Tetrahydrobiopterin biosynthesis as an off-target of sulfa drugs

From bacteria to fish: ecotoxicological insights into sulfamethoxazole and trimethoprim

Sulfamethoxazole (SMX) and trimethoprim (TRIM) are two of the most used antibiotics in the last 50 years, to prevent and treat bacterial infections; however, the available literature about toxicity to non-target organisms is quite discrepant and incomplete. This study aims to assess the SMX and TRIM ecotoxicological effects in standard species: Aliivibrio fischeri (bioluminescence inhibition), Escherichia coli ATCC 25922 (growth inhibition), Lemna minor (growth inhibition and biochemical biomarkers), Daphnia magna (immobilization/mortality, life history traits, and biochemical biomarkers), and Danio rerio (survival, hatching, abnormalities, and biochemical biomarkers). The species tested showed different acute sensitivities to SMX (A. fischeri < D. magna < E. coli < L. minor) and TRIM (L. minor < A. fischeri < D. magna < E. coli). Overall, TRIM reveals less toxicity than SMX, except for E. coli (Ecotoxicological approach based on Antimicrobial Susceptibility Testing - EcoAST procedure). Both antibiotics affect individually (e.g., growth and survival) and sub-individually (e.g., antioxidant defenses) L. minor, D. magna, and D. rerio. This study allowed us to generate relevant data and fill gaps in the literature regarding the effects of SMX and TRIM in aquatic organisms. The here-obtained results can be used to (i) complete and re-evaluate the Safety Data Sheet to improve the assessment of environmental safety and management of national and international entities; (ii) clarify the environmental risks of these antibiotics in aquatic ecosystems reinforcing the inclusion in the 4th Watch List of priority substances to be monitored in whole inland waters by the Water Framework Directive; and (iii) combat the development of antimicrobial resistance, as well as supporting the definition of environmental measurements in the context of European One Health Action Plan. However, it is essential to continue studying these antibiotics to better understand their toxicity at ecologically relevant concentrations and their long-term effects under different climatic change scenarios.

Drugs with a negative impact on cognitive functions (part 3): antibacterial agents in patients with chronic kidney disease

The relationship between chronic kidney disease (CKD) and cognitive function has received increased attention in recent years. Antibacterial agents (ABs) represent a critical component of therapy regimens in patients with CKD due to increased susceptibility to infections. Following our reviewing work on the neurocognitive impact of long-term medications in patients with CKD, we propose to focus on AB-induced direct and indirect consequences on cognitive function. Patients with CKD are predisposed to adverse drug reactions (ADRs) due to altered drug pharmacokinetics, glomerular filtration decline, and the potential disruption of the blood-brain barrier. ABs have been identified as a major cause of ADRs in vulnerable patient populations. This review examines the direct neurotoxic effects of AB classes (e.g. beta-lactams, fluoroquinolones, aminoglycosides, and metronidazole) on the central nervous system (CNS) in patients with CKD. We will mainly focus on the acute effects on the CNS associated with AB since they are the most extensively studied effects in CKD patients. Moreover, the review describes the modulation of the gut microbiota by ABs, potentially influencing CNS symptoms. The intricate brain-gut-kidney axis emerges as a pivotal focus, revealing the interplay between microbiota alterations induced by ABs and CNS manifestations in patients with CKD. The prevalence of antibiotic-associated encephalopathy in patients with CKD undergoing intravenous AB therapy supports the use of therapeutic drug monitoring for ABs to reduce the number and seriousness of ADRs in this patient population. In conclusion, elucidating AB-induced cognitive effects in patients with CKD demands a comprehensive understanding and tailored therapeutic strategies that account for altered pharmacokinetics and the brain-gut-kidney axis.

Novel sulfonamide derivatives as a tool to combat methicillin-resistant Staphylococcus aureus

Increasing resistance in Staphylococcus aureus has created a critical need for new drugs, especially those effective against methicillin-resistant strains (methicillin-resistant Staphylococcus aureus [MRSA]). Sulfonamides are a privileged scaffold for the development of novel antistaphylococcal agents. This review covers recent advances in sulfonamides active against MRSA. Based on the substitution patterns of sulfonamide moieties, its derivatives can be tuned for desired properties and biological activity. Contrary to the traditional view, not only N-monosubstituted 4-aminobenzenesulfonamides are effective. Novel sulfonamides have various mechanisms of action, not only 'classical' inhibition of the folate biosynthetic pathway. Some of them can overcome resistance to classical sulfa drugs and cotrimoxazole, are bactericidal and active in vivo. Hybrid compounds with distinct bioactive scaffolds are particularly advantageous.

The aminosalicylate - folate connection

Two aminosalicylate isomers have been found to possess useful pharmacological behavior: p-aminosalicylate (PAS, 4AS) is an anti-tubercular agent that targets M. tuberculosis, and 5-aminosalicylate (5AS, mesalamine, mesalazine) is used in the treatment of ulcerative colitis (UC) and other inflammatory bowel diseases (IBD). PAS, a structural analog of pABA, is biosynthetically incorporated by bacterial dihydropteroate synthase (DHPS), ultimately yielding a dihydrofolate (DHF) analog containing an additional hydroxyl group in the pABA ring: 2'-hydroxy-7,8-dihydrofolate. It has been reported to perturb folate metabolism in M. tuberculosis, and to selectively target M. tuberculosis dihydrofolate reductase (mtDHFR). Studies of PAS metabolism are reviewed, and possible mechanisms for its mtDHFR inhibition are considered. Although 5AS is a more distant structural relative of pABA, multiple lines of evidence suggest a related role as a pABA antagonist that inhibits bacterial folate biosynthesis. Structural data support the likelihood that 5AS is recognized by the DHPS pABA binding site, and its effects probably range from blocking pABA binding to formation of a dead-end dihydropterin-5AS adduct. These studies suggest that mesalamine acts as a gut bacteria-directed antifolate, that selectively targets faster growing, more folate-dependent species.

