Chronic Treatment with the IDO1 Inhibitor 1-Methyl-D-Tryptophan Minimizes the Behavioural and Biochemical Abnormalities Induced by Unpredictable Chronic Mild Stress in Mice - Comparison with Fluoxetine

Role of Probiotics in Depression: Connecting Dots of Gut-Brain-Axis Through Hypothalamic-Pituitary Adrenal Axis and Tryptophan/Kynurenic Pathway involving Indoleamine-2,3-dioxygenase

Depression is one of the most disabling mental disorders worldwide and characterized by symptoms including worthlessness, anhedonia, sleep, and appetite disturbances. Recently, studies have suggested that tryptophan (Trp) metabolism plays a key role in depressed mood through serotonin and kynurenine pathway involving enzyme tryptophan 5-monooxygenase (TPH) and indoleamine-2,3-dioxygenase (IDO) respectively. Moreover, during neuroinflammation, IDO is activated by proinflammatory cytokines and affects neurogenesis, cognition, disturbed hypothalamic-pituitary-adrenal (HPA) axis, and gut homeostasis by altering the gut bacteria and its metabolites like Trp derivatives. Furthermore, over the decades, researchers have focused on understanding communication between the human microbiome, especially gut microbiota, and mental health, called gut-brain-axis (GBA), particularly through Trp metabolism. Supplementation of probiotics in depression has gained attention from researchers and clinicians. However, there is limited information about probiotics supplementation on depression involving enzyme IDO and kynurenine pathway metabolites. This review discussed the potential role of probiotics in depression through the tryptophan/kynurenine pathway.

Lactobacillus fermentum ATCC 9338 Supplementation Prevents Depressive-Like Behaviors Through Glucocorticoid Receptor and N-Methyl-D-aspartate2b in Chronic Unpredictable Mild Stress Mouse Model

Depression is a long-term, related to stress neuropsychiatric disorder, leading to psychological health issues including worthlessness, anhedonia, sleep and appetite disturbances, dysregulated HPA axis, neuronal cell death, and alterations in the gut microbiota (GM). Dysregulated HPA axis increases level of glucocorticoids that induce proinflammatory response with activation of abnormal kynurenine pathway via metabolizing indoleamine-2,3-dioxygenase (IDO). Kynurenine pathway leads to excitotoxicity of N-methyl-D-aspartate (NMDA) receptor responsible for neuronal cell death. Further, probiotics supplementation gained attention from researchers and clinicians to treat neuropsychiatric diseases. GM alteration remains a key reason for depression; however, there is limited information about the role of probiotics on depression involving glucocorticoid receptor and NMDA excitotoxicity through IDO. Chronic unpredictable mild stress (CUMS) model was prepared to check the role of Lactobacillus fermentum ATCC 9338 (LF) and 1-methyl-D-tryptophan (1-MT) in depression. Herein, mice were placed into experimental groups: control, CUMS stressed, CUMS vehicle, CUMS LF, CUMS 1-MT, and CUMS UT (untreated). Results showed that peroral administration of 1 × 108 CFU/day/mouse LF and intraperitoneal dose of 1-MT (15 mg/kg BW/day) alleviate depressive-like behavior and improve motor coordination and walking patterns. Mice supplemented with LF and 1-MT exhibited a decreased expression of GR and NMDAR2b in the cortex, hippocampus, and medulla. Acetylcholinesterase, SOD, and CAT activities were improved in CUMS mice with supplementation of LF and 1-MT. The GM abundance in LF mice was similar to that in control mice. Such study suggests the roles of LF and 1-MT in depression and oxidative stress, and helpful to understand their therapeutic potential through the HPA axis and IDO.

IDO-Kynurenine pathway mediates NLRP3 inflammasome activation-induced postoperative cognitive impairment in aged mice

AIM

Postoperative cognitive dysfunction (POCD) is a common postoperative complication, especially in elderly patients. It extends hospital stay, increases the mortality rate and are heavy burdens to the family and society. Accumulating research has indicated that overactivation of pyrin domain-containing protein 3 (NLRP3) inflammasomes is related to POCD andplays a critical role in activating pro-inflammatory cytokines. According to existing studies, indoleamine 2,3-dioxygenase (IDO) is potently up-regulated by inflammatory factors, tryptophan in brain is mainly catalyzed by IDO to kynurenine (KYN), KYN metabolism may contribute to the development of depressive disorder and memory deficits. Hence, this study elucidated whether IDO-Kynurenine pathway mediates NLRP3 inflammasome activation-induced postoperative cognitive impairment in aged mice.

