Activation of the Serotonin Pathway is Associated with Poor Outcome in COPD Exacerbation: Results of a Long-Term Cohort Study

Association of tryptophan pathway metabolites with mortality and effectiveness of nutritional support among patients at nutritional risk: secondary analysis of a randomized clinical trial

Tryptophan is an essential amino acid and is the precursor of many important metabolites and neurotransmitters. In malnutrition, the availability of tryptophan is reduced, potentially putting patients at increased risks. Herein, we investigated the prognostic implications of the tryptophan metabolism in a secondary analysis of the Effect of Early Nutritional Support on Frailty, Functional Outcomes, and Recovery of Malnourished Medical Inpatients Trial (EFFORT), a randomized, controlled trial comparing individualized nutritional support to usual care in patients at risk for malnutrition. Among 238 patients with available measurements, low plasma levels of metabolites were independently associated with 30-day mortality with adjusted hazard ratios (HR) of 1.77 [95% CI 1.05-2.99, p 0.034] for tryptophan, 3.49 [95% CI 1.81-6.74, p < 0.001] for kynurenine and 2.51 [95% CI 1.37-4.63, p 0.003] for serotonin. Nutritional support had more beneficial effects on mortality in patients with high tryptophan compared to patients with low tryptophan levels (adjusted HR 0.61 [95% CI 0.29-1.29] vs. HR 1.72 [95% CI 0.79-3.70], p for interaction 0.047). These results suggest that sufficient circulating levels of tryptophan might be a metabolic prerequisite for the beneficial effect of nutritional interventions in this highly vulnerable patient population.

Omega-3 Polyunsaturated Fatty Acids in Managing Comorbid Mood Disorders in Chronic Obstructive Pulmonary Disease (COPD): A Review

Chronic obstructive pulmonary disease (COPD) is the third-leading cause of mortality globally, significantly affecting people over 40 years old. COPD is often comorbid with mood disorders; however, they are frequently neglected or undiagnosed in COPD management, thus resulting in unintended treatment outcomes and higher mortality associated with the disease. Although the exact link between COPD and mood disorders remains to be ascertained, there is a broader opinion that inflammatory reactions in the lungs, blood, and inflammation-induced changes in the brain could orchestrate the onset of mood disorders in COPD. Although the current management of mood disorders such as depression in COPD involves using antidepressants, their use has been limited due to tolerability issues. On the other hand, as omega-3 polyunsaturated fatty acids (n-3 PUFAs) play a vital role in regulating inflammatory responses, they could be promising alternatives in managing mood disorders in COPD. This review discusses comorbid mood disorders in COPD as well as their influence on the progression and management of COPD. The underlying mechanisms of comorbid mood disorders in COPD will also be discussed, along with the potential role of n-3 PUFAs in managing these conditions.

Disturbances in branched-chain amino acid profile and poor daily functioning in mildly depressed chronic obstructive pulmonary disease patients

BACKGROUND

Depression is one of the most common and untreated comorbidities in chronic obstructive pulmonary disease (COPD), and is associated with poor health outcomes (e.g. increased hospitalization/exacerbation rates). Although metabolic disturbances have been suggested in depressed non-diseased conditions, comprehensive metabolic phenotyping has never been conducted in those with COPD. We examined whether depressed COPD patients have certain clinical/functional features and exhibit a specific amino acid phenotype which may guide the development of targeted (nutritional) therapies.

METHODS

Seventy-eight outpatients with moderate to severe COPD (GOLD II-IV) were stratified based on presence of depression using a validated questionnaire. Lung function, disease history, habitual physical activity and protein intake, body composition, cognitive and physical performance, and quality of life were measured. Comprehensive metabolic flux analysis was conducted by pulse stable amino acid isotope administration. We obtained blood samples to measure postabsorptive kinetics (production and clearance rates) and plasma concentrations of amino acids by LC-MS/MS. Data are expressed as mean [95% CI]. Stats were done by graphpad Prism 9.1.0. ɑ < 0.05.

RESULTS

The COPD depressed (CD, n = 27) patients on average had mild depression, were obese (BMI: 31.7 [28.4, 34.9] kg/m2), and were characterized by shorter 6-min walk distance (P = 0.055), physical inactivity (P = 0.03), and poor quality of life (P = 0.01) compared to the non-depressed COPD (CN, n = 51) group. Lung function, disease history, body composition, cognitive performance, and daily protein intake were not different between the groups. In the CD group, plasma branched chain amino acid concentration (BCAA) was lower (P = 0.02), whereas leucine (P = 0.01) and phenylalanine (P = 0.003) clearance rates were higher. Reduced values were found for tyrosine plasma concentration (P = 0.005) even after adjustment for the large neutral amino acid concentration (= sum BCAA, tyrosine, phenylalanine and tryptophan) as a marker of dopamine synthesis (P = 0.048).

