Tryptophan Metabolism and Its Relationship with Depression and Cognitive Impairment Among HIV-infected Individuals

Tryptophan-Kynurenine Pathway Activation and Cognition in Virally Suppressed Women With HIV

BACKGROUND

Immune and cognitive dysfunction persists even in virally suppressed women with HIV (VS-WWH). Since inflammation and HIV proteins induce the enzyme indoleamine 2,3-dioxygenase (IDO), converting tryptophan (T) to kynurenine (K) while producing downstream neurotoxic metabolites, we investigated IDO activation (KT ratio) in relation to cognition in VS-WWH and demographically similar women without HIV (WWoH).

METHODS

Ninety-nine VS-WWH on stable antiretroviral therapy and 102 WWoH (median age 52 vs 54 years; 73% vs 74% Black, respectively) from the New York and Chicago sites of the Women's Interagency HIV Study (WIHS) completed a neuropsychological test battery assessing motor function, processing speed, attention/working memory, verbal fluency, verbal learning and memory, and executive function and had plasma measured for tryptophan-kynurenine metabolites through liquid chromatography-tandem mass spectrometry and monocyte-derived [soluble cluster of differentiation-14 (sCD14), soluble cluster of differentiation-163 (sCD163), monocyte chemoattractant protein-1 (MCP-1)] plus general inflammatory markers [tumor necrosis factor alpha-2 receptor (TNF-R2), high-sensitivity C-reactive protein, high-sensitivity interleukin-6] through enzyme-linked immunosorbent assays between 2017 and 2020.

RESULTS

VS-WWH had a higher KT ratio (P < 0.01) and higher sCD14 levels (P < 0.05) compared with WWoH. Higher sCD163 was associated with higher KT ratio (R = 0.29, P < 0.01) and worse fine motor function in VS-WWH; after adjusting for sCD163 and sCD14 in multivariable regressions, higher KT ratio remained significantly associated with impaired fine motor function in VS-WWH only (standardized β = -0.29, P < 0.05). IDO activation was not associated with cognition in WWoH.

CONCLUSIONS

IDO activation (K:T) was associated with worse fine motor control in VS-WWH independent of measured systemic inflammation. Further studies investigating biological mechanisms linking IDO activation to fine motor function among VS-WWH are warranted.

Distinct Effects of Selective Serotonin Reuptake Inhibitors and Serotonin-Norepinephrine Reuptake Inhibitors on Soluble Biomarkers in Blood and Cerebrospinal Fluid of People With HIV

BACKGROUND

Persistent inflammation affects people with HIV (PWH) despite antiretroviral therapy (ART). Selective serotonin and serotonin-norepinephrine reuptake inhibitors (SSRIs, SNRIs), HMG-CoA reductase-inhibitors (statins), and angiotensin-converting enzyme inhibitors (ACEIs) have immunomodulant properties. We evaluated the potential impact of these drugs on inflammation and neurodegeneration in PWH.

METHODS

Cross-sectional single-center (United States) analysis in 184 PWH on ART with plasma HIV RNA < 200 copies/mL. All participants had 10 biomarkers measured in blood and cerebrospinal fluid (CSF). To reduce dimensionality, hierarchical clustering and principal components (PCs) analysis were employed. The analyses were adjusted for duration of the drugs and clinical conditions.

RESULTS

Participants were mostly middle-aged men, with median CD4+ T cells of 620/µL. In adjusted models, SSRI use was associated with 3 PCs: higher CSF and plasma Aβ42 and CSF CCL2 (aβ=.14, P = .040); lower CSF 8-oxo-dG, total tau, and sCD14 (aβ=-.12, P = .042); and higher plasma sCD14 with lower sCD40L (aβ=.15, P = .042). SNRI use was associated with higher values of CSF and plasma neopterin and CSF sTNFR-II (aβ=.22, P = .004). Statins and ACEIs showed no association.

CONCLUSIONS

SSRIs and SNRIs had distinct biomarker signatures. SSRIs were associated with reduced neurodegeneration, immune activation, and oxidative stress in CSF, suggesting a role of SSRIs as adjunctive therapy in PWH.

Serum neuroactive metabolites of the tryptophan pathway in patients with acute phase of affective disorders

Background

Many studies showed disrupted tryptophan metabolism in patients with affective disorders. The aims of this study were to explore the differences in the metabolites of tryptophan pathway (TP) and the relationships between TP metabolites and clinical symptoms, therapeutic effect in patients with bipolar disorder with acute manic episode (BD-M), depressive episode (BD-D) and major depressive disorder (MDD).

Methods

Patients with BD-M (n=52) and BD-D (n=39), MDD (n=48) and healthy controls (HCs, n=49) were enrolled. The serum neuroactive metabolites levels of the TP were measured by liquid chromatography-tandem mass spectrometry. Hamilton Depression Scale-17 item (HAMD-17) and Young Mania Rating Scale (YMRS) were used to evaluate depressive and manic symptoms at baseline and after 8 weeks of antidepressants, mood stabilizers, some also received antipsychotic medication.

Results

The levels of tryptophan (TRP) and kynurenic acid (KYNA) were significantly lower and the ratios of tryptophan/kynurenine (TRP/KYN), 5-hydroxytryptamine/tryptophan (5-HT/TRP), quinolinic acid/kynurenic acid (QUIN/KYNA) were higher in BD-M, BD-D, MDD vs. HC. The levels of QUIN and the ratios of QUIN/KYNA were higher in BD-M than in BD-D, MDD, and HCs. The 5-hydroxyindoleacetic acid (5-HIAA) levels of patients with MDD were significantly higher than those in BD-M and BD-D. Binary logistic regression analysis showed the lower peripheral KYNA, the higher the QUIN level, and the higher the risk of BD-M; the lower peripheral KYNA and the higher KYN/TRP and 5-HT/TRP, the higher the risk of BD-D; and the lower the peripheral KYNA level and the higher the KYN/TRP and 5-HT/TRP, the higher the risk of MDD. Correlation analysis, showing a significant association between tryptophan metabolites and improvement of clinical symptoms, especially depression symptoms.

Conclusions

Patients with affective disorders had abnormal tryptophan metabolism, which involved in 5-HT and kynurenine pathway (KP) sub-pathway. Tryptophan metabolites might be potential biomarkers for affective disorders and some metabolites have been associated with remission of depressive symptoms.

KYNA Ameliorates Glutamate Toxicity of HAND by Enhancing Glutamate Uptake in A2 Astrocytes

Reactive astrocytes are key players in HIV-associated neurocognitive disorders (HAND), and different types of reactive astrocytes play opposing roles in the neuropathologic progression of HAND. A recent study by our group found that gp120 mediates A1 astrocytes (neurotoxicity), which secrete proinflammatory factors and promote HAND disease progression. Here, by comparing the expression of A2 astrocyte (neuroprotective) markers in the brains of gp120 tgm mice and gp120+/α7nAChR-/- mice, we found that inhibition of alpha 7 nicotinic acetylcholine receptor (α7nAChR) promotes A2 astrocyte generation. Notably, kynurenine acid (KYNA) is an antagonist of α7nAChR, and is able to promote the formation of A2 astrocytes, the secretion of neurotrophic factors, and the enhancement of glutamate uptake through blocking the activation of α7nAChR/NF-κB signaling. In addition, learning, memory and mood disorders were significantly improved in gp120 tgm mice by intraperitoneal injection of kynurenine (KYN) and probenecid (PROB). Meanwhile, the number of A2 astrocytes in the mouse brain was significantly increased and glutamate toxicity was reduced. Taken together, KYNA was able to promote A2 astrocyte production and neurotrophic factor secretion, reduce glutamate toxicity, and ameliorate gp120-induced neuropathological deficits. These findings contribute to our understanding of the role that reactive astrocytes play in the development of HAND pathology and provide new evidence for the treatment of HAND via the tryptophan pathway.