Exploring the differences in serum metabolite profiles after intake of red meat in women with rheumatoid arthritis and a matched control group

PURPOSE

Studies have suggested that women with RA tend to avoid red meat more often than women without RA, based on their perception that it exacerbates their symptoms. Therefore, the aim of this study is to investigate and compare the postprandial metabolic response following the consumption of a red meat meal in patients with RA and a matched control group.

METHODS

Participants were challenged with a meal with red meat and blood samples were collected before and at 0.5, 1, 2, 3 and 5 h after the meal. Serum metabolites were quantified by Nuclear Magnetic Resonance (NMR) analysis. Orthogonal Projections to Latent Structures with Discriminant Analysis (OPLS-DA) was used to evaluate separation by metabolites due to diagnosis of RA or not and to identify changes in metabolites related to RA. Incremental area under the curve was calculated for univariate comparisons for 23 metabolites.

RESULTS

The matched groups, including 22 women with RA and 22 women without RA, did not differ significantly in age, body mass index, diet quality or reported physical activity. OPLS-DA models had a limited quality indicating that there were no differences in metabolite patterns between the groups. However, phenylalanine was significantly higher in concentration in women with RA compared to controls in both fasting and postprandial samples.

CONCLUSION

To conclude, this well-controlled postprandial intervention study found a significantly higher concentration of phenylalanine in both fasting and postprandial samples of women with RA compared to matched women without RA. These findings warrant further investigation in larger studies.

TRIAL REGISTRATION

The PIRA (Postprandial Inflammation in Rheumatoid Arthritis) trial is Registered at Clinicaltrials.gov (NCT04247009).

Identification of Chemicals That Abrogate Folate-Dependent Inhibition of Starch Accumulation in Non-Photosynthetic Plastids of Arabidopsis

Folate, also known as vitamin B9, is an essential cofactor for a variety of enzymes and plays a crucial role in many biological processes. We previously reported that plastidial folate prevents starch biosynthesis triggered by the influx of sugar into non-starch-accumulating plastids, such as etioplasts, and chloroplasts under darkness; hence the loss of plastidial folate induces the accumulation of starch in plastids. To understand the molecular mechanism underlying this phenomenon, we screened our in-house chemical library and searched their derivatives to identify chemicals capable of inducing starch accumulation in etioplasts. The results revealed four chemicals, compounds #120 and #375 and their derivatives, compounds #120d and #375d, respectively. The derivative compounds induced starch accumulation in etioplasts and suppressed hypocotyl elongation in dark-grown Arabidopsis seedlings. They also inhibited the post-germinative growth of seedlings under illumination. All four chemicals contained the sulfonamide group as a consensus structure. The sulfonamide group is also found in sulfa drugs, which exhibit antifolate activity, and in sulfonylurea herbicides. Further analyses revealed that compound #375d induces starch accumulation by inhibiting folate biosynthesis. By contrast, compound #120d neither inhibited folate biosynthesis nor exhibited the herbicide activity. Protein and metabolite analyses suggest that compound #120d abrogates folate-dependent inhibition of starch accumulation in etioplasts by enhancing starch biosynthesis.

Photocatalytic Three-Component Reaction for the Synthesis of Multifunctional Diaryl Sulfides

A photocatalytic three-component reaction of a nitroarene, a thiophenol, and a ketone for the synthesis of multifunctional diaryl sulfides was reported using a nitro group as the nitrogen source and thiophenol as the sulfur source. Thiophenol also serves as a proton donor to reduce nitroarene to arylamine as a key intermediate for the formation of C-N and C-S bonds. Good functional group tolerance and mild reaction conditions make this method have practical synthetic value for diversified multifunctional diaryl sulfides.

Sulfonamides (SAs) exposure causes neurobehavioral toxicity at environmentally relevant concentrations (ERCs) in early development of zebrafish

Antibiotics, due to their stability and persistence in the environment, can have chronic impacts on various ecosystems and organisms. However, the molecular mechanisms underlying antibiotic toxicity at environmental concentrations, particularly the neurotoxic effects of sulfonamides (SAs), remain poorly understood. In this study, we assessed the neurotoxicity of six SAs including the sulfadiazine (SD), sulfathiazole (ST), sulfamethoxazole (SMX), sulfisoxazole (SIZ), sulfapyridine (SPD), and sulfadimethoxine (SDM) by exposing zebrafish to environmentally relevant concentrations (ERCs). The SAs exhibited concentration-dependent effects on zebrafish behavior, including spontaneous movement, heartbeat, survival rate, and body metrics, ultimately leading to depressive-like symptoms and sublethal toxicity during early life stages. Notably, even the lowest SA concentration (0.05 μg/L) induced neurotoxicity and behavioral impairment in zebrafish. We observed a dose-dependent increase in melancholy behavior as indicated by increased resting time and decreased motor activity in zebrafish larvae. Following exposure to SAs from 4 to 120 h post-fertilization (hpf), key genes involved in folate synthesis [sepiapterin reductase a (spra), phenylalanine hydroxylase (pah), tyrosine hydroxylase (th), and tryptophan hydroxylase 1 (tryptophan 5-monooxygenase) a tryptophan hydroxylase (tph1a)] and carbonic anhydrase (CA) metabolism [carbonic anhydrase II (ca2), carbonic anhydrase IV a (ca4a), carbonic anhydrase VII (ca7), and carbonic anhydrase XIV (ca14)] were significantly downregulated or inhibited at different concentrations. Our findings demonstrate that acute exposure to six SAs at environmentally relevant concentrations induces developmental and neurotoxic effects in zebrafish, impacting folate synthesis pathways and CA metabolism. These results provide valuable insights into the potential role of antibiotics in depressive disorders and neuroregulatory pathways.

