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l-4-Chlorokynurenine (l-4-Cl-Kyn) is a neuropharmaceutical drug candidate that is in development for the treatment of major depressive disorder. Recently, this amino acid was naturally found as a residue in the lipopeptide antibiotic taromycin. Herein, we report the unprecedented conversion of l-tryptophan into l-4-Cl-Kyn catalyzed by four enzymes in the taromycin biosynthetic pathway from the marine bacterium Saccharomonospora sp. CNQ-490. We used genetic, biochemical, structural, and analytical techniques to establish l-4-Cl-Kyn biosynthesis, which is initiated by the flavin-dependent tryptophan chlorinase Tar14 and its flavin reductase partner Tar15. This work revealed the first tryptophan 2,3-dioxygenase (Tar13) and kynurenine formamidase (Tar16) enzymes that are selective for chlorinated substrates. The substrate scope of Tar13, Tar14, and Tar16 was examined and revealed intriguing promiscuity, thereby opening doors for the targeted engineering of these enzymes as useful biocatalysts.

Human indoleamine 2,3-dioxygenase 1 (hIDO1) and tryptophan dioxygenase (hTDO) catalyze the same dioxygenation reaction of Trp to generate N-formyl kynurenine (NFK). They share high structural similarity, especially in the active site. However, hIDO1 possesses a unique inhibitory substrate binding site (Si) that is absent in hTDO. In addition, in hIDO1, the indoleamine group of the substrate Trp is H-bonded to S167 through a bridging water, while that in hTDO is directly H-bonded to H76. Here we show that Trp binding to the Si site or the mutation of S167 to histidine in hIDO1 retards its turnover activity and that the inhibited activity can be rescued by an effector, 3-indole ethanol (IDE). Kinetic studies reveal that the inhibited activity introduced by Trp binding to the Si site is a result of retarded recombination of the ferryl moiety with Trp epoxide to form NFK and that IDE reverses the effect by preventing Trp from binding to the Si site. In contrast, the abolished activity induced by the S167H mutation is primarily a result of ∼5000-fold reduction in the O2 binding rate constant, possibly due to the blockage of a ligand delivery tunnel, and that IDE binding to the Si site reverses the effect by reopening the tunnel. The data offer new insights into structure-based design of hIDO1-selective inhibitors.

Disease tolerance is the ability of the host to reduce the effect of infection on host fitness. Analysis of disease tolerance pathways could provide new approaches for treating infections and other inflammatory diseases. Typically, an initial exposure to bacterial lipopolysaccharide (LPS) induces a state of refractoriness to further LPS challenge (endotoxin tolerance). We found that a first exposure of mice to LPS activated the ligand-operated transcription factor aryl hydrocarbon receptor (AhR) and the hepatic enzyme tryptophan 2,3-dioxygenase, which provided an activating ligand to the former, to downregulate early inflammatory gene expression. However, on LPS rechallenge, AhR engaged in long-term regulation of systemic inflammation only in the presence of indoleamine 2,3-dioxygenase 1 (IDO1). AhR-complex-associated Src kinase activity promoted IDO1 phosphorylation and signalling ability. The resulting endotoxin-tolerant state was found to protect mice against immunopathology in Gram-negative and Gram-positive infections, pointing to a role for AhR in contributing to host fitness.

The review focuses on those enzymes that catalyze oxidation reactions and those for which crystal structures are available. There are two broad classes of heme enzyme oxidants: oxygenases that use O2 to oxidize, oxygenate, substrates and peroxidases that use 2O2 to oxidize. The review demonstrates that out of the oxidants molecular oxygen is the most unusual, as O2 is not a reactive molecule despite the oxidation of nearly all biological molecules by O2 being a thermodynamically favorable process. The reason is that there is a large kinetic barrier to these reactions owing to O2 being a paramagnetic molecule so that the reaction between a majority of biological molecules that have paired spins is a spin forbidden process.

