Tetrahydrobiopterin regulates monoamine neurotransmitter sulfonation

Cytosolic sulfotransferases in endocrine disruption

The mammalian cytosolic sulfotransferases (SULTs) catalyze the sulfation of endocrine hormones as well as a broad array of drugs, environmental chemicals, and other xenobiotics. Many endocrine-disrupting chemicals (EDCs) interact with these SULTs as substrates and inhibitors, and thereby alter sulfation reactions responsible for metabolism and regulation of endocrine hormones such as estrogens and thyroid hormones. EDCs or their metabolites may also regulate expression of SULTs through direct interaction with nuclear receptors and other transcription factors. Moreover, some sulfate esters derived from EDCs (EDC-sulfates) may serve as ligands for endocrine hormone receptors. While the sulfation of an EDC can lead to its excretion in the urine or bile, it may also result in retention of the EDC-sulfate through its reversible binding to serum proteins and thereby enable transport to other tissues for intracellular hydrolysis and subsequent endocrine disruption. This mini-review outlines the potential roles of SULTs and sulfation in the effects of EDCs and our evolving understanding of these processes.

Menopause-Associated Depression: Impact of Oxidative Stress and Neuroinflammation on the Central Nervous System-A Review

Perimenopausal depression, occurring shortly before or after menopause, is characterized by symptoms such as emotional depression, anxiety, and stress, often accompanied by endocrine dysfunction, particularly hypogonadism and senescence. Current treatments for perimenopausal depression primarily provide symptomatic relief but often come with undesirable side effects. The development of agents targeting the specific pathologies of perimenopausal depression has been relatively slow. The erratic fluctuations in estrogen and progesterone levels during the perimenopausal stage expose women to the risk of developing perimenopausal-associated depression. These hormonal changes trigger the production of proinflammatory mediators and induce oxidative stress, leading to progressive neuronal damage. This review serves as a comprehensive overview of the underlying mechanisms contributing to perimenopausal depression. It aims to shed light on the complex relationship between perimenopausal hormones, neurotransmitters, brain-derived neurotrophic factors, chronic inflammation, oxidative stress, and perimenopausal depression. By summarizing the intricate interplay between hormonal fluctuations, neurotransmitter activity, brain-derived neurotrophic factors, chronic inflammation, oxidative stress, and perimenopausal depression, this review aims to stimulate further research in this field. The hope is that an increased understanding of these mechanisms will pave the way for the development of more effective therapeutic targets, ultimately reducing the risk of depression during the menopausal stage for the betterment of psychological wellbeing.

From Steroid and Drug Metabolism to Glycobiology, Using Sulfotransferase Structures to Understand and Tailor Function

Sulfotransferases are ubiquitous enzymes that transfer a sulfo group from the universal cofactor donor 3'-phosphoadenosine 5'-phosphosulfate to a broad range of acceptor substrates. In humans, the cytosolic sulfotransferases are involved in the sulfation of endogenous compounds such as steroids, neurotransmitters, hormones, and bile acids as well as xenobiotics including drugs, toxins, and environmental chemicals. The Golgi associated membrane-bound sulfotransferases are involved in post-translational modification of macromolecules from glycosaminoglycans to proteins. The sulfation of small molecules can have profound biologic effects on the functionality of the acceptor, including activation, deactivation, or enhanced metabolism and elimination. Sulfation of macromolecules has been shown to regulate a number of physiologic and pathophysiological pathways by enhancing binding affinity to regulatory proteins or binding partners. Over the last 25 years, crystal structures of these enzymes have provided a wealth of information on the mechanisms of this process and the specificity of these enzymes. This review will focus on the general commonalities of the sulfotransferases, from enzyme structure to catalytic mechanism as well as providing examples into how structural information is being used to either design drugs that inhibit sulfotransferases or to modify the enzymes to improve drug synthesis. SIGNIFICANCE STATEMENT: This manuscript honors Dr. Masahiko Negishi's contribution to the understanding of sulfotransferase mechanism, specificity, and roles in biology by analyzing the crystal structures that have been solved over the last 25 years.