A pilot investigation of the association between HIV-1 Vpr amino acid sequence diversity and the tryptophan-kynurenine pathway as a potential mechanism for neurocognitive impairment

HIV infection compromises both the peripheral and central immune systems due to its pathogenic and neuropathogenic features. The mechanisms driving HIV-1 pathogenesis and neuropathogenesis involve a series of events, including metabolic dysregulation. Furthermore, HIV-subtype-specific variations, particularly alterations in the amino acid sequences of key viral proteins, are known to influence the severity of clinical outcomes in people living with HIV. However, the impact of amino acid sequence variations in specific viral proteins, such as Viral protein R (Vpr), on metabolites within the Tryptophan (Trp)-kynurenine (Kyn) pathway in people living with HIV remains unclear. Our research aimed to explore the relationship between variations in the Vpr amino acid sequence (specifically at positions 22, 41, 45, and 55, as these have been previously linked to neurocognitive function) and peripheral Trp-Kyn metabolites. Additionally, we sought to clarify the systems biology of Vpr sequence variation by examining the link between Trp-Kyn metabolism and peripheral inflammation, as a neuropathogenic mechanism. In this preliminary study, we analyzed a unique cohort of thirty-two (n = 32) South African cART naïve people living with HIV. We employed Sanger sequencing to ascertain blood-derived Vpr amino acid sequence variations and a targeted LC-MS/MS metabolomics platform to assess Trp-Kyn metabolites, such as Trp, Kyn, kynurenic acid (KA), and quinolinic acid (QUIN). Particle-enhanced turbidimetric assay and Enzyme-linked immunosorbent assays were used to measure immune markers, hsCRP, IL-6, suPAR, NGAL and sCD163. After applying Bonferroni corrections (p =.05/3) and adjusting for covariates (age and sex), only the Vpr G41 and A55 groups was nearing significance for higher levels of QUIN compared to the Vpr S41 and T55 groups, respectively (all p =.023). Multiple regression results revealed that Vpr amino acid variations at position 41 (adj R2 = 0.049, β = 0.505; p =.023), and 55 (adj R2 = 0.126, β = 0.444; p =.023) displayed significant associations with QUIN after adjusting for age and sex. Lastly, the higher QUIN levels observed in the Vpr G41 group were found to be correlated with suPAR (r =.588, p =.005). These results collectively underscore the importance of specific Vpr amino acid substitutions in influencing QUIN and inflammation (specifically suPAR levels), potentially contributing to our understanding of their roles in the pathogenesis and neuropathogenesis of HIV-1.

In Vitro Human Monoamine Oxidase Inhibition and Human Dopamine D4 Receptor Antagonist Effect of Natural Flavonoids for Neuroprotection

Natural flavone and isoflavone analogs such as 3',4',7-trihydroxyflavone (1), 3',4',7-trihydroxyisoflavone (2), and calycosin (3) possess significant neuroprotective activity in Alzheimer's and Parkinson's disease. This study highlights the in vitro human monoamine oxidase (hMAO) inhibitory potential and functional effect of those natural flavonoids at dopamine and serotonin receptors for their possible role in neuroprotection. In vitro hMAO inhibition and enzyme kinetics studies were performed using a chemiluminescent assay. The functional effect of three natural flavonoids on dopamine and serotonin receptors was tested via cell-based functional assays followed by a molecular docking simulation to predict interactions between a compound and the binding site of the target protein. A forced swimming test was performed in the male C57BL/6 mouse model. Results of in vitro chemiluminescent assays and enzyme kinetics depicted 1 as a competitive inhibitor of hMAO-A with promising potency (IC50 value: 7.57 ± 0.14 μM) and 3 as a competitive inhibitor of hMAO-B with an IC50 value of 7.19 ± 0.32 μM. Likewise, GPCR functional assays in transfected cells showed 1 as a good hD4R antagonist. In docking analysis, these active flavonoids interacted with a determinant-interacting residue via hydrophilic and hydrophobic interactions, with low docking scores comparable to reference ligands. The post-oral administration of 1 to male C57BL/6 mice did not reduce the immobility time in the forced swimming test. The results of this study suggest that 1 and 3 may serve as effective regulators of the aminergic system via hMAO inhibition and the hD4R antagonist effect, respectively, for neuroprotection. The route of administration should be considered.

Depression and HIV: a scoping review in search of neuroimmune biomarkers

People with HIV are at increased risk for depression, though the neurobiological mechanisms underlying this are unclear. In the last decade, there has been a substantial rise in interest in the contribution of (neuro)inflammation to depression, coupled with rapid advancements in the resolution and sensitivity of biomarker assays such as Luminex, single molecular array and newly developed positron emission tomography radioligands. Numerous pre-clinical and clinical studies have recently leveraged these next-generation immunoassays to identify biomarkers that may be associated with HIV and depression (separately), though few studies have explored these biomarkers in co-occurring HIV and depression. Using a systematic search, we detected 33 publications involving a cumulative N = 10 590 participants which tested for associations between depressive symptoms and 55 biomarkers of inflammation and related processes in participants living with HIV. Formal meta-analyses were not possible as statistical reporting in the field was highly variable; future studies must fully report test statistics and effect size estimates. The majority of included studies were carried out in the United States, with samples that were primarily older and primarily men. Substantial further work is necessary to diversify the geographical, age, and sex distribution of samples in the field. This review finds that alterations in concentrations of certain biomarkers of neuroinflammation (interleukin-6, tumour necrosis factor-α, neopterin) may influence the association between HIV and depression. Equally, the chemokines monocyte chemoattractant protein-1 (MCP-1) and interleukin-8 (IL-8) or the metabolic index kynurenine:tryptophan (Kyn:Trp), which have been the focus of several studies, do not appear to be associated with depressive symptoms amongst people living with HIV, as all (MCP-1) or most (IL-8 and Kyn:Trp) available studies of these biomarkers reported non-significant associations. We propose a biomarker-driven hypothesis of the neuroimmunometabolic mechanisms that may precipitate the increased risk of depression among people with HIV. Chronically activated microglia, which trigger key neuroinflammatory cascades shown to be upregulated in people with HIV, may be the central link connecting HIV infection in the central nervous system with depressive symptoms. Findings from this review may inform research design in future studies of HIV-associated depression and enable concerted efforts towards biomarker discovery.

Therapeutically targeting the consequences of HIV-1-associated gastrointestinal dysbiosis: Implications for neurocognitive and affective alterations

Approximately 50 % of the individuals living with human immunodeficiency virus type 1 (HIV-1) are plagued by debilitating neurocognitive impairments (NCI) and/or affective alterations. Sizeable alterations in the composition of the gut microbiome, or gastrointestinal dysbiosis, may underlie, at least in part, the NCI, apathy, and/or depression observed in this population. Herein, two interrelated aims will be critically addressed, including: 1) the evidence for, and functional implications of, gastrointestinal microbiome dysbiosis in HIV-1 seropositive individuals; and 2) the potential for therapeutically targeting the consequences of this dysbiosis for the treatment of HIV-1-associated NCI and affective alterations. First, gastrointestinal microbiome dysbiosis in HIV-1 seropositive individuals is characterized by decreased alpha (α) diversity, a decreased relative abundance of bacterial species belonging to the Bacteroidetes phylum, and geographic-specific alterations in Bacillota (formerly Firmicutes) spp. Fundamentally, changes in the relative abundance of Bacteroidetes and Bacillota spp. may underlie, at least in part, the deficits in γ-aminobutyric acid and serotonin neurotransmission, as well as prominent synaptodendritic dysfunction, observed in this population. Second, there is compelling evidence for the therapeutic utility of targeting synaptodendritic dysfunction as a method to enhance neurocognitive function and improve motivational dysregulation in HIV-1. Further research is needed to determine whether the therapeutics enhancing synaptic efficacy exert their effects by altering the gut microbiome. Taken together, understanding gastrointestinal microbiome dysbiosis resulting from chronic HIV-1 viral protein exposure may afford insight into the mechanisms underlying HIV-1-associated neurocognitive and/or affective alterations; mechanisms which can be subsequently targeted via novel therapeutics.

