Selective increase of cerebrospinal fluid IL-6 during experimental systemic inflammation in humans: association with depressive symptoms

The prospects for early detection with optical coherence tomography (OCT) and OCT angiography in major depressive disorder

BACKGROUND

Research has shown the diagnostic potential of optical coherence tomography (OCT) and OCT angiography (OCTA) in various psychiatric disorders. However, there is few research focusing on changes specific to Major Depressive Disorder (MDD), and the diagnostic value of OCT combined with OCTA parameters for MDD remains unclear.

METHODS

In this study, we investigated microvascular and morphology changes in the retina of MDD patients using a combination of OCTA and OCT parameters, and to examine their correlation with MDD mood and cognitive function in order to assess their diagnostic capability.

RESULTS

Our findings revealed a significant decline in macular vessel density (MVD) in the superficial retinal capillary plexus (SRCP) across all subfields, except the NO area. We also observed a significant positive correlation between fovea and Stroop-1, as well as between temporal inner (TI) and Stroop-3 in MDD patients. Furthermore, we identified a negative correlation between fovea and Self-Rating Depression Scale, as well as between Superior outer (SO) and Difficulties in Emotion Regulation Scale-C in MDD patients.

LIMITATIONS

The sample size was small. Anatomical variables in blood flow may contribute to variability between subjects and outcomes.

CONCLUSIONS

The diagnostic value of OCTA suggests their potential as valuable tools for monitoring and diagnosing MDD.

Gut inflammation associated with age and Alzheimer's disease pathology: a human cohort study

Age-related disease may be mediated by low levels of chronic inflammation ("inflammaging"). Recent work suggests that gut microbes can contribute to inflammation via degradation of the intestinal barrier. While aging and age-related diseases including Alzheimer's disease (AD) are linked to altered microbiome composition and higher levels of gut microbial components in systemic circulation, the role of intestinal inflammation remains unclear. To investigate whether greater gut inflammation is associated with advanced age and AD pathology, we assessed fecal samples from older adults to measure calprotectin, an established marker of intestinal inflammation which is elevated in diseases of gut barrier integrity. Multiple regression with maximum likelihood estimation and Satorra-Bentler corrections were used to test relationships between fecal calprotectin and clinical diagnosis, participant age, cerebrospinal fluid biomarkers of AD pathology, amyloid burden measured using 11C-Pittsburgh compound B positron emission tomography (PiB PET) imaging, and performance on cognitive tests measuring executive function and verbal learning and recall. Calprotectin levels were elevated in advanced age and were higher in participants diagnosed with amyloid-confirmed AD dementia. Additionally, among individuals with AD dementia, higher calprotectin was associated with greater amyloid burden as measured with PiB PET. Exploratory analyses indicated that calprotectin levels were also associated with cerebrospinal fluid markers of AD, and with lower verbal memory function even among cognitively unimpaired participants. Taken together, these findings suggest that intestinal inflammation is linked with brain pathology even in the earliest disease stages. Moreover, intestinal inflammation may exacerbate the progression toward AD.

How Can Experimental Endotoxemia Contribute to Our Understanding of Pain? A Narrative Review

The immune system and the central nervous system exchange information continuously. This communication is a prerequisite for adaptive responses to physiological and psychological stressors. While the implicate relationship between inflammation and pain is increasingly recognized in clinical cohorts, the underlying mechanisms and the possibilities for pharmacological and psychological approaches aimed at neuro-immune communication in pain are not fully understood yet. This calls for preclinical models which build a bridge from clinical research to laboratory research. Experimental models of systemic inflammation (experimental endotoxemia) in humans have been increasingly recognized as an approach to study the direct and causal effects of inflammation on pain perception. This narrative review provides an overview of what experimental endotoxemia studies on pain have been able to clarify so far. We report that experimental endotoxemia results in a reproducible increase in pain sensitivity, particularly for pressure and visceral pain (deep pain), which is reflected in responses of brain areas involved in pain processing. Increased levels of blood inflammatory cytokines are required for this effect, but cytokine levels do not always predict pain intensity. We address sex-dependent differences in immunological responses to endotoxin and discuss why these differences do not necessarily translate to differences in behavioral measures. We summarize psychological and cognitive factors that may moderate pain sensitization driven by immune activation. Together, studying the immune-driven changes in pain during endotoxemia offers a deeper mechanistic understanding of the role of inflammation in chronic pain. Experimental endotoxemia models can specifically help to tease out inflammatory mechanisms underlying individual differences, vulnerabilities, and comorbid psychological problems in pain syndromes. The model offers the opportunity to test the efficacy of interventions, increasing their translational applicability for personalized medical approaches.

Endotoxin-Induced Physiological and Psychological Sickness Responses in Healthy Humans: Insights into the Post-Acute Phase

INTRODUCTION

Experimental endotoxemia is a translational model of systemic inflammation that has contributed significantly to our current understanding of sickness behavior and inflammation-associated depression. Previous studies using this model revealed a strong association between cytokine levels, endocrine changes, and psychological sickness symptoms during the acute phase of inflammation. The objective of this randomized, double-blind, placebo-controlled crossover study was to gain insight into potential post-acute physiological and psychological consequences of endotoxin administration that may either persist or newly emerge between 24 and 72 h after injection. The main focus was on associations between serum levels of C-reactive protein (CRP) and affective symptoms as well as alterations in diurnal cortisol profile, the two key features of inflammation-associated depression.

METHODS

Healthy male volunteers (N = 18) received an injection of either endotoxin (0.8 ng/kg) or placebo on two separate but otherwise identical study days, 7 days apart. Blood and saliva samples were collected during acute and post-acute phases after injection to measure blood inflammatory markers (interleukin [IL]-6, IL-1 receptor antagonist [ra], CRP) and salivary cortisol levels. In addition, participants completed a comprehensive battery of questionnaires to assess physical and psychological sickness symptoms.

RESULTS

Endotoxin treatment induced a short-time rise in plasma IL-6 and a longer increase in IL-1ra. The increase in serum CRP was delayed compared to cytokines, peaking at 24 h and gradually decreasing until 72 h after injection. The inflammatory response was accompanied by bodily and psychological sickness symptoms which occurred only in the acute phase, whereas none of the symptoms persisted or recurred in the post-acute phase. Salivary cortisol levels were significantly increased during the acute phase and exhibited pronounced circadian changes. However, no significant differences in diurnal cortisol profiles were observed between placebo and endotoxin conditions on the days after treatment.

CONCLUSION

Our findings suggest that CRP, which is elevated in patients with inflammation-associated depression, does not appear to be responsible for depressive symptomatology. Moreover, a single inflammatory episode is not sufficient to alter diurnal cortisol profiles, as observed in inflammation-associated depression. In addition, the absence of persistent lipopolysaccharide-induced psychological and physiological changes beyond the acute phase further supports the safety of endotoxin administration in humans.

