The immune-kynurenine pathway in social anxiety disorder

Priming of hippocampal microglia by IFN-γ/STAT1 pathway impairs social memory in mice

Social behavior is inextricably linked to the immune system. Although IFN-γ is known to be involved in social behavior, yet whether and how it encodes social memory remains unclear. In the current study, we injected with IFN-γ into the lateral ventricle of male C57BL/6J mice, and three-chamber social test was used to examine the effects of IFN-γ on their social preference and social memory. The morphology of microglia in the hippocampus, prelimbic cortex and amygdala was examined using immunohistochemistry, and the phenotype of microglia were examined using immunohistochemistry and enzyme-linked immunosorbent assays. The IFN-γ-injected mice were treated with lipopolysaccharide, and effects of IFN-γ on behavior and microglial responses were evaluated. STAT1 pathway and microglia-neuron interactions were examined in vivo or in vitro using western blotting and immunohistochemistry. Finally, we use STAT1 inhibitor or minocycline to evaluated the role of STAT1 in mediating the microglial priming and effects of primed microglia in IFN-γ-induced social dysfunction. We demonstrated that 500 ng of IFN-γ injection results in significant decrease in social index and social novelty recognition index, and induces microglial priming in hippocampus, characterized by enlarged cell bodies, shortened branches, increased expression of CD68, CD86, CD74, CD11b, CD11c, CD47, IL-33, IL-1β, IL-6 and iNOS, and decreased expression of MCR1, Arg-1, IGF-1 and BDNF. This microglia subpopulation is more sensitive to LPS challenge, which characterized by more significant morphological changes and inflammatory responses, as well as induced increased sickness behaviors in mice. IFN-γ upregulated pSTAT1 and STAT1 and promoted the nuclear translocation of STAT1 in the hippocampal microglia and in the primary microglia. Giving minocycline or STAT1 inhibitor fludarabin blocked the priming of hippocampal microglia induced by IFN-γ, ameliorated the dysfunction in hippocampal microglia-neuron interactions and synapse pruning by microglia, thereby improving social memory deficits in IFN-γ injected mice. IFN-γ initiates STAT1 pathway to induce priming of hippocampal microglia, thereby disrupts hippocampal microglia-neuron interactions and neural circuit link to social memory. Blocking STAT1 pathway or inhibiting microglial priming may be strategies to reduce the effects of IFN-γ on social behavior.

Social fear extinction susceptibility is associated with Microbiota-Gut-Brain axis alterations

Social anxiety disorder is a common psychiatric condition that severely affects quality of life of individuals and is a significant societal burden. Although many risk factors for social anxiety exist, it is currently unknown how social fear sensitivity manifests biologically. Furthermore, since some individuals are resilient and others are susceptible to social fear, it is important to interrogate the mechanisms underpinning individual response to social fear situations. The microbiota-gut-brain axis has been associated with social behaviour, has recently been linked with social anxiety disorder, and may serve as a therapeutic target for modulation. Here, we assess the potential of this axis to be linked with social fear extinction processes in a murine model of social anxiety disorder. To this end, we correlated differential social fear responses with microbiota composition, central gene expression, and immune responses. Our data provide evidence that microbiota variability is strongly correlated with alterations in social fear behaviour. Moreover, we identified altered gene candidates by amygdalar transcriptomics that are linked with social fear sensitivity. These include genes associated with social behaviour (Armcx1, Fam69b, Kcnj9, Maoa, Serinc5, Slc6a17, Spata2, and Syngr1), inflammation and immunity (Cars, Ckmt1, Klf5, Maoa, Map3k12, Pex5, Serinc5, Sidt1, Spata2), and microbe-host interaction (Klf5, Map3k12, Serinc5, Sidt1). Together, these data provide further evidence for a role of the microbiota-gut-brain axis in social fear responses.

Unlocking the potential of the 3-hydroxykynurenine/kynurenic acid ratio: a promising biomarker in adolescent major depressive disorder

Metabolites disruptions in tryptophan (TRP) and kynurenine pathway (KP) are believed to disturb neurotransmitter homeostasis and contribute to depressive symptoms. This study aims to investigate serum levels of KP metabolites in adolescent major depressive disorder (AMDD), and examine their relationship with depression severities. Liquid chromatography-tandem mass spectrometry (LC-MS/MS) was used to analyze serum levels of TRP, kynurenic acid (KYNA), kynurenine (KYN), and 3-hydroxy-kynurenine (3-HK) in 143 AMDD participants and 98 healthy controls (HC). Clinical data, including Children's Depression Inventory (CDI) scores, were collected and analyzed using statistical methods, such as ANOVA, logistic regression, Receiver operating characteristic curve analysis and a significance level of p < 0.05 was used for all analyses. AMDD showed significantly decreased serum levels of KYNA (-25.5%), KYN (-14.2%), TRP (-11.0%) and the KYNA/KYN ratio (-11.9%) compared to HC (p < 0.01). Conversely, significant increases were observed in 3-HK levels (+50.4%), the 3-HK/KYNA ratio (+104.3%) and the 3-HK/KYN ratio (+93.0%) (p < 0.01). Logistic regression analysis identified increased level of 3-HK as a contributing factor to AMDD, while increased level of KYNA acted as a protective factor against AMDD. The 3-HK/KYNA ratio demonstrated an area under the curve (AUC) of 0.952. This study didn't explore AMDD's inflammatory status and its metabolites relationship explicitly. These findings indicate that metabolites of TRP and KP may play a crucial role in the pathogenesis of AMDD, emphasizing the potential of the 3-HK/KYNA ratio as a laboratory biomarker for early detection and diagnosis of AMDD.