Kynurenic acid blunts A1 astrocyte activation against neurodegeneration in HIV-associated neurocognitive disorders

Despite extensive astrocyte activation in patients suffering from HIV-associated neurocognitive disorders (HAND), little is known about the contribution of astrocytes to HAND neuropathology. Here, we report that the robust activation of neurotoxic astrocytes (A1 astrocytes) in the CNS promotes neuron damage and cognitive deficits in HIV-1 gp120 transgenic mice. Notably, knockout of α7 nicotinic acetylcholine receptors (α7nAChR) blunted A1 astrocyte responses, ultimately facilitating neuronal and cognitive improvement in the gp120tg mice. Furthermore, we provide evidence that Kynurenic acid (KYNA), a tryptophan metabolite with α7nAChR inhibitory properties, attenuates gp120-induced A1 astrocyte formation through the blockade of α7nAChR/JAK2/STAT3 signaling activation. Meanwhile, compared with gp120tg mice, mice fed with tryptophan showed dramatic improvement in cognitive performance, which was related to the inhibition of A1 astrocyte responses. These initial and determinant findings mark a turning point in our understanding of the role of α7nAChR in gp120-mediated A1 astrocyte activation, opening up new opportunities to control neurotoxic astrocyte generation through KYNA and tryptophan administration.

Blood concentrations of neopterin and biopterin in subjects with depression: A systematic review and meta-analysis

INTRODUCTION

Pteridines, such as neopterin, biopterin, and tetrahydrobiopterin (BH₄), may be involved in depression pathophysiology owing to their links to immune-inflammatory response, oxidative and nitrosative stress, and monoaminergic transmission. Nonetheless, studies assessing pteridines in depression are inconsistent. We conducted a systematic review and meta-analysis of observational studies comparing blood pteridine concentrations between subjects with depression and healthy controls (HCs).

METHODS

We searched Embase, MEDLINE, and PsycInfo for articles indexed through November 2021. Study quality was appraised, evaluating age and gender comparability between groups, sample representativeness, and methods to assess depression. Random-effects meta-analyses were carried out, generating pooled standardized mean differences (SMDs). Heterogeneity across studies was estimated using the I² statistic.

RESULTS

Twenty-four studies, involving 3075 subjects, were included. Individuals with depression showed blood neopterin concentrations higher than HCs (k = 19; SMD = 0.36; p < 0.001) with moderate heterogeneity across studies (I² = 58.2%). No moderating role of age, gender, or type of blood sample was found. Sensitivity analyses showed no impact of inconsistency and quality of studies on findings. Neopterin concentrations were higher among individuals with major depressive disorder compared to HCs (SMD = 0.44; p < 0.001). This held true also when considering only drug-free subjects (SMD = 0.68; p = 0.003). No differences in biopterin concentrations were found between subjects with depression and HCs (k = 5; SMD = -0.35; p = 0.086), though this result was limited by inconsistency of findings (I² = 77.9%) and quality of studies. Finally, no sufficient data were available for a meta-analysis on BH₄.

CONCLUSIONS

As a whole, our work partly supports the hypothesis of an imbalance of pteridine metabolism in depression.

The IDOze Study: The Link Between Sleep Disruption and Tryptophan-Kynurenine Pathway Activation in Women With Human Immunodeficiency Virus

BACKGROUND

Poor sleep is associated with human immunodeficiency virus (HIV), particularly among women with HIV (WWH), although mechanisms are unclear. We explored cross-sectional associations between sleep disruption and tryptophan-kynurenine (T/K) pathway activation, measured by the kynurenine-to-tryptophan ratio (K:T).

METHODS

HIV-uninfected women (HIV-) and WWH aged 35-70 years and on stable antiretroviral therapy were included. Sleep metrics were measured using wrist actigraphy. Plasma T/K pathway metabolites were measured using liquid chromatography-tandem mass spectrometry. Multivariate linear regression models examined relationships between K:T and actigraphy-based sleep metrics by HIV status.

RESULTS

WWH (n = 153) and HIV- women (n = 151) were demographically similar. Among WWH, median CD4 was 751 cells/µL; 92% had undetectable HIV RNA. Compared to HIV- women, WWH had higher K:T (P < .001) and kynurenine (P = .01) levels but similar tryptophan levels (P = .25). Higher K:T was associated with more wake bouts (P = .001), more time awake after sleep onset (P = .01), and lower sleep efficiency (P = .03) in WWH only.

CONCLUSIONS

HIV infection was associated with T/K pathway activation; this activation was associated with poorer sleep efficiency and more fragmented sleep. While longitudinal studies are needed to elucidate the directionality of these associations, these findings may help identify treatments to reduce sleep disruption in WWH by targeting residual inflammation and T/K pathway activation.

Microbiome-Related Indole and Serotonin Metabolites are Linked to Inflammation and Psychiatric Symptoms in People Living with HIV

Background:

People living with HIV (PLHIV) exhibit dysregulation of tryptophan metabolism. Altered gut microbiome composition in PLHIV might be involved. Mechanistic consequences within the 3 major tryptophan metabolism pathways (serotonin, kynurenine, and indoles), and functional consequences for platelet, immune and behavioral functions are unknown. We investigated plasma tryptophan metabolites, gut microbiome composition, and their association with platelet function, inflammation, and psychiatric symptoms.

Methods:

This study included 211 PLHIV on long-term antiretroviral treatment (ART). Plasma tryptophan pathway metabolites were measured using time-of-flight mass spectrometry. Bacterial composition was profiled using metagenomic sequencing. Platelet reactivity and serotonin levels were quantified by flowcytometry and ELISA, respectively. Circulating inflammatory markers were determined using ELISA. Symptoms of depression and impulsivity were measured by DASS-42 and BIS-11 self-report questionnaires, respectively.

Results:

Plasma serotonin and indole metabolites were associated with gut bacterial composition. Notably, species enriched in PLHIV were associated with 3-methyldioxyindole. Platelet serotonin concentrations were elevated in PLHIV, without effects on platelet reactivity. Plasma serotonin and indole metabolites were positively associated with plasma IL-10 and TNF-α concentrations. Finally, higher tryptophan, serotonin, and indole metabolites were associated with lower depression and anxiety, whereas higher kynurenine metabolites were associated with increased impulsivity.

Conclusion:

Our results suggest that gut bacterial composition and dysbiosis in PLHIV on ART contribute to tryptophan metabolism, which may have clinical consequences for immune function and behavior.

Disturbance of neurotransmitter metabolism in drug-naïve, first-episode major depressive disorder: a comparative study on adult and adolescent cohorts

Neurotransmitter metabolism plays a critical role in the pathophysiology of major depressive disorder (MDD). However, whether the neurotransmitter metabolism in adolescent MDD is differentiated from adult MDD is still elusive. In the current study, plasma concentrations of monoamine and amino acid neurotransmitters as well as their metabolites, including tryptophan (TRP), kynurenine (KYN), kynurenic acid (KYNA), serotonin (5-HT), 5-hydroxyindoleacetic acid (5-HIAA), dopamine (DA), 3,4-dihydroxyphenylacetic acid (DOPAC), homovanillic acid (HVA), norepinephrine (NE), vanillylmandelic acid (VMA), 3-methoxy-4-hydroxyphenylglycol (MHPG), glutamine (GLN), glutamate (GLU) and gamma-aminobutyric acid (GABA), were measured and compared in two cohorts of subjects (adult cohort: 31 first-episode MDD vs. 35 healthy controls; adolescent cohort: 33 first-episode MDD vs. 30 healthy controls). To assess the effects of antidepressant treatment, we also analyzed the concentrations of these indexes pre- and post-treatment in adult and adolescent cohorts. At baseline, the deficits of neurotransmitter metabolism in adult MDD were manifested in all the neurotransmitter systems. In contrast, for adolescent MDD, the dysregulation of neurotransmission was mainly indicated in the catecholaminergic systems. After antidepressant treatment, adult MDD showed increased TRP, KYN, KYNA and GLU levels, together with decreased levels of 5-HIAA and DOPAC. Adolescent MDD illustrated an increased level of 5-HT and decreased levels of TRP and GABA. The improvements of Hamilton total scores correlated with the changes in plasma TRP and the turnover of KYN/TRP after treatment in all MDD patients. However, these correlations were only manifested in the adult MDD rather than in adolescent MDD patients. The findings highlight the shared and distinguished neurotransmitter pathways in MDD and emphasize the different antidepressant responses between adults and adolescents. Potentially, the neurotransmitters above could serve as diagnostic biomarkers and provide a novel pharmacological treatment strategy for MDD.

