Sulfate-conjugated methylprednisolone: Evaluation as a colon-specific methylprednisolone prodrug and comparison with sulfate-conjugated prednisolone and dexamethasone

Methylprednisolone 21-sulfate sodium (MPS) was prepared and evaluated as a colon-specific methylprednisolone prodrug and its colon-specific property was compared with prednisolone 21-sulfate sodium (PDS) and dexamethasone 21-sulfate sodium (DS), reported previously as colon-specific prodrugs of the glucocorticoids. The synthetic process and yield of MPS was simple and high. The apparent partition coefficient of methylprednisolone (MP) was greatly reduced by sulfate conjugation. The sulfate conjugates MPS, PDS, and DS were (bio)chemically stable in the homogenates of the upper intestine. In marked contrast, the sulfate conjugates were deconjugated to liberate the corresponding glucocorticoids in the cecal contents. Although the rates of deconjugation were not significantly different, the corresponding glucocorticoids were accumulated with distinct profiles depending on the metabolic susceptibility of the unconjugated glucocorticoids to microbial reductase(s). Upon oral administration of the sulfate conjugates to rats, the plasma concentrations of the conjugates were extremely low and the urinary recoveries were less than 5% of the doses. These results suggest that, like PDS and DS, MPS administered orally is delivered efficiently to the large intestine followed by deconjugation to liberate MP and the metabolic susceptibility of the unconjugated glucocorticoids may affect therapeutic availability of the sulfate conjugates.     

Kinetic analysis of bile acid sulfation by stably expressed human sulfotransferase 2A1 (SULT2A1)

1. Human sulfotransferase 2A1 (SULT2A1) is a member of the hydroxysteroid sulfotransferase (SULT2) family that mediates sulfo-conjugation of a variety of endogenous molecules including dehydroepiandrosterone (DHEA) and bile acids. In this study, we have constructed a stable cell line expressing SULT2A1 by transfection into HEK293 cells. The expression system was used to characterize and compare the sulfation kinetics of DHEA and 15 human bile acids by SULT2A1.

2. Formation of DHEA sulfate demonstrated Michaelis–Menten kinetics with apparent K_m and V_max values of 3.8?μM and 130.8 pmol min^?1 mg^?1 protein, respectively. Sulfation kinetics of bile acids also demonstrated Michaelis–Menten kinetics with a marked variation in apparent K_m and V_max values between individual bile acids.

3. Sulfation affinity was inversely proportional to the number of hydroxyl groups of bile acids. The monohydroxy- and most toxic bile acid (lithocholic acid) had the highest affinity, whereas the trihydroxy- and least toxic bile acid (cholic acid) had the lowest affinity to sulfation by SULT2A1. Intrinsic clearance (CL_int) of ursodeoxycholic acid (UDCA) was approximately 1.5- and 9.0-fold higher than that of deoxycholic acid (DCA) and chenodeoxycholic acid (CDCA), respectively, despite the fact that all three are dihydroxy bile acids.

     

Sulfated Metabolites of Polychlorinated Biphenyls Are High-Affinity Ligands for the Thyroid Hormone Transport Protein Transthyretin

Background: The displacement of l-thyroxine (T₄) from binding sites on transthyretin (TTR) is considered a significant contributing mechanism in polychlorinated biphenyl (PCB)-induced thyroid disruption. Previous research has discovered hydroxylated PCB metabolites (OH-PCBs) as high-affinity ligands for TTR, but the binding potential of conjugated PCB metabolites such as PCB sulfates has not been explored.Objectives: We evaluated the binding of five lower-chlorinated PCB sulfates to human TTR and compared their binding characteristics to those determined for their OH-PCB precursors and for T₄.Methods: We used fluorescence probe displacement studies and molecular docking simulations to characterize the binding of PCB sulfates to TTR. The stability of PCB sulfates and the reversibility of these interactions were characterized by HPLC analysis of PCB sulfates after their binding to TTR. The ability of OH-PCBs to serve as substrates for human cytosolic sulfotransferase 1A1 (hSULT1A1) was assessed by OH-PCB–dependent formation of adenosine-3´,5´-diphosphate, an end product of the sulfation reaction.Results: All five PCB sulfates were able to bind to the high-affinity binding site of TTR with equilibrium dissociation constants (K_d values) in the low nanomolar range (4.8–16.8 nM), similar to that observed for T₄ (4.7 nM). Docking simulations provided corroborating evidence for these binding interactions and indicated multiple high-affinity modes of binding. All OH-PCB precursors for these sulfates were found to be substrates for hSULT1A1.Conclusions: Our findings show that PCB sulfates are high-affinity ligands for human TTR and therefore indicate, for the first time, a potential relevance for these metabolites in PCB-induced thyroid disruption.     