Salivary CRP predicts treatment response to virtual reality exposure therapy for social anxiety disorder

BACKGROUND

Social anxiety disorder (SAD) places a profound burden on public health and individual wellbeing. Systemic inflammation may be important to the onset and maintenance of SAD, and anti-inflammatory treatments have shown promise in relieving symptoms of SAD. In the present study, we conducted secondary analyses on data from a randomized clinical trial to determine whether C-reactive protein (CRP) concentrations and social anxiety symptoms decreased over the course of virtual reality exposure therapy, and whether changes in social anxiety symptoms as a function of treatment varied as a function of CRP.

METHOD

Adult participants (N = 78) with a diagnosis of SAD (59 % female) were randomized to receive exposure therapy alone, or exposure therapy supplemented with scopolamine. Social anxiety symptoms, salivary CRP, and subjective units of distress were measured across three exposure therapy sessions, at a post-treatment extinction retest, and at a 1-month follow-up.

RESULTS

CRP decreased over the course of treatment, b = -0.03 (SE = 0.01), p =.02 95 %CI [-0.06, -0.004], as did all social anxiety symptom domains and subjective distress. Higher CRP was associated with greater decreases from pre-treatment to 1-month follow-up in fear, b = -0.45 (SE = 0.15), p =.004 95 %CI [-0.74, -0.15], and avoidance, b = -0.62 (SE = 0.19), p =.002 95 %CI [-1.01, -0.23], and in-session subjective distress from pre-treatment to post-treatment, b = -0.42 (SE = 0.21), p =.05 95 %CI [-0.83, -0.001]. However, declines in CRP were not correlated with declines in fear, r = -0.07, p =.61, or avoidance, r = -0.10, p =.49, within-persons.

CONCLUSIONS

Virtual reality exposure therapy may be associated with an improvement in systemic inflammation in patients with severe SAD. Pre-treatment CRP may also be of value in predicting which patients stand to benefit the most from this treatment.

Longitudinal associations of plasma kynurenines and ratios with anxiety and depression scores in colorectal cancer survivors up to 12 months post-treatment

INTRODUCTION

Colorectal cancer (CRC) survivors often experience neuropsychological symptoms, including anxiety and depression. Mounting evidence suggests a role for the kynurenine pathway in these symptoms due to potential neuroprotective and neurotoxic roles of involved metabolites. However, evidence remains inconclusive and insufficient in cancer survivors. Thus, we aimed to explore longitudinal associations of plasma tryptophan, kynurenines, and their established ratios with anxiety and depression in CRC survivors up to 12 months post-treatment.

METHODS

In 249 stage I-III CRC survivors, blood samples were collected at 6 weeks, 6 months, and 12 months post-treatment to analyze plasma concentrations of tryptophan and kynurenines using liquid-chromatography tandem-mass spectrometry (LC/MS-MS). At the same timepoints, anxiety and depression were assessed using the Hospital Anxiety and Depression Scale (HADS). Confounder-adjusted linear mixed models were used to analyze longitudinal associations. Sensitivity analyses with false discovery rate (FDR) correction were conducted to adjust for multiple testing.

RESULTS

Higher plasma tryptophan concentrations were associated with lower depression scores (β as change in depression score per 1 SD increase in the ln-transformed kynurenine concentration: -0.31; 95%CI: -0.56,-0.05), and higher plasma 3-hydroxyanthranilic acid concentrations with lower anxiety scores (-0.26; -0.52,-0.01). A higher 3-hydroxykynurenine ratio (HKr; the ratio of 3-hydroxykynurenine to the sum of kynurenic acid, xanthurenic acid, anthranilic acid, and 3-hydroxyanthranilic acid) was associated with higher depression scores (0.34; 0.04,0.63) and higher total anxiety and depression scores (0.53; 0.02,1.04). Overall associations appeared to be mainly driven by inter-individual associations, which were statistically significant for tryptophan with depression (-0.60; -1.12,-0.09), xanthurenic acid with total anxiety and depression (-1.04; -1.99,-0.10), anxiety (-0.51; -1.01,-0.01), and depression (-0.56; -1.08,-0.05), and kynurenic-acid-to-quinolinic-acid ratio with depression (-0.47; -0.93,-0.01). In sensitivity analyses, associations did not remain statistically significant after FDR adjustment.

CONCLUSION

We observed that plasma concentrations of tryptophan, 3-hydroxyanthranilic acid, xanthurenic acid, 3-hydroxykynurenine ratio, and kynurenic-acid-to-quinolinic-acid ratio tended to be longitudinally associated with anxiety and depression in CRC survivors up to 12 months post-treatment. Future studies are warranted to further elucidate the association of plasma kynurenines with anxiety and depression.