Individuals with depression exhibiting a pro-inflammatory phenotype receiving omega-3 polyunsaturated fatty acids experience improved motivation-related cognitive function: Preliminary results from a randomized controlled trial

Cognitive impairment related to major depressive disorder (MDD) is highly prevalent, debilitating and is lacking in effective treatments; dysregulated inflammatory physiology is a putative mechanism and may represent a therapeutic target. In depressed individuals exhibiting a pro-inflammatory phenotype who were enrolled in a 12-week randomized placebo-controlled trial of 3 doses of omega-3 polyunsaturated fatty acids (ω-3-FA), we examined: (i) the relationship between dysregulated inflammatory physiology and baseline cognitive impairment; (ii) improvement in cognitive impairment following treatment; and (iii) the association between baseline inflammatory biomarkers and change in cognitive impairment for those receiving treatment. We randomized 61 unmedicated adults aged 45.50 years (75% female) with DSM-5 MDD, body mass index >25 kg/m², and C-reactive protein (CRP) ≥3.0 mg/L to three doses of ω-3-FA (1, 2, or 4 g daily) or matching placebo. Analyses focused on 45 study completers who had inflammatory biomarkers assessed [circulating CRP, interleukin-6 (IL-6) and tumor necrosis factor-α (TNFα) as well as lipopolysaccharide (LPS)-stimulated concentrations of IL-6 and TNFα in peripheral blood mononuclear cells (PBMC)] and on the highest dose ω-3-FA (4 g daily; n = 11) compared to placebo (n = 10). Impairment in motivational symptoms (e.g., alertness, energy, enthusiasm) and higher-order cognitive functions (e.g., word-finding, memory) were assessed by a validated self-report measure. Among all 45 participants at baseline, lower concentrations of IL-6 in LPS-stimulated PBMC were associated with greater impairment in higher-order cognitive functions (r = -0.35, p = .02). Based on hierarchical linear modeling, individuals receiving 4 g/day of ω-3-FA reported significant improvement in motivational symptoms compared to placebo (B = -0.07, p = .03); in the 4 g/day group, lower baseline concentrations of TNFα in LPS-stimulated PBMC were associated with significant improvement in motivational symptoms (Ρ = .71, p = .02) following treatment. In this exploratory clinical trial, daily supplementation with 4 g of ω-3-FA improves motivational symptoms in depressed individuals exhibiting an inflammatory phenotype.

Oral exposure to an acceptable daily intake dose of aspartame induced a delayed proinflammatory cytokine response in the cerebrospinal fluid of rats

This study aimed to investigate the effect of exposure to aspartame (ASP) at safe levels on proinflammatory cytokines in the cerebrospinal fluid (CSF) of rats. Sprague Dawley rats were sacrificed after 1, 2, 4 or 8 week(s) of continuous exposure to ASP (40 mg/kg body weight). Serum, CSF and brain tissue samples were prepared, and the levels of the IL-1β, IL-6 and TNF-α were analyzed by ELISA. In serum, the levels of all three cytokines showed a two-phase alteration, a decrease followed by an increase in the ASP group. In the brain, their levels increased from the second or fourth week compared with the control group. In CSF, the levels of these cytokines showed a similar change to that in brain tissue, but the increase appeared at a later time point. For each cytokine, there was a significant positive correlation between its levels in serum, brain tissue and CSF. This is the first discovery that ASP exposure increased the levels of proinflammatory cytokines in CSF in rats, which emerged later than in blood and brain tissue. This study suggests the necessity of conducting related clinical studies to evaluate potential neuroinflammatory effects induced by chronic ASP exposure through CSF analysis.

Towards Novel Potential Molecular Targets for Antidepressant and Antipsychotic Pharmacotherapies

Depression and schizophrenia are two highly prevalent and severely debilitating neuropsychiatric disorders. Both conventional antidepressant and antipsychotic pharmacotherapies are often inefficient clinically, causing multiple side effects and serious patient compliance problems. Collectively, this calls for the development of novel drug targets for treating depressed and schizophrenic patients. Here, we discuss recent translational advances, research tools and approaches, aiming to facilitate innovative drug discovery in this field. Providing a comprehensive overview of current antidepressants and antipsychotic drugs, we also outline potential novel molecular targets for treating depression and schizophrenia. We also critically evaluate multiple translational challenges and summarize various open questions, in order to foster further integrative cross-discipline research into antidepressant and antipsychotic drug development.

Microfluidic/HPLC combination to study carnosine protective activity on challenged human microglia: Focus on oxidative stress and energy metabolism

Carnosine (β-alanyl-L-histidine) is a naturally occurring endogenous peptide widely distributed in excitable tissues such as the brain. This dipeptide possesses well-demonstrated antioxidant, anti-inflammatory, and anti-aggregation properties, and it may be useful for treatment of pathologies characterized by oxidative stress and energy unbalance such as depression and Alzheimer's disease (AD). Microglia, the brain-resident macrophages, are involved in different physiological brain activities such synaptic plasticity and neurogenesis, but their dysregulation has been linked to the pathogenesis of numerous diseases. In AD brain, the activation of microglia towards a pro-oxidant and pro-inflammatory phenotype has found in an early phase of cognitive decline, reason why new pharmacological targets related to microglia activation are of great importance to develop innovative therapeutic strategies. In particular, microglia represent a common model of lipopolysaccharides (LPS)-induced activation to identify novel pharmacological targets for depression and AD and numerous studies have linked the impairment of energy metabolism, including ATP dyshomeostasis, to the onset of depressive episodes. In the present study, we first investigated the toxic potential of LPS + ATP in the absence or presence of carnosine. Our studies were carried out on human microglia (HMC3 cell line) in which LPS + ATP combination has shown the ability to promote cell death, oxidative stress, and inflammation. Additionally, to shed more light on the molecular mechanisms underlying the protective effect of carnosine, its ability to modulate reactive oxygen species production and the variation of parameters representative of cellular energy metabolism was evaluated by microchip electrophoresis coupled to laser-induced fluorescence and high performance liquid chromatography, respectively. In our experimental conditions, carnosine prevented LPS + ATP-induced cell death and oxidative stress, also completely restoring basal energy metabolism in human HMC3 microglia. Our results suggest a therapeutic potential of carnosine as a new pharmacological tool in the context of multifactorial disorders characterize by neuroinflammatory phenomena including depression and AD.

Association between self-rated depressive symptoms and mucosal expression of NF-κ B in patients with upper gastrointestinal symptoms

BACKGROUND

Previous clinical studies have reported elevated levels of depressive symptoms in selected samples of patients with gastritis. The objective of this study was to examine the associations of specific biomarkers of inflammation expressed in mucosal tissue from the stomach with mood and anxiety symptoms in adult patients with upper gastrointestinal symptoms.