Peripheralized sepiapterin reductase inhibition as a safe analgesic therapy

The development of novel analgesics for chronic pain in the last 2 decades has proven virtually intractable, typically failing due to lack of efficacy and dose-limiting side effects. Identified through unbiased gene expression profiling experiments in rats and confirmed by human genome-wide association studies, the role of excessive tetrahydrobiopterin (BH4) in chronic pain has been validated by numerous clinical and preclinical studies. BH4 is an essential cofactor for aromatic amino acid hydroxylases, nitric oxide synthases, and alkylglycerol monooxygenase so a lack of BH4 leads to a range of symptoms in the periphery and central nervous system (CNS). An ideal therapeutic goal therefore would be to block excessive BH4 production, while preventing potential BH4 rundown. In this review, we make the case that sepiapterin reductase (SPR) inhibition restricted to the periphery (i.e., excluded from the spinal cord and brain), is an efficacious and safe target to alleviate chronic pain. First, we describe how different cell types that engage in BH4 overproduction and contribute to pain hypersensitivity, are themselves restricted to peripheral tissues and show their blockade is sufficient to alleviate pain. We discuss the likely safety profile of peripherally restricted SPR inhibition based on human genetic data, the biochemical alternate routes of BH4 production in various tissues and species, and the potential pitfalls to predictive translation when using rodents. Finally, we propose and discuss possible formulation and molecular strategies to achieve peripherally restricted, potent SPR inhibition to treat not only chronic pain but other conditions where excessive BH4 has been demonstrated to be pathological.

In Silico Investigation of the Human GTP Cyclohydrolase 1 Enzyme Reveals the Potential of Drug Repurposing Approaches towards the Discovery of Effective BH4 Therapeutics

The GTP cyclohydrolase 1 enzyme (GTPCH1) is the rate-limiting enzyme of the tetrahydrobiopterin (BH₄) biosynthetic pathway. Physiologically, BH₄ plays a crucial role as an essential cofactor for the production of catecholamine neurotransmitters, including epinephrine, norepinephrine and dopamine, as well as the gaseous signaling molecule, nitric oxide. Pathological levels of the cofactor have been reported in a number of disease states, such as inflammatory conditions, neuropathic pain and cancer. Targeting the GTPCH1 enzyme has great potential in the management of a number of disease pathologies associated with dysregulated BH₄ physiology. This study is an in silico investigation of the human GTPCH1 enzyme using virtual screening and molecular dynamic simulation to identify molecules that can be repurposed to therapeutically target the enzyme. A three-tier molecular docking protocol was employed in the virtual screening of a comprehensive library of over 7000 approved medications and nutraceuticals in order to identify hit compounds capable of binding to the GTPCH1 binding pocket with the highest affinity. Hit compounds were further verified by molecular dynamic simulation studies to provide a detailed insight regarding the stability and nature of the binding interaction. In this study, we identify a number of drugs and natural compounds with recognized anti-inflammatory, analgesic and cytotoxic effects, including the aminosalicylate olsalazine, the antiepileptic phenytoin catechol, and the phlorotannins phlorofucofuroeckol and eckol. Our results suggest that the therapeutic and clinical effects of hit compounds may be partially attributed to the inhibition of the GTPCH1 enzyme. Notably, this study offers an understanding of the off-target effects of a number of compounds and advocates the potential role of aminosalicylates in the regulation of BH₄ production in inflammatory disease states. It highlights an in silico drug repurposing approach to identify a potential means of safely targeting the BH₄ biosynthetic pathway using established therapeutic agents.

Transition Metal-Free Iodine-Catalyzed Denitrative C-S Cross-Coupling: An Atypical Route to Access Thiochromane Derivatives

An iodine-catalyzed denitrative C-S cross-coupling reaction has been developed to attain thiochromanones from 2'-nitrochalcones and xanthate. The strategy was extended for a three-component synthesis of thiochromenes via intermolecular C-S cross-coupling followed by aldol reaction. The reaction proceeds via activation of the keto group of chalcone through a halogen bond complex with iodine/denitrative C-S bond formation with xanthate/sulfa-Michael addition to chalcones. The methodology was also demonstrated for chemoselective reduction of chalcones. The protocol was also employed to synthesize biologically important 3'-hydroxythioflavone and thiochromenones.