Objective: The objective of this study was to observe the changes in the levels of indoleamine 2, 3-dioxygenase (IDO) and tryptophan-2, 3-dioxygenase (TDO) in patients with major depressive disorder (MDD) and investigate their potential role as novel biomarkers for diagnosing MDD., Methods: A total of 55 MDD patients and 55 healthy controls (HC) were enrolled in the study. The severity of MDD was assessed using the 24-item Hamilton Depression Rating Scale (HAMD-24) before and after treatment. The serum concentrations of IDO and TDO were measured at baseline and after treatment. The correlations between the serum levels of IDO and TDO and HAMD-24 scores were evaluated using Pearson's correlation test. Receiver operating characteristic (ROC) curve analysis was used to evaluate the area under the curve (AUC) of serum levels of IDO and TDO for discriminating MDD patients from HC., Results: The serum IDO and TDO concentrations were significantly higher in patients with MDD at baseline than in healthy controls, and decreased significantly after 2 weeks or 1 month of treatment. The levels of IDO and TDO were significantly positively correlated with HAMD-24 scores. Furthermore, the AUC values for IDO and TDO were 0.999 and 0.966, respectively., Conclusion: The study suggests that serum IDO and TDO may serve as novel biomarkers for diagnosing MDD. These findings may lead to a better understanding of the pathogenesis of MDD and the development of new therapeutic targets., (© 2024. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

The enzyme tryptophan 2,3-dioxygenase (TDO2) has been implicated in the dysregulation across a variety of human cancers. Despite this association, the implications of TDO2 in the progression of bladder cancer have eluded thorough understanding. In this study, we demonstrate that TDO2 expression is notably elevated in bladder cancer tissues and serves as an unfavorable prognostic factor for overall survival. Through a series of biological functional assays, we have determined that TDO2 essentially enhances cell proliferation, metastatic potential, and imparts a decreased sensitivity to the chemotherapeutic agent cisplatin. Our mechanistic investigations reveal that TDO2 augments aryl hydrocarbon receptor (AhR) signaling pathways and subsequently upregulates the expression of SPARC and FILIP1L. Importantly, we have identified a positive correlation between TDO2 levels and the basal/squamous subtype of bladder cancer, and we provide evidence to suggest that TDO2 expression is modulated by the tumor suppressors RB1 and TP53. From a therapeutic perspective, we demonstrate that the targeted inhibition of TDO2 with the molecular inhibitor 680C91 markedly attenuates tumor growth and metastasis while concurrently enhancing the efficacy of cisplatin. These findings open a new therapeutic avenue for the management of bladder cancer., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024. Published by Elsevier Inc.)

Kaempferol (KAE) is a natural flavonoid with powerful reactive oxygen species (ROS) scavenging properties and beneficial effects on ex vivo sperm functionality. In this paper, we studied the ability of KAE to prevent or ameliorate structural, functional or oxidative damage to frozen-thawed bovine spermatozoa. The analysis focused on conventional sperm quality characteristics prior to or following thermoresistance tests, namely the oxidative profile of semen alongside sperm capacitation patterns, and the levels of key proteins involved in capacitation signaling. Semen samples obtained from 30 stud bulls were frozen in the presence of 12.5, 25 or 50 μM KAE and compared to native ejaculates (negative control-Ctrl N ) as well as semen samples cryopreserved in the absence of KAE (positive control-Ctrl C ). A significant post-thermoresistance test maintenance of the sperm motility ( p < 0.001), membrane ( p < 0.001) and acrosome integrity ( p < 0.001), mitochondrial activity ( p < 0.001) and DNA integrity ( p < 0.001) was observed following supplementation with all KAE doses in comparison to Ctrl C . Experimental groups supplemented with all KAE doses presented a significantly lower proportion of prematurely capacitated spermatozoa ( p < 0.001) when compared with Ctrl C . A significant decrease in the levels of the superoxide radical was recorded following administration of 12.5 ( p < 0.05) and 25 μM KAE ( p < 0.01). At the same time, supplementation with 25 μM KAE in the cryopreservation medium led to a significant stabilization of the activity of Mg 2+ -ATPase ( p < 0.05) and Na + /K + -ATPase ( p < 0.0001) in comparison to Ctrl C . Western blot analysis revealed that supplementation with 25 μM KAE in the cryopreservation medium prevented the loss of the protein kinase A (PKA) and protein kinase C (PKC), which are intricately involved in the process of sperm activation. In conclusion, we may speculate that KAE is particularly efficient in the protection of sperm metabolism during the cryopreservation process through its ability to promote energy synthesis while quenching excessive ROS and to protect enzymes involved in the process of sperm capacitation and hyperactivation. These properties may provide supplementary protection to spermatozoa undergoing the freeze-thaw process., Competing Interests: The authors declare no conflicts of interest. The funders had no role in the design of the study; in the collection, analyses or interpretation of data; in the writing of the manuscript; or in the decision to publish the results.