MATERIAL AND METHODS

POCD model was established in aged C57BL/6J mice by exploratory laparotomy under isoflurane anesthesia. Learning and memory were determined using Morris water maze.

RESULTS

The data showed that IDO and kynurenine aminotransferase-II (KAT-II) mRNA in hippocampus was up-regulated, and NLRP3, caspase recruitment domain (ASC), interleukin-1b (IL-1b) and IDO overexpressed, KYN levels increased after anesthesia and surgery. NLRP3 inflammasome inhibitor (MCC950) reversed NLRP3, ASC, IL-1b and IDO overexpression, and the elevation of KYN levels. To clarify the role of IDO-Kynurenine pathway in postoperative cognitive impairment, IDO inhibitor (1-methyl-Ltryptophan 1-MT) reduced the elevation of KYN and kynurenic acid (KYNA) levels, reduction of tryptophan (TRP), as well as improved learning and memory abilities. Finally, KAT-II inhibitor (PF-04859989) reduced brain KYNA levels and restored the cognitive impairment.

CONCLUSION

These results reveal that IDO-Kynurenine pathway mediates NLRP3 inflammasome activation-induced postoperative cognitive impairment.

Exploring the pathophysiological influence of heme oxygenase-1 on neuroinflammation and depression: A study of phytotherapeutic-based modulation

BACKGROUND

The heme oxygenase (HO) system plays a significant role in neuroprotection and reduction of neuroinflammation and neurodegeneration. The system, via isoforms HO-1 and HO-2, regulates cellular redox balance. HO-1, an antioxidant defense enzyme, is highlighted due to its association with depression, characterized by heightened neuroinflammation and impaired oxidative stress responses.

METHODOLOGY

We observed the pathophysiology of HO-1 and phytochemicals as its modulator. We explored Science Direct, Scopus, and PubMed for a comprehensive literature review. Bibliometric and temporal trend analysis were done using VOSviewer.

RESULTS

Several phytochemicals can potentially alleviate neuroinflammation and oxidative stress-induced depressive symptoms. These effects result from inhibiting the MAPK and NK-κB pathways - both implicated in the overproduction of pro-inflammatory factors - and from the upregulation of HO-1 expression mediated by Nrf2. Bibliometric and temporal trend analysis further validates these associations.

CONCLUSION

In summary, our findings suggest that antidepressant agents can mitigate neuroinflammation and depressive disorder pathogenesis via the upregulation of HO-1 expression. These agents suppress pro-inflammatory mediators and depressive-like symptoms, demonstrating that HO-1 plays a significant role in the neuroinflammatory process and the development of depression.

Subjective experience of the environment determines serotoninergic antidepressant treatment outcome in male mice

BACKGROUND

The effects of the selective serotonin reuptake inhibitors (SSRIs), the first-line antidepressant treatment, have been proposed to be affected, at least in part, by the living environment. Since the quality of the environment depends not only on its objective features, but also on the subjective experience, we hypothesized that the latter plays a key role in determining SSRI treatment outcome.

METHODS

We chronically administered the SSRI fluoxetine to two groups of adult CD-1 male mice that reportedly show distinct subjective experiences of the environment measured as consistent and significantly different responses to the same emotional and social stimuli. These distinct socioemotional profiles were generated by rearing mice either in standard laboratory conditions (SN) or in a communal nest (CN) where three dams breed together their offspring, sharing caregiving behavior.

RESULTS

At adulthood, CN mice displayed higher levels of agonistic and anxiety-like behaviors than SN mice, indicating that they experience the environment as more socially challenging and potentially dangerous. We then administered fluoxetine, which increased offensive and anxious response in SN, while producing opposite effects in CN mice. BDNF regulation was modified by the treatment accordingly.

LIMITATIONS

Subjective experience in mice was assessed as behavioral response to the environment.

CONCLUSIONS

These results show that the subjective experience of the environment determines fluoxetine outcome. In a translational perspective, our findings suggest considering not only the objective quality, but also the subjective appraisal, of the patient's living environment for developing effective personalized therapeutic approaches in psychiatry.