Tetrahydrobiopterin in Cell Function and Death Mechanisms

Significance: Tetrahydrobiopterin (BH4) is most well known as a required cofactor for enzymes regulating cellular redox homeostasis, aromatic amino acid metabolism, and neurotransmitter synthesis. Less well known are the effects dependent on the cofactor's availability, factors governing its synthesis and recycling, redox implications of the cofactor itself, and protein-protein interactions that underlie cell death. This review provides an understanding of the recent advances implicating BH4 in the mechanisms of cell death and suggestions of possible therapeutic interventions. Recent Advances: The levels of BH4 often reflect the sum of synthetic and recycling enzyme activities. Enhanced expression of GTP cyclohydrolase, the rate-limiting enzyme in biosynthesis, increases BH4, leading to improved cell function and survival. Pharmacologically increasing BH4 levels has similar beneficial effects, leading to enhanced production of neurotransmitters and nitric oxide or reducing oxidant levels. The GTP cyclohydrolase-BH4 pairing has been implicated in a type of cell death, ferroptosis. At the cellular level, BH4 counteracts anticancer therapies directed to enhance ferroptosis via glutathione peroxidase 4 (GPX4) activity inhibition. Critical Issues: Because of the multitude of intertwined mechanisms, a clear relationship between BH4 and cell death is not well understood yet. The possibility that the cofactor directly influences cell viability has not been excluded in previous studies when modulating BH4-producing enzymes. Future Directions: The importance of cellular BH4 variations and BH4 biosynthetic enzymes to cell function and viability makes it essential to better characterize temporal changes, cofactor activity, and the influence on redox status, which in turn would help develop novel therapies. Antioxid. Redox Signal. 37, 171-183.

The N-Terminus of Human Sulfotransferase 2B1b─a Sterol-Sensing Allosteric Site

Among human cytosolic sulfotransferases, SULT2B1b is highly specific for oxysterols─oxidized cholesterol derivatives, including nuclear-receptor ligands causally linked to skin and neurodegerative diseases, cancer and atherosclerosis. Sulfonation of signaling oxysterols redirects their receptor-binding functions, and controlling these functions is expected to prove valuable in disease prevention and treatment. SULT2B1b is distinct among the human SULT2 isoforms by virtue of its atypically long N-terminus, which extends 15 residues beyond the next longest N-terminus in the family. Here, in silico studies are used to predict that the N-terminal extension forms an allosteric pocket and to identify potential allosteres. One such allostere, quercetin, is used to confirm the existence of the pocket and to demonstrate that allostere binding inhibits turnover. The structure of the pocket is obtained by positioning quercetin on the enzyme, using spin-label-triangulation NMR, followed by NMR distance-constrained molecular dynamics docking. The model is confirmed using a combination of site-directed mutagenesis and initial-rate studies. Stopped-flow ligand-binding studies demonstrate that inhibition is achieved by stabilizing the closed form of the enzyme active-site cap, which encapsulates the nucleotide, slowing its release. Finally, endogenous oxysterols are shown to bind to the site in a highly selective fashion─one of the two immediate biosynthetic precursors of cholesterol (7-dehydrocholesterol) is an inhibitor, while the other (24-dehydrocholesterol) is not. These findings provide insights into the allosteric dialogue in which SULT2B1b participates in in vivo and establishes a template against which to develop isoform-specific inhibitors to control SULT2B1b biology.

Genetic and Neurological Deficiencies in the Visual System of mct8 Mutant Zebrafish

Thyroid hormones (THs; T3 and T4) enter cells using specific transporters and regulate development and metabolism. Mutation in the TH transporter monocarboxylate transporter 8 (MCT8, SLC16A2) is associated with brain hypothyroidism and neurological impairment. We established mct8 mutant (mct8-/-) zebrafish as a model for MCT8 deficiency, which causes endocrinological, neurological, and behavioral alterations. Here, we profiled the transcriptome of mct8-/- larvae. Among hundreds of differentially expressed genes, the expression of a cluster of vision-related genes was distinct. Specifically, the expression of the opsin 1 medium wave sensitive 2 (opn1mw2) decreased in two mct8 mutants: mct8-/- and mct8^-25bp-/- larvae, and under pharmacological inhibition of TH production. Optokinetic reflex (OKR) assays showed a reduction in the number of conjugated eye movements, and live imaging of genetically encoded Ca²⁺ indicator revealed altered neuronal activity in the pretectum area of mct8^-25bp-/- larvae. These results imply that MCT8 and THs regulate the development of the visual system and suggest a mechanism to the deficiencies observed in the visual system of MCT8-deficiency patients.