Acid-resistance systems are essential for pathogenic Escherichia coli to survive in the strongly acidic environment of the human stomach (pH < 2.5). Among these, the glutamic acid decarboxylase (GAD) system is the most effective. However, the precise mechanism of GAD induction is unknown. We previously reported that a tolC mutant lacking the TolC outer membrane channel was defective in GAD induction. Here, we show that indole, a substrate of TolC-dependent efflux pumps and produced by the tryptophanase encoded by the tnaA gene, negatively regulates GAD expression. GAD expression was restored by deleting tnaA in the tolC mutant; in wild-type E. coli, it was suppressed by adding indole to the growth medium. RNA-sequencing revealed that tnaA mRNA levels drastically decreased upon exposure to moderately acidic conditions (pH 5.5). This decrease was suppressed by RNase E deficiency. Collectively, our results demonstrate that the RNase E-dependent degradation of tnaA mRNA is accelerated upon acid exposure, which decreases intracellular indole concentrations and triggers GAD induction. [ABSTRACT FROM AUTHOR]

Background: We previously found that the respiratory epithelial cells could eliminate the invaded group A streptococcus (GAS) through autophagy induced by binding a fibronectin (Fn) binding protein (FnBp) expressed on the surface of GAS to plasma protein Fn and its receptor integrin α5β1 of epithelial cells. Is autophagy initiated by FnBp + bacteria via FnBp-Fn-Integrin α5β1 axis a common event in respiratory epithelial cells?, Methods: We chose Staphylococcus aureus ( S. aureus/S. a ) and Listeria monocytogenes ( L. monocytogenes/L. m ) as representatives of extracellular and intracellular FnBp + bacteria, respectively. The FnBp of them was purified and the protein function was confirmed by western blot, viable bacteria count, confocal and pull-down. The key molecule downstream of the action axis was detected by IP, mass spectrometry and bio-informatics analysis., Results: We found that different FnBp from both S. aureus and L. monocytogenes could initiate autophagy through FnBp-Fn-integrin α5β1 axis and this could be considered a universal event, by which host tries to remove invading bacteria from epithelial cells. Importantly, we firstly reported that S100A8, as a key molecule downstream of integrin β1 chain, is highly expressed upon activation of integrin α5β1, which in turn up-regulates autophagy., Conclusions: Various FnBp from FnBp + bacteria have the ability to initiate autophagy via FnBp-Fn-Integrin α5β1 axis to promote the removal of invading bacteria from epithelial cells in the presence of fewer invaders. S100A8 is a key molecule downstream of Integrin α5β1 in this autophagy pathway., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2024 Meng, Wang, Li, Wang, Wang, Li, Gao, Li, Ma and Wei.)

In the last decade, the kynurenine pathway, which is the primary metabolic route for tryptophan (TRP) catabolism, has sparked great interest in the pharmaceutical sciences due to its role in immune regulation and cancer immunoediting. In this context, the development of cell-based assays might represent a tool to: i) characterize the cell secretome according to cell types; ii) gain more insight into the role of kynurenines in different disease scenarios; iii) screen hIDO1 (human indoleamine 2,3-dioxygenase) inhibitors and evaluate their effect on downstream TRP-catabolizing enzymes. This paper reports a validated Liquid Chromatography with tandem mass spectrometry (LC-MS/MS) method to simultaneously quantify TRP, L-kynurenine (KYN), xanthurenic acid (XA), 3-hydroxykynurenine (3OHKYN), kynurenic acid (KA), 3-hydroxyanthranilic acid (3OHAA), anthranilic acid (AA), 5-hydroxytryptamine (serotonin, 5HT) and tryptamine (TRYP) in Dulbecco's Modified Eagle and Eagle's Minimum Essential Media (DMEM and EMEM, respectively). The quantitative method was validated according to FDA, ICH and EMA guidelines, later applied: i) to assess the impact of selective inhibition of hIDO1 or hTDO (human tryptophan 2,3-dioxygenase) on the kynurenine pathway in A375 (melanoma), MDA-MB-231 (breast cancer), and U87 (glioblastoma) cell lines using multivariate analysis (MVA); ii) to determine the IC 50 values of both well-known (i.e., epacadostat, linrodostat) and the novel hIDO1 inhibitor (i.e., BL5) in the aforementioned cell lines. The proposed LC-MS/MS method is reliable and robust. Furthermore, it is highly versatile and suitable for applications in the preclinical drug research and in vitro assays., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 The Authors. Published by Elsevier B.V. All rights reserved.)

