L-Tryptophan

CONTEXT: L-tryptophan (Trp) has been documented to aid sleep, but a systematic compilation of its effect on sleep quality is still limited. OBJECTIVE: We assessed the effect of Trp supplementation on sleep quality via meta-analysis and meta-regression. The effects of daily Trp dose (<1 g and ≥1 g) were also assessed. DATA SOURCES: A database search was done in PubMed, Medline (Ovid), Cumulative Index to Nursing and Allied Health Literature (CINAHL), and Cochrane and a total of 18 articles were collected. DATA EXTRACTION: Extracted data from 4 articles were also analyzed using random-effect meta-analysis and meta-regression. Standardized mean difference (SMD) was used in meta-analysis. DATA ANALYSIS: Results from the study suggested that Trp supplementation can shorten wake after sleep onset (-81.03 min/g, P = 0.017; SMD, -1.08 min [95%CI, -1.89 to -0.28]). In addition, the group receiving ≥1 g Trp supplementation had a shorter wake after sleep onset than the group with Trp < 1g supplementation (Trp <1 g vs Trp ≥1 g: 56.55 vs 28.91 min; P = 0.001). However, Trp supplementation did not affect other sleep components. CONCLUSION: Trp supplementation, especially at ≥1 g can help improve sleep quality. © The Author(s) 2021. Published by Oxford University Press on behalf of the International Life Sciences Institute.All rights reserved. For permissions, please e-mail: [email protected].

Respiratory and gastrointestinal infections are leading causes of morbidity in children. Increasing evidence highlights the gut-lung axis as a key regulatory interface influencing infection susceptibility. Bifidobacterium longum subsp. infantis B8762 (B8762) has shown clinical efficacy in reducing such infections, but its mechanistic basis remains unclear. In a randomized, double-blind, placebo-controlled study involving 115 infants (probiotic group: n = 57, placebo group: n = 58; aged 6-12 months), fecal metagenomic sequencing was performed to assess microbial and functional changes after four weeks of B8762 supplementation (0.5 × 1010 CFU/day). B8762 significantly altered the gut microbial structure (β-diversity, P < 0.05) without affecting α-diversity. The intervention enriched beneficial taxa including Bifidobacterium longum, Eubacterium limosum, and Roseburia hominis, while reducing potential pathogens such as Staphylococcus aureus and Candida parapsilosis (P < 0.05). Functionally, B8762 upregulated metabolic pathways involved in coenzyme A and L-tryptophan biosynthesis and enhanced predicted production of immunoregulatory metabolites including butyrate, inosine, and chenodeoxycholic acid. In summary, this study suggests that B8762 modulates the pediatric gut microbiota toward a composition and metabolic profile that supports mucosal barrier integrity and systemic immune regulation. These findings provide mechanistic insight into its protective role against respiratory and gastrointestinal infections in children, supporting its use as a targeted gut-lung axis probiotic intervention.

INTRODUCTION: Melatonin plays a key role in sleep regulation. Combining melatonin with its precursors, L-tryptophan (LT) and 5-Hydroxytryptophan (5HTP), may influence sleep-related outcomes, but evidence in children with neurodevelopmental disorders (NDDs) is limited. This exploratory study compares the effects of melatonin combined with 5HTP (M-5HTP) and melatonin combined with LT (M-LT) on sleep disorders in children with NDDs. METHODS: This single-center, randomized pilot comparative trial involved children under five years of age with NDDs free of sleep-inducing drugs. Baseline evaluations and actigraphy monitoring were performed. Children were randomly assigned to either M-5HTP (1 mg Melatonin +10 mg 5HTP) or M-LT (1 mg Melatonin +20 mg LT) treatment at 8 p.m. for at least four weeks. Post-treatment actigraphy monitoring assessed sleep parameters. RESULTS: Of 51 screened children, 26 were enrolled and 13 completed the study (M-5HTP: 9, M-LT: 4). No statistically significant between-group differences in change scores were observed. Within-group analyses showed a significant reduction in the Sleep Movement Index (SMI) from baseline to follow-up in the M-5HTP group (T0: 6.55; T1: 1.25; p=0.006), whereas no significant changes were observed in the M-LT group. DISCUSSION: In this exploratory pilot study, a within-group reduction in nocturnal motor activity was observed among M-5HTP completers. Given the small sample size, high attrition rate, and limited statistical power, these findings should be interpreted cautiously and considered hypothesis-generating.