Animal gut microbiome mediates the effects of antibiotic pollution on an artificial freshwater system

The antibiotic pollution has become an emerging environmental problem worldwide, but the ecological outcomes remain to be elucidated, especially very little is known about the interactions between antibiotics and different ecological elements. In this study, the long-term influences of three representative antibiotics, i.e., tetracycline, erythromycin, and sulfamethoxazole, were investigated focusing on a simplified artificial freshwater system composed of amphibian tadpoles, gut and environmental bacterial and fungi communities, and water parameters. Results demonstrated that antibiotic exposure reduced tadpole's fitness with increased mortality and physiological abnormality, and altered the water quality, particularly the nitrogen homeostasis. Sequential analyses at organism, symbiont, and systematic levels revealed that antibiotics disrupted tadpole metabolome (e.g., tetrahydrobiopterin metabolism) directly by off-target effects. Antibiotics also reshaped the tadpole gut bacterial and fungi diversity and composition, which partly accounted for the tadpole's health condition. Moreover, changes of tadpole gut microbiome (i.e., Cyanobacteria and Basidiomycota OTUs) partly explained the variations of water parameters. In contrast, environmental microbiota and metagenome stayed relatively stable, and didn't contribute to the environmental variations. These results highlighted the pivotal role of gut microbiome in mediating the effects of antibiotics on the host and the environment, which would extend our understanding on the ecological outcomes caused by antibiotic pollution.

Solvent-Driven Mono- and Bis-sulfenylation of (E)-β-Iodovinyl Sulfones with Thiols for Flexible Synthesis of 1,2-Thiosulfonylalkenes and 1,2-Dithioalkenes

The nature of solvent is a key factor for stereoselective mono- and bis-thiolation of (E)-β-iodovinyl sulfones with thiols under basic conditions. A novel and unprecedented vicinal bisthiolation of (E)-β-iodovinyl sulfones with thiols under the influence of K₂CO₃/DMSO at room temperature for quick assembly of (E)-1,2-dithio-1-alkenes is presented. Solvent-induced stereoselective monosulfenylation of (E)-β-iodovinyl sulfones with thiols has also been established for the synthesis of both (E)- and (Z)-1,2-thiosulfonylethenes in MeCN and MeOH, respectively. Moreover, K₂CO₃-mediated desulfonylative-sulfenylation of (Z)-1,2-thiosulfonylethenes with thiols in DMSO furnished unsymmetrical (Z)-1,2-dithio-1-alkenes for the first time. The solvent-dependent versatile reactivity of (E)-β-iodovinyl sulfones has been successfully explored to provide a set of (E)-/(Z)-1,2-dithio-1-alkenes and (E)-/(Z)-1,2-thiosulfonyl-1-alkenes in good to high yields with excellent stereoselectivities. Notably, this operationally simple process utilizes a broad substrate scope with good functional group tolerance and compatibility. The efficacy of the process has been proven for gram-scale reactions, and plausible mechanistic models are outlined on the basis of experimental results and control experiments.

Ruthenium Catalyzed Intramolecular C-X (X=C, N, O, S) Bond Formation via C-H Functionalization: An Overview

Ruthenium catalyzed C-H activation is well known for its high tolerance towards the functional group and broad applicability in organic synthesis and molecular sciences, with significant applications in pharmaceutical industries, material sciences, and polymer industry. In the last few decades, enormous progress has been observed with ruthenium-catalyzed C-H activation chemistry. Notably, the vast majority of the C-H functionalization known in the literature are intermolecular, although the intramolecular variant provides fascinating new structural facet starting from the simple molecular scaffolds. Intramolecular C-H functionalization is atom economical and step efficient, results in less formation of undesired products which is easy to purify. This has created a lot of interest in organic chemistry in developing new synthetic strategies for such functionalization. The focus of this review is to present the relatively unexplored intramolecular functionalization of C-H bonds into C-X (X=C, N, O, S) bonds utilizing versatile ruthenium catalysts, their scope, and brief mechanistic discussion.

Aerobic Cross-Dehydrogenative Coupling Reactions for Selective Mono- and Dithiolation of Phenols

A highly efficient strategy for the direct thiolation of phenols under transition metal-free and solvent-free conditions has been developed. These reactions are operationally simple with employing air (molecular oxygen) as an ideal oxidant and can selectively provide mono- and dithiolation products in good to excellent yields under basic conditions. The reaction tolerates a broad range of aryl thiols and arenes and is especially applicable for large-scale synthesis.

Visible Light Mediated Photocatalyst Free C-S Cross Coupling: Domino Synthesis of Thiochromane Derivatives via Photoinduced Electron Transfer

An efficient visible light mediated photocatalyst free C-S cross-coupling reaction has been developed for the synthesis of thiochromane derivatives through photoinduced electron transfer (PET). This methodology was further utilized for the synthesis of thiochroman-4-ol through intermolecular three-component cross-coupling reaction. The reaction proceeds via C-S bond formation through EDA complex/thioester cleavage/inter-or intramolecular sulfa-Michael addition followed by aldol reaction sequence. The EDA complex formation between aryl iodides and xanthate has been substantiated using spectroscopic experiments and DFT calculations.

Cp*Ir(iii)- and Cp*Rh(iii)-catalyzed C(sp2)–H amination of arenes using thioethers as directing groups

A mild and selective Cp*Ir(iii)- and Cp*Rh(iii)-catalyzed direct C(sp²)–H amination of arenes and three types of nitrene precursor reagents is reported, with the assistance of a thioether directing group.