Background: Childhood trauma is one of the most extensively studied and well-supported environmental risk factors for the development of mental health problems. The human tryptophan hydroxylase 2 (TPH2) gene is one of the most promising candidate genes in numerous psychiatric disorders. However, it is now widely acknowledged that neither genetic variation nor environmental exposure alone can fully explain all the phenotypic variance observed in psychiatric disorders. Therefore, it is necessary to consider the interaction between the two factors in psychiatric research., Methods: We enrolled a sizable nonclinical cohort of 786 young, healthy adults who underwent structural MRI scans and completed genotyping, the Childhood Trauma Questionnaire (CTQ) and behavioural scores. We identified the interaction between childhood trauma and the TPH2 rs7305115 gene polymorphism in the gray matter volume (GMV) of specific brain subregions and the behaviour in our sample using a multiple linear regression framework. We utilized mediation effect analysis to identify environment /gene-brain-behaviour relationships., Results: We found that childhood trauma and TPH2 rs7305115 interacted in both behaviour and the GMV of brain subregions. Our findings indicated that the GMV of the right posterior parietal thalamus served as a significant mediator supporting relationship between childhood trauma (measured by CTQ score) and anxiety scores in our study population, and the process was partly modulated by the TPH2 rs7305115 gene polymorphism. Moreover, we found only a main effect of childhood trauma in the GMV of the right parahippocampal gyrus area, supporting the relationship between childhood trauma and anxiety scores as a significant mediator., Conclusions: Our findings suggest that early-life trauma may have a specific and long-term structural effect on brain GMV, potentially leading to altered cognitive and emotional processes involving the parahippocampal gyrus and thalamus that may also be modulated by the TPH2 gene polymorphism. This finding highlights the importance of considering genetic factors when examining the impact of early-life experiences on brain structure and function. Gene‒environment studies can be regarded as a powerful objective supplement for targeted therapy, early diagnosis and treatment evaluation in the future., (© 2023. The Author(s).)

Aim: As the second most prevalent subtype of epithelial ovarian cancers, ovarian clear cell carcinoma (OCCC) is known for its chemoresistance to conventional platinum-based therapy. In this work, we examined the tryptophan (Trp) metabolism enzymes' differential expression in patients with OCCC to assess the potential for personalised treatment., Methods: A total of 127 OCCC tissues were used to construct tissue microarrays, and immunohistochemistry (IHC) staining of the Trp enzymes IDO1, IDO2, TDO2 and IL4I1 was performed. The correlations between Trp enzyme expression and clinical characteristics were analysed., Results: Positive IDO1, IDO2, TDO2 and IL4I1 staining was identified in 26.8%, 94.5%, 75.6% and 82.7% of OCCC respectively. IDO1-positive samples were more common in the chemoresistant group than in the platinum-sensitive group (46.7% vs. 19.8%). Moreover, positive expression of IDO1, TDO2 and IL4I1 was related to advanced stage, metastasis, bilateral tumours, endometriosis and tumour rupture (p < 0.05) respectively. Univariate analysis revealed a significant association between bilateral tumours, lymph node metastasis, advanced stage, distant metastasis and aberrant cytology with a poor prognosis for OCCC, while the absence of residual tumour was correlated with a favourable outcome (p < 0.05). However, only bilateral tumours and lymph node metastases were related to a poor prognosis after multivariate analysis., Conclusion: This is the first study to investigate the expression of the Trp enzymes IDO1, IDO2, TDO2 and IL4I1 in OCCC tissues. IDO2, TDO2 and IL4I1 were detected in the majority of OCCC. Clinical traits were correlated with IDO1, IDO2, TDO2 and IL4I1 expression. IDO1 may be used as a therapeutic target given the large percentage of chemoresistant cases with IDO1 expression. These results will aid the development of personalised therapies for OCCC., (© 2023 The Authors. Cancer Medicine published by John Wiley & Sons Ltd.)