AIMS/HYPOTHESIS: In healthy men, lauric acid (C12) and L-tryptophan (Trp), when administered intraduodenally in loads of 1.26 and 0.42 kJ/min (0.3 and 0.1 kcal/min), respectively, that are individually ineffective, stimulate glucagon-like peptide-1 (GLP-1) and cholecystokinin (CCK), when combined. Both hormones slow gastric emptying, suppress energy intake and lower postprandial glucose. We have now investigated the hypothesis that combined intraduodenal administration of these nutrients reduces postprandial glucose in type 2 diabetes. METHODS: In a randomised, blinded (investigators and participants), crossover study performed in the University of Adelaide Clinical Research Facility, 11 men with type 2 diabetes (age: 69 ± 7 years; HbA1c: 51 ± 5 mmol/mol [6.8 ± 0.3%]; BMI: 28 ± 1 kg/m2), each received, on four separate occasions, 45 min intraduodenal infusions of C12 (1.26 kJ/min), Trp (0.42 kJ/min), C12+Trp (1.68 kJ/min), or 0.9% saline (control), 30 min before a mixed-nutrient drink (350 ml, 2092 kJ (500 kcal), 74 g carbohydrate) containing 100 mg 13C-acetate. Plasma glucose, GLP-1, glucose-dependent insulinotropic polypeptide (GIP), insulin, C-peptide and CCK concentrations were measured at baseline, following treatments alone, and for 180 min post-drink. Gastric emptying was assessed via 13C-acetate breath test. RESULTS: C12+Trp, but not C12 or Trp, reduced overall (p=0.02) and peak (mmol/l; control: 11.1 ± 0.6, Trp: 10.3 ± 0.5, C12: 10.7 ± 0.6, C12+Trp: 9.8 ± 0.5; p=0.01) plasma glucose. C12+Trp slowed gastric emptying (p=0.001), and increased pre-drink plasma GLP-1, GIP and CCK (all p<0.05), without affecting insulin or C-peptide. No treatment effects were observed postprandially. CONCLUSIONS/INTERPRETATION: In type 2 diabetes, intraduodenal C12+Trp lowers postprandial glucose, probably primarily by slowing of gastric emptying and mediated by GLP-1 and CCK. These findings support further exploration of nutrient-based gastrointestinal strategies to optimise glycaemic management in type 2 diabetes. TRIAL REGISTRATION: Australian New Zealand Clinical Trials Registry ( www.anzctr.org.au ) ACTRN12623000778684 FUNDING: JAS and VB were each supported by Adelaide

BACKGROUND: L-tryptophan ("Trp") and L-leucine ("Leu"), when administered intraduodenally, increase plasma cholecystokinin (CCK) and glucagon-like peptide 1 (GLP-1) and stimulate pyloric pressures, which all slow gastric emptying and suppress subsequent energy intake. The circulating Trp-to-large-neutral-amino-acids ("Trp/LNAAs") ratio is also inversely related to energy intake. OBJECTIVES: This exploratory study characterized the impact of standardized changes in the plasma Trp/LNAAs ratio, achieved by combining a fixed-load intraduodenal infusion of Trp with increasing loads of Leu, on the appetite-inhibitory effects of enteral Trp. METHODS: Twelve males of normal weight [mean ± standard deviation; age: 23 ± 2 y; body mass index (in kg/m2: 23±1)], received on 4 separate occasions, 90-min iso-osmotic intraduodenal infusions of 1) isotonic 0.9% saline ("control"), 2) Trp (0.15 kcal/min; "Trp"), 3) Trp + Leu (0.22 kcal/min; "Trp+Leu-0.22"), or 4) Trp + Leu (0.45 kcal/min; "Trp+Leu-0.45"), in a randomized, double-blind, cross-over fashion. Immediately postinfusion ad-libitum energy intake was quantified. Plasma CCK, GLP-1, amino acid concentrations, and antropyloroduodenal pressures were measured throughout. RESULTS: Although there was a transient stimulation of CCK and GLP-1 by Trp + Leu - 0.45 (at t = 15 min), only Trp led to a sustained increase in plasma CCK (P = 0.04) and GLP-1 (P = 0.009) from t = 60-90 min, and stimulated pyloric pressures (P = 0.01), compared with control. Only Trp reduced energy intake [kcal (mean ± standard error of the mean); control: 1085 ± 49, Trp: 881 ± 75, Trp + Leu - 0.22: 963 ± 57, Trp + Leu - 0.45: 932 ± 60] compared with control (P = 0.008). The Trp/LNAAs ratio was dose-dependently decreased by Trp + Leu - 0.22 and Trp + Leu - 0.45, compared with Trp (all P = 0.001), and energy intake correlated inversely with the Trp/LNAAs ratio (R = -0.38; P = 0.02). CONCLUSIONS: Acute reduction in the Trp/LNAAs ratio appears to be associated with a diminished capacity of Trp to stimulate CCK and GLP-1 and suppress energy intake. Although these observations should be interpreted with caution given the exploratory nature of the study, they atte