Involvement of UDP-Glucuronosyltransferases in the Extensive Liver and Intestinal First-Pass Metabolism of Flavonoid Baicalein

Purpose The present study aims to investigate the involvement of UDP-glucuronosyltranferase (UGT) in the extensive liver and intestinal first-pass glucuronidation of baicalein (B) in both rats and humans and also to study sulfation and P450 mediated hydroxylation of B.Materials and Methods B was incubated with liver and intestine microsome, cytosol, S9 fractions from human, rat and various human recombinant UGT isozymes, respectively. The generated metabolites were identified by HPLC/MS/MS and quantified by HPLC/UV.Results Three metabolites of B namely baicalein 7-O-glucuronide (BG), the isomer of baicalein 7-O-glucuronide (BG’), and baicalein sulfate were found. BG, the predominant metabolite of B, was extensively generated in liver and jejunum microsomes in both humans and rats. Its formation was mainly catalyzed by UGT 1A9 and also mediated by UGT 1A1, 1A3, 1A8, 1A7 and 2B15 with different kinetic profiles. UGT 1A8 mediated formation of BG’ was mainly found in human intestine and rat liver microsomes. Sulfation and P450 mediated hydroxylation of B were much less significant than glucuronidation.Conclusions Extensive liver and intestinal first-pass glucuronidation of B were found in both humans and rats. Under the current experimental conditions, UGT 1A9 and UGT 1A8 demonstrated the fastest formation rate of BG in human liver preparations and BG’ in human intestine preparations, respectively.     

2-去氧-2,3-去氢-N-乙酰基神经氨酸8-硫酸酯、9-硫酸酯衍生物的合成及其生物活性

对2-去氧-2,3-去氢-N-乙酰基神经氨酸(Neu5Ac2en)的8-羟基和9-羟基进行选择性硫酸酯化,以比较不同取代位置的硫酸酯基对唾液酸酶抑制活性的影响.采用三苯甲基氯保护9-羟基后,对8-羟基进行选择性硫酸酯化;在4,7,8-三羟基乙酰化后,酸性条件下水解9-三苯甲基醚,对9-羟基进行选择性硫酸酯化.得到7个结构全新的Neu5Ac2en8-硫酸酯衍生物、9-硫酸酯衍生物.初步生物活性试验表明,这些化合物均具有一定的唾液酸酶抑制活性,9-硫酸酯衍生物的酶抑制活性高于8-硫酸酯衍生物.     

Oral bioavailability and pharmacokinetics of elimination of 9-hydroxybenzo[a]pyrene and its glucoside and sulfate conjugates after administration to male and female American lobsters, Homarus americanus.