Tryptophan 2,3-dioxygenase (TDO), an immunosuppressive enzyme, can involve in immune evasion and tumor tolerance. TDO inhibitors can boost the efficacy of chemotherapeutics by promoting immunity. Herein, a strategy to introduce a TDO inhibitor into Pt(IV) complexes for reversing tumor immune suppression was adopted. A mono-modified Pt(IV) complex, 3, displayed significant antitumor activity against human liver cancer cells. Flow cytometry study revealed that complex 3 could induce cell death via a mitochondrial-dependent apoptosis pathway and arrest the cell cycle at S phase. Furthermore, complex 3 was effective to enhance T-cell immune responses by inhibiting the TDO enzyme expression to block the kynurenine production and inactivating the downstream of aryl hydrocarbon receptor (AHR). A Pt(IV) hybrid containing a tryptophan 2,3-dioxygenase (TDO) inhibitor could enhance antitumor immune response by inhibiting the TDO enzyme expression to block the kynurenine production and induce HepG-2 cancer cell apoptosis via DNA damage through releasing the TDO inhibitor and cisplatin under reduction. Unlabelled Image • Novel Pt(IV) hybrids with a TDO (tryptophan dioxygenase) inhibitor were described. • In vitro anticancer screening for the targeted hybrids was made. • Complex 3 displayed significant antitumor activity against HepG-2 cancer cells. • Complex 3 could inhibit the TDO expression to block the kynurenine production. • Complex 3 was effective to enhance T-cell immune responses. [ABSTRACT FROM AUTHOR]

Major depressive disorder (MDD) is a very common stress-related mental disorder that carries a huge burden for affected patients and the society. It is associated with a high mortality that derives from suicidality and the development of serious medical conditions such as heart diseases, diabetes, and stroke. Although a range of effective antidepressants are available, more than 50% of the patients do not respond to the first treatment they are prescribed and around 30% fail to respond even after several treatment attempts. The heterogeneous condition of MDD, the lack of biomarkers matching patients with the right treatments and the situation that almost all available drugs are only targeting the serotonin, norepinephrine, or dopamine signaling, without regulating other potentially dysregulated systems may explain the insufficient treatment status. The hypothalamic-pituitary-adrenal (HPA) axis is one of these other systems, there is numerous and robust evidence that it is implicated in MDD and other stress-related conditions, but up to date there is no specific drug targeting HPA axis components that is approved and no test that is routinely used in the clinical setting identifying patients for such a specific treatment. Is there still hope after these many years for a breakthrough of agents targeting the HPA axis? This review will cover tests detecting altered HPA axis function and the specific treatment options such as glucocorticoid receptor (GR) antagonists, corticotropin-releasing hormone 1 (CRH1) receptor antagonists, tryptophan 2,3-dioxygenase (TDO) inhibitors and FK506 binding protein 5 (FKBP5) receptor antagonists. [ABSTRACT FROM AUTHOR]