CONTEXT: In males of normal weight, intraduodenal administration of calcium enhances the effects of the amino acid L-tryptophan (Trp) to suppress energy intake, associated with greater stimulation of cholecystokinin (CCK), glucagon-like peptide-1 (GLP-1), and peptide tyrosine-tyrosine (PYY) secretion (key mechanisms underlying the regulation of pyloric motility and gastric emptying) but not gastrin or glucose-dependent insulinotropic polypeptide (GIP). OBJECTIVE: Given the implications for the management of obesity, the current study evaluated the effects of calcium, when administered alone and in combination with Trp, on gut hormone secretion, antropyloroduodenal motility, and energy intake in males with obesity. METHODS: Fifteen males with obesity and without type 2 diabetes (mean ± SD; age: 27 ± 8 years; body mass index: 30 ± 2 kg/m2; hemoglobin A1c: 5.3 ± 0.2%), received 150-minute intraduodenal infusions of 0, 500, or 1000 mg calcium, each combined with Trp (load: 0.1 kcal/min, known to have submaximal energy-intake suppressant effects) from t = 75-150 minutes, on 3 separate occasions, in a randomized, double-blind, cross-over order. Plasma concentrations of gastrin, CCK, GIP, GLP-1, PYY, and pyloric pressures were measured during the infusions. Immediately postinfusion (t = 150-180 minutes), energy intake at a standardized buffet-style lunch was quantified. RESULTS: Calcium, in a dose of 1000 mg, stimulated GLP-1, PYY, and pyloric pressures alone (all P < .05) and enhanced the effects of Trp to stimulate CCK, GLP-1, and PYY (all P < .05), associated with greater suppression of energy intake (P = .01). Energy intake (R = -0.64; P = .001) was inversely related to the dose of calcium, while plasma concentrations of CCK (R = 0.44; P = .05), GLP-1 (R = 0.60; P = .01), and PYY (R = 0.83; P = .01) were directly related. CONCLUSION: Intraduodenal calcium enhances the effect of intraduodenal Trp to stimulate CCK, GLP-1, and PYY and suppress energy intake in males with obesity. © The Author(s) 2025. Published by Oxford University Press on behalf of the Endocrine Society.

INTRODUCTION: Transcutaneous auricular vagus nerve stimulation (taVNS) is a promising therapy for irritable bowel syndrome (IBS). The aims of this clinical trial were to evaluate the influence of taVNS on autonomic functions, rectal sensation, and acetylcholine (Ach) levels and to explore potential mechanisms involving gut microbiota and metabolic profiles. METHODS: This study was a single-center, single-blind, randomized controlled trial executed at the First Affiliated Hospital of USTC, Anhui, China. Individual patients' constipation-predominant IBS (IBS-C)-related symptoms and mental health were assessed and scored using questionnaires at baseline and at week 4. Levels of serum Ach and nitric oxide, anorectal manometry, and heart rate variability were assessed both before and after the therapy. Fecal samples from each group were assessed to compare the gut microbiota, short-chain fatty acids, and gut microbiota-derived tryptophan metabolites. RESULTS: Between September 2023 and May 2024, 40 patients (n = 20 in both taVNS and sham-taVNS groups) completed the 4-week study by performing an intention-to-treat analysis. No differences in all parameters between taVNS and sham-taVNS groups at the baseline were found. The taVNS significantly improved the visual analog scale score ( P < 0.001), IBS Severity Scoring System score ( P < 0.001), weekly frequency of spontaneous bowel movements ( P < 0.001), weekly frequency of complete spontaneous bowel movements ( P = 0.004), Bristol Stool Form Scale score ( P < 0.001), Hamilton Anxiety Scale score ( P < 0.001), Hamilton Depression Scale score ( P < 0.001), and IBS Quality of Life score ( P < 0.001). Furthermore, taVNS improved rectal sensation in patients with IBS-C, including improvements in the threshold volume for initial sensation ( P = 0.033), urge to defecate ( P = 0.022), and rectoanal inhibitory reflex ( P = 0.002). Moreover, taVNS elevated serum levels of Ach ( P = 0.005) and reduced nitric oxide ( P = 0.016) while also enhancing vagal activity ( P < 0.001) as determined by spectral analysis of heart rate variability. Three patients in the taVNS group and 2 in the control group had adverse consequences, which we

