A polyoxometalate/chitosan-Ti3C2Tx MXene nanocomposite constructed by electrostatically mediated strategy for electrochemical detecting L-tryptophan in milk.

L-tryptophan (L-Trp) is crucial for human metabolism, and its imbalance or deficiency can lead to certain diseases, such as insomnia, depression, and heart disease. Since the body cannot synthesize L-Trp and must obtain it from external sources, accurately monitoring L-Trp levels in food is essential. Herein, a nanocomposite film based on polyoxometalate (P2Mo17V), Ti3C2Tx MXene, and chitosan (Cs) was developed through a green electrostatically mediated layer-by-layer self-assembly strategy for electrochemical detection of L-Trp. The composite film exhibits fast electron transfer and remarkable electrocatalytic performance for L-Trp with a wide linear range (0.1-103 µM), low limit of detection (0.08 µM, S/N = 3), good selectivity, reproducibility, and repeatability. In milk sample, the recoveries of L-Trp were from 95.78% and 104.31%. The P2Mo17V/Cs-Ti3C2Tx electrochemical sensor not only provides exceptional recognition and detection capabilities for L-Trp but also shows significant potential for practical applications, particularly in food safety and quality control.

The molecular determinants of calcium ATPase inhibition by curcuminoids.

The natural product curcumin and some of its analogs are known inhibitors of the transmembrane enzyme sarco/endoplasmic reticulum calcium ATPase (SERCA). Despite their widespread use, the curcuminoids' binding site in SERCA and their relevant interactions with the enzyme remain elusive. This lack of knowledge has prevented the development of curcuminoids into valuable experimental tools or into agents of therapeutic value. We used the crystal structures of SERCA in its E1 conformation in conjunction with computational tools such as docking and surface screens to determine the most likely curcumin binding site, along with key enzyme/inhibitor interactions. Additionally, we determined the inhibitory potencies and binding affinities for a small set of curcumin analogs. The predicted curcumin binding site is a narrow cleft in the transmembrane section of SERCA, close to the transmembrane/cytosol interface. In addition to pronounced complementarity in shape and hydrophobicity profiles between curcumin and the binding pocket, several hydrogen bonds were observed that were spread over the entire curcumin scaffold, involving residues on several transmembrane helices. Docking-predicted interactions were compatible with experimental observations for inhibitory potencies and binding affinities. Based on these findings, we propose an inhibition mechanism that assumes that the presence of a curcuminoid in the binding site arrests the catalytic cycle of SERCA by preventing it from converting from the E1 to the E2 conformation. This blockage of conformational change is accomplished by a combination of steric hinderance and hydrogen-bond-based cross-linking of transmembrane helices that require flexibility throughout the catalytic cycle.

Electrochemical chiral sensor for recognition of amino acid enantiomers with cyclodextrin-based microporous organic networks.

BACKGROUND: Chirality is a ubiquitous phenomenon in nature, but enantiomers exhibit different pharmacological activities and toxicological effects. Therefore, Chiral recognition plays a pivotal role in various fields such as life sciences, chemical synthesis, drug development, and materials science. The synthesis of novel chiral composites with well-defined loading capabilities and ordered structures holds significant potential for electrochemical chiral recognition applications. However, the design of selective and stable electrochemical chiral recognition materials remains a challenging task. RESULT: In this work, we construct a simple and rapid electrochemical sensing platform for tryptophan (Trp) enantiomer recognition using cyclodextrin-modified microporous organic network as chiral recognition agent. CD-MON with chiral microenvironment was prepared by Sonogashira-Hagihara coupling reaction of the chiral molecule heptyl-6-iodo-6-deoxyß-cyclodextrin and 1, 4-Diethynylbenzene. The adhesion of BSA makes CD-MON firmly fixed on the electrode surface, and as a chiral protein, it can improve the chiral recognition ability through synergistic effect. Chiral amino acids are in full contact with the chiral microenvironment during pore conduction of MON, and L-Trp is more stably bound to CD-MON/BSA due to steric hindrance, host-guest recognition and hydrogen bonding. Therefore, the electrochemical sensor can effectively identify tryptophan enantiomers (IL-Trp/ID-Trp = 2.02), and it exhibits a detection limit of 2.6 µM for L-Trp. UV-Vis spectroscopy confirmed the adsorption capacity of CD-MON towards tryptophan enantiomers in agreement with electrochemistry results. SIGNIFICANCE: The prepared chiral sensor has excellent stability, reproducibility (RSD = 3.7%) and selectivity, realizes the quantitative detection of single isomer in tryptophan racemic and quantitative analysis in real samples with 94.0%-101.0% recovery. This work represents the first application of MON in chiral electrochemistry which expands the application scope of chiral sensors and holds great significance in separation science and electrochemical sensing.