Retention of stress susceptibility in the mdx mouse model of Duchenne muscular dystrophy after PGC-1α overexpression or ablation of IDO1 or CD38

Duchenne muscular dystrophy (DMD) is a lethal degenerative muscle wasting disease caused by the loss of the structural protein dystrophin with secondary pathological manifestations including metabolic dysfunction, mood and behavioral disorders. In the mildly affected mdx mouse model of DMD, brief scruff stress causes inactivity, while more severe subordination stress results in lethality. Here, we investigated the kynurenine pathway of tryptophan degradation and the nicotinamide adenine dinucleotide (NAD+) metabolic pathway in mdx mice and their involvement as possible mediators of mdx stress-related pathology. We identified downregulation of the kynurenic acid shunt, a neuroprotective branch of the kynurenine pathway, in mdx skeletal muscle associated with attenuated peroxisome proliferator-activated receptor-gamma coactivator 1 alpha (PGC-1α) transcriptional regulatory activity. Restoring the kynurenic acid shunt by skeletal muscle-specific PGC-1α overexpression in mdx mice did not prevent scruff -induced inactivity, nor did abrogating extrahepatic kynurenine pathway activity by genetic deletion of the pathway rate-limiting enzyme, indoleamine oxygenase 1. We further show that reduced NAD+ production in mdx skeletal muscle after subordination stress exposure corresponded with elevated levels of NAD+ catabolites produced by ectoenzyme cluster of differentiation 38 (CD38) that have been implicated in lethal mdx response to pharmacological β-adrenergic receptor agonism. However, genetic CD38 ablation did not prevent mdx scruff-induced inactivity. Our data do not support a direct contribution by the kynurenine pathway or CD38 metabolic dysfunction to the exaggerated stress response of mdx mice.

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.

Guanosine treatment prevents lipopolysaccharide-induced depressive-like behavior in mice

Guanosine is a purinergic nucleoside that has been shown to have neuroprotective effects, mainly through its ability to modulate the glutamatergic system. An increase in pro-inflammatory cytokine levels triggers the activation of the enzyme indoleamine 2,3-dioxygenase 1 (IDO-1), leading to glutamatergic excitotoxicity, which has important roles in the pathophysiology of depression. The aim of this study was to investigate the possible antidepressant-like effects and underlying mechanisms of action of guanosine against lipopolysaccharide (LPS)-induced depression in a mouse model. Mice were orally pre-treated with saline (0.9% NaCl), guanosine (8 or 16 mg/kg), or fluoxetine (30 mg/kg) for 7 days before LPS (0.5 mg/kg, intraperitoneal) injection. One day after LPS injection, mice were subjected to the forced swim test (FST), tail suspension test (TST), and open field test (OFT). After the behavioral tests, mice were euthanized and the levels of tumor necrosis factor-α (TNF-α), IDO-1, glutathione, and malondialdehyde in the hippocampus were measured. Pretreatment with guanosine was able to prevent LPS- induced depressive-like behaviors in the TST and FST. In the OFT, no locomotor changes were observed with any treatment. Both guanosine (8 and 16 mg/kg/day) and fluoxetine treatment prevented the LPS-induced increase in TNF-α and IDO expression and lipid peroxidation as well as decrease of reduced glutathione levels in the hippocampus. Taken together, our findings suggest that guanosine may have neuroprotective effects against LPS-induced depressive-like behavior through preventing oxidative stress and the expression of IDO-1 and TNF-α in the hippocampus.

Rifaximin ameliorates depression-like behaviour in chronic unpredictable mild stress rats by regulating intestinal microbiota and hippocampal tryptophan metabolism

BACKGROUND

Chronic unpredictable mild stress (CUMS) can induce depressive behaviours and alter the composition of the gut microbiome. Although modulating gut microbiota can improve depression-like behaviour in rats, the mechanism of action is unclear. Additionally, gut microbiota can affect brain function through the neuroendocrine pathway. This pathway may function by regulating the secretion of neurotransmitters such as tryptophan (TRP). Metabolites of TRP, such as 5-hydroxytryptamine (5-HT) and kynurenine (KYN), are related to the pathophysiological process of depression. Indoleamine-2, 3-dioxygenase-1 (IDO1) and Tryptophan hydroxylase 2 (TPH2) are the key rate-limiting enzymes in TRP metabolism and play an important role in KYN and 5-HT metabolism.

METHODS

Rats were subjected to four weeks of CUMS and given rifaximin150 mg/kg by oral gavage daily. After modelling, we investigated the rat's behaviours, composition of the faecal microbiome, neurotransmitter metabolism and key metabolic enzymes of the TRP pathway in the hippocampus (HIP).

RESULTS

Rifaximin administration improved depressive behaviour in rats, corrected intestinal microbiota disorders and HIP TRP metabolism and regulated the expression of IDO1 and TPH2 in the HIP.

CONCLUSIONS

Rifaximin improves depression-like behaviour in CUMS rats by influencing the gut microbiota and tryptophan metabolism.