BACKGROUND: In humans, intraduodenal infusion of L-tryptophan (Trp) increases plasma concentrations of gastrointestinal hormones and stimulates pyloric pressures, both key determinants of gastric emptying and associated with potent suppression of energy intake. The stimulation of gastrointestinal hormones by Trp has been shown, in preclinical studies, to be enhanced by extracellular calcium and mediated in part by the calcium-sensing receptor. OBJECTIVES: This study aim was to determine whether intraduodenal calcium can enhance the effects of Trp to stimulate gastrointestinal hormones and pyloric pressures and, if so, whether it is associated with greater suppression of energy intake, in healthy males. METHODS: Fifteen males with normal weight (mean ± standard deviation; age: 26 ± 7 years; body mass index: 22 ± 2 kg/m2), received on 3 separate occasions, 150-min intraduodenal infusions of 0, 500, or 1000 mg calcium (Ca), each combined with Trp (load: 0.1 kcal/min, with submaximal energy intake-suppressant effects) from t = 75-150 min, in a randomized, double-blind, crossover study. Plasma concentrations of GI hormones [gastrin, cholecystokinin, glucose-dependent insulinotropic polypeptide (GIP), glucagon-like peptide (GLP)-1, and peptide tyrosine-tyrosine (PYY)], and Trp and antropyloroduodenal pressures were measured throughout. Immediately postinfusions (t = 150-180 min), energy intake at a standardized buffet-style meal was quantified. RESULTS: In response to calcium alone, both 500- and 1000-mg doses stimulated PYY, while only the 1000-mg dose stimulated GLP-1 and pyloric pressures (all P < 0.05). The 1000-mg dose also enhanced the effects of Trp to stimulate cholecystokinin and GLP-1, and both doses stimulated PYY but, surprisingly, reduced the stimulation of GIP (all P < 0.05). Both doses substantially and dose dependently enhanced the effects of Trp to suppress energy intake (Ca-0+Trp: 1108 ± 70 kcal; Ca-500+Trp: 961 ± 90 kcal; and Ca-1000+Trp: 922 ± 96 kcal; P < 0.05). CONCLUSIONS: Intraduodenal administration of calcium enhances the effect of Trp to stimulate plasma cholecystokinin, GLP-1, and PYY and suppress energy intake in healthy males. These findi

9. Am J Physiol Gastrointest Liver Physiol. 2024 Jun 1;326(6):G687-G696. doi: 10.1152/ajpgi.00306.2023. Epub 2024 Apr 9. Oral tryptophan activates duodenal aryl hydrocarbon receptor in healthy subjects: a crossover randomized controlled trial. Rueda GH(1), Causada-Calo N(1), Borojevic R(1), Nard

182. Nutrients. 2023 Apr 11;15(8):1837. doi: 10.3390/nu15081837. The Usefulness of the Low-FODMAP Diet with Limited Tryptophan Intake in the Treatment of Diarrhea-Predominant Irritable Bowel Syndrome. Chojnacki C(1), Poplawski T(2), Blonska A(1), Konrad P(1), Chojnacki J(1), Blasiak J(3). Author information: (1)Department of Clinical Nutrition and Gastroenterological Diagnostics, Medical University of Lodz, 90-647 Lodz, Poland. (2)Department of Pharmaceutical Microbiology and Biochemistry, Medical University of Lodz, 90-236 Lodz, Poland. (3)Department of Molecular Genetics, Faculty of Biology and Environmental Protection, University of Lodz, 90-236 Lodz, Poland. (1) Background: A low-FODMAP diet is often recommended in the treatment of irritable bowel syndrome, but it does not improve abdominal symptoms in all patients, and an alternative diet is desirable. The purpose of this study was to evaluate the efficacy of a low-FODMAP diet with a concomitant reduction in tryptophan (TRP) intake in irritable bowel syndrome with diarrhea predominance (IBS-D) in relation to its metabolism via the serotonin and kynurenine pathways. (2) Methods: 40 healthy people (Group I, Controls) and 80 patients with IBS-D were included in the study. IBS-D patients were randomly divided into two groups of 40 each (Groups IIA and IIB). In Group IIA, the low-FODMAP diet was recommended, while in Group IIB, the same diet was recommended but with limited TRP intake for 8 weeks. The TRP intake was analyzed with the use of the nutritional calculator. Abdominal complaints were assessed using the Gastrointestinal Symptom Rating Scale (GSRS-IBS), and psychological status was simultaneously determined using two scales: the Hamilton Anxiety Scale (HAM-A) and the Hamilton Depression Scale (HAM-D). TRP and its metabolites: 5-hydoxyindoleacetic acid (5-HIAA), kynurenine (KYN), kynurenic acid (KYNA), and quinolinic acid (QA) were measured in urine using liquid chromatography tandem mass spectrometry (LC-MS/MS). (3) Results: The consumption of TRP per mg/kg/b.w./24 h has decreased in Group IIA from 20.9 ± 2.39 to 17.45 ± 2.41 (16.5%) and in Group IIB from 21.3 ± 2.33 to 14.32 (34.4%). Significantly great