Tetrahydrobioterin (BH4) Pathway: From Metabolism to Neuropsychiatry

Tetrahydrobipterin (BH4) is a pivotal enzymatic cofactor required for the synthesis of serotonin, dopamine and nitric oxide. BH4 is essential for numerous physiological processes at periphery and central levels, such as vascularization, inflammation, glucose homeostasis, regulation of oxidative stress and neurotransmission. BH4 de novo synthesis involves the sequential activation of three enzymes, the major controlling point being GTP cyclohydrolase I (GCH1). Complementary salvage and recycling pathways ensure that BH4 levels are tightly kept within a physiological range in the body. Even if the way of transport of BH4 and its ability to enter the brain after peripheral administration is still controversial, data showed increased levels in the brain after BH4 treatment. Available evidence shows that GCH1 expression and BH4 synthesis are stimulated by immunological factors, notably pro-inflammatory cytokines. Once produced, BH4 can act as an anti- inflammatory molecule and scavenger of free radicals protecting against oxidative stress. At the same time, BH4 is prone to autoxidation, leading to the release of superoxide radicals contributing to inflammatory processes, and to the production of BH2, an inactive form of BH4, reducing its bioavailability. Alterations in BH4 levels have been documented in many pathological situations, including Alzheimer's disease, Parkinson's disease and depression, in which increased oxidative stress, inflammation and alterations in monoaminergic function are described. This review aims at providing an update of the knowledge about metabolism and the role of BH4 in brain function, from preclinical to clinical studies, addressing some therapeutic implications.

Novel Schiff base-bridged multi-component sulfonamide imidazole hybrids as potentially highly selective DNA-targeting membrane active repressors against methicillin-resistant Staphylococcus aureus

A new type of Schiff base-bridged multi-component sulfonamide imidazole hybrids with antimicrobial potential was developed. Some target compounds showed significant antibacterial potency. Observably, butylene hybrids 4h exhibited remarkable inhibitory efficacy against clinical MRSA (MIC = 1 µg/mL), but had no significant toxic effect on normal mammalian cells (RAW 264.7). The highly active molecule 4h was revealed by molecular modeling study that it could insert into the base-pairs of DNA hexamer duplex and bind with the ASN-62 residue of human carbonic anhydrase isozyme II through hydrogen bonding. Furthermore, further preliminary antibacterial mechanism experiments confirmed that compound 4h could effectively interfere with MRSA membrane and insert into bacterial DNA isolated from clinical MRSA strains through non-covalent bonding to produce a supramolecular complex, thus exerting its strong antibacterial efficacy by impeding DNA replication. These findings strongly implied that the highly active hybrid 4h could be used as a potential DNA-targeting template for the development of valuable antimicrobial agent.

Environmentally Sensitive Color-Shifting Fluorophores for Bioimaging

We introduce color-shifting fluorophores that reversibly switch between a green and red fluorescent form through intramolecular spirocyclization. The equilibrium of the spirocyclization is environmentally sensitive and can be directly measured by determining the ratio of red to green fluorescence, thereby enabling the generation of ratiometric fluorescent probes and biosensors. Specifically, we developed a ratiometric biosensor for imaging calcium ions (Ca2+ ) in living cells, ratiometric probes for different proteins, and a bioassay for the quantification of nicotinamide adenine dinucleotide phosphate.

An unexpected discovery toward novel membrane active sulfonyl thiazoles as potential MRSA DNA intercalators

Aim: With the increasing emergence of drug-resistant bacteria, the need for new antimicrobial agents has become extremely urgent. This work was to develop sulfonyl thiazoles as potential antibacterial agents. Results & methodology: Novel hybrids of sulfonyl thiazoles were developed from commercial acetanilide and acetylthiazole. Hybrids 6e and 6f displayed excellent inhibitory efficacy against clinical methicillin-resistant Staphylococcus aureus (MRSA) (minimum inhibitory concentration = 1 μg/ml) without obvious toxicity toward normal mammalian cells (RAW 264.7). The combination uses were found to improve the antimicrobial ability. Further preliminary antibacterial mechanism experiments showed that the active molecule 6f could effectively interfere with MRSA membrane and insert into MRSA DNA. Conclusion: Compounds 6e and 6f could serve as potential DNA-targeting templates toward the development of promising antimicrobial agents.

Sepiapterin reductase: Characteristics and role in diseases

Sepiapterin reductase, a homodimer composed of two subunits, plays an important role in the biosynthesis of tetrahydrobiopterin. Furthermore, sepiapterin reductase exhibits a wide distribution in different tissues and is associated with many diseases, including brain dysfunction, chronic pain, cardiovascular disease and cancer. With regard to drugs targeting sepiapterin reductase, many compounds have been identified and provide potential methods to treat various diseases. However, the underlying mechanism of sepiapterin reductase in many biological processes is unclear. Therefore, this article summarized the structure, distribution and function of sepiapterin reductase, as well as the relationship between sepiapterin reductase and different diseases, with the aim of finding evidence to guide further studies on the molecular mechanisms and the potential clinical value of sepiapterin reductase. In particular, the different effects induced by the depletion of sepiapterin reductase or the inhibition of the enzyme suggest that the non-enzymatic activity of sepiapterin reductase could function in certain biological processes, which also provides a possible direction for sepiapterin reductase research.

Kynurenine and Tetrahydrobiopterin Pathways Crosstalk in Pain Hypersensitivity

Despite the identification of molecular mechanisms associated with pain persistence, no significant therapeutic improvements have been made. Advances in the understanding of the molecular mechanisms that induce pain hypersensitivity will allow the development of novel, effective, and safe therapies for chronic pain. Various pro-inflammatory cytokines are known to be increased during chronic pain, leading to sustained inflammation in the peripheral and central nervous systems. The pro-inflammatory environment activates additional metabolic routes, including the kynurenine (KYN) and tetrahydrobiopterin (BH4) pathways, which generate bioactive soluble metabolites with the potential to modulate neuropathic and inflammatory pain sensitivity. Inflammation-induced upregulation of indoleamine 2,3-dioxygenase 1 (IDO1) and guanosine triphosphate cyclohydrolase I (GTPCH), both rate-limiting enzymes of KYN and BH4 biosynthesis, respectively, have been identified in experimental chronic pain models as well in biological samples from patients affected by chronic pain. Inflammatory inducible KYN and BH4 pathways upregulation is characterized by increase in pronociceptive compounds, such as quinolinic acid (QUIN) and BH4, in addition to inflammatory mediators such as interferon gamma (IFN-γ) and tumor necrosis factor alpha (TNF-α). As expected, the pharmacologic and genetic experimental manipulation of both pathways confers analgesia. Many metabolic intermediates of these two pathways such as BH4, are known to sustain pain, while others, like xanthurenic acid (XA; a KYN pathway metabolite) have been recently shown to be an inhibitor of BH4 synthesis, opening a new avenue to treat chronic pain. This review will focus on the KYN/BH4 crosstalk in chronic pain and the potential modulation of these metabolic pathways that could induce analgesia without dependence or abuse liability.