Effect of Gestational Diabetes on Postpartum Depression-like Behavior in Rats and Its Mechanism

Recent studies have reported a strong association between gestational diabetes mellitus (GDM) and postpartum depression (PPD), but little is known about the underlying physiological mechanism. In this study, a GDM rat model was used to evaluate the direct effect of GDM on PPD and to explore the mechanism. After parturition, the GDM dams were divided into two groups: blood glucose not recovered group (GH group) and blood glucose recovered group (GL group). Fasting plasma glucose (FPG), cortisol (COR) and serotonin (5-hydroxytryptamine, 5-HT) metabolism were continuously monitored during the lactation period, until postnatal day 21. PPD was evaluated by behavioral tests. At the endpoint, the expression of the key enzymes of Trp metabolic pathway in colon and brain tissues was analyzed by immunohistochemistry and western blot. The microbe composition of colonic contents was determined by 16S rDNA gene sequencing. The results showed that GDM induced postpartum depression-like behavior in rats. The HPA axis hormone did not show the typical stress state of depression, but the level of 5-HT decreased significantly in serum, prefrontal cortex and hippocampus, and the Kyn/Trp ratio increased significantly in serum and prefrontal cortex, implying the switch of the tryptophan (Trp) metabolism from the 5-HT pathway to the kynurenine (Kyn) pathway. The expression of Indoleamine 2,3-dioxygenase (IDO), a key rate-limiting enzyme in Kyn metabolism, was up-regulated in the colon and brain, which was an important reason for this switch. This switch was accelerated by a decrease in the expression of tryptophan hydroxylase (TPH), a key enzyme of the 5-HT production pathway, in the colon. GDM dams displayed significant changes in gut microbiome profiles, which were correlated with depression. The ratio of Firmicutes to Bacteroidetes decreased. Lactobacillus and Bacteroides were negatively correlated with 5-HT level and positively correlated with Kyn level, whereas Clostridium XlVa and Ruminococcus were positively correlated with 5-HT level. These results suggest that GDM disrupts both the Trp pathway and the composition of the gut microbiota, which provide a putative physiological basis for PPD.

Involvement of the microbiota-gut-brain axis in chronic restraint stress: disturbances of the kynurenine metabolic pathway in both the gut and brain

Emerging evidence suggests that the gut microbiota may interact with the host brain and play pivotal roles in the pathogenesis of neuropsychiatric disorders. However, the mechanism underlying reciprocal interactions along the microbiota-gut-brain axis in depression remains unclear. In this study, a murine model of chronic restraint stress (CRS) was established to investigate the metabolic signaling of tryptophan (Trp) neurotransmission at the intestinal and central levels in depression. The results showed that CRS mice displayed depression- and anxiety-like behaviors. Additionally, kynurenine (Kyn) and its metabolites, an important Trp metabolic pathway, were strongly activated in the brain. Intriguingly, the Kyn toxic signaling was exacerbated in the gut, especially in the colon. Indoleamine 2,3-dioxygenase (IDO), a rate-limiting enzyme responsible for Kyn metabolic pathway initiation, was significantly upregulated in the brain and gut in CRS mice compared with control mice, promoting transfer of Trp metabolic pathway to Kyn signaling. Additionally, administration of IDO inhibitor, 1-methyl-tryptophan (1-MT), partially rescued CRS-induced depression- and anxiety-like changes. Moreover, the enhanced intestinal permeability mediated by CRS allowed toxic metabolites to "leak" into the bloodstream. The microbiome profiles of CRS mice displayed obviously altered taxonomic composition and negative correlations were observed between Enterorhabdus, Parabacteroides and Kyn levels in the brain. Reciprocal crosstalk between the brain and gut was further validated by citalopram treatment, IDO inhibitor and microbiota intervention, which counteracted depression-like behavior, Kyn metabolic signaling and microbiota composition in CRS mice. Meanwhile, Parabacteroides treatment affected Trp metabolism in mouse hippocampus, manifesting as elevated concentration of 5-HT as well as ratio of 5-HT to Trp. These results suggest that long-term stress disrupts Kyn metabolism and endocrine function along the gut-brain axis, accompanied by the disrupted homeostasis of certain microbiota, which collectively contribute to the development of depression-like behavior.