Abstract Tryptophan 2,3-dioxygenase (TDO) is becoming a promising therapeutic target due to its involvement in cancer and neurodegenerative diseases. Development of efficient TDO inhibitors is a prime strategy in disease treatment. However, the lack of a TDO inhibitor bioassay system slows the progress of TDO inhibitor research. Herein, an active recombinant human TDO (hTDO) was prepared under optimal expression conditions, an enzymatic assay was optimized, and two cellular assays of TDO activity were developed. Then, the potential TDO inhibitory activities of nine tryptanthrin derivatives (5a - 5i) were evaluated, and the inhibitory constants (Ki), enzymatic and cellular half maximal inhibitory concentrations (IC 50) were measured, and the type of inhibition was determined. The tryptanthrins had various levels of TDO inhibitory activities; tryptanthrins with a substituent at 8-position had stronger inhibitory activities than the other derivatives. Moreover, most of the compounds, except 5g and 5h , exhibited better inhibitory activities than the previously reported TDO inhibitor LM10. Furthermore, the molecular docking study of compounds 5c and 5d revealed that the O atom of the tryptanthrin ring is directed toward the heme iron (Fe) of hTDO via strong coordination interactions. These findings suggest that tryptanthrin and its derivatives have the potential to be developed as promising molecules for TDO-related target therapy. Graphical abstract Image 1 Highlights • New cellular assays of TDO activity are established. • Tryptanthrin and its derivatives are potential TDO inhibitors. • Molecular docking studies suggest 5c and 5d bind to the active site of hTDO. [ABSTRACT FROM AUTHOR]

Introduction: Tryptophan metabolism is indirectly involved in immune tolerance and promotes response to anticancer drugs. However, the mechanisms underlying tryptophan metabolism and immune landscape in bladder urothelial carcinoma (BLCA) are not fully understood., Methods: A BLCA dataset containing 406 tumor samples with clinical survival information and 19 normal samples were obtained from the Cancer Genome Atlas database. The validation set, GSE32894, contained 223 BLCA tumor samples with survival information, and the single-cell dataset, GSE135337, included seven BLCA tumor samples; both were obtained from the gene expression omnibus database. Univariate and multivariate Cox regression analyses were conducted to evaluate clinical parameters and risk scores. Immune infiltration and checkpoint analyses were performed to explore the immune landscape of BLCA. Single-cell analysis was conducted to further identify the roles of model genes in BLCA. Finally, NAMPT expression in BLCA and adjacent tissues was detected using RT-qPCR, CCK-8 and Transwell assays were conducted to determine the role of NAMPT in BLCA cells., Results: Six crossover genes (TDO2, ACAT1, IDO1, KMO, KYNU, and NAMPT) were identified by overlap analysis of tryptophan metabolism-related genes, immune-related genes, and differentially expressed genes (DEGs). Three biomarkers, NAMPT, IDO1, and ACAT1, were identified using Cox regression analysis. Accordingly, a tryptophan metabolism- and immune-related gene risk model was constructed, and the patients were divided into high- and low-risk groups. There were significant differences in the clinical parameters, prognosis, immune infiltration, and immunotherapy response between the risk groups. RT-qPCR revealed that NAMPT was upregulated in BLCA samples. Knocking down NAMPT significantly inhibited BLCA cell proliferation, migration, and invasion., Discussion: In our study, we constructed a tryptophan metabolism- and immune-related gene risk model based on three biomarkers, namely NAMPT, IDO1, and ACAT1, that were significantly associated with the progression and immune landscape of BLCA. The risk model could effectively predict patient prognosis and immunotherapy response and can guide individualized immunotherapy., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest. The handling editor WC declared a shared parent affiliation with the authors at the time of review., (Copyright © 2023 Zhou, Qin, Zhang, Zhao and Xue.)