Remote magnetically stimulated xanthan-biochar-Fe3O4-molecularly imprinted biopolymer hydrogel toward electrochemical enantioselection of l-tryptophan.

Monitoring the levels of L-Tryptophan (L-Trp) in body fluids is crucial due to its significant role in metabolism and protein synthesis, which ultimately affects neurological health. Herein, we have developed a novel magneto-responsive electrochemical enantioselective sensor for the recognition of L-Trp based on oriented biochar derived from Loofah, Fe3O4 nanoparticles, and molecularly imprinted polydopamine (MIPDA) in xanthan hydrogel. The successful synthesis of these materials has been confirmed through physicochemical and electrochemical characterization. Various operational factors such as pH, response time, loading sample volume, and loading of active materials were optimized. As a result, the sensor exhibited an affordable linear range of 1.0-60.0 µM, with a desirable limit of detection of 0.44 µM. Furthermore, the proposed electrochemical sensor demonstrated good reproducibility and desirable selectivity for the determination of L-Trp, making it suitable for analyzing L-Trp levels in human plasma and serum samples. The development presented offers an appealing, easily accessible, and efficient strategy. It utilizes xanthan hydrogel to improve mass transfer and adhesion, biochar-stabilized Fe3O4 to facilitate magnetic orientation and accelerate mass transfer and sensitivity, and polydopamine MIP to enhance selectivity. This approach enables on-site evaluation of L-Trp levels, which holds significant value for healthcare monitoring and early detection of related conditions.

Jianpi Jiedu decoction suppresses colorectal cancer growth by inhibiting M2 polarization of TAMs through the tryptophan metabolism-AhR pathway.

BACKGROUND: Traditional Chinese medicine, JianpiJiedu decoction (JPJDF), has been utilized in colorectal cancer (CRC) treatment for over forty years. The potential of JPJDF to inhibit CRC through modulation of intestinal microbiota and their metabolites remains uncertain. AIMS: This study aims to further investigate the therapeutic mechanisms of JPJDF in CRC. METHODS: CAC mouse models were developed using azoxymethane (AOM) and dextran sulfate sodium (DSS). Intestinal tissues and contents underwent 16S rRNA gene sequencing and untargeted metabolomics analysis. Serum levels of IL-1ß and TNF-α were measured using ELISA. Immunohistochemistry was utilized to assess the expression of Ki67, ZO-1, Occludin, CD68, and CD206. Furthermore, western blotting was performed to evaluate the protein expression of AhR and NF-κB. RESULTS: JPJDF inhibited colorectal tumourigenesis in AOM/DSS treated mice, while also suppressing tumor cell proliferation and upregulating the expression of tight junction proteins. The results of 16S rRNA gene sequencing analysis revealed that JPJDF altered intestinal microbiota composition by increasing the abundance of beneficial bacteria. Additionally, JPJDF reduced tryptophan metabolites, effectively alleviating inflammation and significantly restoring intestinal barrier function in CAC mice. Molecular biology experiments confirmed that JPJDF suppressed the expression levels of AhR and M2-type tumor-associated macrophages, thereby promoting anti-tumor immunity and exerting inhibitory effects on CAC growth. CONCLUSION: JPJDF can regulate the tryptophan metabolism-AhR pathway by modulating the gut microbiota, reducing intestinal inflammation, improving intestinal barrier function, enhancing anti-tumor immunity, and effectively inhibiting CAC growth.