METHODS

In this monocentric, observational study, a total of 32 study participants were included who were referred for a routine diagnostic upper endoscopic assessment based on the suspected clinical diagnosis of gastritis. All participants completed the Hospital Anxiety and Depression Scale (HADS) before undergoing gastroscopy. Immunohistochemical stainings from biopsy sections were performed to evaluate the expression level of nuclear factor kappa B (NF-κ B), myeloperoxidase (MPO) and inducible nitric oxide synthase (iNOS).

RESULTS

Our findings confirmed that nearly half of the study cohort (n = 13; 41%) displayed positive HADS depression scores above the clinically relevant cut-off level of ≥ 8. Regression models demonstrated that depressive symptoms were significantly and positively associated with the expression level of NF-κ B in biopsies from the upper gastrointestinal tract.

CONCLUSIONS

In summary, our study showed a significant association between NF-κ B expression and clinically relevant depressive symptoms in patients with gastritis, as assessed by a self-rated psychometric questionnaire. Further investigations are needed to confirm this relationship and to identify the pathophysiological mechanisms involved.

Radiation-induced neuroinflammation monitoring by the level of peripheral blood monocytes with high expression of translocator protein

PURPOSE

Currently there are no effective diagnostic methods for the control of neuroinflammation before manifestation of cognitive impairment after head irradiation. The translocator protein (TSPO) is highly expressed in glial cells upon brain damage, therefore we compared the changes in the number of cells with high TSPO expression in the brain and peripheral blood during radiation-induced neuroinflammation.

MATERIALS AND METHODS

Hippocampal cytokines mRNA expression and the content of cells with high TSPO expression in the brain and peripheral blood monocytes were analyzed up to eight months after mice head γ-irradiation at a dose of 2 Gy or 8Gy.

RESULTS

Mice irradiation at a dose of 8 Gy causes neuroinflammation, accompanied by an increase of M1 microglia and TSPOhigh cells in the brain, elevated gene expression of pro-inflammatory and decreased of anti-inflammatory cytokines along with an increased number of microglia and astrocytes in the hippocampus. The content of TSPOhigh cells in the brain correlates with the level TSPOhigh monocytes in three days, one month and two months after exposure.

CONCLUSIONS

An increase in the level of the monocytes with high expression of TSPO may be considered as a marker for an early diagnostics of post-radiation brain damage leading to cognitive impairment.

Inflammation shapes neural processing of interoceptive fear predictors during extinction learning in healthy humans

Inflammation could impact on the formation and persistence of interoceptive fear and hypervigilance, with relevance to psychiatric disorders and chronic pain. To systematically analyze effects of inflammation on fear learning and extinction, we performed two complementary randomized, double-blind, placebo-controlled functional magnetic resonance imaging (fMRI) studies combining experimental endotoxemia as a translational model of acute systemic inflammation with a two-day multiple-threat fear conditioning paradigm involving interoceptive and exteroceptive unconditioned stimuli (US). Healthy volunteers (N = 95) were randomized to receive intravenous injections of either endotoxin (lipopolysaccharide, LPS; 0.4 ng/kg) or placebo prior to fear acquisition (study 1) or extinction training (study2). Treatment effects on behavioral and neural responses to conditioned stimuli (CS) predicting interoceptive or exteroceptive threat were assessed during fear learning and extinction phases, along with US valence ratings. Despite robust inflammatory and emotional responses triggered by LPS, no direct effects of inflammation on US ratings or on the formation or extinction of conditioned fear, as assessed with CS valence ratings, were observed. However, in the group treated with LPS prior to acquisition (i.e., study 1), we found enhanced neural responses to the interoceptive but not the exteroceptive CS in key regions of the central fear circuitry during extinction learning. After extinction, this group further showed enhanced negative valence ratings selectively for the interoceptive US during unexpected US re-exposure when compared to the placebo group. Together, inflammation during fear acquisition may promote the establishment of a more robust neural signature of the interoceptive fear memory trace, which may contribute to altered interoceptive pain perception. The fear extinction circuitry engaged during interoceptive fear memory processing may be particularly vulnerable to inflammation, with transdiagnostic implications for gut-brain mechanisms underlying disturbed interoception in psychiatric conditions and chronic visceral pain.

The sex-dependent response to psychosocial stress and ischaemic heart disease

Stress is an important risk factor for modern chronic diseases, with distinct influences in males and females. The sex specificity of the mammalian stress response contributes to the sex-dependent development and impacts of coronary artery disease (CAD). Compared to men, women appear to have greater susceptibility to chronic forms of psychosocial stress, extending beyond an increased incidence of mood disorders to include a 2- to 4-fold higher risk of stress-dependent myocardial infarction in women, and up to 10-fold higher risk of Takotsubo syndrome-a stress-dependent coronary-myocardial disorder most prevalent in post-menopausal women. Sex differences arise at all levels of the stress response: from initial perception of stress to behavioural, cognitive, and affective responses and longer-term disease outcomes. These fundamental differences involve interactions between chromosomal and gonadal determinants, (mal)adaptive epigenetic modulation across the lifespan (particularly in early life), and the extrinsic influences of socio-cultural, economic, and environmental factors. Pre-clinical investigations of biological mechanisms support distinct early life programming and a heightened corticolimbic-noradrenaline-neuroinflammatory reactivity in females vs. males, among implicated determinants of the chronic stress response. Unravelling the intrinsic molecular, cellular and systems biological basis of these differences, and their interactions with external lifestyle/socio-cultural determinants, can guide preventative and therapeutic strategies to better target coronary heart disease in a tailored sex-specific manner.

Neuronal-microglial liver X receptor β activating decrease neuroinflammation and chronic stress-induced depression-related behavior in mice

Depression is accompanied by excessive neuroinflammation. Liver X receptor β (LXRβ) has been reported as a newly emerging target that exerts systemic and organic inflammation modulation. However, the modulatory mechanism in alleviating neuroinflammation are far from being revealed. In the current study, depression-related behaviors in mice were induced by chronic unpredictable mild stress (CUMS) and corticosterone (CORT) drinking. Mice received either TO901317, PLX-5622 and intra- bilateral basolateral amygdale (BLA) injection of rAAV9-hSyn-hM3D(Gq)-eGFP to activate LXRβ, eliminate microglia and pharmacogenetic activate neurons in BLA, respectively, followed by behavioral tests. Microglial pro-inflammatory and pro-phagocytic activation, as well as nuclear factor-κB (NF-κB) signaling pathway, NLRP3 inflammasome activation and interleukin-1β (IL-1β) release in BLA were investigated. Moreover, pro-inflammatory activation of BV2 cells-induced by CORT with or without TO901317 was detected. Neuroinflammation indicated by IL-1β release was measured in a co-culture system of HT22-primary microglia with or without TO901317. Our results indicated that chronic stress induced depression-related behaviors, which were accompanied with microglial pro-inflammatory and pro-phagocytic activation, as well as NF-κB signaling pathway and NLRP3 inflammasome activation in BLA. Accordingly, pharmacological activation of LXRβ inhibited microglial pro-inflammatory and pro-phagocytic activation, as well as NF-κB signaling pathway and NLRP3 inflammasome activation, and IL-1β release both in vivo and in vitro. Finally, both elimination of microglia and pharmacogenetic activation of neurons in BLA protected mice from chronic stress-induced depression-related behavior. Collectively, pharmacological activation of neuronal-microglial LXRβ alleviates depression-related behavior by modulating excessive neuroinflammation via inhibiting NF-κB signaling pathway and NLRP3 inflammasome activation.