INTRODUCTION: An estimated 15%-29% of patients report new gastrointestinal (GI) symptoms after coronavirus-19 disease (COVID-19) while 4%-31% report new depressive symptoms. These symptoms may be secondary to gut microbiome tryptophan metabolism and 5-hydroxytryptamine (5-HT)-based signaling. METHODS: This study used specimens from 2 patient cohorts: (i) fecal samples from patients with acute COVID-19 who participated in a randomized controlled trial testing prebiotic fiber and (ii) blood samples from patients with acute COVID-19. Six months after recovering from COVID-19, both cohorts answered questions related to GI symptoms and anxiety or depression. Microbiome composition and function, focusing on tryptophan metabolism-associated pathways, and plasma 5-HT were assessed. RESULTS: In the first cohort (n = 13), gut microbiome L-tryptophan biosynthesis during acute COVID-19 was decreased among those who developed more severe GI symptoms (2.0-fold lower log activity comparing those with the most severe GI symptoms vs those with no symptoms, P = 0.06). All tryptophan pathways showed decreased activity among those with more GI symptoms. The same pathways were also decreased in those with the most severe mental health symptoms after COVID-19. In an untargeted analysis, 5 additional metabolic pathways significantly differed based on subsequent development of GI symptoms. In the second cohort (n = 39), plasma 5-HT concentration at the time of COVID-19 was increased 5.1-fold in those with GI symptoms alone compared with those with mental health symptoms alone ( P = 0.02). DISCUSSION: Acute gut microbiome-mediated reduction in 5-HT signaling may contribute to long-term GI and mental health symptoms after COVID-19. Future studies should explore modification of 5-HT signaling to reduce post-COVID symptoms.

Indoleamine 2,3-dioxygenase 1 (IDO1) is an immune checkpoint that degrades L-tryptophan to kynurenine (Kyn) and enhance immunosuppression, which can be an attractive target for treating colon cancer. IDO1 inhibitors have limited efficacy when used as monotherapies, and their combination approach has been shown to provide synergistic benefits. Many studies have shown that targeting chemokines can promote the efficacy of immune checkpoint inhibitors. Therefore, this study explored the use of IDO1 inhibitors with multiple chemokines to develop a new combination regimen for IDO1 inhibitors. We found that IDO1 inhibitors reduce the secretion of C-X-C motif ligand 10(CXCL10) in cancer cells, and CXCL10 supplementation significantly improved the anticancer effect of IDO1 inhibitors. The combination of the IDO1 inhibitor with CXCL10 or its agonist axitinib had a synergistic inhibitory effect on the growth of colon cancer cells and transplanted CT26 tumors. This synergistic effect may be achieved by inhibiting cancer cell proliferation, promoting cancer cell apoptosis, promoting CD8+T cell differentiation and decreasing Tregs. Two downstream pathways of IDO1 affect CXCL10 secretion. One being the Kyn-aryl hydrocarbon receptor (AHR) pathway, the other is the general control nonderepressible 2(GCN2). Our study provides a new reference for combination regimens of IDO1 inhibitors.

Myeloid-derived suppressor cells (MDSCs) play a crucial role in immunosuppression in tumor-bearing hosts. MDSCs express arginase-I and indoleamine 2,3-dioxygenase; they suppress T-cell function by reducing the levels of l-arginine and l-tryptophan, respectively. We examined the anticancer effects of supplementation of these amino acids in CT26 colon carcinoma-bearing mice. Oral supplementation of l-arginine or l-tryptophan (30 mg/mouse) did not affect tumor growth, whereas oral supplementation of d-arginine was lethal. Supplementation of l-arginine showed a tendency to augment the efficacy of cyclophosphamide (CP). CP reduced the proportions of granulocytic MDSCs and increased the proportions of monocytic MDSCs in the spleen and tumor tissues of CT26-bearing mice. l-Arginine supplementation alone did not affect the MDSC subsets. CP treatment tended to reduce the plasma levels of l-arginine in CT26-bearing mice and significantly increased the number of tumor-infiltrating CD8+ T cells. In addition, l-arginine supplementation significantly increased the proportions of tumor peptide-specific CD8+ T cells in draining lymph nodes. Importantly, additional supplementation of l-arginine significantly increased the number of cured mice that were treated with CP and anti-PD-1 antibody. Totally, l-arginine supplementation shows promise for boosting the therapeutic efficacy of chemoimmunotherapy. © 2020 The Authors. Cancer Science published by John Wiley & Sons Australia, Ltd on behalf of Japanese Cancer Association.