A rapid method to monitor structural perturbations of High-Concentrated therapeutic antibody solutions using Intrinsic tryptophan fluorescence emission spectroscopy.

Drug product development of therapeutic antibody formulations is still dictated by the risk of protein particle formation during processing or storage, which can lead to loss of potency and potential immunogenic reactions. Since structural perturbations are the main driver for irreversible protein aggregation, the conformational integrity of antibodies should be closely monitored. The present study evaluated the applicability of a plate reader-based high throughput method for intrinsic tryptophan fluorescence emission (ITFE) spectroscopy to detect protein aggregation due to protein unfolding in high-concentrated therapeutic antibody samples. The impact of fluorophore concentration on the ITFE signal in microplate readers was investigated by analysis of dilution series of two therapeutic antibodies and pure tryptophan. At low antibody concentrations (<5 mg/mL, equivalent to 0.8 mM tryptophan), the low inner filter effect suggests a quasi-linear relationship between antibody concentration and ITFE intensity. In contrast, the constant ITFE intensity at high protein concentrations (>40 mg/mL, equivalent to 6.1 mM tryptophan) indicate that ITFE spectroscopy measurements of IgG1 antibodies are feasible in therapeutically relevant concentrations (up to 223 mg/mL). Furthermore, the capability of the method to detect low levels of unfolding (around 1 %) was confirmed by limit of detection (LOD) determination with temperature-stressed antibody samples as degradation standards. Change of fluorescence intensity at the maximum (ΔIaM) was identified as sensitive descriptor for protein degradation, providing the lowest LOD values. The results demonstrate that ITFE spectroscopy performed in a microplate reader is a valuable tool for high-throughput monitoring of protein degradation in therapeutic antibody formulations.

Dysregulated tryptophan metabolism and AhR pathway contributed to CXCL10 upregulation in stable non-segmental vitiligo.

BACKGROUND: Tryptophan metabolism dysregulation has been observed in vitiligo. However, drawing a mechanistic linkage between this metabolic disturbance and vitiligo pathogenesis remains challenging. OBJECTIVE: Aim to reveal the characterization of tryptophan metabolism in vitiligo and investigate the role of tryptophan metabolites in vitiligo pathophysiology. METHODS: LC-MS/MS, dual-luciferase reporter assay, ELISA, qRT-PCR, small interfering RNA, western blotting, and immunohistochemistry were employed. RESULTS: Kynurenine pathway activation and KYAT enzyme-associated deviation to kynurenic acid (KYNA) in the plasma of stable non-segmental vitiligo were determined. Using a public microarray dataset, we next validated the activation of kynurenine pathway was related with inflammatory-related genes expression in skin of vitiligo patients. Furthermore, we found that KYNA induced CXCL10 upregulation in keratinocytes via AhR activation. Moreover, the total activity of AhR agonist was increased while the AhR concentration per se was decreased in the plasma of vitiligo patients. Finally, higher KYAT, CXCL10, CYP1A1 and lower AhR expression in vitiligo lesional skin were observed by immunohistochemistry staining. CONCLUSION: This study depicts the metabolic and genetic characterizations of tryptophan metabolism in vitiligo and proposes that KYNA, a tryptophan-derived AhR ligand, can enhance CXCL10 expression in keratinocytes.

Biosynthesis of Halogenated Tryptophans for Protein Engineering using Genetic Code Expansion.