The relationship between Central Nervous System morphometry changes and key symptoms in Crohn’s disease

Alterations in grey matter volume (GMV) and cortical thickness (CT) in Crohn’s disease (CD) patients has been previously documented. However, the findings are inconsistent, and not a true representation of CD burden, as only CD patients in remission have been studied thus far. We investigate alterations in brain morphometry in patients with active CD and those in remission, and study relationships between brain structure and key symptoms of fatigue, abdominal pain, and extraintestinal manifestations (EIM). Magnetic Resonance Imaging brain scans were collected in 89 participants; 34 CD participants with active disease, 13 CD participants in remission and 42 healthy controls (HCs); Voxel based morphometry (VBM) assessed GMV and white matter volume (WMV), and surface-based analysis assessed cortical thickness (CT). We show a significant reduction in global cerebrospinal fluid (CSF) volume in CD participants compared with HCs, as well as, a reduction in regional GMV, WMV and CT in the left precentral gyrus (motor cortex), and an increase in GMV in the frontal brain regions in CD compared with HCs. Atrophy of the supplementary motor area (SMA) was associated with greater fatigue in CD. We also show alterations in brain structure in multiple regions in CD associated with abdominal pain and extraintestinal inflammations (EIMs). These brain structural alterations likely reflect neuroplasticity to a chronic systemic inflammatory response, abdominal pain, EIMs and fatigue. These findings will aid our understanding of the cross-linking between chronic inflammation, brain structural changes and key unexplained CD symptomatology like fatigue.

Resolution of depression: antidepressant actions of resolvins

Major depressive disorder, one of the most widespread mental illnesses, brings about enormous individual and socioeconomic consequences. Conventional monoaminergic antidepressants require weeks to months to produce a therapeutic response, and approximately one-third of the patients fail to respond to these drugs and are considered treatment-resistant. Although recent studies have demonstrated that ketamine, an N-methyl-D-aspartate receptor antagonist, produces rapid antidepressant effects in treatment-resistant patients, it also has undesirable side effects. Hence, rapid-acting antidepressants that have fewer adverse effects than ketamine are urgently required. D-series (RvD1-RvD6) and E-series (RvE1-RvE4) resolvins are endogenous lipid mediators derived from docosahexaenoic and eicosapentaenoic acids, respectively. These mediators reportedly play a pivotal role in the resolution of acute inflammation. In this review, we reveal that intracranial infusions of RvD1, RvD2, RvE1, RvE2, and RvE3 produce antidepressant-like effects in various rodent models of depression. Moreover, the behavioral effects of RvD1, RvD2, and RvE1 are mediated by the activation of the mechanistic target of rapamycin complex 1, which is essential for the antidepressant-like actions of ketamine. Finally, we briefly provide our perspective on the possible role of endogenous resolvins in stress resilience.

Involvement of the IL-6 Signaling Pathway in the Anti-Anhedonic Effect of the Antidepressant Agomelatine in the Chronic Mild Stress Model of Depression

Neuroinflammation has emerged as an important factor in the molecular underpinnings of major depressive disorder (MDD) pathophysiology and in the mechanism of action of antidepressants. Among the inflammatory mediators dysregulated in depressed patients, interleukin (IL)-6 has recently been proposed to play a crucial role. IL-6 activates a signaling pathway comprising the JAK/STAT proteins and characterized by a specific negative feedback loop exerted by the cytoplasmic protein suppressor of cytokine signalling-3 (SOCS3). On these bases, here, we explored the potential involvement of IL-6 signaling in the ability of the antidepressant drug agomelatine to normalize the anhedonic-like phenotype induced in the rat by chronic stress exposure. To this aim, adult male Wistar rats were subjected to the chronic mild stress (CMS) paradigm and chronically treated with vehicle or agomelatine. The behavioral evaluation was assessed by the sucrose consumption test, whereas molecular analyses were performed in the prefrontal cortex. We found that CMS was able to stimulate IL-6 production and signaling, including SOCS3 gene and protein expression, but the SOCS3-mediated feedback-loop inhibition failed to suppress the IL-6 cascade in stressed animals. Conversely, agomelatine treatment normalized the stress-induced decrease in sucrose consumption and restored the negative modulation of the IL-6 signaling via SOCS3 expression and activity. Our results provide additional information about the pleiotropic mechanisms that contribute to agomelatine’s therapeutic effects.

LPS activates neuroinflammatory pathways to induce depression in Parkinson’s disease-like condition

Aim: This study aimed to observe the effects of lipopolysaccharide (LPS) intraperitoneal (i.p.) injection on rats and investigate how neuroinflammation contributes to the pathogenesis of depression in Parkinson’s disease (dPD).

Methods: Rats were administered LPS (0.5 mg/kg, i.p.) for either 1, 2, or 4 consecutive days to establish a rat model of dPD. The sucrose preference test (SPT), the open field test (OFT), and the rotarod test evaluated depression-like and motor behaviors. Magnetic resonance imaging was used to detect alterations in the intrinsic activity and the integrity of white matter fibers in the brain. The expression of c-Fos, ionized calcium-binding adapter molecule (Iba-1), and tyrosine hydroxylase (TH) was evaluated using immunohistochemistry. The concentration of interleukin-6 (IL-6), tumor necrosis factor (TNF-α), and interleukin-10 (IL-10) was measured using Luminex technology.

Results: LPS i.p. injections decreased sucrose preference in the SPT, horizontal and center distance in the OFT, and standing time in the rotarod test. The intrinsic activities in the hippocampus (HIP) were significantly reduced in the LPS-4 d group. The integrity of white matter fibers was greatly destroyed within 4 days of LPS treatment. The expression of c-Fos and Iba-1 in the prefrontal cortex, HIP, and substantia nigra increased dramatically, and the number of TH⁺ neurons in the substantia nigra decreased considerably after LPS injection. The levels of IL-6, TNF-α, and IL-10 were higher in the LPS-4 d group than those in the control group.