Microglial MyD88-dependent pathways are regulated in a sex specific manner in the context of HMGB1-induced anxiety

Chronic stress is a major risk factor for development and recurrence of anxiety disorders. Chronic stress has been shown to impact the immune system, causing microglial activation in the medial prefrontal cortex (mPFC), a brain region involved in the pathogenesis of anxiety. HMGB1 is both an established modulator of neuronal firing and a potent pro-inflammatory stimulus that is released from neuronal and non-neuronal cells following stress. HMGB1 in the context of stress acts as a danger associated molecular pattern (DAMP) instigating robust proinflammatory responses throughout the brain; so much so, that localized drug delivery of HMGB1 alters behavior in the absence of any other forms of stress i.e. social isolation, or behavioral stress models. Few studies have investigated the molecular mechanisms which underlie HMGB1 associated behavioral effects in a cell-specific manner. The aim of this study is to investigate cellular and molecular mechanisms underlying HMGB1 induced behavioral dysfunction with regards to cell-type specificity and potential sex differences. Here, we report that both male and female mice exhibited anxiety-like behavior following increased HMGB1 in the mPFC as well as changes in microglial morphology. However, only female mice showed microglial activation characterized by increased phagocytic capacity and decreased Tmem119 expression. Moreover, when measuring RNA from isolated microglia and non-microglial cells from the frontal cortex we found that female HMGB1 treated mice displayed a robust increase of RAGE and MyD88. Given these findings, to further investigate the underlying molecular mechanisms associated with HMGB1 induced anxiety-like behavior and microglia activation in mice, we used cKO (conditional knockout) mice with conditional deletion of MyD88 in microglia and repeated the paradigm. For males, we saw that the genetic manipulation did not prevent behavioral deficits in response to HMGB1 treatment. However, female cKO mice were protected from HMGB1- induced behavioral deficits. This study supports the hypothesis that the MyD88 signaling in microglia may be a crucial mediator of stress response in adult female mice.

Role of the immune-kynurenine pathway in treatment-resistant schizophrenia

BACKGROUND

The immune-inflammatory response system (IRS) and kynurenine pathway (KP) have been implicated in the pathophysiology of schizophrenia. Studies have shown inflammation-related effects on KP metabolism in patients with schizophrenia. This study investigated the relationship between KP metabolites, IRS, and the compensatory immune-regulatory reflex system (CIRS) in patients with treatment-resistant schizophrenia (TRS).

METHODS

Patients with (n = 53) and without TRS (n = 47), and healthy controls (HCs, n = 49) were enrolled. We quantified plasma levels of pro-inflammatory cytokines (interleukin [IL]-1β, IL-2, IL-6, soluble(s)IL-6 receptor, IL-8, IL-12, IL-17, IL-18, interferon-γ, and tumor necrosis factor[TNF]-α) and anti-inflammatory cytokines (IL-1 receptor antagonist, IL-4, IL-10, tumor growth factor [TGF]-β1, TGF-β2, soluble (s) IL-2 receptor subunit α, sIL-2 receptor subunit β, and sTNF-α receptor 1) and calculated the IRS/CIRS ratio. We also tested serum metabolites of the KP, including kynurenine (KYN), kynurenic acid (KYNA), and quinolinic acid (QUIN), along with the QUIN/KYNA ratio.

RESULTS

Patients with TRS had significantly higher IRS/CIRS ratio than non-TRS patients (p = 0.002) and HCs (p = 0.007), and significantly lower KYN (p = 0.001) and KYNA (p = 0.01) levels than HCs. Binary logistic regression analysis revealed that a younger age at illness onset (odds ratio [OR] = 0.91, p = 0.02) and a higher IRS/CIRS ratio (OR = 1.22; p = 0.007) were risk factors for patients with TRS. After further adjusted for age of onset, the QUIN/KYNA ratio (β = 0.97; p = 0.02) significantly moderated the relationship between IRS/CIRS and TRS, showing that in the higher QUIN/KYNA condition, higher IRS/CIRS ratio were significantly and more likely to be associated with patients with TRS (β = 0.12, z = 3.19, p = 0.001), whereas in the low QUIN/KYNA condition, the association between IRS/CIRS ratio and TRS was weak and insignificant.

CONCLUSIONS

The peripheral immune response was imbalanced in TRS and was preferentially directed towards the IRS compared to patients without TRS and healthy controls, which is likely to play a role in neurotoxicity. Additionally, peripheral KP activation was also imbalanced, as evidenced by significantly reduced KYN and KYNA levels in patients with TRS compared to healthy controls, but none of KP metabolisms were significantly difference in non-TRS patients compared to healthy controls. QUIN/KYNA ratio involving to the degree of activation of NMDA receptors, indicated the neurotoxic level of the KP activation. The interaction between IRS/CIRS and QUIN/KYNA ratio was significant in predicting TRS, and our findings suggest a potential role for the immune-kynurenine pathway in TRS pathogenesis.

The dangerous "West Coast Swing" by hyperglycaemia and chronic stress in the mouse hippocampus: Role of kynurenine catabolism

Growing epidemiological studies highlight a bi-directional relationship between depressive symptoms and diabetes mellitus. However, the detrimental impact of their co-existence on mental health suggests the need to treat this comorbidity as a separate entity rather than the two different pathologies. Herein, we characterized the peculiar mechanisms activated in mouse hippocampus from the concurrent development of hyperglycaemia, characterizing the different diabetes subtypes, and chronic stress, recognized as a possible factor predisposing to major depression. Our work demonstrates that kynurenine overproduction, leading to apoptosis in the hippocampus, is triggered in a different way depending on hyperglycaemia or chronic stress. Indeed, in the former, kynurenine appears produced by infiltered macrophages whereas, in the latter, peripheral kynurenine preferentially promotes resident microglia activation. In this scenario, QA, derived from kynurenine catabolism, appears a key mediator causing glutamatergic synapse dysfunction and apoptosis, thus contributing to brain atrophy. We demonstrated that the coexistence of hyperglycaemia and chronic stress worsened hippocampal damage through alternative mechanisms, such as GLUT-4 and BDNF down-expression, denoting mitochondrial dysfunction and apoptosis on one hand and evoking the compromission of neurogenesis on the other. Overall, in the degeneration of neurovascular unit, hyperglycaemia and chronic stress interacted each other as the partners of a "West Coast Swing" in which the leading role can be assumed alternatively by each partner of the dance. The comprehension of these mechanisms can open novel perspectives in the management of diabetic/depressed patients, but also in the understanding the pathogenesis of other neurodegenerative disease characterized by the compromission of hippocampal function.