Neuropathic pain is a well-documented phenomenon in experimental and clinical diabetes; however, current treatment is unsatisfactory. Serotoninergic-containing neurons are key components of the descending autoinhibitory pathway, and a decrease in their activity may contribute at least in part to diabetic neuropathic pain (DNP). A streptozotocin (STZ)-treated rat was used as a model for type 1 diabetes mellitus (T1DM). Pain transmission was evaluated using well-established nociceptive-based techniques, including the Hargreaves apparatus, cold plate and dynamic plantar aesthesiometer. Using qRT-PCR, Western blotting, immunohistochemistry, and HPLC-based techniques, we also measured in the central nervous system and peripheral nervous system of diabetic animals the expression and localization of 5-HT1A receptors (5-HT1AR), levels of key enzymes involved in the synthesis and degradation of tryptophan and 5-HT, including tryptophan hydroxylase-2 (Tph-2), tryptophan 2,3-dioxygenase (Tdo), indoleamine 2,3-dioxygenase 1 (Ido1) and Ido2. Moreover, spinal concentrations of 5-HT, 5-hydroxyindoleacetic acid (5-HIAA, a metabolite of 5-HT) and quinolinic acid (QA, a metabolite of tryptophan) were also quantified. Diabetic rats developed thermal hyperalgesia and cold/mechanical allodynia, and these behavioral abnormalities appear to be associated with the upregulation in the levels of expression of critical molecules related to the serotoninergic nervous system, including presynaptic 5-HT1AR and the enzymes Tph-2, Tdo, Ido1 and Ido2. Interestingly, the level of postsynaptic 5-HT1AR remains unaltered in STZ-induced T1DM. Chronic treatment of diabetic animals with 8-hydroxy-2-(dipropylamino)tetralin (8-OH-DPAT), a selective 5-HT1AR agonist, downregulated the upregulation of neuronal presynaptic 5-HT1AR, increased spinal release of 5-HT (↑ 5-HIAA/5-HT) and reduced the concentration of QA, decreased mRNA expression of Tdo , Ido1 and Ido2 , arrested neuronal degeneration and ameliorated pain-related behavior as exemplified by thermal hyperalgesia and cold/mechanical allodynia. These data show that 8-OH-DPAT alleviates DNP and other components of the serotoninergic system, including the ratio of 5-HIAA/5-HT and 5-HT1AR, and could be a useful therapeutic agent for managing DNP.

l -Tryptophan oxidase, VioA from Chromobacterium violaceum, which has a high substrate specificity for tryptophan, is useful for quantitative assay of tryptophan. However, stability of wild type VioA is not enough for its application in clinical or industrial use. To improve the thermal stability of the enzyme, we developed a VioA (C395A) mutant, with higher stability than wild type VioA. The VioA (C395A) exhibited similar specificity and kinetic parameter for tryptophan to wild type. Conventionally, the quantity of tryptophan is determined by instrumental methods, such as high-performance liquid chromatography (HPLC) after pre-column-derivatization. Using the mutant enzyme, we succeeded in the tryptophan quantification in human plasma samples, to an accuracy of <2.9% when compared to the instrumental method, and to a precision of CV <3.2%. To analyse the improvement in storage stability and substrate specificity, we further determined the crystal structures of VioA (C395A) complexed with FAD, and with FAD and tryptophan at 1.8 Å resolution. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • 48 Naphthoindolizine and indolizinoquinoline-5,12-dione derivatives were synthesized. • These compounds showed significant IDO1 inhibition and high selectivity over TDO. • The most potent 5c (IDO1 IC 50 23 nM) is a low cytotoxic, promising lead compound. Abstract Indoleamine 2,3-dioxygenase 1 (IDO1) is regarded as a promising target for cancer immunotherapy. Many naphthoquinone derivatives have been reported as IDO1 inhibitors so far. Herein, two series of naphthoquinone derivatives, naphthoindolizine and indolizinoquinoline-5,12-dione derivatives, were synthesized and evaluated for their IDO1 inhibitory activity. Most of the target compounds showed significant inhibition potency and high selectivity for IDO1 over tryptophan 2,3-dioxygenase (TDO). The structure-activity relationship was also summarized. The most potent compounds 5c (IC 50 23 nM, IDO1 enzyme), and 5b′ (IC 50 372 nM, HeLa cell) were identified as promising lead compounds. [ABSTRACT FROM AUTHOR]