Conclusion: Injection of LPS (0.5 mg/kg, i.p.) for 4 consecutive days can activate microglia, cause the release of inflammatory cytokines, reduce intrinsic activities in the HIP, destroy the integrity of white matter fibers, induce anhedonia and behavioral despair, and finally lead to dPD. This study proved that LPS injection (0.5 mg/kg, i.p.) for 4 consecutive days could be used to successfully create a rat model of dPD.

Interaction effect of the serum interleukin-6 level and anxiety on the 12-week pharmacotherapeutic responses of patients with depressive disorders

BACKGROUND

Despite the pathogenic role played by interleukin-6 (IL-6) signaling in depression, the association between baseline peripheral IL-6 signaling and the antidepressant treatment responses noted in clinical studies remains controversial. We investigated the effects of the baseline serum IL-6 (sIL-6) level and anxiety symptoms on the 12-week remission rate of depressed outpatients who received stepwise antidepressant treatments.

METHODS

At baseline, sIL-6 levels were measured, and anxiety symptoms were evaluated using the Hospital Anxiety Depression Scale-Anxiety subscale (HADS-A), in 1094 patients. All received stepwise antidepressant treatment. Subsequently, 12-week remission, defined as a Hamilton Depression Rating Scale (HAMD) score ≤ 7, was assessed.

RESULTS

The individual and interaction effects of the sIL-6 level (as a binary [low vs. high, based on the median value of 1.65 pg/mL] or continuous variable) and the HADS-A score (as a binary [<12 vs. ≥12] or continuous variable) on the 12-week remission rate were analyzed using logistic regression models after adjusting for relevant covariates. Patients with both low sIL-6 levels (<1.65 pg/mL) and HADS-A scores <12 had the highest 12-week remission rate; a significant interaction effect was also apparent. This effect was significant even when the data were analyzed as continuous variables.

CONCLUSIONS

Our study suggests that the sIL-6 level can serve as a biomarker predicting the outcome of antidepressant treatment according to the severity of anxiety symptoms.

Mangiferin Alleviates Postpartum Depression-Like Behaviors by Inhibiting MAPK Signaling in Microglia

Postpartum depression (PPD), a severe mental health disorder, is closely associated with decreased gonadal hormone levels during the postpartum period. Mangiferin (MGF) possesses a wide range of pharmacological activities, including anti-inflammation. Growing evidence has suggested that neuroinflammation is involved in the development of depression. However, the role of MGF in the development of PPD is largely unknown. In the present study, by establishing a hormone-simulated pregnancy PPD mouse model, we found that the administration of MGF significantly alleviated PPD-like behaviors. Mechanistically, MGF treatment inhibited microglial activation and neuroinflammation. Moreover, we found that MGF treatment inhibited mitogen-activated protein kinase (MAPK) signaling in vivo and in vitro. Together, these results highlight an important role of MGF in microglial activation and thus give insights into the potential therapeutic strategy for PPD treatment.

The Nervous System Contributes to the Tumorigenesis and Progression of Human Digestive Tract Cancer

Tumors of the gastrointestinal tract are one of the highest incidences of morbidity and mortality in humans. Recently, a growing number of researchers have indicated that nerve fibers and nerve signals participate in tumorigenesis. The current overarching view based on the responses to therapy revealed that tumors are partly promoted by the tumor microenvironment (TME), endogenous oncogenic factors, and complex systemic processes. Homeostasis of the neuroendocrine-immune axis (NEI axis) maintains a healthy in vivo environment in humans, and dysfunction of the axis contributes to various cancers, including the digestive tract. Interestingly, nerves might promote tumor development via multiple mechanisms, including perineural invasion (PNI), central level regulation, NEI axis effect, and neurotransmitter induction. This review focuses on the association between digestive tumors and nerve regulation, including PNI, the NEI axis, stress, and neurotransmitters, as well as on the potential clinical application of neurotherapy, aiming to provide a new perspective on the management of digestive cancers.

HDAC3-Regulated PGE2 Production by Microglia Induces Phobic Anxiety Susceptibility After Stroke and Pointedly Exploiting a Signal-Targeted Gamma Visual Stimulation New Therapy

Background

Phobic anxiety present after stroke (called poststroke anxiety, PSA) can hamper the rehabilitation of patients and disrupt their usual activities. Besides, the symptoms and mechanisms of PSA are different from those in nonstroke populations that have generalized anxiety disorder. What’s more, the treatment approaches for phobic anxiety are confined to unitary or general methods with poor efficiency.

Methods

Behavioural test screen combined bioinformatics analysis explored molecular changes between generalized anxiety disorder in nonstroke mice (restraint stress, RS) and photothrombotic stroke mice exposed to environmental stress (PTS + RS, mimicking PSA). Multiple molecular biological and neurobiological methods were employed to explain mechanisms in vitro and in vivo. And exploiting gamma flicker stimulation device for therapy.

Results

Microglial (MG) overactivation is a prominent characteristic of PTS + RS. HDAC3 was mainly upregulated in activated-microglia from damaged cortex and that local prostaglandin E2 (PGE₂) production increased in MG via HDAC3-mediated activation of NF-κB signalling by p65 deacetylation. A high content of PGE₂ in damaged ischaemic cortex could diffuse freely to amygdala, eliciting anxiety susceptibility of PSA via EP2. Importantly, gamma flicker stimulation relieved anxious behaviour of PTS + RS by modulating the HDAC3/Cox1/EP2 network at some extent.

Conclusions

HDAC3-regulated PGE₂ production by microglia constitutes phobic anxiety susceptibility after stroke and a protective approach of gamma visual stimulation can be a candidate new therapy.

Serum amyloid P component level is associated with clinical response to escitalopram treatment in patients with major depressive disorder

Serum amyloid P component (SAP) is a universal constituent of human amyloid deposits, which has been implicated in Alzheimer's disease and major depressive disorder (MDD). However, the relationship between SAP level and depression severity remains obscure. The aims of this study were to investigate how SAP is involved in depression and to explore the association between SAP level and antidepressant treatment response. Patients with MDD (n = 85) who received escitalopram monotherapy for 8-12 weeks were selected from a multicenter open-label randomized clinical trial. The same number of healthy controls was recruited. Depression severity was measured according to the Hamilton Depression Rating Scale (HAMD-17) at baseline and weeks 4, 8, and 12. The plasma levels of SAP were measured at baseline, week 2 and week 12. As a result, baseline levels of SAP were significantly higher in depressed patients than in control subjects (p < 0.001). SAP levels at baseline were negatively associated with depression severity after escitalopram treatment (p < 0.05), and the changes in SAP levels from baseline to week 12 were highly correlated with the severity of depressive symptoms based on the HAMD-17 score (p < 0.05). Interestingly, treatment with escitalopram significantly decreased the plasma levels of SAP in females, but not in males. Altogether, our results suggest that SAP not only involved in the pathobiology of depression but also mediates the action of antidepressant medications.