CONCLUSION

Mild depression in COPD is associated with poor daily performance and quality of life, and a set of metabolic changes in depressed COPD that include perturbation of large neutral amino acids, specifically the BCAAs. Trial registration clinicaltrials.gov: NCT01787682, 11 February 2013-Retrospectively registered; NCT02770092, 12 May 2016-Retrospectively registered; NCT02780219, 23 May 2016-Retrospectively registered; NCT03796455, 8 January 2019-Retrospectively registered.

Metabolite profiles associated with disease progression in influenza infection

BACKGROUND

We performed metabolomic profiling to identify metabolites that correlate with disease progression and death.

METHODS

We performed a study of adults hospitalized with Influenza A(H1N1)pdm09. Cases (n = 32) were defined by a composite outcome of death or transfer to the intensive care unit during the 60-day follow-up period. Controls (n = 64) were survivors who did not require transfer to the ICU. Four hundred and eight metabolites from eight families were measured on plasma sample at enrollment using a mass spectrometry based Biocrates platform. Conditional logistic regression was used to summarize the association of the individual metabolites and families with the composite outcome and its major two components.

RESULTS

The ten metabolites with the strongest association with disease progression belonged to five different metabolite families with sphingolipids being the most common. The acylcarnitines, glycerides, sphingolipids and biogenic metabolite families had the largest odds ratios based on the composite endpoint. The tryptophan odds ratio for the composite is largely associated with death (OR 17.33: 95% CI, 1.60-187.76).

CONCLUSIONS

Individuals that develop disease progression when infected with Influenza H1N1 have a metabolite signature that differs from survivors. Low levels of tryptophan had a strong association with death.

REGISTRY

ClinicalTrials.gov Identifier: NCT01056185.

Untargeted Urinary Metabolomics and Children's Exposure to Secondhand Smoke: The Influence of Individual Differences

Children’s exposure to secondhand smoke (SHS) is a severe public health problem. There is still a lack of evidence regarding panoramic changes in children’s urinary metabolites induced by their involuntary exposure to SHS, and few studies have considered individual differences. This study aims to clarify the SHS-induced changes in urinary metabolites in preschool children by using cross-sectional and longitudinal metabolomics analyses. Urinary metabolites were quantified by using untargeted ultra high-performance liquid chromatography-mass spectrometry (UPLC^(c)-MS/MS). Urine cotinine-measured SHS exposure was examined to determine the exposure level. A cross-sectional study including 17 children in a low-exposure group, 17 in a medium-exposure group, and 17 in a high-exposure group was first conducted. Then, a before–after study in the cohort of children was carried out before and two months after smoking-cessation intervention for family smokers. A total of 43 metabolites were discovered to be related to SHS exposure in children in the cross-sectional analysis (false discovery rate (FDR) corrected p < 0.05, variable importance in the projection (VIP) > 1.0). Only three metabolites were confirmed to be positively associated with children’s exposure to SHS (FDR corrected p < 0.05) in a follow-up longitudinal analysis, including kynurenine, tyrosyl-tryptophan, and 1-(3-pyridinyl)-1,4-butanediol, the latter of which belongs to carbonyl compounds, peptides, and pyridines. Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis indicated that 1-(3-pyridinyl)-1,4-butanediol and kynurenine were significantly enriched in xenobiotic metabolism by cytochrome P450 (p = 0.040) and tryptophan metabolism (p = 0.030), respectively. These findings provide new insights into the pathophysiological mechanism of SHS and indicate the influence of individual differences in SHS-induced changes in urinary metabolites in children.