HIV-1 Tat and cocaine impact astrocytic energy reservoirs and epigenetic regulation by influencing the LINC01133-hsa-miR-4726-5p-NDUFA9 axis

Clinical research has proven that HIV-positive (HIV+) individuals with cocaine abuse show behavioral and neurocognitive disorders. Noncoding RNAs (ncRNAs), such as long ncRNAs (lncRNAs) and microRNAs (miRNAs), are known to regulate gene expression in the contexts of HIV infection and drug abuse. However, there are no specific lncRNA or miRNA biomarkers associated with HIV-1 Transactivator of transcription protein (Tat) and cocaine coexposure. In the central nervous system (CNS), astrocytes are the primary regulators of energy metabolism, and impairment of the astrocytic energy supply can trigger neurodegeneration. The aim of this study was to uncover the roles of lncRNAs and miRNAs in the regulation of messenger RNA (mRNA) targets affected by HIV infection and cocaine abuse. Integrative bioinformatics analysis revealed altered expression of 10 lncRNAs, 10 miRNAs, and 4 mRNA/gene targets in human primary astrocytes treated with cocaine and HIV-1 Tat. We assessed the alterations in the expression of two miRNAs, hsa-miR-2355 and hsa-miR-4726-5p; four lncRNAs, LINC01133, H19, HHIP-AS1, and NOP14-AS1; and four genes, NDUFA9, KYNU, HKDC1, and LIPG. The results revealed interactions in the LINC01133-hsa-miR-4726-5p-NDUFA9 axis that may eventually help us understand cocaine- and HIV-1 Tat-induced astrocyte dysfunction that may ultimately result in neurodegeneration.

The Role of Tryptophan Metabolites in Neuropsychiatric Disorders

In recent decades, neuropsychiatric disorders such as major depressive disorder, schizophrenia, bipolar, etc., have become a global health concern, causing various detrimental influences on patients. Tryptophan is an important amino acid that plays an indisputable role in several physiological processes, including neuronal function and immunity. Tryptophan’s metabolism process in the human body occurs using different pathways, including the kynurenine and serotonin pathways. Furthermore, other biologically active components, such as serotonin, melatonin, and niacin, are by-products of Tryptophan pathways. Current evidence suggests that a functional imbalance in the synthesis of Tryptophan metabolites causes the appearance of pathophysiologic mechanisms that leads to various neuropsychiatric diseases. This review summarizes the pharmacological influences of tryptophan and its metabolites on the development of neuropsychiatric disorders. In addition, tryptophan and its metabolites quantification following the neurotransmitters precursor are highlighted. Eventually, the efficiency of various biomarkers such as inflammatory, protein, electrophysiological, genetic, and proteomic biomarkers in the diagnosis/treatment of neuropsychiatric disorders was discussed to understand the biomarker application in the detection/treatment of various diseases.

Neuroinflammation in HIV-associated depression: evidence and future perspectives

People living with HIV face a high risk of mental illness, especially depression. We do not yet know the precise neurobiological mechanisms underlying HIV-associated depression. Depression severity in the general population has been linked to acute and chronic markers of systemic inflammation. Given the associations between depression and peripheral inflammation, and since HIV infection in the brain elicits a neuroinflammatory response, it is possible that neuroinflammation contributes to the high prevalence of depression amongst people living with HIV. The purpose of this review was to synthesise existing evidence for associations between inflammation, depression, and HIV. While there is strong evidence for independent associations between these three conditions, few preclinical or clinical studies have attempted to characterise their interrelationship, representing a major gap in the literature. This review identifies key areas of debate in the field and offers perspectives for future investigations of the pathophysiology of HIV-associated depression. Reproducing findings across diverse populations will be crucial in obtaining robust and generalisable results to elucidate the precise role of neuroinflammation in this pathophysiology.

HIV-1 gp120 Impairs Spatial Memory Through Cyclic AMP Response Element-Binding Protein

HIV-associated neurocognitive disorders (HAND) remain an unsolved problem that persists despite using antiretroviral therapy. We have obtained data showing that HIV-gp120 protein contributes to neurodegeneration through metabolic reprogramming. This led to decreased ATP levels, lower mitochondrial DNA copy numbers, and loss of mitochondria cristae, all-important for mitochondrial biogenesis. gp120 protein also disrupted mitochondrial movement and synaptic plasticity. Searching for the mechanisms involved, we found that gp120 alters the cyclic AMP response element-binding protein (CREB) phosphorylation on serine residue 133 necessary for its function as a transcription factor. Since CREB regulates the promoters of PGC1α and BDNF genes, we found that CREB dephosphorylation causes PGC1α and BDNF loss of functions. The data was validated in vitro and in vivo. The negative effect of gp120 was alleviated in cells and animals in the presence of rolipram, an inhibitor of phosphodiesterase protein 4 (PDE4), restoring CREB phosphorylation. We concluded that HIV-gp120 protein contributes to HAND via inhibition of CREB protein function.

Altered Expression of ACE2 and Co-receptors of SARS-CoV-2 in the Gut Mucosa of the SIV Model of HIV/AIDS

The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection, the cause of the COVID-19 pandemic, is initiated by its binding to the ACE2 receptor and other co-receptors on mucosal epithelial cells. Variable outcomes of the infection and disease severity can be influenced by pre-existing risk factors. Human immunodeficiency virus (HIV), the cause of AIDS, targets the gut mucosal immune system and impairs epithelial barriers and mucosal immunity. We sought to determine the impact and mechanisms of pre-existing HIV infection increasing mucosal vulnerability to SARS-CoV-2 infection and disease. We investigated changes in the expression of ACE2 and other SARS-CoV-2 receptors and related pathways in virally inflamed gut by using the SIV infected rhesus macaque model of HIV/AIDS. Immunohistochemical analysis showed sustained/enhanced ACE2 expression in the gut epithelium of SIV infected animals compared to uninfected controls. Gut mucosal transcriptomic analysis demonstrated enhanced expression of host factors that support SARS-CoV-2 entry, replication, and infection. Metabolomic analysis of gut luminal contents revealed the impact of SIV infection as demonstrated by impaired mitochondrial function and decreased immune response, which render the host more vulnerable to other pathogens. In summary, SIV infection resulted in sustained or increased ACE2 expression in an inflamed and immune-impaired gut mucosal microenvironment. Collectively, these mucosal changes increase the susceptibility to SARS-CoV-2 infection and disease severity and result in ineffective viral clearance. Our study highlights the use of the SIV model of AIDS to fill the knowledge gap of the enteric mechanisms of co-infections as risk factors for poor disease outcomes, generation of new viral variants and immune escape in COVID-19.

Age-Associated Gut Dysbiosis, Marked by Loss of Butyrogenic Potential, Correlates With Altered Plasma Tryptophan Metabolites in Older People Living With HIV

BACKGROUND

Imbalance in tryptophan (TRP) metabolism and its neuroactive metabolites, serotonin and kynurenine (KYN), is a known pathogenic mechanism underlying neurocognitive impairment. Gut microbiota plays an important role in TRP metabolism, and the production of these neuroactive molecules affects neurocognitive function. Although both HIV infection and normal aging independently induce gut dysbiosis and influence TRP metabolism, their interactive effects on compositional/functional changes in gut microbiota and consequent alterations in TRP metabolites remain largely undetermined.

METHODS

Older people living with HIV infection (PLWH, aged 50-70 years, n = 22) were enrolled in this cross-sectional pilot study. Metagenomic analysis of fecal microbiome using 16S Ribosomal ribonucleic acid gene sequencing and metabolomics analysis of plasma using mass spectrometry with a reverse-phase iquid chromatography tandem mass spectrometry were performed. Statistical analyses included the univariate linear regression and Spearman correlation analyses.