The Central Inflammatory Network: A Hypothalamic fMRI Study of Experimental Endotoxemia in Humans

INTRODUCTION

Inflammation is a mechanism of the immune system that is part of the reaction to pathogens or injury. The central nervous system closely regulates inflammation via neuroendocrine or direct neuroimmune mechanisms, but our current knowledge of the underlying circuitry is limited. Therefore, we aimed to identify hypothalamic centres involved in sensing or modulating inflammation and to study their association with known large-scale brain networks.

METHODS

Using high-resolution functional magnetic resonance imaging (fMRI), we recorded brain activity in healthy male subjects undergoing experimental inflammation from intravenous endotoxin. Four fMRI runs covered key phases of the developing inflammation: pre-inflammatory baseline, onset of endotoxemia, onset of pro-inflammatory cytokinemia, and peak of pro-inflammatory cytokinemia. Using masked independent component analysis, we identified functionally homogeneous subregions of the hypothalamus, which were further tested for changes in functional connectivity during inflammation and for temporal correlation with tumour necrosis factor and adrenocorticotropic hormone serum levels. We then studied the connection of these inflammation-associated hypothalamic subregions with known large-scale brain networks.

RESULTS

Our results show that there are at least 6 hypothalamic subregions associated with inflammation in humans including the paraventricular nucleus, supraoptic nucleus, dorsomedial hypothalamus, bed nucleus of the stria terminalis, lateral hypothalamic area, and supramammillary nucleus. They are functionally embedded in at least 3 different large-scale brain networks, namely a medial frontoparietal network, an occipital-pericentral network, and a midcingulo-insular network.

CONCLUSION

Measuring how the hypothalamus detects or modulates systemic inflammation is a first step to understand central nervous immunomodulation.

Inflammation and Cognition in Depression: A Narrative Review

The authors aim to present a narrative review of research on the inflammatory aetiology of depression. Depression is a psychiatric disorder, constituting the most common reason of disability due to a health condition. It has been estimated that at least one in six people suffer from depression at some point of their lives. The aetiology of depression, although researched extensively all around the world, still remains unclear. Authors discuss the possible role of inflammation in depression, the neurodevelopmental theory of depression as well as associations between cognition and depression. Possible associations between memory dysfunction among depressive patients and inflammatory markers are included. The associations between the immune system, depression and cognition are observed. Possible mediating factors between these areas include personality traits, hormonal imbalance and functioning of the brain areas. The question as to what mediating factors are involved is still open to research.

Changes in Functional Glucocorticoid Sensitivity of Isolated Splenocytes Induced by Chronic Psychosocial Stress - A Time Course Study

Chronic psychosocial stress is a risk factor for the development of numerous disorders, of which most are associated with chronic low-grade inflammation. Given the immunosuppressive effects of glucocorticoids (GC), one underlying mechanism might be the development of stress-induced GC resistance in certain immune cell subpopulations. In line with this hypothesis, male mice exposed to the chronic subordinate colony housing (CSC, 19 days) model develop GC resistance of in vitro lipopolysaccharide (LPS)-stimulated splenocytes, splenomegaly and an increased percentage of splenic CD11b⁺ cells. Here male C57BL/6N mice were euthanized at different days during CSC, and following 30 days of single housing after stressor termination to assess when CSC-induced splenic GC resistance starts to develop and whether this is a transient effect. Moreover, splenic CD11b, GC receptor (GR) and/or macrophage migration inhibiting factor (MIF) protein levels were quantified at respective days. While mild forms of CSC-induced GC resistance, increased splenic CD11b expression and/or splenomegaly were detectable on days 8 and 9 of CSC, more severe forms took until days 15 and 16 to develop, but normalized almost completely within 30 days following stressor termination (day 51). In contrast, splenic GR expression was decreased in CSC versus single-housed control (SHC) mice at all days assessed. While MIF expression was increased on days 15 and 16 of CSC, it was decreased in CSC versus SHC mice on day 20 despite persisting splenomegaly, increased CD11b expression and functional GC resistance. In summary, our data indicate that GC resistance and CD11b⁺ cell-mediated splenomegaly develop gradually and in parallel over time during CSC exposure and are transient in nature. Moreover, while we can exclude that CSC-induced reduction in splenic GR expression is sufficient to induce functional GC resistance, the role of MIF in CD11b⁺ cell-mediated splenomegaly and GC resistance requires further investigation.

Magnolol attenuates depressive-like behaviors by polarizing microglia towards the M2 phenotype through the regulation of Nrf2/HO-1/NLRP3 signaling pathway

PURPOSE

Magnolol (MA) exhibits anti-depressant effect by inhibiting inflammation. However, its effect on microglia polarization remains not fully understood. Herein, our study was performed to evaluate the effect of MA on microglia polarization in chronic unpredictable mild stress (CUMS)-induced depression and explore its potential mechanism.

STUDY DESIGN

The CUMS procedure was conducted, and the mice were intragastrically treated with MA. BV2 cells were pretreated with MA prior to LPS/ATP challenge.

METHODS

The levels of TNF-α, IL-1β, IL-6 and IL-4, IL-10 in brain and BV2 cells were examined by ELISA. The mRNA expressions of Arg1, Ym1, Fizz1 and Klf4 in brains were measured. ROS content was determined using flow cytometry. Immunofluorescence was employed to evaluate Iba-1 level, Nrf2 nuclear translocation, Iba-1⁺CD16/32⁺ and Iba-1⁺CD206⁺ cell population. The protein expressions of Nrf2, HO-1, NLRP3, caspase-1 p20 and IL-1β in brains and BV2 cells were investigated by western blot. Nrf2 siRNA was induced in experiments to explore the role of Nrf2 in MA-mediated microglia polarization. The ubiquitination of Nrf2 was visualized by Co-IP.

RESULTS

The treatment with MA notably relieved depressive like behaviors, suppressed pro-inflammatory cytokines, promoted anti-inflammatory cytokines and the transcription of M2 phenotype microglia-specific indicators. MA upregulated the expression of Nrf2, HO-1, downregulated the expression of NLRP3, caspase-1 p20, IL-1β both in vivo and in vitro. MA also reduced ROS concentration, promoted Nrf2 nucleus translocation and prevented Nrf2 ubiquitination. Nrf2 Knockdown by siRNA abolished the MA-mediated microglia polarization.

CONCLUSION

The present research demonstrated that MA attenuated CUMS-stimulated depression by inhibiting M1 polarization and inducing M2 polarization via Nrf2/HO-1/NLRP3 signaling.