Effects of different chronic restraint stress periods on anxiety- and depression-like behaviors and tryptophan-kynurenine metabolism along the brain-gut axis in C57BL/6N mice

Chronic restraint stress (CRS) is a widely used stimulus to induce anxiety- and depression-like behaviors, linked to alterations in tryptophan-kynurenine (TRP-KYN) metabolism in animals. This study assessed the effects of different CRS periods on anxiety- or depression-like behaviors and TRP-KYN metabolism along brain-gut axis in C57BL/6N mice. Results showed that one-week CRS decreased the open arm entries of mice in elevated plus maze and delayed latency of feeding in novelty suppressed feeding test. Four-week CRS reduced sucrose preference, increases forced swimming immobility time, and also induced anxiety-like behaviors of mice. UPLC-MS/MS analysis revealed decreased levels of the neurotoxic 3-hydroxykynurenine (3-HK) and quinolinic acid (QA), and an increase in the neuroprotective kynurenic acid (KA) in the hippocampus of one-week CRS mice; meanwhile, four-week CRS mice displayed a reduction in KA and increases in 3-HK and QA. In the colon, both one-week and four-week CRS mice exhibited significant reductions in 3-HK and QA, with a marked increase of KA exclusively in four-week CRS mice. Briefly, one-week CRS only induced anxiety-like behaviors with hippocampal neuroprotection in TRP-KYN metabolism, whereas four-week CRS caused anxiety- and depression-like behaviors with neurotoxicity. In the colon, during both CRS periods, KYN was metabolized in the direction of NAD+ production. However, four-week CRS triggered intestinal inflammation risk with increased KA. Summarily, slightly short-term stress has beneficial effects on mice, while prolonged chronic stress can lead to pathological changes. This study offers valuable insights into stress-induced emotional disturbances.

Social anxiety disorder-associated gut microbiota increases social fear

Social anxiety disorder (SAD) is a crippling psychiatric disorder characterized by intense fear or anxiety in social situations and their avoidance. However, the underlying biology of SAD is unclear and better treatments are needed. Recently, the gut microbiota has emerged as a key regulator of both brain and behaviour, especially those related to social function. Moreover, increasing data supports a role for immune function and oxytocin signalling in social responses. To investigate whether the gut microbiota plays a causal role in modulating behaviours relevant to SAD, we transplanted the microbiota from SAD patients, which was identified by 16S rRNA sequencing to be of a differential composition compared to healthy controls, to mice. Although the mice that received the SAD microbiota had normal behaviours across a battery of tests designed to assess depression and general anxiety-like behaviours, they had a specific heightened sensitivity to social fear, a model of SAD. This distinct heightened social fear response was coupled with changes in central and peripheral immune function and oxytocin expression in the bed nucleus of the stria terminalis. This work demonstrates an interkingdom basis for social fear responses and posits the microbiome as a potential therapeutic target for SAD.

Kynurenine, Kynurenic Acid, Quinolinic Acid and Interleukin-6 Levels in the Serum of Patients with Autism Spectrum Disorder

Background and Objectives: It is known that inflammatory processes play a role in the pathogenesis of autism spectrum disorder (ASD). It is also reported that immune activation induces the kynurenine pathway (KP), as known as the tryptophan destruction pathway. In our study, we aimed to investigate whether the serum levels of KP products and interleukin (IL)-6 activating indolamine 2-3 dioxygenase (IDO) enzyme are different in healthy developing children and children with ASD. Materials and Methods: Forty-three ASD children aged 2-9 were included in this study. Forty-two healthy developing children, similar to the patient group in terms of age and gender, were selected as the control group. Serum levels of kynurenic acid, kynurenine, quinolinic acid and IL-6 were analyzed using the ELISA method. ASD severity was evaluated with the Autism Behavior Checklist (ABC). Results: The mean age of children with ASD was 42.4 ± 20.5 months, and that of healthy controls was 48.1 ± 15.8 months. While the serum levels of kynurenic acid, kynurenine and interleukin-6 were higher in the group with ASD (p < 0.05), there was no significant difference (p > 0.05) in terms of the quinolinic acid level. There was no significant difference between the ABC total and subscale scores of children with ASD and biochemical parameters (p > 0.05). Conclusions: We conclude that these biomarkers must be measured in all ASD cases. They may be important for the diagnosis of ASD.