OBJECT Indoleamine 2,3-dioxygenase (IDO), a key enzyme of tryptophan (Trp) metabolism, is involved in tumor-derived immune suppression through depletion of Trp and accumulation of the metabolite kynurenine, resulting in inactivation of natural killer cells and generation of regulatory T cells (Tregs). It has been reported that high expression of IDO in cancer cells is associated with suppression of the antitumor immune response and is consistent with a poor prognosis. Thus, IDO may be a therapeutic target for malignant cancer. The authors have recently shown that IDO expression is markedly increased in human glioblastoma and secondary glioblastoma with malignant change, suggesting that IDO targeting may also have therapeutic potential for patients with glioma. The aim of this study was to investigate the antitumor effect of IDO inhibition and to examine the synergistic function of IDO inhibitor and temozolomide (TMZ) in a murine glioma model. METHODS Murine glioma GL261 cells and human glioma U87 cells were included in this study. The authors used 3 mouse models to study glioma cell growth: 1) a subcutaneous ectopic model, 2) a syngeneic intracranial orthotopic model, and 3) an allogenic intracranial orthotopic model. IDO inhibition was achieved via knockdown of IDO in GL261 cells using short hairpin RNA (shRNA) and through oral administration of the IDO inhibitor, 1-methyl-l-tryptophan (1-MT). Tumor volume in the subcutaneous model and survival time in the intracranial model were evaluated. RESULTS In the subcutaneous model, oral administration of 1-MT significantly suppressed tumor growth, and synergistic antitumor effects of 1-MT and TMZ were observed (p < 0.01). Mice containing intracranially inoculated IDO knockdown cells had a significantly longer survival period as compared with control mice (p < 0.01). CONCLUSIONS These results suggest that IDO expression is implicated in immunosuppression and tumor progression in glioma cells. Therefore, combining IDO inhibition with standard TMZ treatment could be an encouraging therapeutic strategy for patients with malignant glioma.

Evolution has fine-tuned proteins to accomplish a variety of tasks. Yet, with aging, some proteins assemble into harmful amyloid aggregates associated with neurodegenerative diseases, such as Alzheimer's disease (AD), which presents a complex and costly challenge to our society. Thus, far, drug after drug has failed to slow the progression of AD, characterized by the self-assembly of the 39-43 amino acid β-amyloid (Aβ) protein into extracellular senile plaques that form a cross-β structure. While there is experimental evidence that the Aβ small oligomers are the primary toxic species, standard tools of biology have failed to provide structures of these transient, inhomogeneous assemblies. Despite extensive experimental studies, researchers have not successfully characterized the nucleus ensemble, the starting point for rapid fibril formation. Similarly scientists do not have atomic data to show how the compounds that reduce both fibril formation and toxicity in cells bind to Aβ42 oligomers. In this context, computer simulations are important tools for gaining insights into the self-assembly of amyloid peptides and the molecular mechanism of inhibitors. This Account reviews what analytical models and simulations at different time and length scales tell us about the dynamics, kinetics, and thermodynamics of amyloid fibril formation and, notably, the nucleation process. Though coarse-grained and mesoscopic protein models approximate atomistic details by averaging out unimportant degrees of freedom, they provide generic features of amyloid formation and insights into mechanistic details of the self-assembly process. The thermodynamics and kinetics vary from linear peptides adopting straight β-strands in fibrils to longer peptides adopting in parallel U shaped conformations in fibrils. In addition, these properties change with the balance between electrostatic and hydrophobic interactions and the intrinsic disorder of the system. However, simulations suggest that the critical nucleus size might be on the order of 20 chains under physiological conditions. The transition state might be characterized by a simultaneous change from mixed antiparallel/parallel β-strands wi