Dlg1 Knockout Inhibits Microglial Activation and Alleviates Lipopolysaccharide-Induced Depression-Like Behavior in Mice

Microglia-mediated neuroinflammation is widely perceived as a contributor to numerous neurological diseases and mental disorders including depression. Discs large homolog 1 (Dlg1), an adaptor protein, regulates cell polarization and the function of K⁺ channels, which are reported to regulate the activation of microglia. However, little is known about the role of Dlg1 in microglia and the maintenance of central nervous system homeostasis. In this study, we found that Dlg1 knockdown suppressed lipopolysaccharide (LPS)-induced inflammation by down-regulating the activation of nuclear factor-κB signaling and the mitogen-activated protein kinase pathway in microglia. Moreover, using an inducible Dlg1 microglia-specific knockout (Dlg1^flox/flox; CX3CR1^CreER) mouse line, we found that microglial Dlg1 knockout reduced the activation of microglia and alleviated the LPS-induced depression-like behavior. In summary, our results demonstrated that Dlg1 plays a critical role in microglial activation and thus provides a potential therapeutic target for the clinical treatment of depression.

Depression and interleukin-6 signaling: A Mendelian Randomization study

BACKGROUND

A large body of research has reported associations between depression and elevated interleukin-6 (IL-6), a cytokine with several roles including pro-inflammatory signaling. The nature and directionality of this relationship are not yet clear. In this study we use Mendelian Randomization to examine the possibility of a causal relationship between IL-6 and depressive symptoms, and to explore multiple signaling pathways that could serve as mechanisms for this relationship.

METHODS

This study uses a two-sample Mendelian Randomization design. Data come from the UK Biobank (n = 89,119) and published summary statistics from six existing GWAS analyses. The primary analysis focuses on the soluble interleukin-6 receptor (sIL-6R), which is involved in multiple signaling pathways. Exploratory analyses use C-reactive protein (CRP) and soluble glycoprotein 130 (sgp130) to further examine potential underlying mechanisms.

RESULTS

Results are consistent with a causal effect of sIL-6R on depression (PCA-IVW Odds Ratio: 1.023 (95% Confidence Interval: 1.006-1.039), p = 0.006). Exploratory analyses demonstrate that the relationship could be consistent with either decreased classical signaling or increased trans signaling as the underlying mechanism.

DISCUSSION

These results strengthen the body evidence implicating IL-6 signaling in depression. When compared with existing observational and animal findings, the direction of these results suggests involvement of IL-6 trans signaling. Further study is needed to examine whether IL6R genetic variants might influence IL-6 trans signaling in the brain, as well as to explore other potential pathways linking depression and inflammation.

Qigong exercise enhances cognitive functions in the elderly via an interleukin-6-hippocampus pathway: A randomized active-controlled trial

BACKGROUND

Evidence has suggested that exercise protects against cognitive decline in aging, but the recent lockdown measures associated with the COVID-19 pandemic have limited the opportunity for outdoor exercise. Herein we tested the effects of an indoor exercise, Qigong, on neurocognitive functioning as well as its potential neuro-immune pathway.

METHODS

We conducted a 12-week randomized active-controlled trial with two study arms in cognitively healthy older people. We applied Wu Xing Ping Heng Gong (Qigong), which was designed by an experienced Daoist Qigong master, to the experimental group, whereas we applied the physical stretching exercise to the control group. The Qigong exercise consisted of a range of movements involving the stretching of arms and legs, the turning of the torso, and relaxing, which would follow the fundamental principles of Daoism and traditional Chinese medicine (e.g., Qi). We measured aging-sensitive neurocognitive abilities, serum interleukin-6 (IL-6) levels, and brain structural volumes in the experimental (Qigong, n = 22) and control groups (stretching, n = 26) before and after the 12-week training.

RESULTS

We observed that Qigong caused significant improvement in processing speed (t (46) = 2.03, p = 0.048) and sustained attention (t (46) = -2.34, p = 0.023), increased hippocampal volume (t (41) = 3.94, p < 0.001), and reduced peripheral IL-6 levels (t (46) = -3.17, p = 0.003). Moreover, following Qigong training, greater reduction of peripheral IL-6 levels was associated with a greater increase of processing speed performance (bootstrapping CI: [0.16, 3.30]) and a more significant training-induced effect of hippocampal volume on the improvement in sustained attention (bootstrapping CI: [-0.35, -0.004]).

CONCLUSION

Overall, these findings offer significant insight into the mechanistic role of peripheral IL-6-and its intricate interplay with neural processes-in the beneficial neurocognitive effects of Qigong. The findings have profound implications for early identification and intervention of older individuals vulnerable to cognitive decline, focusing on the neuro-immune pathway. The trial was registered at clinicaltrials.gov (identifier: NCT04641429).

Neuroimmune Mechanisms as Novel Treatment Targets for Substance Use Disorders and Associated Comorbidities

Recent studies examining the neurobiology of substance abuse have revealed a significant role of neuroimmune signaling as a mechanism through which drugs of abuse induce aberrant changes in synaptic plasticity and contribute to substance abuse-related behaviors. Immune signaling within the brain and the periphery critically regulates homeostasis of the nervous system. Perturbations in immune signaling can induce neuroinflammation or immunosuppression, which dysregulate nervous system function including neural processes associated with substance use disorders (SUDs). In this review, we discuss the literature that demonstrates a role of neuroimmune signaling in regulating learning, memory, and synaptic plasticity, emphasizing specific cytokine signaling within the central nervous system. We then highlight recent preclinical studies, within the last 5 years when possible, that have identified immune mechanisms within the brain and the periphery associated with addiction-related behaviors. Findings thus far underscore the need for future investigations into the clinical potential of immunopharmacology as a novel approach toward treating SUDs. Considering the high prevalence rate of comorbidities among those with SUDs, we also discuss neuroimmune mechanisms of common comorbidities associated with SUDs and highlight potentially novel treatment targets for these comorbid conditions. We argue that immunopharmacology represents a novel frontier in the development of new pharmacotherapies that promote long-term abstinence from drug use and minimize the detrimental impact of SUD comorbidities on patient health and treatment outcomes.

Brain-immune crosstalk in the treatment of major depressive disorder

A growing number of studies are pointing out the need for a conceptual shift from a brain-centered to a body-inclusive approach in mental health research. In this perspective, the link between the immune and the nervous system, which are deeply interconnected and continuously interacting, is one of the most important novel theoretical framework to investigate the biological bases of major depressive disorder and, more in general, mental illness. Indeed, depressed patients show high levels of inflammatory markers, administration of pro-inflammatory drugs triggers a depressive symptomatology and antidepressant efficacy is reduced by excessive immune system activation. A number of molecular and cellular mechanisms have been hypothesized to act as a link between the immune and brain function, thus representing potential pharmacologically targetable processes for the development of novel and effective therapeutic strategies. These include the modulation of the kynurenine pathway, the crosstalk between metabolic and inflammatory processes, the imbalance in acquired immune responses, in particular T cell responses, and the interplay between neural plasticity and immune system activation. In the personalized medicine approach, the assessment and regulation of these processes have the potential to lead, respectively, to novel diagnostic approaches for the prediction of treatment outcome according to the patient's immunological profile, and to improved efficacy of antidepressant compounds through immune modulation.