The role of sociability in social instability stress: Behavioral, neuroendocrine and monoaminergic effects

Extensive literature has reported a link between social stress and mental health. In this complex relationship, individual strategies for coping with social stress are thought to have a possible modulating effect, with sociability being a key factor. Despite the higher incidence of affective disorders in females and sex-related neurochemical differences, female populations have been understudied. The aim of the present study was, therefore, to analyze the behavioral, neuroendocrine, and neurochemical effects of stress in female OF1 mice, paying special attention to social connectedness (female mice with high vs low sociability). To this end, subjects were exposed to the Chronic Social Instability Stress (CSIS) model for four weeks. Although female mice exposed to CSIS had increased arousal, there was no evidence of depressive-like behavior. Neither did exposure to CSIS affect corticosterone levels, although it did increase the MR/GR ratio by decreasing GR expression. Female mice exposed to CSIS had higher noradrenaline and dopamine levels in the hippocampus and striatum respectively, with a lower monoaminergic turnover, resulting in an increased arousal. CSIS increased serotonin levels in both the hippocampus and striatum. Similarly, CSIS was found to reduce kynurenic acid, 3-HK, and IDO and iNOS enzyme levels in the hippocampus. Interestingly, the observed decrease in IDO synthesis and the increased serotonin and dopamine levels in the striatum were only found in subjects with high sociability. These highly sociable female mice also had significantly lower levels of noradrenaline in the striatum after CSIS application. Overall, our model has produced neuroendocrine and neurochemical but not behavioral changes, so it has not allowed us to study sociability in depth. Therefore, a model that induces both molecular and behavioral phenotypes should be applied to determine the role of sociability.

Interaction between high interleukin-2 and high cortisol levels is associated with psychopathology in patients with chronic schizophrenia

BACKGROUND

Both cortisol and interleukins appear at abnormal levels in schizophrenia. Our previous study has shown that cortisol and interleukins are associated with psychopathology and response to antipsychotic medications in a relatively small sample size of patients with schizophrenia. The current study was designed to investigate how cortisol, interleukins (ILs) and their interactions would correlate with clinical presentation in a relatively large sample size of patients with schizophrenia.

METHODS

We compared serum cortisol, IL-2, IL-6, and IL-8 levels in 162 medicated schizophrenia patients (including 27 patients in remission) and 62 healthy controls. Serum levels of cortisol and interleukins were measured by radioimmunoassay and quantitative ELISA, respectively. Clinical symptoms were assessed according to the Positive and Negative Syndrome Scale (PANSS).

RESULTS

Patients with schizophrenia had significantly higher levels of cortisol and IL-2 compared to controls. Patients in remission had higher levels of IL-6 than non-remitting patients. PANSS positive symptoms, general psychopathology, cortisol and IL-2 were the most central nodes in the cortisol-IL-symptom network. The interaction between cortisol and IL-2 was associated with PANSS positive symptoms, general psychopathology and depressive factor. For patients with cortisol level above the median, IL-2 was negatively associated with PANSS positive symptoms and general psychopathology.

CONCLUSIONS

Our results indicated that the interaction between cytokines and cortisol may be associated with the pathophysiology of some symptoms in chronic schizophrenia. In particular, the interaction between cortisol and IL-2 is associated with the clinical phenotypes of schizophrenia.

The Muscle-Gut-Brain Axis and Psychiatric Illness

The microbiota-gut-brain axis (MGBA) has been the subject of much research over the past decade, offering an exciting new paradigm for the treatment of psychiatric disorders. In this review, the MGBA is extended to include skeletal muscle and the potential role of an expanded "muscle-gut-brain axis" (MuGBA) in conditions such as anxiety and depression is discussed. There is evidence, from both preclinical and human studies, of bidirectional links between the gut microbiome and skeletal muscle function and structure. The therapeutic role of exercise in reducing depressive and anxiety symptoms is widely recognised, and the potential role of the gut microbiota-skeletal muscle link is discussed within this context. Potential pathways of communication involved in the MuGBA including the tryptophan-kynurenine pathway, intestinal permeability, immune modulation, and bacterial metabolites such as short-chain-fatty-acids are explored.

Altered gut microbiota profile in patients with perimenopausal panic disorder

Introduction

Females in the perimenopausal period are susceptible to mood disorders. Perimenopausal panic disorder (PPD) is characterized by repeated and unpredictable panic attacks during perimenopause, and it impacts the patient's physical and mental health and social function. Pharmacotherapy is limited in the clinic, and its pathological mechanism is unclear. Recent studies have demonstrated that gut microbiota is strongly linked to emotion; however, the relation between PPD and microbiota is limitedly known.

Methods

This study aimed to discover specific microbiota in PPD patients and the intrinsic connection between them. Gut microbiota was analyzed in PPD patients (n = 40) and healthy controls (n = 40) by 16S rRNA sequencing.

Results

The results showed reduced α-diversity (richness) in the gut microbiota of PPD patients. β-diversity indicated that PPD and healthy controls had different intestinal microbiota compositions. At the genus level, 30 species of microbiota abundance had significantly different between the PPD and healthy controls. In addition, HAMA, PDSS, and PASS scales were collected in two groups. It was found that Bacteroides and Alistipes were positively correlated with PASS, PDSS, and HAMA.

Discussion

Bacteroides and Alistipes dysbiosis dominate imbalanced microbiota in PPD patients. This microbial alteration may be a potential pathogenesis and physio-pathological feature of PPD. The distinct gut microbiota can be a potential diagnostic marker and a new therapeutic target for PPD.