Genetic Code Expansion technology offers significant potential in incorporating noncanonical amino acids into proteins at precise locations, allowing for the modulation of protein structures and functions. However, this technology is often limited by the need for costly and challenging-to-synthesize external noncanonical amino acid sources. In this study, we address this limitation by developing autonomous cells capable of biosynthesizing halogenated tryptophan derivatives and introducing them into proteins using Genetic Code Expansion technology. By utilizing inexpensive halide salts and different halogenases, we successfully achieve the selective biosynthesis of 6-chloro-tryptophan, 7-chloro-tryptophan, 6-bromo-tryptophan, and 7-bromo-tryptophan. These derivatives are introduced at specific positions with corresponding bioorthogonal aminoacyl-tRNA synthetase/tRNA pairs in response to the amber codon. Following optimization, we demonstrate the robust expression of proteins containing halogenated tryptophan residues in cells with the ability to biosynthesize these tryptophan derivatives. This study establishes a versatile platform for engineering proteins with various halogenated tryptophans.

Metabolomic and transcriptomic analyses of peach leaves and fruits in response to pruning.

BACKGROUND: Pruning is an important cultivation management option that has important effects on peach yield and quality. However, the effects of pruning on the overall genetic and metabolic changes in peach leaves and fruits are poorly understood. RESULTS: The transcriptomic and metabolomic profiles of leaves and fruits from trees subjected to pruning and unpruning treatments were measured. A total of 20,633 genes and 622 metabolites were detected. Compared with those in the control, 1,127 differentially expressed genes (DEGs) and 77 differentially expressed metabolites (DEMs) were identified in leaves from pruned and unpruned trees (pdLvsupdL), whereas 423 DEGs and 29 DEMs were identified in fruits from the pairwise comparison pdFvsupdF. The content of three auxin analogues was upregulated in the leaves of pruned trees, the content of all flavonoids detected in the leaves decreased, and the expression of almost all genes involved in the flavonoid biosynthesis pathway decreased. The phenolic acid and amino acid metabolites detected in fruits from pruned trees were downregulated, and all terpenoids were upregulated. The correlation analysis revealed that DEGs and DEMs in leaves were enriched in tryptophan metabolism, auxin signal transduction, and flavonoid biosynthesis. DEGs and DEMs in fruits were enriched in flavonoid and phenylpropanoid biosynthesis, as well as L-glutamic acid biosynthesis. CONCLUSIONS: Pruning has different effects on the leaves and fruits of peach trees, affecting mainly the secondary metabolism and hormone signalling pathways in leaves and amino acid biosynthesis in fruits.

Metabolomic Disparities in Intraocular Fluid Across Varied Stages of Cataract Progression: Implications for the Analysis of Cataract Development.

Introduction: The lens's metabolic demands are met through a continuous circulation of aqueous humor, encompassing a spectrum of components such as organic and inorganic ions, carbohydrates, glutathione, urea, amino acids, proteins, oxygen, carbon dioxide, and water. Metabolomics is a pivotal tool, offering an initial insight into the complexities of integrated metabolism. In this investigative study, we systematically scrutinize the composition of intraocular fluid in individuals afflicted with cataracts. Methods: The investigation involved a comprehensive analysis of aqueous humor samples from a cohort comprising 192 patients. These individuals were stratified by utilizing the SPONCS classification system, delineating distinct groups characterized by the hardness of cataracts. The analytical approach employed targeted quantitative metabolite analysis using HILIC-based liquid chromatography coupled with high-resolution mass spectrometric detection. The metabolomics data analysis was performed with MetaboAnalyst 5.0. Results: The results of the enrichment analysis have facilitated the inference that the discerned disparities among groups arise from disruptions in taurine and hypotaurine metabolism, variations in tryptophan metabolism, and modifications in mitochondrial beta-oxidation of short-chain saturated fatty acids and pyrimidine metabolism. Conclusion: A decline in taurine concentration precipitates diminished glutathione activity, prompting an elevated requirement for NAD+ and instigating tryptophan metabolism along the kynurenine pathway. Activation of this pathway is additionally prompted by interferon-gamma and UV radiation, leading to the induction of IDO. Concurrently, heightened mitochondrial beta-oxidation signifies a distinctive scenario in translocating fatty acids into the mitochondria, enhancing energy production.