Sepiapterin reductase promotes hepatocellular carcinoma progression via FoxO3a/Bim signaling in a nonenzymatic manner

Sepiapterin reductase plays an enzymatic role in the biosynthesis of tetrahydrobiopterin, which is reported in limited studies to regulate the progression of several tumors. However, the role of sepiapterin reductase in hepatocellular carcinoma remains largely unknown. Here, we found that sepiapterin reductase was frequently highly expressed in human hepatocellular carcinoma, which was significantly associated with higher T stage, higher tumor node metastasis stage, and even shorter survival of hepatocellular carcinoma patients. Furthermore, cell and animal experiments showed that sepiapterin reductase depletion inhibited cancer cell proliferation and promoted cancer cell apoptosis. Importantly, the results suggested that sepiapterin reductase enzymatic activity was not necessary for the progression of hepatocellular carcinoma, based on the comparison between SMMC-7721 and SMMC-7721 containing sepiapterin reductase mutant. Moreover, we showed that sepiapterin reductase regulated the development of hepatocellular carcinoma via the FoxO3a/Bim-signaling pathway. Collectively, our study suggests that sepiapterin reductase controls hepatocellular carcinoma progression via FoxO3a/Bim signaling in a nonenzymatic manner, which provides a potential prognostic factor and therapeutic strategy for hepatocellular carcinoma.

Engaging Sulfonamides: Intramolecular Cross-Electrophile Coupling Reaction of Sulfonamides with Alkyl Chlorides

The application of amine derivatives as coupling partners is rare due to the inherent strength of the C-N bond. Herein, we report the first cross-electrophile coupling reaction of unstrained benzylic sulfonamides. Nickel-catalyzed intramolecular cross-electrophile coupling reactions of acyclic and cyclic benzylic sulfonamides with pendant alkyl chlorides generate cyclopropane products. Mechanistic experiments and DFT calculations are consistent with initiation of the reaction by magnesium iodide accelerated oxidative addition of the benzylic sulfonamide. This work establishes neutral and unstrained amine derivatives as XEC partners, furnishes structural rearrangement of benzylic sulfonamides, and provides valuable information regarding catalyst design for the development of new cross-electrophile coupling reactions of carbon-heteroatom bonds.

Sepiapterin Reductase Inhibition Leading to Selective Reduction of Inflammatory Joint Pain in Mice and Increased Urinary Sepiapterin Levels in Humans and Mice

OBJECTIVE

To evaluate the antiinflammatory and analgesic effects of sepiapterin reductase (SPR) inhibition in a mouse model of inflammatory joint disease, and to determine whether urinary sepiapterin levels, as measured in mice and healthy human volunteers, could be useful as a noninvasive, translational biomarker of SPR inhibition/target engagement.

METHODS

The collagen antibody-induced arthritis (CAIA) model was used to induce joint inflammation in mice. The effects of pharmacologic inhibition of SPR on thresholds of heat-, cold-, and mechanical-evoked pain sensitivity and on signs of inflammation were tested in mice with CAIA. In addition, mice and healthy human volunteers were treated with SPR inhibitors, and changes in urinary sepiapterin levels were analyzed by high-performance liquid chromatography.

RESULTS

CAIA in mice was characterized by 2 phases: in the acute inflammation (early) phase, joint inflammation and heat-, mechanical-, and cold-induced pain hypersensitivity were present, while in the postinflammation (late) phase, no joint inflammation was observed but heat- and mechanical-induced hypersensitivity, but not cold hypersensitivity, were present. Inhibition of SPR in mice with CAIA significantly attenuated the heat-induced hyperalgesia in both phases, and the mechanical allodynia in the late phase. Signs of inflammation were unaffected by SPR inhibition. Urinary tetrahydrobiopterin levels, as a marker of inflammatory pain, were increased during inflammation in mice with CAIA (2-fold increase over controls; P < 0.05) and significantly reduced by SPR inhibition (P < 0.05 versus vehicle-treated mice). Increased urinary sepiapterin levels in the presence of SPR inhibition in both mice and healthy human volunteers were associated with high sensitivity (70-85%) and high specificity (82-88%) for the prediction of SPR inhibition/target engagement.

CONCLUSION

SPR inhibition reduces the pain associated with joint inflammation, thus showing its potential utility as an analgesic strategy for inflammatory joint pain. In addition, SPR inhibition increases urinary sepiapterin levels, indicating the potential of this measurement as a noninvasive biomarker of target engagement of SPR inhibitors, such as sulfasalazine, a disease-modifying antirheumatic drug that is currently used as a first-line treatment for rheumatoid arthritis.