Metabolic reprograming of LPS-stimulated human lung macrophages involves tryptophan metabolism and the aspartate-arginosuccinate shunt

Lung macrophages (LM) are in the first line of defense against inhaled pathogens and can undergo phenotypic polarization to the proinflammatory M1 after stimulation with Toll-like receptor agonists. The objective of the present work was to characterize the metabolic alterations occurring during the experimental M1 LM polarization. Human LM were obtained from resected lungs and cultured for 24 hrs in medium alone or with 10 ng.mL-1 lipopolysaccharide. Cells and culture supernatants were subjected to extraction for metabolomic analysis with high-resolution LC-MS (HILIC and reverse phase -RP- chromatography in both negative and positive ionization modes) and GC-MS. The data were analyzed with R and the Worklow4Metabolomics and MetaboAnalyst online infrastructures. A total of 8,741 and 4,356 features were detected in the intracellular and extracellular content, respectively, after the filtering steps. Pathway analysis showed involvement of arachidonic acid metabolism, tryptophan metabolism and Krebs cycle in the response of LM to LPS, which was confirmed by the specific quantitation of selected compounds. This refined analysis highlighted a regulation of the kynurenin pathway as well as the serotonin biosynthesis pathway, and an involvement of aspartate-arginosuccinate shunt in the malate production. Macrophages M1 polarization is accompanied by changes in the cell metabolome, with the differential expression of metabolites involved in the promotion and regulation of inflammation and antimicrobial activity. The analysis of this macrophage immunometabolome may be of interest for the understanding of the pathophysiology of lung inflammatory disesases.

Dysregulation of the Tryptophan Pathway Evidences Gender Differences in COPD

Increased activity of indoleamine 2,3-dioxygenase (IDO) and tryptophan hydroxylase (TPH) have been reported in individuals with chronic obstructive pulmonary disease (COPD). We therefore investigated the effect of gender stratification upon the observed levels of tryptophan metabolites in COPD. Tryptophan, serotonin, kynurenine, and kynurenic acid were quantified in serum of never-smokers (n = 39), smokers (n = 40), COPD smokers (n = 27), and COPD ex-smokers (n = 11) by liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS). The individual metabolite associations with lung function, blood, and bronchoalveolar lavage (BAL) immune-cell composition, as well as chemokine and cytokine levels, were investigated. Stratification by gender and smoking status revealed that the observed alterations in kynurenine and kynurenic acid, and to a lesser extent serotonin, were prominent in males, irrespective of COPD status (kynurenine p = 0.005, kynurenic acid p = 0.009, and serotonin p = 0.02). Inferred serum IDO activity and kynurenine levels decreased in smokers relative to never-smokers (p = 0.005 and p = 0.004, respectively). In contrast, inferred tryptophan hydroxylase (TPH) activity and serotonin levels showed an increase with smoking that reached significance with COPD (p = 0.01 and p = 0.01, respectively). Serum IDO activity correlated with blood CXC chemokine ligand 9 (CXCL9, p = 0.0009, r = 0.93) and chemokine (C-C motif) ligand 4 (CCL4.(p = 0.04, r = 0.73) in female COPD smokers. Conversely, serum serotonin levels correlated with BAL CD4+ T-cells (%) (p = 0.001, r = 0.92) and CD8+ T-cells (%) (p = 0.002, r = -0.90) in female COPD smokers, but not in male COPD smokers (p = 0.1, r = 0.46 and p = 0.1, r = -0.50, respectively). IDO- and TPH-mediated tryptophan metabolites showed gender-based associations in COPD, which were primarily driven by smoking status.

Stimulatory Effect of 5-Hydroxytryptamine (5-HT) on Rat Capsaicin-Sensitive Lung Vagal Sensory Neurons via Activation of 5-HT3 Receptors

5-hydroxytryptamine (5-HT) is an inflammatory mediator known to be released in lung. Capsaicin-sensitive lung vagal (CSLV) afferents function as a primary sensor for detecting chemical stimuli and produce consequent reflexes during lung inflammation. To characterize the effect of 5-HT on CSLV afferents, responses of cardiorespiratory reflexes and single-unit C-fiber afferents to right-atrial injections of 5-HT were investigated in anesthetized Sprague-Dawley rats. Bolus injection of 5-HT (8 μg/kg) caused an immediate augmented breath and apnea, accompanied by hypotension and bradycardia. These initial responses were then followed by a brief pressor response and a more sustained depressor response. After a perineural treatment of both cervical vagi with capsaicin to block the conduction of C fibers, 5-HT still triggered the augmented breath, but no longer evoked the apnea, bradycardia and hypotension, indicating an involvement of C-fiber activation. The remaining augmented breath induced by 5-HT after perineural capsaicin treatment was totally eliminated by vagotomy. To further study the effect of 5-HT on CSLV afferents, activities arising from these afferents were determined using the single-fiber recording technique. Right-atrial injection of 5-HT evoked an intense discharge in CSLV afferents in a dose-dependent manner. The highest dose of 5-HT (16 μg/kg) activated 79% (19/24) of CSLV afferents which were also sensitive to capsaicin (0.8 μg/kg). The pretreatment of tropisetron, a selective antagonist of the 5-HT₃ receptor, completely blocked CSLV-afferents stimulation induced by 5-HT but did not affect that by capsaicin. Furthermore, a similar afferent response of CSLV afferents was mimicked by phenylbiguanide, a selective agonist of the 5-HT₃ receptor. In isolated rat lung vagal C neurons, 5-HT induced intense calcium transients in a dose-dependent manner. The highest concentration (3 μM) of 5-HT activated 67% (18/27) of the CSLV neurons. The 5-HT-induced response was totally abolished by pretreatment of tropisetron. In conclusion, 5-HT exerts an intense stimulatory effect on lung C-fiber terminals mediated through an activation of the 5-HT₃ receptor, which may contribute to the airway hypersensitivity under lung inflammation.