Baitouweng decoction alleviates ulcerative colitis by regulating tryptophan metabolism through DOPA decarboxylase promotion.

Background: Baitouweng decoction (BTW) is a classic botanical drugs formula that has been widely used clinically for the treatment of gut-related disorders in China. However, its role in ameliorating ulcerative colitis (UC) remains to be explored. Purpose: The study aimed to determine the therapeutic efficacy and potential mechanism of action of BTW on dextran sodium sulfate (DSS)-induced colitis mice. Methods: In vivo: 3.5% DSS-induced experimental colitis mice were treated with BTW (Pulsatilla chinensis (Bunge) Regel, Phellodendron chinense C. K. Schneid, Coptis chinensis Franch and Fraxinus chinensis Roxb), kynurenine or DOPA decarboxylase (DDC) inhibitor (carbidopa). In vitro: Caco-2 cells were stimulated with TNF-α to activate inflammation and later treated with various concentrations of BTW and carbidopa. Model evaluation included body weight, disease activity index (DAI) score, colon length and histopathology. Cytokine levels were measured by flow cytometry. Protein levels were analyzed by proteomics and functionally annotated. The levels of tryptophan metabolites in mouse serum and colon were detected by liquid chromatography-tandem mass spectrometry (LC-MS/MS). Alcian Blue/Phosphate Acid Schiff (AB/PAS) staining, immunohistochemistry and western blot were used to assess the intestinal barrier function and detect the protein expression levels. Results: BTW significantly reduced the DAI, ameliorated colonic injury and regulated inflammatory cytokines in DSS-induced colitis mice. The botanical drugs formula also promoted intestinal epithelial barrier repair by enhancing the expression of the tight junction (TJ) proteins. Tryptophan metabolic signaling pathway was significantly enriched in DSS-induced UC mice, and BTW decreased the level of kynurenine, increased indole metabolites. The therapeutic effect of BTW was evidently reduced when kynurenine was given to mice. Also, BTW promoted DDC protein expression and activated the aryl hydrocarbon receptor (AHR)/IL-22 signaling pathway. Conclusion: BTW improves ulcerative colitis by promoting DDC expression, regulating the conversion of tryptophan metabolism from the kynurenine pathway to the indole metabolism pathway, thereby modulating tryptophan metabolism to increase indole metabolites, and activating AHR receptors to restore intestinal barrier function.

Direct measurements of neurosteroid binding to specific sites on GABAA receptors.

BACKGROUND AND PURPOSE: Neurosteroids are allosteric modulators of GABAA currents, acting through several functional binding sites although their affinity and specificity for each site are unknown. The goal of this study was to measure steady-state binding affinities of various neurosteroids for specific sites on the GABAA receptor. EXPERIMENTAL APPROACH: Two methods were developed to measure neurosteroid binding affinity: (1) quenching of specific tryptophan residues in neurosteroid binding sites by the neurosteroid 17-methylketone group, and (2) FRET between MQ290 (an intrinsically fluorescent neurosteroid) and tryptophan residues in the binding sites. The assays were developed using ELIC-α1GABAAR, a chimeric receptor containing transmembrane domains of the α1-GABAA receptor. Tryptophan mutagenesis was used to identify specific interactions. KEY RESULTS: Allopregnanolone (3α-OH neurosteroid) was shown to bind at intersubunit and intrasubunit sites with equal affinity, whereas epi-allopregnanolone (3ß-OH neurosteroid) binds at the intrasubunit site. MQ290 formed a strong FRET pair with W246, acting as a site-specific probe for the intersubunit site. The affinity and site-specificity of several neurosteroid agonists and inverse agonists was measured using the MQ290 binding assay. The FRET assay distinguishes between competitive and allosteric inhibition of MQ290 binding and demonstrated an allosteric interaction between the two neurosteroid binding sites. CONCLUSIONS AND IMPLICATIONS: The affinity and specificity of neurosteroid binding to two sites in the ELIC-α1GABAAR were directly measured and an allosteric interaction between the sites was revealed. Adaptation of the MQ290 FRET assay to a plate-reader format will enable screening for high affinity agonists and antagonists for neurosteroid binding sites.

