant SULT1A1 and SULT1A3. Of the latter, SULT1A1 clearly shows the highest affinity for both iodothyronines and PAPS, but it remains to be established whether it is the prominent isoenzyme for sulfation of thyroid hormone in human liver and kidney.

Adult↗