The pharmacokinetics of [(3)H]-9-hydroxybenzo[a]pyrene (9-OH-BaP), a highly lipophilic primary metabolite of benzo(a)pyrene, were examined after intrapericardial (iv) or oral doses of 50 or 200 microg/kg to intermolt American lobsters, Homarus americanus. Combining data for all lobsters, the average terminal elimination half-life of parent 9-OH-BaP was 97.3 h after iv and 56.5 h after oral administration, considerably less than found previously for benzo(a)pyrene (720 h). The oral bioavailability of parent 9-OH-BaP, calculated from the area under the hemolymph concentration curve, was 15.9%. The low bioavailability and variable elimination rates were attributed to extensive first-pass conjugation and sequestration in the hepatopancreas. BaP-9-sulfate was the major metabolite. Hemolymph concentrations of BaP-9-sulfate increased up to one day after the dose, and then decreased, with a terminal elimination half-life of 45 h. BaP 9-beta-D-glucoside was a minor metabolite in most hemolymph and tissue samples; an exception was hemolymph from the iv high-dose group. Concentrations of 9-OH-BaP and metabolites in the edible muscle tissue were similar to those in hemolymph, and 9-OH-BaP residues at 10 to 16 days after the dose were 3 to 12 ng/g muscle. Sulfotransferase and UDP-glucosyltransferase (UGT) activities with 9-OH-BaP were found in the antennal gland, intestinal mucosa, and hepatopancreas (UGT only). Sulfatase activity with BaP-9-sulfate, found in both the hepatopancreas and the antennal gland, was thought to contribute to metabolite cycling. These studies showed that 9-OH-BaP was readily conjugated to sulfate and glucose in the lobster, and that despite their high lipophilicity, 9-OH-BaP and conjugates were excreted from the lobster hemolymph and tissues much more rapidly than benzo[a]pyrene.     

Replacing PAPS: In vitro phase II sulfation of steroids with the liver S9 fraction employing ATP and sodium sulfate

In vitro technologies provide the capacity to study drug metabolism where in vivo studies are precluded due to ethical or financial constraints. The metabolites generated by in vitro studies can assist anti‐doping laboratories to develop protocols for the detection of novel substances that would otherwise evade routine screening efforts. In addition, professional bodies such as the Association of Official Racing Chemists (AORC) currently permit the use of in‐vitro‐derived reference materials for confirmation purposes providing additional impetus for the development of cost effective in vitro metabolism platforms. In this work, alternative conditions for in vitro phase II sulfation using human, equine or canine liver S9 fraction were developed, with adenosine triphosphate (ATP) and sodium sulfate in place of the expensive and unstable co‐factor 3′‐phosphoadenosine‐5′‐phosphosulfate (PAPS), and employed for the generation of six representative steroidal sulfates. Using these conditions, the equine in vitro phase II metabolism of the synthetic or so‐called designer steroid furazadrol ([1′,2′]isoxazolo[4′,5′:2,3]‐5α‐androstan‐17β‐ol) was investigated, with ATP and Na₂SO₄ providing comparable metabolism to reactions using PAPS. The major in vitro metabolites of furazadrol matched those observed in a previously reported equine in vivo study. Finally, the equine in vitro phase II metabolism of the synthetic steroid superdrol (methasterone, 17β‐hydroxy‐2α,17α‐dimethyl‐5α‐androstan‐3‐one) was performed as a prediction of the in vivo metabolic profile.     

Sulfated tyrosines 27 and 29 in the N-terminus of human CXCR3 participate in binding native IP-10

Aim： Human CXCR3, a seven-transmembrane segment （7TMS）, is predominantly expressed in Th1-mediated responses. Interferon-y-inducible protein 10 （IP-10） is an important ligand for CXCR3. Their interaction is pivotal for leukocyte migration and activation. Tyrosine sulfation in 7TMS is a posttranslational modification that contributes substantially to ligand binding. We aimed to study the role of tyrosine sulfation of CXCR3 in the protein＇s binding to IP-10. Methods： Plasmids encoding CXCR3 and its mutants were prepared by PCR and site-directed mutagenesis. HEK 293T cells were transfected with plasmids encoding CXCR3 or its variants using calcium phosphate. Transfected cells were labeled with [^35S]-cysteine and methionine or [35S]-Na2SO3 and then analyzed by immunoprecipitation to measure sulfation. Experiments with ^125 I-labeled IP-10 were carried out to evaluate the affinity of CXCR3 for its ligand. Calcium influx assays were used to measure intercellular signal transduction. Results： Our data show that sulfate moieties are added to tyrosines 27 and 29 of CXCR3. Mutation of these two tyrosines to phenylalanines substantially decreases binding of CXCR3 to IP-10 and appears to eliminate the associated signal transduction. Tyrosine sulfation of CXCR3 is enhanced by tyrosyl protein sulfotransferases （TPSTs）, and it is weakened by shRNA constructs. The binding ability of CXCR3 to IP-10 is increased by TPSTs and decreased by shRNAs. Conclusion： This study identifies two sulfated tyrosines in the N-terminus of CXCR3 as part of the binding site for IP-10, and it underscores the fact that tyrosine sulfation in the N-termini of 7TMS receptors is functionally important for ligand interactions. Our study suggests a molecular target for inhibiting this ligand-receptor interaction.     