RESULTS

Age-associated changes in plasma levels of key neuroactive TRP metabolites, serotonin and KYN, were seen in PLWH. Specifically, we observed age-dependent decreases in serotonin and increases in KYN and KYN-to-TRP ratio, indicative of dysfunctional TRP metabolism. Furthermore, the gut dysbiosis seen in older PLWH is characterized by a reduction of Firmicutes/Bacteroidetes ratio and butyrate-producing microbial families Lachnospiraceae and Lactobacillaceae. Of importance, correspondent with gut dysbiosis, increasing age was significantly associated with decreased plasma butyrate levels, which in turn correlated positively with serotonin and negatively with KYN/TRP ratio.

CONCLUSIONS

Age-dependent gut microbial dysbiosis distinguished by a decrease in butyrogenic potential is a key pathogenic feature associated with the shift in TRP metabolism from serotonin to KYN in older PLWH.

Cerebrospinal fluid metabolomics: detection of neuroinflammation in human central nervous system disease

The high morbidity and mortality of neuroinflammatory diseases drives significant interest in understanding the underlying mechanisms involved in the innate and adaptive immune response of the central nervous system (CNS). Diagnostic biomarkers are important to define treatable neuroinflammation. Metabolomics is a rapidly evolving research area offering novel insights into metabolic pathways, and elucidation of reliable metabolites as biomarkers for diseases. This review focuses on the emerging literature regarding the detection of neuroinflammation using cerebrospinal fluid (CSF) metabolomics in human cohort studies. Studies of classic neuroinflammatory disorders such as encephalitis, CNS infection and multiple sclerosis confirm the utility of CSF metabolomics. Additionally, studies in neurodegeneration and neuropsychiatry support the emerging potential of CSF metabolomics to detect neuroinflammation in common CNS diseases such as Alzheimer's disease and depression. We demonstrate metabolites in the tryptophan-kynurenine pathway, nitric oxide pathway, neopterin and major lipid species show moderately consistent ability to differentiate patients with neuroinflammation from controls. Integration of CSF metabolomics into clinical practice is warranted to improve recognition and treatment of neuroinflammation.

Abnormal Tryptophan Metabolism in HIV and Mycobacterium tuberculosis Infection

Host metabolism has recently gained more attention for its roles in physiological functions and pathologic conditions. Of these, metabolic tryptophan disorders generate a pattern of abnormal metabolites that are implicated in various diseases. Here, we briefly highlight the recent advances regarding abnormal tryptophan metabolism in HIV and Mycobacterium tuberculosis infection and discuss its potential impact on immune regulation, disease progression, and neurological disorders. Finally, we also discuss the potential for metabolic tryptophan interventions toward these infectious diseases.

Cerebrospinal fluid metabolites in tryptophan-kynurenine and nitric oxide pathways: biomarkers for acute neuroinflammation

AIM

To explore the cerebrospinal fluid (CSF) metabolite features in acute neuroinflammatory diseases and identify potential biomarkers to diagnose and monitor neuroinflammation.

METHOD

A cohort of 14 patients (five females, nine males; mean [median] age 7y 9mo [9y], range 6mo-13y) with acute encephalitis (acute disseminated encephalomyelitis n=6, unknown suspected viral encephalitis n=3, enteroviral encephalitis n=2, seronegative autoimmune encephalitis n=2, herpes simplex encephalitis n=1) and age-matched non-inflammatory neurological disease controls (n=14) were investigated using an untargeted metabolomics approach. CSF metabolites were analyzed with liquid chromatography coupled to high resolution mass spectrometry, followed by subsequent multivariate and univariate statistical methods.

RESULTS

A total of 35 metabolites could be discriminated statistically between the groups using supervised orthogonal partial least squares discriminant analysis and analysis of variance. The tryptophan-kynurenine pathway contributed nine key metabolites. There was a statistical increase of kynurenine, quinolinic acid, and anthranilic acid in patients with encephalitis, whereas tryptophan, 3-hydroxyanthrnailic acid, and kynurenic acid were decreased. The nitric oxide pathway contributed four metabolites, with elevated asymmetric dimethylarginine and argininosuccinic acid, and decreased arginine and citrulline in patients with encephalitis. An increase in the CSF kynurenine/tryptophan ratio (p<0.001), anthranilic acid/3-hydroxyanthranilic acid ratio (p<0.001), asymmetric dimethylarginine/arginine ratio (p<0.001), and neopterin (p<0.001) strongly predicted neuroinflammation.

INTERPRETATION

The combination of alterations in the tryptophan-kynurenine pathway, nitric oxide pathway, and neopterin represent a useful potential panel for neuroinflammation and holds potential for clinical translation practice.

WHAT THIS PAPER ADDS

The kynurenine/tryptophan and anthranilic acid/3-hydroxyanthranilic acid ratios hold great potential as biomarkers of neuroinflammation. Elevation of the asymmetric dimethylarginine/arginine ratio in acute brain inflammation shows dysregulation of the nitric oxide pathway.

Tryptophan depletion predicts lower positive affect in sexual minority men living with HIV who use methamphetamine

This longitudinal study with 76 sexual minority men living with HIV who use methamphetamine examined whether dysregulation of essential amino acid precursors for neurotransmitters at baseline predicted positive and negative affect at 15 months. After controlling for covariates including baseline positive affect, a higher baseline kynurenine/tryptophan (K/T) ratio independently predicted lower positive affect at 15 months (β = - 18.31; 95% CI = - 35.35, - 1.27; p = 0.036). Future clinical research should examine whether bio-behavioral interventions targeting tryptophan degradation could optimize treatments for people living with co-occurring HIV and stimulant use disorders.

Impact of extended-release niacin on immune activation in HIV-infected immunological non-responders on effective antiretroviral therapy

BACKGROUND

Background: Tryptophan (Trp) catabolism into immunosuppressive kynurenine (Kyn) is involved in immune dysregulation during HIV infection. Niacin (vitamin B3) could control the excess of tryptophan depletion and represents a potential strategy to improve immune functions and CD4 count recovery in immunological non-responder HIV-infected individuals on antiretroviral therapy (ART).

METHODS

Methods: In the CTN PT006 phase 2 pilot randomized trial, 20 adults on ART with CD4 ≤ 350 cells/µl, despite an undetectable viral load (VL) for at least 3 months, received 2000 mg of extended-release (ER)-niacin orally once daily for 24 weeks. Side effects, VL, CD4/CD8 counts, lipid profile, T-cell activation and senescence, Tregs and Th17 cell frequencies, Kyn/Trp ratio, and levels of IL-6, IP-10, sST2, I-FABP, and LBP were assessed following ER-niacin treatment.

RESULTS

Results: Thirteen participants completed the study. Treatment was interrupted in 4 patients due to loss of follow-up or personal reasons and 3 patients were discontinued due to comorbidity risks. All participants maintained a VL < 40 copies/ml, while ER-niacin did not affect CD4 and CD8 cell counts. Plasma levels of triglycerides, total, and LDL cholesterol significantly decreased, following ER-niacin treatment. ER-niacin also diminished Kyn plasma levels and slightly decreased CD4 T-cell activation. However, no improvement in CD8 subsets, Kyn/Trp ratio, Th17/Treg balance, and plasma inflammatory markers was observed.

CONCLUSIONS

Conclusions: Although ER-niacin combined with ART was well-tolerated among immune non-responders and decreased plasma lipids, it did not improve systemic inflammation, Kyn/Trp ratio, and CD4 cell recovery. Overall, ER-niacin was not effective to overcome chronic inflammation in PLWH.