Excess Folic Acid Supplementation before and during Pregnancy and Lactation Alters Behaviors and Brain Gene Expression in Female Mouse Offspring

Use of folic acid (FA) during early pregnancy protects against birth defects. However, excess FA has shown gender-specific neurodevelopmental toxicity. Previously, we fed the mice with 2.5 times the recommended amount of FA one week prior to mating and during the pregnancy and lactation periods, and detected the activated expression of Fos and related genes in the brains of weaning male offspring, as well as behavioral abnormalities in the adults. Here, we studied whether female offspring were affected by the same dosage of FA. An open field test, three-chamber social approach and social novelty test, an elevated plus-maze, rotarod test and the Morris water maze task were used to evaluate their behaviors. RNA sequencing was performed to identify differentially expressed genes in the brains. Quantitative real time-PCR (qRT-PCR) and Western blots were applied to verify the changes in gene expression. We found increased anxiety and impaired exploratory behavior, motor coordination and spatial memory in FA-exposed females. The brain transcriptome revealed 36 up-regulated and 79 down-regulated genes in their brains at weaning. The increase of Tlr1; Sult1a1; Tph2; Acacb; Etnppl; Angptl4 and Apold1, as well as a decrease of Ppara mRNA were confirmed by qRT-PCR. Among these genes; the mRNA levels of Etnppl; Angptl4andApold1 were increased in the both FA-exposed female and male brains. The elevation of Sult1a1 protein was confirmed by Western blots. Our data suggest that excess FA alteres brain gene expression and behaviors in female offspring, of which certain genes show apparent gender specificity.

Selanzylimidazopyridine abolishes inflammation- and stress-induced depressive-like behaviors and decreases oxidonitrosative stress in the prefrontal cortex and hippocampus of mice

The 3-[(4-methoxyphenyl)selanyl]-2-phenylimidazo[1,2-a] pyridine (MPI), a novel organic selenium compound, has been receiving increased attention due to its antioxidant effects and its ability to protect against depression-like behaviours. However, it remains elusive whether MPI is able to reverse depressive-like symptoms and biochemical alterations in mice. In the present work, we explored the ability of MPI (10 mg/kg, i.g.) to reverse inflammation- and stress-induced depression-like behaviours in mice injected with tumour necrosis factor (TNF-α) or submitted to acute restraint stress. Depression-like behaviours were evaluated by the tail suspension and splash test and the open field test was used to evaluate the locomotor activity of mice. The prefrontal cortex and hippocampus of mice were used for the evaluation of parameters of oxidonitrosative stress. Here, we showed that a single administration of MPI abolished the depressive-like behaviours induced by TNF-α and acute restraint stress without having an effect per se. The oxidative and nitrosative stress presented in mice with depression-like behaviours were also decreased by MPI in the prefrontal cortex and hippocampus. Our findings suggest that MPI presents antidepressant-like activity which is associated with the biochemical regulation of oxidative stress in the prefrontal cortex and hippocampus of mice, arising as a promising strategy for the management of depressive symptoms.

The molecular basis of OH-PCB estrogen receptor activation

Polychlorinated bisphenols (PCBs) continue to contaminate food chains globally where they concentrate in tissues and disrupt the endocrine systems of species throughout the ecosphere. Hydroxylated PCBs (OH-PCBs) are major PCB metabolites and high-affinity inhibitors of human estrogen sulfotransferase (SULT1E1), which sulfonates estrogens and thus prevents them from binding to and activating their receptors. OH-PCB inhibition of SULT1E1 is believed to contribute significantly to PCB-based endocrine disruption. Here, for the first time, the molecular basis of OH-PCB inhibition of SULT1E1 is revealed in a structure of SULT1E1 in complex with OH-PCB1 (4ʹ-OH-2,6-dichlorobiphenol) and its substrates, estradiol (E2), and PAP (3’-phosphoadenosine-5-phosphosulfate). OH-PCB1 prevents catalysis by intercalating between E2 and catalytic residues and establishes a new E2-binding site whose E2 affinity and positioning are greater than and competitive with those of the reactive-binding pocket. Such complexes have not been observed previously and offer a novel template for the design of high-affinity inhibitors. Mutating residues in direct contact with OH-PCB weaken its affinity without compromising the enzyme’s catalytic parameters. These OH-PCB resistant mutants were used in stable transfectant studies to demonstrate that OH-PCBs regulate estrogen receptors in cultured human cell lines by binding the OH-PCB binding pocket of SULT1E1.