Neuroinflammation and the Kynurenine Pathway in CNS Disease: Molecular Mechanisms and Therapeutic Implications

Diseases of the central nervous system (CNS) remain a significant health, social and economic problem around the globe. The development of therapeutic strategies for CNS conditions has suffered due to a poor understanding of the underlying pathologies that manifest them. Understanding common etiological origins at the cellular and molecular level is essential to enhance the development of efficacious and targeted treatment options. Over the years, neuroinflammation has been posited as a common link between multiple neurological, neurodegenerative and neuropsychiatric disorders. Processes that precipitate neuroinflammatory conditions including genetics, infections, physical injury and psychosocial factors, like stress and trauma, closely link dysregulation in kynurenine pathway (KP) of tryptophan metabolism as a possible pathophysiological factor that 'fuel the fire' in CNS diseases. In this study, we aim to review emerging evidence that provide mechanistic insights between different CNS disorders, neuroinflammation and the KP. We provide a thorough overview of the different branches of the KP pertinent to CNS disease pathology that have therapeutic implications for the development of selected and efficacious treatment strategies.

Increased serum QUIN/KYNA is a reliable biomarker of post-stroke cognitive decline

BACKGROUND

Strokes are becoming less severe due to increased numbers of intensive care units and improved treatments. As patients survive longer, post-stroke cognitive impairment (PSCI) has become a major health public issue. Diabetes has been identified as an independent predictive factor for PSCI. Here, we characterized a clinically relevant mouse model of PSCI, induced by permanent cerebral artery occlusion in diabetic mice, and investigated whether a reliable biomarker of PSCI may emerge from the kynurenine pathway which has been linked to inflammatory processes.

METHODS

Cortical infarct was induced by permanent middle cerebral artery occlusion in male diabetic mice (streptozotocin IP). Six weeks later, cognitive assessment was performed using the Barnes maze, hippocampi long-term potentiation using microelectrodes array recordings, and neuronal death, white matter rarefaction and microglia/macrophages density assessed in both hemispheres using imunohistochemistry. Brain and serum metabolites of the kynurenin pathway were measured using HPLC and mass fragmentography. At last, these same metabolites were measured in the patient's serum, at the acute phase of stroke, to determine if they could predict PSCI 3 months later.

RESULTS

We found long-term spatial memory was impaired in diabetic mice 6 weeks after stroke induction. Synaptic plasticity was completely suppressed in both hippocampi along with increased neuronal death, white matter rarefaction in both striatum, and increased microglial/macrophage density in the ipsilateral hemisphere. Brain and serum quinolinic acid concentrations and quinolinic acid over kynurenic acid ratios were significantly increased compared to control, diabetic and non-diabetic ischemic mice, where PSCI was absent. These putative serum biomarkers were strongly correlated with degradation of long-term memory, neuronal death, microglia/macrophage infiltration and white matter rarefaction. Moreover, we identified these same serum biomarkers as potential predictors of PSCI in a pilot study of stroke patients.

CONCLUSIONS

we have established and characterized a new model of PSCI, functionally and structurally, and we have shown that the QUIN/KYNA ratio could be used as a surrogate biomarker of PSCI, which may now be tested in large prospective studies of stroke patients.

Chronic stress followed by social isolation promotes depressive-like behaviour, alters microglial and astrocyte biology and reduces hippocampal neurogenesis in male mice

Unpredictable chronic mild stress (UCMS) is one of the most commonly used, robust and translatable models for studying the neurobiological basis of major depression. Although the model currently has multiple advantages, it does not entirely follow the trajectory of the disorder, whereby depressive symptomology can often present months after exposure to stress. Furthermore, patients with depression are more likely to withdraw in response to their stressful experience, or as a symptom of their depression, and, in turn, this withdrawal/isolation can further exacerbate the stressful experience and the depressive symptomology. Therefore, we investigated the effect(s) of 6 weeks of UCMS followed by another 6 weeks of social isolation (referred to as UCMSI), on behaviour, corticosterone stress responsivity, immune system functioning, and hippocampal neurogenesis, in young adult male mice. We found that UCMSI induced several behavioural changes resembling depression but did not induce peripheral inflammation. However, UCMSI animals showed increased microglial activation in the ventral dentate gyrus (DG) of the hippocampus and astrocyte activation in both the dorsal and ventral DG, with increased GFAP-positive cell immunoreactivity, GFAP-positive cell hypertrophy and process extension, and increased s100β-positive cell density. Moreover, UCMSI animals had significantly reduced neurogenesis in the DG and reduced levels of peripheral vascular endothelial growth factor (VEGF) - a trophic factor produced by astrocytes and that stimulates neurogenesis. Finally, UCMSI mice also had normal baseline corticosterone levels but a smaller increase in corticosterone following acute stress, that is, the Porsolt Swim Test. Our work gives clinically relevant insights into the role that microglial and astrocyte functioning, and hippocampal neurogenesis may play in the context of stress, social isolation and depression, offering a potentially new avenue for therapeutic target.