Key Enzymes of the Serotonergic System - Tryptophan Hydroxylase 2 and Monoamine Oxidase A - In the Brain of Rats Selectively Bred for a Reaction toward Humans: Effects of Benzopentathiepin TC-2153.

At the Institute of Cytology and Genetics (Novosibirsk, Russia) for over 85 generations, gray rats have been selected for high aggression toward humans (aggressive rats) or its complete absence (tame rats). Aggressive rats are an interesting model for studying fear-induced aggression. Benzopentathiepin TC-2153 exerts an antiaggressive effect on aggressive rats and affects the serotonergic system: an important regulator of aggression. The aim of this study was to investigate effects of TC-2153 on key serotonergic-system enzymes - tryptophan hydroxylase 2 (TPH2) and monoamine oxidase A (MAOA) - in the brain of aggressive and tame rats. Either TC-2153 (10 or 20 mg/kg) or vehicle was administered once intraperitoneally to aggressive and tame male rats. TPH2 and MAOA enzymatic activities and mRNA and protein levels were assessed. The selection for high aggression resulted in upregulation of Tph2 mRNA in the midbrain, of the TPH2 protein in the hippocampus, and of proteins TPH2 and MAOA in the hypothalamus, as compared to tame rats. MAO enzymatic activity was higher in the midbrain and hippocampus of aggressive rats while TPH2 activity did not differ between the strains. The single TC-2153 administration decreased TPH2 and MAO activity in the hypothalamus and midbrain, respectively. The drug affected MAOA protein levels in the hypothalamus: upregulated them in aggressive rats and downregulated them in tame ones. Thus, this study shows profound differences in the expression and activity of key serotonergic system enzymes in the brain of rats selectively bred for either highly aggressive behavior toward humans or its absence, and the effects of benzopentathiepin TC-2153 on these enzymes may point to mechanisms of its antiaggressive action.

Intracellular Polysaccharides of Eurotium cristatum Exhibited Anticolitis Effects in Association with Gut Tryptophan Metabolism.

This study is to investigate the protective effects of Eurotium cristatum intracellular polysaccharides (ECIP) on dextran sodium sulfate (DSS)-induced ulcerative colitis (UC). The oral administration of ECIP could downregulate the disease activity index (DAI) and ameliorate the colonic shortening, immune stress, and damage caused by DSS. In addition, ECIP treatment increased the colonic contents of SCFAs including acetic, propionic, and butyric acids in UC mice. Targeted and untargeted metabolic analysis suggested that ECIP dramatically altered the tryptophan metabolism in the feces of UC mice and promoted the conversion of tryptophan into indole metabolites including indolepyruvate and indole-3-acetic acid (IAA) and indolealdehyde (IAId). Moreover, ECIP observably increased the content of colonic IL-22 and stimulated the relative concentration and relative expression of tight junction molecules in mRNA and proteins levels. Conclusively, consumption of ECIP can improve colon damage and its related effects of UC by promoting the production of IAA and IAId to reinforce intestinal barriers.

Indole Lactic Acid in Plasma and Urine: A Potential Biomarker for Chronic Kidney Disease and Inflammatory.