The Role of Iron Regulation in Immunometabolism and Immune-Related Disease

Immunometabolism explores how the intracellular metabolic pathways in immune cells can regulate their function under different micro-environmental and (patho-)-physiological conditions (Pearce, 2010; Buck et al., 2015; O'Neill and Pearce, 2016). In the last decade great advances have been made in studying and manipulating metabolic programs in immune cells. Immunometabolism has primarily focused on glycolysis, the TCA cycle and oxidative phosphorylation (OXPHOS) as well as free fatty acid synthesis and oxidation. These pathways are important for providing the energy needs of cell growth, membrane rigidity, cytokine production and proliferation. In this review, we will however, highlight the specific role of iron metabolism at the cellular and organismal level, as well as how the bioavailability of this metal orchestrates complex metabolic programs in immune cell homeostasis and inflammation. We will also discuss how dysregulation of iron metabolism contributes to alterations in the immune system and how these novel insights into iron regulation can be targeted to metabolically manipulate immune cell function under pathophysiological conditions, providing new therapeutic opportunities for autoimmunity and cancer.

HPAanalyze: an R package that facilitates the retrieval and analysis of the Human Protein Atlas data

Background

The Human Protein Atlas (HPA) aims to map human proteins via multiple technologies including imaging, proteomics and transcriptomics. Access of the HPA data is mainly via web-based interface allowing views of individual proteins, which may not be optimal for data analysis of a gene set, or automatic retrieval of original images.

Results

HPAanalyze is an R package for retrieving and performing exploratory analysis of data from HPA. HPAanalyze provides functionality for importing data tables and xml files from HPA, exporting and visualizing data, as well as downloading all staining images of interest. The package is free, open source, and available via Bioconductor and GitHub. We provide examples of the use of HPAanalyze to investigate proteins altered in the deadly brain tumor glioblastoma. For example, we confirm Epidermal Growth Factor Receptor elevation and Phosphatase and Tensin Homolog loss and suggest the importance of the GTP Cyclohydrolase I/Tetrahydrobiopterin pathway. Additionally, we provide an interactive website for non-programmers to explore and visualize data without the use of R.

Conclusions

HPAanalyze integrates into the R workflow with the tidyverse framework, and it can be used in combination with Bioconductor packages for easy analysis of HPA data.

Electronic supplementary material

The online version of this article (10.1186/s12859-019-3059-z) contains supplementary material, which is available to authorized users.

Sulfhydryl-Directed Iridium-Catalyzed C-H/Diazo Coupling and Tandem Annulation of Naphthalene-1-thiols

The first sulfhydryl-directed iridium-catalyzed C-H/diazo coupling and tandem annulation of naphthalene-1-thiols has been developed. The framework of naphtho[1,8-bc]thiopyrans was constructed in a one-step reaction with good yields. This transformation provides a practical synthetic route for the widely used naphtho[1,8-bc]thiopyran derivatives.

Repurposing of Tranilast for Potential Neuropathic Pain Treatment by Inhibition of Sepiapterin Reductase in the BH4 Pathway

Tetrahydrobiopterin (BH₄) is a cofactor in the production of various signaling molecules including nitric oxide, dopamine, adrenaline, and noradrenaline. BH₄ levels are critical for processes associated with cardiovascular function, inflammation, mood, pain, and neurotransmission. Increasing pieces of evidence suggest that BH₄ is upregulated in chronic pain. Sepiapterin reductase (SPR) catalyzes both the reversible reduction of sepiapterin to dihydrobiopterin (BH₂) and 6-pyruvoyl-tetrahydrobiopterin to BH₄ within the BH₄ pathway. Therefore, inhibition of SPR by small molecules can be used to control BH₄ production and ultimately alleviate chronic pain. Here, we have used various in silico and in vitro experiments to show that tranilast, licensed for use in bronchial asthma, can inhibit sepiapterin reduction by SPR. Docking and molecular dynamics simulations suggest that tranilast can bind to human SPR (hSPR) at the same site as sepiapterin including S157, one of the catalytic triad residues of hSPR. Colorimetric assays revealed that tranilast was nearly twice as potent as the known hSPR inhibitor, N-acetyl serotonin. Tranilast was able to inhibit hSPR activity both intracellularly and extracellularly in live cells. Triple quad mass spectrophotometry of cell lysates showed a proportional decrease of BH₄ in cells treated with tranilast. Our results suggest that tranilast can act as a potent hSPR inhibitor and therefore is a valid candidate for drug repurposing in the treatment of chronic pain.

Revitalizing antifolates through understanding mechanisms that govern susceptibility and resistance

In prokaryotes and eukaryotes, folate (vitamin B9) is an essential metabolic cofactor required for all actively growing cells. Specifically, folate serves as a one-carbon carrier in the synthesis of amino acids (such as methionine, serine, and glycine), N-formylmethionyl-tRNA, coenzyme A, purines and thymidine. Many microbes are unable to acquire folates from their environment and rely on de novo folate biosynthesis. In contrast, mammals lack the de novo folate biosynthesis pathway and must obtain folate from commensal microbiota or the environment using proton-coupled folate transporters. The essentiality and dichotomy between mammalian and bacterial folate biosynthesis and utilization pathways make it an ideal drug target for the development of antimicrobial agents and cancer chemotherapeutics. In this minireview, we discuss general aspects of folate biosynthesis and the underlying mechanisms that govern susceptibility and resistance of organisms to antifolate drugs.

Visible-light mediated sulfonylation of thiols via insertion of sulfur dioxide

Photocatalytically generated sulfenyl radicals were coupled with arylsulfonyl radicals at room temperature for accessing unsymmetrical organic thiosulfonates.