Tryptophan degradation is associated with risk-taking propensity in methamphetamine users with treated HIV infection

Few studies have examined neuroimmune pathways that could contribute to impulsivity in people living with HIV who use substances. Eighty-four methamphetamine-using, sexual minority men with an undetectable HIV viral load were administered the Balloon Analogue Risk Task (BART), a behavioral measure of risk-taking propensity. We examined the associations between kynurenine/tryptophan ratio and phenylalanine/tyrosine ratio with BART scores using multiple linear regression. A higher kynurenine/tryptophan ratio was independently associated with greater BART scores (beta = 0.25; 95% CI = 0.05-1.23; p = 0.034). The phenylalanine/tyrosine ratio was not significantly associated with BART scores. Findings support the need for further research to elucidate the neuroimmune mechanisms linking tryptophan degradation with impulsivity to catalyze the development novel pharmacologic treatments for people living with HIV who use methamphetamine.

Modulation of Phenylalanine and Tyrosine Metabolism in HIV-1 Infected Patients with Neurocognitive Impairment: Results from a Clinical Trial

To investigate the effects of oral bacteriotherapy on intestinal phenylalanine and tyrosine metabolism, in this longitudinal, double-arm trial, 15 virally suppressed HIV+ individuals underwent blood and fecal sample collection at baseline and after 6 months of oral bacteriotherapy. A baseline fecal sample was collected from 15 healthy individuals and served as control group for the baseline levels of fecal phenylalanine and tyrosine. CD4 and CD8 immune activation (CD38⁺) was evaluated by flow cytometry. Amino acid evaluation on fecal samples was conducted by Proton Nuclear Magnetic Resonance. Results showed that HIV+ participants displayed higher baseline phenylalanine/tyrosine ratio values than healthy volunteers. A significand reduction in phenylalanine/tyrosine ratio and peripheral CD4⁺ CD38⁺ activation was observed at the end of oral bacteriotherapy. In conclusion, probiotics beneficially affect the immune activation of HIV+ individuals. Therefore, the restoration of intestinal amino acid metabolism could represent the mechanisms through which probiotics exert these desirable effects.

Evaluation of serum amino acids and non-enzymatic antioxidants in drug-naïve first-episode major depressive disorder

BACKGROUND

The alterations of biological markers are thought to be effective tools to understand the pathophysiology and management of major depressive disorder (MDD). A lot of researches has implied many markers for depression, but any of them fully discovered the association between the markers and depression. The present study investigated the serum levels of amino acids and non-enzymatic antioxidants in major depression, and also explained their association with depression.

METHODS

This study examined 247 MDD patients and 248 healthy controls (HCs) matched by age and sex. The Hamilton Depression Rating Scale (Ham-D) was used to all the participants to measure the severity of depression. Quantification of serum amino acids, vitamin A and E were carried out using the HPLC system whereas vitamin C levels were measured by UV-spectrophotometer. All the statistical analysis was performed by SPSS statistical software (version 23.0). The independent sample t-test, the Mann-Whitney U test, and the Fisher's exact test were applied to detect the group differences where a Bonferroni correction applied to the p value.

RESULTS

It was observed that serum levels of four amino acids (methionine, phenylalanine, tryptophan, and tyrosine) along with three non-enzymatic antioxidants (vitamin A, E, and C) were significantly dropped in MDD patients compared to HCs (Cohen's d (d): - 0.45, - 0.50, - 0.68, - 0.21, - 0.27, - 0.65, and - 0.24, respectively). Furthermore, Ham-D scores of cases were negatively correlated with serum levels of methionine (r = - 0.155, p = 0.015) and tyrosine (r = - 0.172, p = 0.007).

CONCLUSION

The present study suggests that lowered serum methionine, phenylalanine, tryptophan, tyrosine, and non-enzymatic antioxidants are associated with depression. The reduction of these parameters in MDD patients may be the consequence, and not the cause, of major depression.

Pathogenesis of Aging and Age-related Comorbidities in People with HIV: Highlights from the HIV ACTION Workshop

People with HIV (PWH) experience accentuated biological aging, as defined by markers of inflammation, immune dysfunction, and the epigenetic clock. They also have an elevated risk of multiple age-associated comorbidities. To discuss current knowledge, research gaps, and priorities in aging and age-related comorbidities in treated HIV infection, the NIH program staff organized a workshop held in Bethesda, Maryland in September 2019. This review article describes highlights of discussions led by the Pathogenesis/Basic Science Research working group that focused on three high priority topics: immunopathogenesis; the microbiome/virome; and aging and senescence. We summarize knowledge in these fields and describe key questions for research on the pathogenesis of aging and age-related comorbidities in PWH. Understanding the drivers and mechanisms underlying accentuated biological aging is a high priority that will help identify potential therapeutic targets to improve healthspan in older PWH.

Serum Metabolic Profiling Reveals the Antidepressive Effects of the Total Iridoids of Valeriana jatamansi Jones on Chronic Unpredictable Mild Stress Mice

Background

Depression is a long-term complex psychiatric disorder, and its etiology remains largely unknown. Valeriana jatamansi Jones ex Roxb (V. jatamansi) is used in the clinic for the treatment of depression, but there are insufficient reports of its antidepressive mechanisms and a poor understanding of its endogenous substance-related metabolism. The objective of this study was to identify biomarkers related to depression in serum samples and evaluate the antidepressive effects of the iridoid-rich fraction of V. jatamansi (IRFV) in a chronic unpredictable mild stress (CUMS) mouse model.

Methods

Here, CUMS was used to establish a mouse model of depression. Behavioral and biochemical indicators were investigated to evaluate the pharmacodynamic effects. A comprehensive serum metabolomics study by nuclear magnetic resonance (NMR) approach was applied to investigate the pharmacological mechanism of IRFV in CUMS mouse. Subsequently, we used multivariate statistical analysis to identify metabolic markers, such as principal component analysis (PCA) and orthogonal projection to latent structure with discriminant analysis (OPLS-DA), to distinguish between the CUMS mouse and the control group.

Results

After IRFV treatment, the immobility time, sucrose preference, and monoamine neurotransmitter were improved. PCA scores showed clear differences in metabolism between the CUMS group and control group. The PLS-DA or OPLS-DA model exhibited 26 metabolites as biomarkers to distinguish between the CUMS mice and the control mouse. Moreover, IRFV could significantly return 21 metabolites to normal levels.

Conclusion

The results confirmed that IRFV exerted an antidepressive effect by regulating multiple metabolic pathways, including the tricarboxylic acid cycle, the synthesis of neurotransmitters, and amino acid metabolism. These findings provide insights into the antidepressive mechanisms of IRFV.

Low Neuroactive Steroids Identifies a Biological Subtype of Depression in Adults with Human Immunodeficiency Virus on Suppressive Antiretroviral Therapy

Background

The prevalence and mortality risk of depression in people with human immunodeficiency virus (HIV) infection receiving antiretroviral therapy (ART) is higher than in the general population, yet biomarkers for therapeutic targeting are unknown. In the current study, we aimed to identify plasma metabolites associated with depressive symptoms in people with HIV receiving ART.

Methods

This is a prospective study of ART-treated HIV-infected adults with or without depressive symptoms assessed using longitudinal Beck Depression Inventory scores. Plasma metabolite profiling was performed in 2 independent cohorts (total n = 99) using liquid and gas chromatography and tandem mass spectrometry.

Results

Participants with depressive symptoms had lower neuroactive steroids (dehydroepiandrosterone sulfate [DHEA-S], androstenediols, and pregnenolone sulfate) compared with those without depressive symptoms. The cortisol/DHEA-S ratio, an indicator of hypothalamic-pituitary-adrenal axis imbalance, was associated with depressive symptoms (P < .01) because of low DHEA-S levels, whereas cortisol was similar between groups. The odds of having depressive symptoms increased with higher cortisol/DHEA-S ratios (adjusted odds ratio, 2.5 per 1-unit increase in z score; 95% confidence interval, 1.3–4.7), independent of age and sex. The kynurenine-to-tryptophan ratio showed no significant associations.

Conclusions

These findings suggest that altered neuroactive steroid metabolism may contribute to the pathophysiological mechanisms of depression in ART-treated HIV-infected adults, representing a potential biological pathway for therapeutic targeting.