The gut microbiome in social anxiety disorder: evidence of altered composition and function

The microbiome-gut-brain axis plays a role in anxiety, the stress response and social development, and is of growing interest in neuropsychiatric conditions. The gut microbiota shows compositional alterations in a variety of psychiatric disorders including depression, generalised anxiety disorder (GAD), autism spectrum disorder (ASD) and schizophrenia but studies investigating the gut microbiome in social anxiety disorder (SAD) are very limited. Using whole-genome shotgun analysis of 49 faecal samples (31 cases and 18 sex- and age-matched controls), we analysed compositional and functional differences in the gut microbiome of patients with SAD in comparison to healthy controls. Overall microbiota composition, as measured by beta-diversity, was found to be different between the SAD and control groups and several taxonomic differences were seen at a genus- and species-level. The relative abundance of the genera Anaeromassillibacillus and Gordonibacter were elevated in SAD, while Parasuterella was enriched in healthy controls. At a species-level, Anaeromassilibacillus sp An250 was found to be more abundant in SAD patients while Parasutterella excrementihominis was higher in controls. No differences were seen in alpha diversity. In relation to functional differences, the gut metabolic module 'aspartate degradation I' was elevated in SAD patients. In conclusion, the gut microbiome of patients with SAD differs in composition and function to that of healthy controls. Larger, longitudinal studies are warranted to validate these preliminary results and explore the clinical implications of these microbiome changes.

Serum metabolomic profiling revealed potential diagnostic biomarkers in patients with panic disorder

BACKGROUND

Currently, specific metabolites and diagnostic biomarkers of panic disorder (PD) patients have not been identified in clinical practice. The aim of this study was to explore metabolites and metabolic pathways in serum through a metabolomics method.

METHODS

Fifty-five PD patients who completed 2 weeks of inpatient treatment and 55 healthy control subjects (HCs) matched for age, sex and BMI were recruited. Ultra-high performance liquid chromatography tandem mass spectrometry (UHPLC-MS/MS) was used to detect metabolites in serum. Multivariate Statistical Analysis was used to identify differential metabolites. The relevant biometabolic pathways were further identified by the online tool MetaboAnalyst 5.0.

RESULTS

43 different metabolites in PD patients compared to HCs (P < 0.05) were screened. Pathway analysis showed that these small molecules were mainly associated with amino acid metabolism. 14 metabolites were significantly changed after 2 weeks of drug treatment (P < 0.05), which were mainly associated with tryptophan metabolism.

CONCLUSION

In conclusion, our analysis of metabolomics of PD patients at baseline and two weeks after treatment screened for differential metabolites that could be potential diagnostic biomarkers involved in PD pathogenesis and influence some biometabolic pathways such as phenylalanine metabolism and tryptophan metabolism. In the future, we can summarize and observe the dynamic changes of differential metabolites that appear more frequently in similar studies to further explore the underlying mechanisms of PD evolution.

Social isolation from early life induces anxiety-like behaviors in adult rats: Relation to neuroendocrine and neurochemical dysfunctions

Subjects suffering from psychosis frequently experience anxiety. However, mechanisms underlying this comorbidity remain still unclear. We investigated whether neurochemical and neuroendocrine dysfunctions were involved in the development of anxiety-like behavior in a rodent model of psychotic-like symptoms, obtained by exposing male rats to social isolation rearing from postnatal day 21 to postnatal day 70. In the elevated zero maze test, isolated rats showed a significant reduction in the time spent in the open arms, as well as an increase in the time spent in the closed arms, compared to controls. An increased grooming time in the open field test was also observed in isolated animals. Isolation-induced anxiety-like behavior was accompanied by a decrease of plasmatic oxytocin, prolactin, ghrelin and melatonin levels, whereas plasmatic amount of Neuropeptide S was not altered. Social isolation also caused a reduction of noradrenaline, serotonin and GABA levels, together with an increase of serotonin turnover and glutamate levels in the amygdala of isolated animals. No significant differences were found in noradrenaline and serotonin levels, as well as in serotonin turnover in hippocampus, while glutamate amount was increased and GABA levels were reduced in isolated rats. Furthermore, there was a reduction in plasmatic serotonin content, and an increase in plasmatic kynurenine levels following social isolation, while no significant changes in serotonin turnover were observed. Taken together, our data provide novel insights in the neurobiological alterations underlying the comorbidity between psychosis and anxiety, and open new perspectives for multi-target therapies acting on both neurochemical and neuroendocrine pathways. DATA AVAILABILITY STATEMENT: The data presented in this study are available on request from the corresponding author.

Kynurenine Pathway in Diabetes Mellitus-Novel Pharmacological Target?

The tryptophan-kynurenine pathway (Trp-KYN) is the major route for tryptophan conversion in the brain and in the periphery. Kynurenines display a wide range of biological actions (which are often contrasting) such as cytotoxic/cytoprotective, oxidant/antioxidant or pro-/anti-inflammatory. The net effect depends on their local concentration, cellular environment, as well as a complex positive and negative feedback loops. The imbalance between beneficial and harmful kynurenines was implicated in the pathogenesis of various neurodegenerative disorders, psychiatric illnesses and metabolic disorders, including diabetes mellitus (DM). Despite available therapies, DM may lead to serious macro- and microvascular complications including cardio- and cerebrovascular disease, peripheral vascular disease, chronic renal disease, diabetic retinopathy, autonomic neuropathy or cognitive impairment. It is well established that low-grade inflammation, which often coincides with DM, can affect the function of KP and, conversely, that kynurenines may modulate the immune response. This review provides a detailed summary of findings concerning the status of the Trp-KYN pathway in DM based on available animal, human and microbiome studies. We highlight the importance of the molecular interplay between the deranged (functionally and qualitatively) conversion of Trp to kynurenines in the development of DM and insulin resistance. The Trp-KYN pathway emerges as a novel target in the search for preventive and therapeutic interventions in DM.