PURPOSE: Our great interest in this work was study the synergism between l-tryptophan and dipyrone or paracetamol as well as the interaction of kynurenic acid (l-tryptophan metabolite) and these analgesics agents utilizing a robust methodology. METHODS: We performed the writhing test induced by acetic acid in mice to evaluate the antinociceptive effect of the treatments isolated and combined (p.o. and i.p.). Dose-response curves were constructed and the values of ED50 for treatment alone and combined were statistically compared. In addition, isobolographic analysis was performed and the experimental values were compared with the theoretical values for simple additive effect. RESULTS: The combined treatment with l-tryptophan and dipyrone or paracetamol reduced significantly the ED50 of these analgesics when compared to the isolated treatments. l-tryptophan alone has no antinociceptive effect. l-Tryptophan increases the central amount of 5-HT and the synergism with dipyrone is antagonized by the 5-HT depletion. The kyna has an antinociceptive dose-related effect and a synergistic interaction with dipyrone and paracetamol verified by isobolographic analyses and confirmed by experimental values of ED50 of combined treatments were statistically lower than theoretical calculated values for simple additive effect. Melatonin antagonist receptor attenuates the antinociceptive synergism between l-tryptophan and dipyrone. CONCLUSION: Our results demonstrate that the increased 5-HT amount on the central nervous system is not per se capable to induce antinociception. The l-tryptophan interacts synergistically with dipyrone and paracetamol both orally and by i.p. route. This effect is dependent on the biotransformation of l-tryptophan to 5-HT and involves kynurenic acid and melatonin receptors.

N-valproyl-L-tryptophan (VPA-Tryp), new antiepileptic drug, was tested on CA1 hippocampal epileptiform bursting activity obtained by increasing potassium and lowering calcium and magnesium concentrations in the fluid perfusing rat brain slices. Each slice was treated with a single concentration (0.2, 0.5, 1 or 2 mM) of Valproate (VPA) or VPA-Tryp. Both burst duration and interburst frequency during and after treatment were off-line compared with baseline values. For both parameters, the latency and the length of statistically significant response periods as well as the magnitude of drug-induced responses were calculated. VPA-Tryp evoked fewer and weaker early excitatory effects than VPA on bursting activity. On the contrary, VPA-Tryp induced powerful and long-lasting inhibitory effects on epileptiform discharge in a significantly higher number of slices than VPA. In fact, greater length and magnitude of VPA-Tryp-induced inhibition on both interburst frequency and burst duration were observed. Furthermore, VPA-Tryp showed antiepileptic activity at lower concentration than VPA and, when testing both drugs at analogue concentrations, VPA-Tryp evoked responses with either shorter latency or greater effect length and magnitude than VPA.

The expression of death receptor 3 (DR3), a member of the tumor necrosis factor (TNF) receptor superfamily, is up-regulated in human tubular epithelial cells (TECs) during renal injury, but its function in this setting remains unknown. We used cisplatin to induce renal injury in wild-type (DR3(+/+)) or congenitally deficient DR3(-/-) mice to examine the in vivo role of DR3. Cisplatin induced the expression of DR3, its ligand, TNF-like ligand 1A (TL1A), and TNF in TECs, as observed in human renal injury. Cisplatin increased apoptotic death of DR3(-/-) TECs by twofold compared with DR3(+/+) TECs, whereas it reduced the number of tubules expressing phospho-NF-κBp65(Ser276) by 50% at 72 hours. Similar degrees of induction of DR3, TL1A, and TNF, and changes in apoptosis and phospho-NF-κBp65(Ser276), were obtained in mouse kidney organ cultures treated with cisplatin for 3 hours, suggesting a direct effect on TECs. TNF was implicated in mediating cisplatin-induced tubular damage given that the in vivo co-administration of GM6001, an inhibitor of TNF maturation and release, significantly reduced TNF production and tubular damage. Moreover, TNF exacerbated, whereas TL1A reduced, cisplatin-induced apoptosis in the DR3(+/+) mouse proximal tubule cell line, TKPTS. Our data demonstrate that cisplatin-induced nephrotoxicity is mitigated by DR3 signaling, suggesting that this occurs by antagonizing pro-apoptotic signals induced by TNF. Therefore, activating DR3 may be beneficial in reducing acute kidney injury.

The aim was to investigate the effect of 5-hydroxy-L-tryptophan (5-HTP) on gaboxadol pharmacokinetics in rats. As both 5-HTP and gaboxadol bind to the human proton-coupled amino acid transporter, hPAT1, a drug-drug interaction at the level of intestinal absorption might occur. The in vitro transport of gaboxadol was measured across the hPAT1-expressing cell line Caco-2, and via the rat organic anion transporter, rOat1, in Xenopus oocytes pre-injected with rOat1 cRNA. The in vivo pharmacokinetic profile of gaboxadol after oral administration to rats was investigated in the absence and presence of a pre-dose of 5-HTP. In Caco-2 cell monolayers >80% of the absorptive gaboxadol transport was suggested to be hPAT1-mediated. In rats, the initial absorption rate of gaboxadol was decreased in the presence of 5-HTP. The AUC of gaboxadol was increased by a factor of 3.6-5.5 when rats were pre-dosed with 5-HTP. Gaboxadol was a substrate for the renal transporter rOat1 with a K(m)-value of 151 microM. 5-HTP did not interact with rOat1. In conclusion, gaboxadol acts as a substrate for hPAT1 and is a substrate of rOat1. In rats, 5-HTP decreased the initial absorption rate and increased AUC of gaboxadol. 5-HTP thus had a significant impact on the pharmacokinetic profile of gaboxadol. Copyright 2009 Elsevier B.V. All rights reserved.