The Human UGT2B7 Nanodisc

The 20 uridine diphosphate glycosyl-transferases (UGTs) encoded in the human genome form an essential homeostatic network of overlapping catalytic functions that surveil and regulate the activity and clearance of scores of small molecule metabolites. Biochemical and biophysical UGT studies have been hampered by the inability to purify these membrane-bound proteins. Here, using cell-free expression and nanodisc technology, we assemble and purify to homogeneity the first UGT nanodisc-the human UGT2B7•nanodisc. The complex is readily isolated in milligram quantities. It is stable and its initial-rate parameters are identical within error to those associated with UGT2B7 in microsomal preparations (i.e., Supersomes). The high purity of the nanodisc preparation simplifies UGT assays, which allows complexities traditionally associated with microsomal assays (latency and the albumin effect) to be circumvented. Each nanodisc is shown to harbor a single UGT2B7 monomer. The methods described herein should be widely applicable to UGTs, and these findings are expected to set the stage for experimentalists to more freely explore the structure, function, and biology of this important area of phase II metabolism. SIGNIFICANCE STATEMENT: Lack of access to pure, catalytically competent human uridine diphosphate glucuronosyl-transferases (UGTs) has long been an impediment to biochemical and biophysical studies of this disease-relevant enzyme family. Here, we demonstrate this barrier can be removed using nanodisc technology-a human UGT2B7•nanodisc is assembled, purified to homogeneity, and shown to have activity comparable to microsomal UGT2B7.

Tetrahydrobiopterin enhances mitochondrial biogenesis and cardiac contractility via stimulation of PGC1α signaling

Tetrahydrobiopterin (BH4) shows therapeutic potential as an endogenous target in cardiovascular diseases. Although it is involved in cardiovascular metabolism and mitochondrial biology, its mechanisms of action are unclear. We investigated how BH4 regulates cardiovascular metabolism using an unbiased multiple proteomics approach with a sepiapterin reductase knock-out (Spr-/-) mouse as a model of BH4 deficiency. Spr-/- mice exhibited a shortened life span, cardiac contractile dysfunction, and morphological changes. Multiple proteomics and systems-based data-integrative analyses showed that BH4 deficiency altered cardiac mitochondrial oxidative phosphorylation. Along with decreased transcription of major mitochondrial biogenesis regulatory genes, including Ppargc1a, Ppara, Esrra, and Tfam, Spr-/- mice exhibited lower mitochondrial mass and severe oxidative phosphorylation defects. Exogenous BH4 supplementation, but not nitric oxide supplementation or inhibition, rescued these cardiac and mitochondrial defects. BH4 supplementation also recovered mRNA and protein levels of PGC1α and its target proteins involved in mitochondrial biogenesis (mtTFA and ERRα), antioxidation (Prx3 and SOD2), and fatty acid utilization (CD36 and CPTI-M) in Spr-/- hearts. These results indicate that BH4-activated transcription of PGC1α regulates cardiac energy metabolism independently of nitric oxide and suggests that BH4 has therapeutic potential for cardiovascular diseases involving mitochondrial dysfunction.

Allosteres to regulate neurotransmitter sulfonation

Catecholamine neurotransmitter levels in the synapses of the brain shape human disposition-cognitive flexibility, aggression, depression, and reward seeking-and manipulating these levels is a major objective of the pharmaceutical industry. Certain neurotransmitters are extensively sulfonated and inactivated by human sulfotransferase 1A3 (SULT1A3). To our knowledge, sulfonation as a therapeutic means of regulating transmitter activity has not been explored. Here, we describe the discovery of a SULT1A3 allosteric site that can be used to inhibit the enzyme. The structure of the new site is determined using spin-label-triangulation NMR. The site forms a cleft at the edge of a conserved ∼30-residue active-site cap that must open and close during the catalytic cycle. Allosteres anchor into the site via π-stacking interactions with two residues that sandwich the planar core of the allostere and inhibit the enzyme through cap-stabilizing interactions with substituents attached to the core. Changes in cap free energy were calculated ab initio as a function of core substituents and used to design and synthesize a series of inhibitors intended to progressively stabilize the cap and slow turnover. The inhibitors bound tightly (34 nm to 7.4 μm) and exhibited progressive inhibition. The cap-stabilizing effects of the inhibitors were experimentally determined and agreed remarkably well with the theoretical predictions. These studies establish a reliable heuristic for the design of SULT1A3 allosteric inhibitors and demonstrate that the free-energy changes of a small, dynamic loop that is critical for SULT substrate selection and turnover can be calculated accurately.