The Association of the Oral Microbiota with the Effects of Acid Stress Induced by an Increase of Brain Lactate in Schizophrenia Patients

The altered cerebral energy metabolism central to schizophrenia can be linked to lactate accumulation. Lactic acid is produced by gastrointestinal bacteria, among others, and readily crosses the blood-brain barrier, leading to the brain acidity. This study aimed to examine the association of the oral microbiota with the effects of acid stress induced by an increase of brain lactate in schizophrenia patients. The study included patients with a diagnosis of acute polyphasic psychotic disorder meeting criteria for schizophrenia at 3-month follow-up. Results: Individuals with a significantly higher total score on the Positive and Negative Syndrome Scale had statistically significantly lower lactate concentrations compared to those with a lower total score and higher brain lactate. We observed a positive correlation between Actinomyces and lactate levels in the anterior cingulate cap and a negative correlation between bacteria associated with lactate metabolism and some clinical assessment scales. Conclusions: Shifts in the oral microbiota in favour of lactate-utilising bacterial genera may represent a compensatory mechanism in response to increased lactate production in the brain. Assessment of neuronal function mediated by ALA-LAC-dependent NMDA regulatory mechanisms may, thus, support new therapies for schizophrenia, for which acidosis has become a differentiating feature of individuals with schizophrenia endophenotypes.

Candidate Biological Markers for Social Anxiety Disorder: A Systematic Review

Social anxiety disorder (SAD) is a common psychiatric condition associated with a high risk of psychiatric comorbidity and impaired social/occupational functioning when not promptly treated. The identification of biological markers may facilitate the diagnostic process, leading to an early and proper treatment. Our aim was to systematically review the available literature about potential biomarkers for SAD. A search in the main online repositories (PubMed, ISI Web of Knowledge, PsychInfo, etc.) was performed. Of the 662 records screened, 61 were included. Results concerning cortisol, neuropeptides and inflammatory/immunological/neurotrophic markers remain inconsistent. Preliminary evidence emerged about the role of chromosome 16 and the endomannosidase gene, as well as of epigenetic factors, in increasing vulnerability to SAD. Neuroimaging findings revealed an altered connectivity of different cerebral areas in SAD patients and amygdala activation under social threat. Some parameters such as salivary alpha amylase levels, changes in antioxidant defenses, increased gaze avoidance and QT dispersion seem to be associated with SAD and may represent promising biomarkers of this condition. However, the preliminary positive correlations have been poorly replicated. Further studies on larger samples and investigating the same biomarkers are needed to identify more specific biological markers for SAD.

Changes in the Serum Concentration Levels of Serotonin, Tryptophan and Cortisol among Stress-Resilient and Stress-Susceptible Individuals after Experiencing Traumatic Stress

BACKGROUND

Stress is a common response to many environmental adversities. However, once dysregulated, this reaction can lead to psychiatric illnesses, such as post-traumatic stress disorder (PTSD). Individuals can develop PTSD after exposure to traumatic events, severely affecting their quality of life. Nevertheless, not all individuals exposed to stress will develop psychiatric disorders, provided they show enhanced stress-resilience mechanisms that enable them to successfully adapt to stressful situations and thus avoid developing a persistent psychopathology.

METHODS

The study involved 93 participants. Of them, 62 comprised a study group and 31 comprised a control group. The aim of the study was to assess serotonin, cortisol and tryptophan concentration levels in subjects with PTSD (stress-susceptible; PTSD-SS) and in healthy individuals (stress-resilient; PTSD-SR), who had experienced a traumatic event but fully recovered after the trauma. The subjects were between 18 and 50 years of age (mean 35.56 ± 8.26 years). The serum concentration levels of serotonin, cortisol and tryptophan were measured with an ELISA kit.

RESULTS

It was found that the serotonin, tryptophan and cortisol concentration levels were consistent with the features of both PTSD-SR and PTSD-SS patients. It was reported that the mean cortisol concentration levels increased more significantly in the PTSD-SS group than in the PTSD-SR group, versus those in the control group. Similarly, the PTSD-SS group was found to show a larger decrease in the mean serotonin concentration levels than the PTSD-SR group, versus those in the control group. No significant changes were found in the tryptophan concentration levels between the study groups, versus those in the control group.

CONCLUSIONS

These findings can be useful when attempting to improve resilience in individuals using neuropharmacological methods. However, it is necessary to conduct more cross-sectional studies that would address different types of negative stress to find out whether they share common pathways.

Relationship between the tryptophan-kynurenine pathway and painful physical symptoms in patients with major depressive disorder

OBJECTIVES

To investigate the relationship between the tryptophan-kynurenine (TRP-KYN) pathway and painful physical symptoms (PPS) in major depressive disorder (MDD).

METHODS

Eighty-four patients with MDD (40 patients with PPS and 44 without PPS) and forty-six healthy controls (HC) were recruited. The serum levels of tryptophan (TRP), kynurenine(KYN), kynurenic acid (KA), quinolinic acid (QA), 3-hydroxy-kynurenine (3-HK), serotonin (5-HT) were measured using high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS). Depression, anxiety and pain were assessed using Hamilton Depression Scale (HAMD), Hamilton Anxiety Scale (HAMA) and Short-form McGill pain questionnaire (SFMPQ) respectively.