Brain PET Imaging: Value for Understanding the Pathophysiology of HIV-associated Neurocognitive Disorder (HAND)

PURPOSE OF REVIEW

The purpose of this review is to summarize recent developments in PET imaging of neuropathologies underlying HIV-associated neurocognitive dysfunction (HAND). We concentrate on the recent post antiretroviral era (ART), highlighting clinical and preclinical brain PET imaging studies.

RECENT FINDINGS

In the post ART era, PET imaging has been used to better understand perturbations of glucose metabolism, neuroinflammation, the function of neurotransmitter systems, and amyloid/tau protein deposition in the brains of HIV-infected patients and HIV animal models. Preclinical and translational findings from those studies shed a new light on the complex pathophysiology underlying HAND. The molecular imaging capabilities of PET in neuro-HIV are great complements for structural imaging modalities. Recent and future PET imaging studies can improve our understanding of neuro-HIV and provide biomarkers of disease progress that could be used as surrogate endpoints in the evaluation of the effectiveness of potential neuroprotective therapies.

Tryptophan Metabolism Activates Aryl Hydrocarbon Receptor-Mediated Pathway To Promote HIV-1 Infection and Reactivation

Multiple cellular metabolic pathways are altered by HIV-1 infection, with an impact on immune activation, inflammation, and acquisition of non-AIDS comorbid diseases. The dysfunction of tryptophan (Trp) metabolism has been observed clinically in association with accelerated HIV-1 pathogenesis, but the underlying mechanism remains unknown. In this study, we demonstrated that the aryl hydrocarbon receptor (AHR), a ligand-activated transcription factor, is activated by Trp metabolites to promote HIV-1 infection and reactivation. AHR directly binds to the HIV-1 5' long terminal repeat (5'-LTR) at the molecular level to activate viral transcription and infection, and AHR activation by Trp metabolites increases its nuclear translocation and association with the HIV 5'-LTR; moreover, the binding of AHR with HIV-1 Tat facilitates the recruitment of positive transcription factors to viral promoters. These findings not only elucidate a previously unappreciated mechanism through which cellular Trp metabolites affect HIV pathogenesis but also suggest that a downstream target AHR may be a potential target for modulating HIV-1 infection.IMPORTANCE Cellular metabolic pathways that are altered by HIV-1 infection may accelerate disease progression. Dysfunction in tryptophan (Trp) metabolism has been observed clinically in association with accelerated HIV-1 pathogenesis, but the mechanism responsible was not known. This study demonstrates that Trp metabolites augment the activation of aryl hydrocarbon receptor (AHR), a ligand-activated transcription factor, to promote HIV-1 infection and transcription. These findings not only elucidate a previously unappreciated mechanism through which cellular Trp metabolites affect HIV pathogenesis but also suggest that a downstream target AHR may be a potential target for modulating HIV-1 infection.

Structural Brain Abnormalities in Successfully Treated HIV Infection: Associations With Disease and Cerebrospinal Fluid Biomarkers

Background

Brain structural abnormalities have been reported in persons living with human immunodeficiency virus (HIV; PLWH) who are receiving suppressive combination antiretroviral therapy (cART), but their pathophysiology remains unclear.

Methods

We investigated factors associated with brain tissue volumes and white matter microstructure (fractional anisotropy) in 134 PLWH receiving suppressive cART and 79 comparable HIV-negative controls, aged ≥45 years, from the Comorbidity in Relation to AIDS cohort, using multimodal neuroimaging and cerebrospinal fluid biomarkers.

Results

Compared with controls, PLWH had lower gray matter volumes (-13.7 mL; 95% confidence interval, -25.1 to -2.2) and fractional anisotropy (-0.0073; 95% confidence interval, -.012 to -.0024), with the largest differences observed in those with prior clinical AIDS. Hypertension and the soluble CD14 concentration in cerebrospinal fluid were associated with lower fractional anisotropy. These associations were independent of HIV serostatus (Pinteraction = .32 and Pinteraction = .59, respectively) and did not explain the greater abnormalities in brain structure in relation to HIV infection.

Conclusions

The presence of lower gray matter volumes and more white matter microstructural abnormalities in well-treated PLWH partly reflect a combination of historical effects of AIDS, as well as the more general influence of systemic factors, such as hypertension and ongoing neuroinflammation. Additional mechanisms explaining the accentuation of brain structure abnormalities in treated HIV infection remain to be identified.

HPLC method for the assessment of tryptophan metabolism utilizing separate internal standard for each detector

The development of a validated method, applicable for the measurement of tryptophan (TRP) and serotonin (5-HT), and that of the neuroprotective branch of the kynurenine pathway from several different biological matrices, including mouse brain, is described. Following the spectral analysis of the metabolites, they were quantified with reversed-phase high-performance liquid chromatography (HPLC), using separate internal standards (ISs) for UV (3-nitro-L-tyrosine) and fluorescent (the newly utilized 4-hydroxyquinazoline-2-carboxylic acid) detectors. With regard to validation parameters, selectivity, linearity, limit of detection, limit of quantification, precision and recovery were determined. Although the linearity ranges were different for the assessed matrices, the correlation coefficient was >0.999 in each case. Furthermore, good intra- and inter-day precision values were obtained with coefficient of variation <5%, and bias <6.5% (except the 5-HT level in brain samples), respectively. The recoveries varied between 82.5% and 116%. The currently developed methods yield opportunities for the assessment of concentration changes in the TRP metabolism from a wide range of biological matrices, therefore they may well be utilized in future clinical and preclinical studies, especially in view that so many metabolites with the application of ISs have not been detected from mouse brain with such a simple HPLC method before.

Altered Immunity and Microbial Dysbiosis in Aged Individuals With Long-Term Controlled HIV Infection

The introduction of highly active antiretroviral therapy (HAART) resulted in a significant increase in life expectancy for HIV patients. Indeed, in 2015, 45% of the HIV+ individuals in the United States were ≥55 years of age. Despite improvements in diagnosis and treatment of HIV infection, geriatric HIV+ patients suffer from higher incidence of comorbidities compared to age-matched HIV- individuals. Both chronic inflammation and dysbiosis of the gut microbiome are believed to be major contributors to this phenomenon, however carefully controlled studies investigating the impact of long-term (>10 years) controlled HIV (LTC-HIV) infection are lacking. To address this question, we profiled circulating immune cells, immune mediators, and the gut microbiome from elderly (≥55 years old) LTC-HIV+ and HIV- gay men living in the Palm Springs area. LTC-HIV+ individuals had lower frequency of circulating monocytes and CD4+ T-cells, and increased frequency CD8+ T-cells. Moreover, levels of systemic INFγ and several growth factors were increased while levels of IL-2 and several chemokines were reduced. Upon stimulation, immune cells from LTC-HIV+ individuals produced higher levels of pro-inflammatory cytokines. Last but not least, the gut microbiome of LTC-HIV+ individuals was enriched in bacterial taxa typically found in the oral cavity suggestive of loss of compartmentalization, while levels of beneficial butyrate producing taxa were reduced. Additionally, prevalence of Prevotella negatively correlated with CD4+ T-cells numbers in LTC-HIV+ individuals. These results indicate that despite long-term adherence and undetectable viral loads, LTC-HIV infection results in significant shifts in immune cell frequencies and gut microbial communities.