Circulating serotonin levels in COPD patients: a pilot study

Background

Chronic obstructive pulmonary disease (COPD) is a major and increasing global health problem. Serotonin is a neurotransmitter that participates in several pulmonary functions and it has been involved in oxidative stress, which plays essential roles in the pathogenesis of COPD. The current study aimed at establishing the levels of circulating serotonin in COPD, and investigating eventual relations between serotonin and oxidative stress markers.

Methods

Whole blood serotonin was assessed in 43 consecutive patients with stable COPD and in 43 age and sex-matched healthy controls.

Results

Serotonin blood levels were significantly higher in COPD patients than in controls (median 0.81 μmol/L, IQR: 0.61–4.02 vs 0.65 μmol/L, IQR: 0.53–1.39, p = 0.02). The univariate logistic regression analysis evidenced that serotonin levels are independently associated with presence of COPD (crude OR = 7.29, 95% CI: 1.296–41.05, p = 0.003) and such an association was confirmed also after adjusting for several confounders (OR 21.92, 95% CI 2.02–237.83; p = 0.011).

Conclusions

Our study showed higher levels of circulating serotonin in COPD and an inverse correlation with the worsening of airway obstruction. Future studies are necessary to investigate the clinical utility of this finding.

Increased kynurenine plasma concentrations and kynurenine-tryptophan ratio in mild-to-moderate chronic obstructive pulmonary disease patients

AIM

Since an increase in kynurenine (Kyn) plasma concentrations has been proposed as marker of immune system activation, we studied the associations between the Kyn levels and presence and severity of chronic obstructive pulmonary disease (COPD).

METHODS & RESULTS

Plasma Kyn, tryptophan (Trp) and Kyn/Trp ratio were measured in 43 COPD patients with clinically defined mild (n = 29) or moderate (n = 14) disease and 43 age- and sex-matched healthy controls. When compared with controls, COPD patients had significantly higher plasma Kyn concentrations and Kyn/Trp ratios. In multiple logistic regression analysis, after adjusting for clinical and demographic confounders, the Kyn/Trp ratio was independently associated with COPD severity.

DISCUSSION & CONCLUSION

Kyn and Kyn/Trp ratio might represent a new, sensitive, biomarker of systemic inflammation in COPD patients.

The role of metabolomic markers for patients with infectious diseases: implications for risk stratification and therapeutic modulation

INTRODUCTION

Metabolomics is a rapidly growing area of research. Metabolomic markers can provide information about the interaction of different organ systems, and thereby improve the understanding of physio-pathological processes, disease risk, prognosis and therapy responsiveness in a variety of diseases. Areas covered: In this narrative review of recent clinical studies investigating metabolomic markers in adult patients presenting with acute infectious disease, we mainly focused on patients with sepsis and lower respiratory tract infections. Currently, there is a growing body of literature showing that single metabolites from distinct metabolic pathways, as well as more complex metabolomic signatures are associated with disease severity and outcome in patients with systemic infections. These pathways include, among others, metabolomic markers of oxidative stress, steroid hormone and amino acid pathways, and nutritional markers. Expert commentary: Metabolic profiling has great potential to optimize patient management, to provide new targets for individual therapy and thereby improve survival of patients. At this stage, research mainly focused on the identification of new predictive signatures and less on metabolic determinants to predict treatment response. The transition from observational studies to implementation of novel markers into clinical practice is the next crucial step to prove the usefulness of metabolomic markers in patient care.