Abstract: Aims: Tryptophan 2,3‐dioxygenase (TDO2) is an initial rate‐limiting enzyme of the kynurenine (Kyn) pathway in tryptophan (Trp) metabolism. The Trp‐degrading enzymes, TDO2 and indoleamine 2,3‐dioxygenase, are activated by stress and/or inflammation. Dysregulation of Trp metabolism, which causes shifts in the balance between Kyn and serotonin (5‐HT) pathways, is associated with psychiatric and neurological disorders. In genetic studies, single‐nucleotide polymorphisms in the TDO2 gene were shown to be involved in psychiatric disorders, such as schizophrenia and depression. It has been reported that targeted deletion of the Tdo2 gene in mice resulted in reduced anxiety‐like behavior, enhanced exploratory activity and cognitive performance, and increased levels of Trp and 5‐HT in the hippocampus and midbrain. However, the effect of Tdo2 gene deletion on behavioral phenotypes has not yet been investigated extensively. Materials & Methods: We conducted tests to further examine the behavioral effects of knockout (KO) of Tdo2 in mice. Results: Deletion of Tdo2 resulted in seemingly lower anxiety‐like behavior, higher locomotor activity, and abnormal gait pattern in mice, though none of them reached study‐wide statistical significance. Tdo2 deficiency had no significant effects on other behaviors, such as prepulse inhibition, and depression‐like and social behaviors. Discussion and Conclusion: He lack of clear phenotypes in Tdo2KO mice in this study might be due to the absence of stress and inflammatory conditions, which could induce expression of Tdo2 mRNA. Further studies are necessary to elucidate the roles of Tdo2 in behavioral phenotypes related to psychiatric disorders. [ABSTRACT FROM AUTHOR]

Heme-based tryptophan dioxygenases are established immunosuppressive metalloproteins with significant biomedical interest. Here, we synthesized two mechanistic probes to specifically test if the a-amino group of the substrate directly participates in a critical step of the O atom transfer during catalysis in human tryptophan 2,3-dioxygenase (TDO). Substitution of the nitrogen atom of the substrate to a carbon (probe 1) or oxygen (probe 2) slowed the catalytic step following the first O atom transfer such that transferring the second O atom becomes less likely to occur, although the dioxygenated products were observed with both probes. A monooxygenated product was also produced from probe 2 in a significant quantity. Analysis of this new product by HPLC coupled UV-vis spectroscopy, high-resolution mass spectrometry, ¹H NMR, 13C NMR, HSQC, HMBC, and infrared (IR) spectroscopies concluded that this monooxygenated product is a furoindoline compound derived from an unstable epoxyindole intermediate. These results prove that small molecules can manipulate the stepwise O atom transfer reaction of TDO and provide a showcase for a tunable mechanism by synthetic compounds. The product analysis results corroborate the presence of a substrate-based epoxyindole intermediate during catalysis and provide the first substantial experimental evidence for the involvement of the substrate a-amino group in the epoxide ring-opening step during catalysis. This combined synthetic, biochemical, and biophysical study establishes the catalytic role of the a-amino group of the substrate during the O atom transfer reactions and thus represents a substantial advance to the mechanistic comprehension of the heme-based tryptophan dioxygenases. [ABSTRACT FROM AUTHOR]

Background The tryptophan-depleting enzyme indoleamine-2,3-dioxygenase ( IDO) is critical for the regulation of immunotolerance and plays an important role in immune-associated skin diseases. Objectives To analyse the level of IDO in condyloma acuminata ( CA) and its role in this condition. Methods IDO expression was assessed in the skin and peripheral blood of healthy controls and patients with CA. To assess the role of skin IDO in immunity, the ability of isolated epidermal cells to metabolize tryptophan and the influence on polyclonal T-cell mitogen ( PHA)-stimulated T-cell proliferation were explored. Results IDO median fluorescence intensities in peripheral blood mononuclear cells from patients with CA were similar to those from healthy controls. Immunohistochemistry showed that IDO+ cells were rare in normal skin and the control skin of patients with CA, but were greatly accumulated in wart tissue. Most fluorescence signals of IDO+ cells did not overlap with those of CD1a+ Langerhans cells. Human papillomavirus ( HPV) DNA probe in situ hybridization showed a large number of IDO+ cells in the HPV− site. Keratinocytes in the skin of healthy controls and the circumcised skin of patients with CA could minimally transform tryptophan into kynurenine, but IDO-competent epidermal cells from warts could transform tryptophan. In addition, these IDO-competent epidermal cells could inhibit PHA-stimulated T-cell proliferation. The addition of an IDO inhibitor, 1-methyl- d-tryptophan, restored the inhibited T-cell proliferation. Conclusions Abnormally localized high IDO expression might be involved in the formation of a local immunotolerant microenvironment. [ABSTRACT FROM AUTHOR]