Cang-Ai Volatile Oil Ameliorates Depressive Behavior Induced by Chronic Stress Through IDO-Mediated Tryptophan Degradation Pathway

Background: Cang-ai volatile oil (CAVO) is a Chinese herbal volatile oil. Previous studies report that CAVO exhibits of anti-depressant and anti-inflammatory effects, and modulates activity of monoamine neurotransmitter. The current study sought to explore whether CAVO exhibits anti-depressant effects of CAVO through inhibition of inflammatory response and regulation of indoleamine 2 and 3-dioxygenase (IDO) mediated tryptophan degradation pathway. Methods: The study established chronic unpredictable mild stress (CUMS) depression-like model using rats. Body weight and food intake of animals were determined, and open field test (OFT), forced swim test (FST), and sucrose preference test (SPT) were performed to explored the behavioral changes of animals. Expression levels of interleukin-6 (IL-6), interleukin-1beta (IL-1β), tumor necrosis factor-alpha (TNF-α), interferon-gamma (IFN-γ), interleukin-4 (IL-4), interleukin-10 (IL-10), kynurenine (KYN), quinolinic acid (QUIN), tryptophan (Trp), kynurenic acid (KYNA), serotonin (5-HT), and 5-hydroxyindole acetic acid (5-HIAA) in the prefrontal cortex of CUMS rats were determined by ELISA. Co-localization of the microglia markers, Iba1 and IL-6 was determined by immunofluorescence. Western blotting was performed to determine the protein expression level of IDO1. Results: The findings of the current study showed that CAVO increased the body weight and food intake of rats and alleviated depression-like behaviors as shown in OFT, FST, and SPT analysis. ELISA assay showed that CAVO decreased IL-6, IL-1β, TNF-α, and IFN-γ levels and increased levels of IL-4 and IL-10 in the prefrontal cortex of CUMS rats. Analysis showed that CAVO significantly reduced KYN and QUIN levels and the ratio of KYN/Trp, whereas it increased the levels of Trp, KYNA, 5-HT, and 5-HIAA. Immunofluorescence analysis showed that CAVO reduced the number of positive cells with co-localization of microglia markers, Iba1 and IL-6. Western blot analysis showed that CAVO decreased the protein expression level of IDO1 in rats. Conclusion: The findings show that the anti-depressant effects of CAVO are mainly attributed to inhibition of the activation of microglia and downregulation of IDO expression, thus inhibiting the kynurenine pathway and reversing the effects exerted on the 5-HT system.

Electroacupuncture Relieves LPS-Induced Depression-Like Behaviour in Rats Through IDO-Mediated Tryptophan-Degrading Pathway

BACKGROUND

Neuroinflammation is an important pathological mechanism of depression that leads to an increase in indoleamine-2,3-dioxygenase (IDO) activity and NMDAR activation. This study aimed to observe the effects of electroacupuncture on depression-like behaviour in lipopolysaccharide (LPS)-treated rats and the underlying mechanism.

METHODS

Wistar rats were intraperitoneally administered LPS (0.5 mg/kg) for 7 consecutive days to establish a depression model. Electroacupuncture treatment was administered 1 hour after daily LPS injection. The open field test (OFT), forced swimming test (FST), and sucrose preference test (SPT) were used to evaluate the depressive-like behaviours. IL-1β, IL-6, and TNF-α levels were determined by enzyme-linked immunosorbent assay (ELISA); Trp, 5-hydroxytryptamine (5-HT), kynurenine (Kyn) and quinolinic acid (Quin) were detected by ultra-high-performance liquid chromatography-tandem mass spectrometry; and N-methyl-D-aspartate receptor (NMDAR) protein and mRNA were assessed by Western blot and real-time qPCR.

RESULTS

The results showed that electroacupuncture treatment successfully corrected LPS-induced depressive-like behaviour, reduced the inflammatory factor (IL-1β, IL-6 and TNF-α) levels in the blood and hippocampus, prevented IDO over-activation and recovered NR2B expression after challenge by LPS.

CONCLUSION

Electroacupuncture treatment provided protection against LPS-induced depressive-like behaviour, and the associated mechanisms may be related to inhibiting the inflammatory response, regulating the IDO-mediated tryptophan-degrading pathway, and inhibiting NR2B activation.