UPLC-Q-TOF/MS法鉴定大鼠体内甘草素的代谢产物

[目的]研究甘草素在大鼠体内的代谢产物。[方法]采用静脉注射(iv)、灌胃(ig)两种给药方式,剂量20 mg/kg,收集大鼠血浆、尿液、粪便、胆汁,应用UPLC-Q-TOF/MS法鉴定甘草素的代谢产物。[结果]血浆、尿液、粪便、胆汁样品中共鉴定15种代谢产物,主要有异甘草素、(异)甘草素葡萄糖醛酸结合物和硫酸结合物、二氢异甘草素、二氢异甘草素硫酸结合物、异甘草素甲基化及甘草素脱氢的代谢产物;其主要代谢途径为异构化、葡萄糖醛酸化、硫酸化、甲基化、脱氢反应。[结论]构建的UPLC-Q-TOF/MS法可用于大鼠体内甘草素代谢产物的研究。     

Competing pathways in drug metabolism. II. An identical,anterior enzymic distribution for 2- and 5-sulfoconjugation and a posterior localization for 5-glucuronidation of gentisamide in the rat liver

Gentisamide (2,5-dihydroxybenzamide, GAM), a substrate that forms two monosulfates at the 2 and 5 positions (GAM-2S and GAM-5S) and a monoglucuronide at the 5 position (GAM-5G), was delivered at 8 or 80 M by normal (N) and retrograde (R) flows to the once-through rat liver preparation. At the lower (8 M) input concentration, ratios of conjugate formation rate, GAM-5S/GAM-5G and GAM-2S/GAM-5G, were decreased significantly (4.01±1.42 to 2.93±0.99, and 1.13±0.65 to 0.66±0.41, respectively) whereas a small but significant increase in the steady-state extraction ratio, E (0.89±0.029 to 0.94±0.016), was observed upon changing the flow direction from N to R. At the higher input GAM concentration (80 M), conjugate formation rate ratios were relatively constant for GAM-5S/GAM-5G (1.18±0.08 to 1.11±0.12) and GAM-2S/GAM-5G (0.33±0.05 to 0.31±0.05) upon changing flow direction from N to R, despite a slight increase in E from 0.87±0.023 to 0.91±0.016 was observed. These results suggest that the sulfotransferase activities responsible for 2- and 5-sulfoconjugations are identically distributed and localized anterior to 5-glucuronidation activities during a normal flow of substrate into the rat liver (entering the portal vein and exiting the hepatic vein), and that the presence of uneven distribution of conjugation activities is discriminated only at the lower input drug concentration. At high concentration (>K_m for all systems), saturation of all pathways occurs, and other, anteriorly/identically distributed competing pathways would fail to perturb downstream intrahepatic drug concentrations arid the resultant conjugation rates. The lack of change in metabolic profiles renders the condition unsuitable for examination of uneven distribution of enzymes in the liver. These observations were generally predicted by theoretical enzymic models of consistent distribution patterns. Because 2- and 5-sulfation were mediated by systems of similar K_m but different V_max values, two possibilities, the same isozyme of sulfotransferase being involved in the formation of two enzyme-substrate complexes to form two distinctly different products or two isozymes of sulfotransferases of identical distribution, were discussed.The work was supported by the Medical Research Council of Canada (DG-263 and MA-9104) and a grant from the Canadian Liver Foundation. M. E. Morris was a recipient of a MRC post doctoral fellowship.