Purpose: We aimed to explore changes in plasma and urine indole lactic acid (ILA) levels and the relationship between inflammation and ILA in chronic kidney disease (CKD) patients and healthy people. Patients and Methods: Forty-seven CKD patients and 30 healthy individuals were included in this study. One-way ANOVA was used for variables with normal distribution and homogeneous variance. A rank-sum test was performed for non-normally distributed variables. Correlation analyses were performed using Pearson's or Spearman correlation analyses. Independent relationship between patients and CKD was analyzed using ordinal and binary logistic regressions. Receiver operating characteristic (ROC) curve was used. Results: Plasma and urine ILA levels were positively correlated (r = 0.51, P < 0.01). Plasma ILA was positively correlated with BMI, age, creatinine, BUN, triglycerides, and uric acid and negatively correlated with hemoglobin levels. Urine ILA levels were positively correlated with age, creatinine, BUN, and uric acid and negatively correlated with hemoglobin and albumin levels. Ordered logistic regression analysis showed that CKD was significantly correlated with plasma ILA (OR=4.49, P < 0.01), urinary ILA (OR=2.14,P < 0.01), urea levels (OR=1.43, P < 0.01) and hemoglobin levels (OR=0.95, P < 0.01) were significantly related. ROC curves indicated that plasma and urinary ILA were reliable predictors of CKD. CKD was correlated with plasma, urine ILA (OR=5.92, P < 0.01; OR=2.79, P < 0.01) and Hs-CRP (OR=2.45, P < 0.01). Conclusion: Plasma and urine ILA can potentially be used as biomarkers of CKD and inflammatory status.

Microbial tryptophan catabolism as an actionable target via diet-microbiome interactions.

In recent years, the role of microbial tryptophan (Trp) catabolism in host-microbiota crosstalk has become a major area of scientific interest. Microbiota-derived Trp catabolites positively contribute to intestinal and systemic homeostasis by acting as ligands of aryl hydrocarbon receptor and pregnane X receptor, and as signaling molecules in microbial communities. Accumulating evidence suggests that microbial Trp catabolism could be therapeutic targets in treating human diseases. A number of bacteria and metabolic pathways have been identified to be responsible for the conversion of Trp in the intestine. Interestingly, many Trp-degrading bacteria can benefit from the supplementation of specific dietary fibers and polyphenols, which in turn increase the microbial production of beneficial Trp catabolites. Thus, this review aims to highlight the emerging role of diets and food components, i.e., food matrix, fiber, and polyphenol, in modulating the microbial catabolism of Trp and discuss the opportunities for potential therapeutic interventions via specifically designed diets targeting the Trp-microbiome axis.

The role of nonesterified fatty acids in cancer biology: Focus on tryptophan and related metabolism.

Plasma nonesterified fatty acids (NEFA) are elevated in cancer, because of decreased albumin levels and of fatty acid oxidation, and increased fatty acid synthesis and lipolysis. Albumin depletion and NEFA elevation maximally release albumin-bound tryptophan (Trp) and increase its flux down the kynurenine pathway, leading to increased production of proinflammatory kynurenine metabolites, which tumors use to undermine T-cell function and achieve immune escape. Activation of the aryl hydrocarbon receptor by kynurenic acid promotes extrahepatic Trp degradation by indoleamine 2,3-dioxygenase and leads to upregulation of poly (ADP-ribose) polymerase, activation of which and also of SIRT1 (silent mating type information regulation 2 homolog 1) could lead to depletion of NAD+ and ATP, resulting in cell death. NEFA also modulate heme synthesis and degradation, changes in which impact homocysteine metabolism and production of reduced glutathione and hydrogen sulphide. The significance of the interactions between heme and homocysteine metabolism in cancer biology has received little attention. Targeting Trp disposition in cancer to prevent the NEFA effects is suggested.

Quinic acid alleviates high-fat diet-induced neuroinflammation by inhibiting DR3/IKK/NF-κB signaling via gut microbial tryptophan metabolites.

With the increasing of aging population and the consumption of high-fat diets (HFD), the incidence of Alzheimer's disease (AD) has skyrocketed. Natural antioxidants show promising potential in the prevention of AD, as oxidative stress and neuroinflammation are two hallmarks of AD pathogenesis. Here, we showed that quinic acid (QA), a polyphenol derived from millet, significantly decreased HFD-induced brain oxidative stress and neuroinflammation and the levels of Aß and p-Tau. Examination of gut microbiota suggested the improvement of the composition of gut microbiota in HFD mice after QA treatment. Metabolomic analysis showed significant increase of gut microbial tryptophan metabolites indole-3-acetic acid (IAA) and kynurenic acid (KYNA) by QA. In addition, IAA and KYNA showed negative correlation with pro-inflammatory factors and AD indicators. Further experiments on HFD mice proved that IAA and KYNA could reproduce the effects of QA that suppress brain oxidative stress and inflammation and decrease the levels of of Aß and p-Tau. Transcriptomics analysis of brain after IAA administration revealed the inhibition of DR3/IKK/NF-κB signaling pathway by IAA. In conclusion, this study demonstrated that QA could counteract HFD-induced brain oxidative stress and neuroinflammation by regulating inflammatory DR3/IKK/NF-κB signaling pathway via gut microbial tryptophan metabolites.