The solvent-controlled chemoselective construction of C–S/S–S bonds via the Michael reaction/thiol coupling of quinoline-2-thiones

The solvent-controlled selective construction of C–S and S–S bonds containing a quinoline skeleton under mild conditions from quinoline-2-thiones has been reported.

Direct access to bis-S-heterocyclesviacopper-catalyzed three component tandem cyclization using S8as a sulfur source

An elemental sulfur atom donor strategy for constructing a thiophene-fused thiazole bis-S-heterocyclic skeletonviaCu-catalyzed three-component tandem cyclization has been developed.

Ru(ii)-Catalysed synthesis of (1H)-isothiochromenes by oxidative coupling of benzylthioethers with internal alkynes

(1H)-Isothiochromenes have been prepared by Ru-catalysed oxidative coupling of benzylthioethers with internal alkynes.

Combining Human and Rodent Genetics to Identify New Analgesics

Most attempts at rational development of new analgesics have failed, in part because chronic pain involves multiple processes that remain poorly understood. To improve translational success, one strategy is to select novel targets for which there is proof of clinical relevance, either genetically through heritable traits, or pharmacologically. Such an approach by definition yields targets with high clinical validity. The biology of these targets can be elucidated in animal models before returning to the patients with a refined therapeutic. For optimal treatment, having biomarkers of drug action available is also a plus. Here we describe a case study in rational drug design: the use of controlled inhibition of peripheral tetrahydrobiopterin (BH4) synthesis to reduce abnormal chronic pain states without altering nociceptive-protective pain. Initially identified in a population of patients with low back pain, the association between BH4 production and chronic pain has been confirmed in more than 12 independent cohorts, through a common haplotype (present in 25% of Caucasians) of the rate-limiting enzyme for BH4 synthesis, GTP cyclohydrolase 1 (GCH1). Genetic tools in mice have demonstrated that both injured sensory neurons and activated macrophages engage increased BH4 synthesis to cause chronic pain. GCH1 is an obligate enzyme for de novo BH4 production. Therefore, inhibiting GCH1 activity eliminates all BH4 production, affecting the synthesis of multiple neurotransmitters and signaling molecules and interfering with physiological function. In contrast, targeting the last enzyme of the BH4 synthesis pathway, sepiapterin reductase (SPR), allows reduction of pathological BH4 production without completely blocking physiological BH4 synthesis. Systemic SPR inhibition in mice has not revealed any safety concerns to date, and available genetic and pharmacologic data suggest similar responses in humans. Finally, because it is present in vivo only when SPR is inhibited, sepiapterin serves as a reliable biomarker of target engagement, allowing potential quantification of drug efficacy. The emerging development of therapeutics that target BH4 synthesis to treat chronic pain illustrates the power of combining human and mouse genetics: human genetic studies for clinical selection of relevant targets, coupled with causality studies in mice, allowing the rational engineering of new analgesics.

8-Mercaptoguanine Derivatives as Inhibitors of Dihydropteroate Synthase

Dihydropteroate synthase (DHPS) is an enzyme of the folate biosynthesis pathway, which catalyzes the formation of 7,8-dihydropteroate (DHPt) from 6-hydroxymethyl-7,8-dihydropterin pyrophosphate (DHPPP) and para-aminobenzoic acid (pABA). DHPS is the long-standing target of the sulfonamide class of antibiotics that compete with pABA. In the wake of sulfa drug resistance, targeting the structurally rigid (and more conserved) pterin site has been proposed as an alternate strategy to inhibit DHPS in wild-type and sulfa drug resistant strains. Following the work on developing pterin-site inhibitors of the adjacent enzyme 6-hydroxymethyl-7,8-dihydropterin pyrophosphokinase (HPPK), we now present derivatives of 8-mercaptoguanine, a fragment that binds weakly within both enzymes, and quantify sub-μm binding using surface plasmon resonance (SPR) to Escherichia coli DHPS (EcDHPS). Eleven ligand-bound EcDHPS crystal structures delineate the structure-activity relationship observed providing a structural framework for the rational development of novel, substrate-envelope-compliant DHPS inhibitors.

Direct thiolation of aza-heteroaromatic N-oxides with disulfides via copper-catalyzed regioselective C–H bond activation

A novel and efficient thiolation reaction of aza-heteroaromatic N-oxides with disulfides via copper catalyzed C–H activation has been developed.

Antimicrobial sulfonamides clear latent Kaposi sarcoma herpesvirus infection and impair MDM2-p53 complex formation

Kaposi sarcoma herpesvirus (KSHV), also known as human herpesvirus 8, is the causative agent of Kaposi sarcoma; this malignant angiosarcoma is usually treated with conventional antitumor agents that can control disease evolution, but do not clear the latent KSHV episome that binds to cellular DNA. Some commercial antibacterial sulfonamides were tested for the ability to suppress latent KSHV. Quantitative PCR (qPCR) and cytofluorometry assays were used for detecting both viral DNA and the latency factor LANA (latency-associated nuclear antigen) in BC3 cells, respectively. The capacity of sulfonamides to impair MDM2-p53 complex formation was detected by an enzyme-linked immunosorbent assay method. The analysis of variance was performed according to one-way analysis of variance with Fisher as a post hoc test. Here we show that sulfonamide antibiotics are able to suppress the KSHV latent state in permanently infected BC3 lymphoma cells and interfere with the formation of the MDM2-p53 complex that KSHV seemingly needs to support latency and to trigger tumor cell transformation. These findings detected a new molecular target for the activity of sulfonamides and offer a new potential perspective for treating KSHV-induced lymphoproliferative diseases.