Isoform-specific therapeutic control of sulfonation in humans

The activities of hundreds, perhaps thousands, of metabolites are regulated by human cytosolic sulfotransferases (SULTs) - a 13-member family of disease relevant enzymes that catalyze transfer of the sulfuryl moiety (-SO₃) from PAPS (3'-phosphoadenosine 5'-phosphosulfonate) to the hydroxyls and amines of acceptors. SULTs harbor two independent allosteric sites, one of which, the focus of this work, binds non-steroidal anti-inflammatory drugs (NSAIDs). The structure of the first NSAID-binding site - that of SULT1A1 - was elucidated recently and homology modeling suggest that variants of the site are present in all SULT isoforms. The objective of the current study was to assess whether the NSAID-binding site can be used to regulate sulfuryl transfer in humans in an isoform specific manner. Mefenamic acid (Mef) is a potent (K_i 27 nM) NSAID-inhibitor of SULT1A1 - the predominant SULT isoform in small intestine and liver. Acetaminophen (APAP), a SULT1A1 specific substrate, is extensively sulfonated in humans. Dehydroepiandrosterone (DHEA) is specific for SULT2A1, which we show here is insensitive to Mef inhibition. APAP and DHEA sulfonates are readily quantified in urine and thus the effects of Mef on APAP and DHEA sulfonation could be studied non-invasively. Compounds were given orally in a single therapeutic dose to a healthy, adult male human with a typical APAP-metabolite profile. Mef profoundly decreased APAP sulfonation during first pass metabolism and substantially decreased systemic APAP sulfonation without influencing DHEA sulfonation; thus, it appears the NSAID site can be used to control sulfonation in humans in a SULT-isoform specific manner.

Microbial production of novel sulphated alkaloids for drug discovery

Natural products from plants are useful as lead compounds in drug discovery. Plant benzylisoquinoline alkaloids (BIAs) exhibit various pharmaceutical activities. Although unidentified BIAs are expected to be of medicinal value, sufficient quantities of such BIAs, for biological assays, are sometimes difficult to obtain due to their low content in natural sources. Here, we showed that high productivity of BIAs in engineered Escherichia coli could be exploited for drug discovery. First, we improved upon the previous microbial production system producing (S)-reticuline, an important BIA intermediate, to obtain yields of around 160 mg/L, which was 4-fold higher than those of the previously reported highest production system. Subsequently, we synthesised non-natural BIAs (O-sulphated (S)-reticulines) by introducing human sulphotransferases into the improved (S)-reticuline production system. Analysis of human primary cells treated with these BIAs demonstrated that they affected a biomarker expression in a manner different from that by the parent compound (S)-reticuline, suggesting that simple side-chain modification altered the characteristic traits of BIA. These results indicated that highly productive microbial systems might facilitate the production of scarce or novel BIAs and enable subsequent evaluation of their biological activities. The system developed here could be applied to other rare natural products and might contribute to the drug-discovery process as a next-generation strategy.

The NSAID allosteric site of human cytosolic sulfotransferases

Non-steroidal anti-inflammatory drugs (NSAIDs) are among the most commonly prescribed drugs worldwide-more than 111 million prescriptions were written in the United States in 2014. NSAIDs allosterically inhibit cytosolic sulfotransferases (SULTs) with high specificity and therapeutically relevant affinities. This study focuses on the interactions of SULT1A1 and mefenamic acid (MEF)-a potent, highly specific NSAID inhibitor of 1A1. Here, the first structure of an NSAID allosteric site-the MEF-binding site of SULT1A1-is determined using spin-label triangulation NMR. The structure is confirmed by site-directed mutagenesis and provides a molecular framework for understanding NSAID binding and isoform specificity. The mechanism of NSAID inhibition is explored using molecular dynamics and equilibrium and pre-steady-state ligand-binding studies. MEF inhibits SULT1A1 turnover through an indirect (helix-mediated) stabilization of the closed form of the active-site cap of the enzyme, which traps the nucleotide and slows its release. Using the NSAID-binding site structure of SULT1A1 as a comparative model, it appears that 11 of the 13 human SULT isoforms harbor an NSAID-binding site. We hypothesize that these sites evolved to enable SULT isoforms to respond to metabolites that lie within their metabolic domains. Finally, the NSAID-binding site structure offers a template for developing isozyme-specific allosteric inhibitors that can be used to regulate specific areas of sulfuryl-transfer metabolism.