Tryptophan metabolism and its relationship with central nervous system toxicity in people living with HIV switching from efavirenz to dolutegravir

The mechanisms underlying central nervous system (CNS) toxicities in antiretroviral-treated persons living with HIV (PLWH) remain elusive. We investigated the associations between markers of tryptophan metabolism and measurements of CNS toxicity in PLWH. In a prospective study, virologically suppressed PLWH receiving efavirenz-containing antiretroviral regimens with ongoing CNS toxicity were switched to dolutegravir-containing regimens and followed up for 12 weeks. Plasma tryptophan and kynurenine concentrations and the kynurenine/tryptophan ratio were calculated. Ten CNS toxicities were graded according to the ACTG adverse events scale. Scores ranged from 0 (none) to 3 (severe) and were summed, giving a total from 0 to 30. Paired-samples t tests and linear mixed model analyses were conducted to assess changes in, and relationships between, laboratory and clinical parameters. Mean kynurenine plasma concentration increased from baseline to week 12 (2.15 to 2.50 μmol/L, p = 0.041). No significant changes were observed for tryptophan (54.74 to 56.42 μmol/L, p = 1.000) or kynurenine/tryptophan ratio (40.37 to 41.08 μmol/L, p = 0.276). Mean CNS toxicity score decreased from 10.00 to 4.63 (p < 0.001). Plasma kynurenine concentration correlated with CNS toxicity score: for every 1 μmol/L increase in kynurenine concentration observed, a 1.7 point decrease was observed in CNS toxicity score (p < 0.038). A similar trend was observed for the kynurenine/tryptophan ratio: for every 1 μmol/mmol increase observed in kynurenine/tryptophan ratio, a 0.1 point decrease was observed in CNS toxicity score (p = 0.054). Switching from efavirenz to dolutegravir was associated with increases in plasma kynurenine concentration and improvements in CNS toxicity scores. Underlying mechanisms explaining the rise in kynurenine concentrations need to be established.

Low Serum Tryptophan Levels as an Indicator of Global Cognitive Performance in Nondemented Women over 50 Years of Age

Aging is a physiological decline process. The number of older adults is growing around the world; therefore, the incidence of cognitive impairment, dementia, and other diseases related to aging increases. The main cellular factors that converge in the aging process are mitochondrial dysfunction, antioxidant impairment, inflammation, and immune response decline, among others. In this context, these cellular changes have an influence on the kynurenine pathway (KP), the main route of tryptophan (Trp) catabolism. KP metabolites have been involved in the aging process and neurodegenerative diseases. Although there are changes in the metabolite levels with age, at this time, there is no study that has evaluated cognitive decline as a consequence of Trp catabolism fluctuation in aging. The aim of this study was to evaluate the relation between the changes in Trp catabolism and cognitive impairment associated with age through KP metabolites level alterations in women over 50 years of age. Seventy-seven nondemented women over 50 years old were examined with a standardized cognitive screening evaluation in Spanish language (Neuropsi), Beck anxiety inventory (BAI), and the geriatric depression scale (GDS). Also, serum levels of Trp, kynurenine (Kyn), kynurenic acid (KYNA), and 3-hydroykynurenine (3-HK) and the glutathione ratio (GSH/GSSG) were measured. Results showed a negative correlation between age and Trp levels and a positive correlation between age and KYNA/Trp and 3-HK/Trp ratios. The level of cognitive impairment showed a significant positive association with age and with kynurenine pathway activation and a significant negative correlation with Trp levels. The GSH/GSSG ratio correlated positively with Trp levels and negatively with Kyn/Trp and 3-HK/Trp ratios. The depression score correlated negatively with Trp and positively with the 3-HK/Trp ratio. We concluded that KP activation increases with age and it is strongly associated with the level of cognition performance in nondemented women over 50 years of age.

Metabolic analysis of the antidepressive effects of Yangxinshi Tablet in a vascular depression model in mice

In recent years, vascular depression has become the focus of international attention. Yangxinshi Tablet (YXST) is usually used in cthe linic for the treatment of arrhythmia and heart failure, but we found that it also has antidepressive effects. The objective of the study was to identify biomarkers related to vascular depression in hippocampus and explore the antidepressive effects of YXST on the mouse model. Untargeted metabolomics based on UHPLC-Q-TOF/MS was applied to identify significantly differential biomarkers between the model group and control group. Unsupervised principal component analysis (PCA) was used to scan the tendency of groups and partial least squares-discriminant analysis (PLS-DA) to distinguish between the vascular depressive mice and the sham. PCA stores showed clear differences in metabolism between the vascular depressive mice and sham groups. The PLS-DA model exhibited 38 metabolites as the biomarkers to distinguish the vascular depressive mice and the sham. Further, YXST significantly regulated 22 metabolites to normal levels. The results suggested that YXST has a comprehensive antidepressive effect on vascular depression via regulation of multiple metabolic pathways including amino acid, the tricarboxylic acid cycle and phosphoglyceride metabolisms. These findings provide insight into the pathophysiological mechanism underlying vascular depression and the mechanism of YXST.

Tryptophan status in autism spectrum disorder and the influence of supplementation on its level

Recent reports show that the worldwide incidence of autism spectrum disorder (ASD) is dramatically increasing, although ASD etiology and pathogenesis are still far to be fully elucidated. Some dietary-derived essential compounds, such as the amino acid tryptophan, appear to be impaired in patients with ASD. Tryptophan (Trp) plays a significant role in the human organism and serves as a precursor for a wide range of bioactive compounds, including major neurotransmitters. Research indicates that tryptophan might be deficient in subjects with ASD. Deficiency in the tryptophan level can be retrieved by investigating Trp levels or its major metabolite kynurenine in urines. The purpose of the present study is to quantify tryptophan content in urine samples (n = 236) of ASD patients, who underwent a supplemented dietary panel with B vitamins and magnesium, compared to controls (without this diet regimen). The samples were analyzed with gas chromatography-mass spectrometry. Additionally, the correlation between body mass index (BMI) and the level of this amino acid in urine was accomplished. Basic parameters of urine samples were also evaluated. Statistical evaluations in the concentration of tryptophan in ASD patients with different severity of symptoms were reported. A significant difference in tryptophan levels in all groups was observed. Supplementation with B vitamins and magnesium has an influence on the Trp concentration. Furthermore, no correlation between BMI and tryptophan levels was found. These results assess that the Trp level in ASD subjects is critical and that intake of B vitamins and magnesium with diet might influence its metabolic homeostasis.

Age Drives Distortion of Brain Metabolic, Vascular and Cognitive Functions, and the Gut Microbiome

Advancing age is the top risk factor for the development of neurodegenerative disorders, including Alzheimer's disease (AD). However, the contribution of aging processes to AD etiology remains unclear. Emerging evidence shows that reduced brain metabolic and vascular functions occur decades before the onset of cognitive impairments, and these reductions are highly associated with low-grade, chronic inflammation developed in the brain over time. Interestingly, recent findings suggest that the gut microbiota may also play a critical role in modulating immune responses in the brain via the brain-gut axis. In this study, our goal was to identify associations between deleterious changes in brain metabolism, cerebral blood flow (CBF), gut microbiome and cognition in aging, and potential implications for AD development. We conducted our study with a group of young mice (5-6 months of age) and compared those to old mice (18-20 months of age) by utilizing metabolic profiling, neuroimaging, gut microbiome analysis, behavioral assessments and biochemical assays. We found that compared to young mice, old mice had significantly increased levels of numerous amino acids and fatty acids that are highly associated with inflammation and AD biomarkers. In the gut microbiome analyses, we found that old mice had increased Firmicutes/Bacteroidetes ratio and alpha diversity. We also found impaired blood-brain barrier (BBB) function and reduced CBF as well as compromised learning and memory and increased anxiety, clinical symptoms often seen in AD patients, in old mice. Our study suggests that the aging process involves deleterious changes in brain metabolic, vascular and cognitive functions, and gut microbiome structure and diversity, all which may lead to inflammation and thus increase the risk for AD. Future studies conducting comprehensive and integrative characterization of brain aging, including crosstalk with peripheral systems and factors, will be necessary to define the mechanisms underlying the shift from normal aging to pathological processes in the etiology of AD.

Major Developments in the Design of Inhibitors along the Kynurenine Pathway

Disrupted kynurenine pathway (KP) metabolism has been implicated in the progression of neurodegenerative disease, psychiatric disorders and cancer. Modulation of enzyme activity along this pathway may therefore offer potential new therapeutic strategies for these conditions. Considering their prominent positions in the KP, the enzymes indoleamine 2,3-dioxygenase, kynurenine 3-monooxygenase and kynurenine aminotransferase, appear the most attractive targets. Already, increasing interest in this pathway has led to the identification of a number of potent and selective enzyme inhibitors with promising pre-clinical data and the elucidation of several enzyme crystal structures provides scope to rationalize the molecular mechanisms of inhibitor activity. The field seems poised to yield one or more inhibitors that should find clinical utility.