The Impact of Immunological Factors on Depression Treatment - Relation Between Antidepressants and Immunomodulation Agents

It is determined that 30% of patients with depression are resistant to antidepressant medication. The increased concentration of inflammation factors, such as C-reactive protein, and pro-inflammatory cytokines, have been detected in serum in these patients. It is necessary to establish new therapeutic possibilities and protocols that are created to overcome the difficulties caused by increased concentration of inflammatory biomarkers in depressive patients. The Selective Serotonin Reuptake Inhibitors (SSRIs) are considered to be the most powerful antidepressants, increasing the level of serotonin in endogenous depression, as well as in that caused by immunological mechanisms. It is believed that agents that influence cytokines, immunological signal pathways and cytokine syntheses, like the inhibitors of cyclooxygenase enzyme and other non-steroidal anti-inflammatory drugs (NSAIDs), are very important in the potential treatment of residual symptoms of depression. Treatment with cytokine antagonists is one of the potential adjuvant therapies, along with antidepressants. Signal pathways blockers, such as the inhibitors of cyclooxygenase and other NSAIDs, are in the phase of research, in terms of their antidepressant effects. Also, it has been shown that the inhibition of indolamin-2,3 deoxygenase (IDO) and kynurenine (KYN) signal pathways in the synthesis of neurotransmitters, by application of IDO antagonists, are leading to suppression of pro-inflammatory cytokine effects. Antidepressants may have anti-inflammatory effects, depending on dose and type, and they achieve this effect through the decrease of pro-inflammatory cytokine production and increase of anti-inflammatory cytokines. Also, antidepressants modulate the humoral and cellular immune system. This work aims to summarise certain neurobiological and neuroimmunological specificities that have been observed in patients with depression, antidepressants and immunomodulation agents. The understanding of complex and heterogenic pathophysiology of depression through the prism of the altered immune system, is of major importance, in terms of better optimisation of pharmacotherapy, and options for a personalised approach in depressive disorder treatment.

Neuroimmune nexus of depression and dementia: Shared mechanisms and therapeutic targets

Dysfunctional immune activity is a physiological component of both Alzheimer's disease (AD) and major depressive disorder (MDD). The extent to which altered immune activity influences the development of their respective cognitive symptoms and neuropathologies remains under investigation. It is evident, however, that immune activity affects neuronal function and circuit integrity. In both disorders, alterations are present in similar immune networks and neuroendocrine signalling pathways, immune responses persist in overlapping neuroanatomical locations, and morphological and structural irregularities are noted in similar domains. Epidemiological studies have also linked the two disorders, and their genetic and environmental risk factors intersect along immune-activating pathways and can be synonymous with one another. While each of these disorders individually contains a large degree of heterogeneity, their shared immunological components may link distinct phenotypes within each disorder. This review will therefore highlight the shared immune pathways of AD and MDD, their overlapping neuroanatomical features, and previously applied, as well as novel, approaches to pharmacologically manipulate immune pathways, in each neurological condition. LINKED ARTICLES: This article is part of a themed section on Therapeutics for Dementia and Alzheimer's Disease: New Directions for Precision Medicine. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v176.18/issuetoc.

LC-MS/MS-based quantification of tryptophan metabolites and neurotransmitters in the serum and brain of mice

l-Tryptophan (Trp) metabolites and related neurotransmitters play crucial roles in physiological functions, and their imbalances are implicated in the pathology of depression, Alzheimer's disease and other diseases. Measurement of Trp metabolites and related neurotransmitters possesses a great potential to elucidate the disease mechanisms and evaluate the outcomes of therapeutic interventions. A simple, rapid, sensitive and specific liquid chromatography-tandem mass spectrometry (LC-MS/MS) method was developed for simultaneous determination of Trp, l-kynurenine (Kyn), kynurenic acid (Kyna), 3-hydroxykynurenine (3-HK), 5-hydroxytryptamine (5-HT), 5-hydroxyindoleacetic acid (5-HIAA), norepinephrine (NE), l-glutamic acid (Glu), γ-aminobutyric acid (GABA) and acetylcholine (ACh) in mice serum and the brain tissues in a single chromatographic run. Samples were spiked with the internal standard, mixed with trifluoroacetic acid to precipitate protein and analyzed by LC-MS/MS. Chromatographic separation was achieved using a Restek Ultra Aqueous C18 column in combination with a gradient elution within 8 min. Mass spectrometric detection was performed using multiple reaction monitoring with electrospray ionization source in positive mode. The method exhibited good selectivity and correlation coefficient values for the calibration curves of each analyte were >0.99. The limit of detection and quantification ranged from 0.96 to 24.48 nmol/L and 3.42 to 244.82 nmol/L, respectively. The intra- and inter-day precision were ≤13.92%. All analytes were stable in prepared samples at room temperature in the autosampler for 24 h. This method was successfully applied to the analysis of biological samples from control and chronic mild stress (CMS) induced depression mice. It was found that Kyn and 3-HK pathways were enhanced by CMS, while the levels of Trp, Kyna, 5-HIAA, Glu, GABA and ACh were significantly reduced. The changes in 5-HT and NE levels were not uniform in the periphery and the brain. This method can therefore be applied to analyze Trp metabolites and related neurotransmitters levels to monitor disease states, study the mechanisms and outcomes of therapeutic interventions.