In this paper, a fast method for the study on the interactions of a series of drugs used in the treatment of hypertension with human serum albumin (HSA) by flow injection-capillary electrophoresis (FI-CE) was developed based on the principle of frontal analysis (FA). The binding parameters were determined by FI-CE-FA from Scatchard equation and compared with results obtained by non-CE methods and literature values. A multiple linear regression (MLR) model between the drug-protein binding constants (K) and structural descriptors of drugs was constructed. L-tryptophan (L-try) and phenylbutazone (PB) were used as displacement reagents to investigate the binding sites of a series of drugs on HSA. The binding synergism effect between drugs and the effects of many metal ions existing in human plasma on protein binding were also investigated systematically.

BACKGROUND AND PURPOSE: Gaboxadol has been in development for treatment of chronic pain and insomnia. The clinical use of gaboxadol has revealed that adverse effects seem related to peak serum concentrations. The aim of this study was to investigate the mechanism of intestinal absorption of gaboxadol in vitro and in vivo. EXPERIMENTAL APPROACH: In vitro transport investigations were performed in Caco-2 cell monolayers. In vivo pharmacokinetic investigations were conducted in beagle dogs. Gaboxadol doses of 2.5 mg.kg(-1) were given either as an intravenous injection (1.0 mL.kg(-1)) or as an oral solution (5.0 mL.kg(-1)). KEY RESULTS: Gaboxadol may be a substrate of the human proton-coupled amino acid transporter, hPAT1 and it inhibited the hPAT1-mediated L-[(3)H]proline uptake in Caco-2 cell monolayers with an inhibition constant K(i) of 6.6 mmol.L(-1). The transepithelial transport of gaboxadol was polarized in the apical to basolateral direction, and was dependent on gaboxadol concentration and pH of the apical buffer solution. In beagle dogs, the absorption of gaboxadol was almost complete (absolute bioavailability, F(a), of 85.3%) and T(max) was 0.46 h. Oral co-administration with 2.5-150 mg.kg(-1) of the PAT1 inhibitor, L-tryptophan, significantly decreased the absorption rate constant, k(a), and C(max), and increased T(max) of gaboxadol, whereas the area under the curve and clearance of gaboxadol were constant. CONCLUSIONS AND IMPLICATIONS: The absorption of gaboxadol across the luminal membrane of the small intestinal enterocytes is probably mediated by PAT1. This knowledge is useful for reducing gaboxadol absorption rates in order to decrease peak plasma concentrations.

We have previously reported that dietary supplementation with up to 5.0 g/d of L-tryptophan (L-Trp) for 21 d has no adverse effects, judging from the levels of general blood variables, in healthy women. We performed a randomized, double-blind, placebo-controlled, crossover intervention study in 17 apparently healthy Japanese women. The subjects were randomly assigned to receive a placebo (0 g/d) or 1.0, 2.0, 3.0, 4.0, or 5.0 g/d of L-Trp for 21 d each with a 5-wk washout period between trials. We examined the 24-h urine profiles on days -1 (1 d before starting L-Trp), 7, 14, and 21 to determine whether administration of L-Trp at doses of up to 5.0 g/d affects time-dependent urinary excretion of L-Trp or its metabolites in healthy women. The urinary excretion of L-Trp, kynurenic acid, 3-hydroxykynurenine, xanthurenic acid, 3-hydroxyanthranilic acid, quinolinic acid, N(1)-methylnicotinamide, N(1)-methyl-2-pyridone-5-carboxamide, and N(1)-methyl-4-pyridone-3-carboxamide increased in an L-Trp dose-dependent manner on day 7. The amount of urinary excretion of these compounds was unchanged on days 14 and 21. The urinary excretion of serotonin, 5-hydroxyindole-3-acetic acid, 2-oxoadipic acid, and nicotinamide was unaffected by L-Trp at any of the doses tested. L-Trp doses had weak effects on the urinary excretion of kynurenine and anthranilic acid. Based on these findings, we conclude that there are no time-dependent effects of L-Trp administration in urinary excretion of L-Trp metabolites. Additionally, L-Trp and its metabolites do not accumulate in the body.