RESULTS

Patients in the MDD group exhibited significantly lower KA and 5-HT levels than HC, whereas MDD patients with PPS showed higher KYN and QA levels, and a higher KYN/TRP ratio than those without. There was a positive correlation between the scores of SFMPQ and QA levels and a negative correlation between the scores of SFMPQ and TRP levels or KA/QA ratios in MDD patients with PPS group. Stepwise multiple regression analysis showed that the KYN/TRP ratios, the KA/QA ratios, and the HAMD scores were significant predictor factors for SFMPQ scores.

CONCLUSIONS

These results demonstrated that the TRP-KYN pathway may play a role in the pathophysiology of pain in patients with major depressive disorder, suggesting that further studies of this pathway as a potential biomarker or therapeutic target are required.

Tryptophan metabolism: Mechanism-oriented therapy for neurological and psychiatric disorders

Neurological and psychiatric disorders are a category of chronic diseases that are widespread and pose serious mental and physical health problems for patients. The substrates, products, and enzymes of Tryptophan metabolism all contribute to the development of neurological and psychiatric disorders. This paper deals with three metabolic pathways of tryptophan that produce a series of metabolites called tryptophan Catabolics (TRYCATs). These metabolites are involved in pathological processes such as excitotoxicity, neuroinflammation, oxidative stress, and mitochondrial damage and are closely associated with neurological and psychiatric disorders such as Alzheimer’s disease and depression. Here, we review the elements that affect how tryptophan metabolism is regulated, including inflammation and stress, exercise, vitamins, minerals, diet and gut microbes, glucocorticoids, and aging, as well as the downstream regulatory effects of tryptophan metabolism, including the regulation of glutamate (Glu), immunity, G-protein coupled receptor 35 (Gpr35), nicotinic acetylcholine receptor (nAChR), aryl hydrocarbon receptor (AhR), and dopamine (DA). In order to advance the general understanding of tryptophan metabolism in neurological and psychiatric disorders, this paper also summarizes the current situation and effective drugs of tryptophan metabolism in the treatment of neurological and psychiatric disorders and considers its future research prospects.

Prenatal exposure to Hurricane Maria is associated with an altered infant nasal microbiome

Background:

Prenatal adverse exposures have been associated with increased risks of development of respiratory diseases in children. The infant nasal microbiome is an important mechanism and indicator.

Objective:

Our aim was to characterize and compare the nasal microbiome of infants who were in utero and exposed to Hurricane Maria in Puerto Rico during 2017 with that of infants who were conceived at least 5 months after the hurricane as controls.

Methods:

We recruited 63 vaginally born infants, 29 of whom were in the exposure group and 34 of whom were in the control group. Nasal swab samples were collected and analyzed by using 16S ribosomal RNA gene sequencing at the community and taxon levels, respectively.

Results:

Infants in the exposure group were more likely to harbor a Staphylococcus-Streptococcus–dominant microbial community in their nose. The richness and diversity of the microbiome was significantly higher in the exposure group than in the control group. In the exposure group, the bacterial genera Rhodocista, Azospirillum, Massilia, Herbaspirillum, Aquabacterium, and Pseudomonas were enriched, whereas Corynebacterium and Ralstonia were depleted. Food insecurity due to Hurricane Maria was associated with an increase in Pseudomonas in the infant nasal microbiome.

Conclusion:

Infants who were exposed to Hurricane Maria during gestation had an altered nasal microbiome, with a higher prevalence of environmental bacteria. More research is needed to evaluate the long-term impacts of extreme weather events occurring in the prenatal stage on a child’s nasal microbiome and respiratory health.

Psychological outcomes of COVID-19 survivors at sixth months after diagnose: the role of kynurenine pathway metabolites in depression, anxiety, and stress

Coronavirus disease 2019 (COVID-19) has resulted in long-term psychiatric symptoms because of the immunologic response to the virus itself as well as fundamental life changes related to the pandemic. This immune response leads to altered tryptophan (TRP)-kynurenine (KYN) pathway (TKP) metabolism, which plays an essential role in the pathophysiology of mental illnesses. We aimed to define TKP changes as a potential underlying mechanism of psychiatric disorders in post-COVID-19 patients. We measured plasma levels of several TKP markers, including KYN, TRP, kynurenic acid (KYNA), 3-hydroxykynurenine (3-HK), and quinolinic acid (QUIN), as well as the TRP/KYN, KYNA/3-HK, and KYNA/QUIN ratios, in 90 post-COVID-19 patients (on the first day of hospitalization) and 59 healthy controls (on the first admission to the Check-Up Center). An online questionnaire that included the Depression, Anxiety and Stress Scale-21 (DASS-21) was used 6 months after the initial assessment in both groups. A total of 32.2% of participants with COVID-19 showed depressive symptoms, 21.1% exhibited anxiety, and 33.3% had signs of stress at follow-up, while 6.6% of healthy controls exhibited depressive and anxiety symptoms and 18.6% had signs of stress. TRP and 3-HK were negative predictors of anxiety and stress, but KYN positively predicted anxiety and stress. Moreover, TRP negatively predicted depression, while KYNA/3-HK was a negative predictor of anxiety. The correlation between depression, anxiety, and stress and TKP activation in COVID-19 could provide prospective biomarkers, especially the reduction in TRP and 3HK levels and the increase in KYN. Our results suggest that the alteration of TKP is not only a potential biomarker of viral infection-related long-term psychiatric disorders but also that the therapy targets future viral infections related to depression and anxiety.