Immunological Aspects of Depressive Disorder – The Review

Depression represents a mood disorder and is considered to be one of the most common mental disorders in general. World Health Organization estimates that depression will be the leading cause of disability-adjusted life years, until 2030. Depression is a complex heterogeneous disorder where immune system and its regulation play an important role. Innate and adaptive immunity mecha nisms are included, along with processes of immune activation and suppression. The expression of humoral factors of innate immunity, especially pro-inflammatory cytokines, is increased, whereas the intensity of cellular immune mechanisms, primarily T cells and NK cells, are impaired. The influence of pro-inflammatory cytokines on depression is reflected in their effect on certain enzymes and ensuing reduction of neurotransmitters serotonin and dopamine. They also affect the neuroendocrine function in central nervous system, resulting in increase of cortisol levels and inactivation of glucocorticoid receptors in the periphery, which leads to neurodegeneration and decrease in neurotransmitter production. Certain cytokines affect neuroplasticity through the decreasing of concentration of neurotrophic brain factor and induction of brain cell apoptosis. The results are often contradictory talking about mechanisms of adaptive immunity. On one hand, an increased activity of Tlymphocytes is observed, while on the other, there are evidence of spontaneous apoptosis and impaired function of these cells in depression. In addition, neuroprotective role of autoreactive and regulatory T cells in prevention of depression has also been demonstrated. The aim of this paper is to analyze the current knowledge on the role of immune mechanisms in the pathogenesis of depression.

Oral Probiotics Ameliorate the Behavioral Deficits Induced by Chronic Mild Stress in Mice via the Gut Microbiota-Inflammation Axis

In recent years, a burgeoning body of research has revealed links between depression and the gut microbiota, leading to the therapeutic use of probiotics for stress-related disorders. In this study, we explored the potential antidepressant efficacy of a multi-strain probiotics treatment (Lactobacillus helveticus R0052, Lactobacillus plantarum R1012, and Bifidobacterium longum R0175) in a chronic mild stress (CMS) mouse model of depression and determined its probable mechanism of action. Our findings revealed that mice subjected to CMS exhibited anxiety- and depressive-like behaviors in the sucrose preference test, elevated plus maze, and forced swim test, along with increased interferon-γ, tumor necrosis factor-α, and indoleamine 2,3-dioxygenase-1 levels in the hippocampus. Moreover, the microbiota distinctly changed from the non-stress group and was characterized by highly diverse bacterial communities associated with significant reductions in Lactobacillus species. Probiotics attenuated CMS-induced anxiety- and depressive-like behaviors, significantly increased Lactobacillus abundance, and reversed the CMS-induced immune changes in the hippocampus. Thus, the possible mechanism involved in the antidepressant-like activity of probiotics is correlated with Lactobacillus species via the gut microbiota-inflammation-brain axis.

Microbiota alteration is associated with the development of stress-induced despair behavior

Depressive disorders often run in families, which, in addition to the genetic component, may point to the microbiome as a causative agent. Here, we employed a combination of behavioral, molecular and computational techniques to test the role of the microbiota in mediating despair behavior. In chronically stressed mice displaying despair behavior, we found that the microbiota composition and the metabolic signature dramatically change. Specifically, we observed reduced Lactobacillus and increased circulating kynurenine levels as the most prominent changes in stressed mice. Restoring intestinal Lactobacillus levels was sufficient to improve the metabolic alterations and behavioral abnormalities. Mechanistically, we identified that Lactobacillus-derived reactive oxygen species may suppress host kynurenine metabolism, by inhibiting the expression of the metabolizing enzyme, IDO1, in the intestine. Moreover, maintaining elevated kynurenine levels during Lactobacillus supplementation diminished the treatment benefits. Collectively, our data provide a mechanistic scenario for how a microbiota player (Lactobacillus) may contribute to regulating metabolism and resilience during stress.