An optimised and validated surrogate analyte A-TEEM-PARAFAC-PLS technique for detecting and quantifying the biological oxygen demand in surface water.

A 5-day test duration makes BOD5 measurement unsatisfactory and hinders the development of a quick technique. Protein-like fluorescence peaks show a strong correlation between the BOD characteristics and the fluorescence intensities. For identifying and measuring BOD in surface water, a simultaneous absorbance-transmittance and fluorescence excitation-emission matrices (A-TEEM) method combined with PARAFAC (parallel factor) and PLS (partial least squares) analyses was developed using a tyrosine and tryptophan (tyr-trpt) mix as a surrogate analyte for BOD. The use of a surrogate analyte was decided upon due to lack of fluorescent BOD standards. Tyr-trpt mix standard solutions were added to surface water samples to prepare calibration and validation samples. PARAFAC analysis of excitation-emission matrices detected the tyr-trpt mix in surface water. PLS modelling demonstrated significant linearity (R2 = 0.991) between the predicted and measured tyr-trypt mix concentrations, and accuracy and robustness were all acceptable per the ICH Q2 (R2) and ASTM multivariate calibration/validation procedures guidelines. Based on a suitable and workable surrogate analyte method, these results imply that BOD can be detected and quantified using the A-TEEM-PARAFAC-PLS method. Very positive comparability between tyr-trypt mix concentrations was found, suggesting that tyr-trypt mix might eventually take the place of a BOD-based sampling protocol. Overall, this approach offers a novel tool that can be quickly applied in water treatment plant settings and is a step in supporting the trend toward rapid BOD determination in waters. Further studies should demonstrate the wide application of the method using real wastewater samples from various water treatment facilities.

A structural role for tryptophan in proteins, and the ubiquitous Trp Cδ1-H...O=C (backbone) hydrogen bond.

Tryptophan is the most prominent amino acid found in proteins, with multiple functional roles. Its side chain is made up of the hydrophobic indole moiety, with two groups that act as donors in hydrogen bonds: the Nϵ-H group, which is a potent donor in canonical hydrogen bonds, and a polarized Cδ1-H group, which is capable of forming weaker, noncanonical hydrogen bonds. Due to adjacent electron-withdrawing moieties, C-H...O hydrogen bonds are ubiquitous in macromolecules, albeit contingent on the polarization of the donor C-H group. Consequently, Cα-H groups (adjacent to the carbonyl and amino groups of flanking peptide bonds), as well as the Cϵ1-H and Cδ2-H groups of histidines (adjacent to imidazole N atoms), are known to serve as donors in hydrogen bonds, for example stabilizing parallel and antiparallel ß-sheets. However, the nature and the functional role of interactions involving the Cδ1-H group of the indole ring of tryptophan are not well characterized. Here, data mining of high-resolution (r ≤ 1.5 Å) crystal structures from the Protein Data Bank was performed and ubiquitous close contacts between the Cδ1-H groups of tryptophan and a range of electronegative acceptors were identified, specifically main-chain carbonyl O atoms immediately upstream and downstream in the polypeptide chain. The stereochemical analysis shows that most of the interactions bear all of the hallmarks of proper hydrogen bonds. At the same time, their cohesive nature is confirmed by quantum-chemical calculations, which reveal interaction energies of 1.5-3.0 kcal mol-1, depending on the specific stereochemistry.