Brain-immune interactions in neuropsychiatric disorders: Lessons from transcriptome studies for molecular targeting

Understanding the pathophysiological mechanisms of neuropsychiatric disorders has been a challenging quest for neurobiologists. Recent years have witnessed enormous technological advances in the field of neuroimmunology, blurring boundaries between the central nervous system and the periphery. Consequently, the discipline has expanded to cover interactions between the nervous and immune systems in health and diseases. The complex interplay between the peripheral and central immune pathways in neuropsychiatric disorders has recently been documented in various studies, but the genetic determinants remain elusive. Recent transcriptome studies have identified dysregulated genes involved in peripheral immune cell activation, blood-brain barrier integrity, glial cell activation, and synaptic plasticity in major depressive disorder, bipolar disorder, autism spectrum disorder, and schizophrenia. Herein, the key transcriptomic techniques applied in investigating differentially expressed genes and pathways responsible for altered brain-immune interactions in neuropsychiatric disorders are discussed. The application of transcriptomics that can aid in identifying molecular targets in various neuropsychiatric disorders is highlighted.

Regulation of emotions during experimental endotoxemia: A pilot study

Even though dysfunctional emotion regulation is prominent in depression and a link between depression and inflammation is well established, there is little knowledge about how inflammation affects the regulation of emotions. The aim of this pilot study was to explore the effect of experimentally induced inflammation on the cognitive reappraisal of emotions, and to assess domain specificity by comparing success in regulation of emotions towards two unpleasant stimuli classes (general negative stimuli and disgust stimuli). In a between-subject design, ten healthy participants were injected with an intravenous injection of lipopolysaccharide (2 ng/kg body weight) and eleven were injected with saline. Participants performed a cognitive reappraisal task, in which they had to down-regulate or up-regulate their emotions towards general negative stimuli and disgust stimuli, 5-6 h post-injection. Contrary to our hypotheses, participants injected with lipopolysaccharide reported greater success in down-regulating emotional responses towards unpleasant stimuli as compared to the saline group. In addition, both groups were poorer at down-regulating emotions towards disgust stimuli as compared to general negative stimuli. The current pilot study indicates that cognitive reappraisal of emotions is affected during experimental endotoxemia, and suggests that disgust stimuli might be difficult to reappraise.

Personalized Medicine Using Neuroimmunological Biomarkers in Depressive Disorders

Major depressive disorder (MDD) is associated with increased suicidal risk and reduced productivity at work. Neuroimmunology, the study of the immune system and nervous system, provides further insight into the pathogenesis and outcome of MDD. Cytokines are the main modulators of neuroimmunology, and their levels are somewhat entangled in depressive disorders as they affect depressive symptoms and are affected by antidepressant treatment. The use of cytokine-derived medication as a treatment option for MDD is currently a topic of interest. Although not very promising, cytokines are also considered as possible prognostic or diagnostic markers for depression. The machine learning approach is a powerful tool for pattern recognition and has been used in psychiatry for finding useful patterns in data that have translational meaning and can be incorporated in daily clinical practice. This review focuses on the current knowledge of neuroimmunology and depression and the possible use of machine learning to widen our understanding of the topic.

Cannabidiol antidepressant-like effect in the lipopolysaccharide model in mice: Modulation of inflammatory pathways

Major Depression is a severe psychiatric condition with a still poorly understood etiology. In the last years, evidence supporting the neuroinflammatory hypothesis of depression has increased. In the current clinical scenario, in which the available treatments for depression is far from optimal, there is an urgent need to develop fast-acting drugs with fewer side effects. In this regard, recent pieces of evidence suggest that cannabidiol (CBD), the major non-psychotropic component of Cannabis sativa with anti-inflammatory properties, appears as a drug with antidepressant properties. In this work, CBD 30 mg/kg was administered systemically to mice 30 min before lipopolysaccharide (LPS; 0.83 mg/kg) administration as a neuroinflammatory model, and behavioral tests for depressive-, anhedonic- and anxious-like behavior were performed. NF-ĸB, IκBα and PPARγ levels were analyzed by western blot in nuclear and cytosolic fractions of cortical samples. IL-6 and TNFα levels were determined in plasma and prefrontal cortex using ELISA and qPCR techniques, respectively. The precursor tryptophan (TRP), and its metabolites kynurenine (KYN) and serotonin (5-HT) were measured in hippocampus and cortex by HPLC. The ratios KYN/TRP and KYN/5-HT were used to estimate indoleamine 2,3-dioxygenase (IDO) activity and the balance of both metabolic pathways, respectively. CBD reduced the immobility time in the tail suspension test and increased sucrose preference in the LPS model, without affecting locomotion and central activity in the open-field test. CBD diminished cortical NF-ĸB activation, IL-6 levels in plasma and brain, and the increased KYN/TRP and KYN/5-HT ratios in hippocampus and cortex in the LPS model. Our results demonstrate that CBD produced antidepressant-like effects in the LPS neuroinflammatory model, associated to a reduction in the kynurenine pathway activation, IL-6 levels and NF-ĸB activation. As CBD stands out as a promising antidepressant drug, more research is needed to completely understand its mechanisms of action in depression linked to inflammation.

Microglial activation elicits a negative affective state through prostaglandin-mediated modulation of striatal neurons

Microglia are activated in many neurological diseases and have been suggested to play an important role in the development of affective disorders including major depression. To investigate how microglial signaling regulates mood, we used bidirectional chemogenetic manipulations of microglial activity in mice. Activation of microglia in the dorsal striatum induced local cytokine expression and a negative affective state characterized by anhedonia and aversion, whereas inactivation of microglia blocked aversion induced by systemic inflammation. Interleukin-6 signaling and cyclooxygenase-1 mediated prostaglandin synthesis in the microglia were critical for the inflammation-induced aversion. Correspondingly, microglial activation led to a prostaglandin-dependent reduction of the excitability of striatal neurons. These findings demonstrate a mechanism by which microglial activation causes negative affect through prostaglandin-dependent modulation of striatal neurons and indicate that interference with this mechanism could milden the depressive symptoms in somatic and psychiatric diseases involving microglial activation.

Advances in novel molecular targets for antidepressants

Depression is the most common psychiatric illness affecting numerous people world-wide. The currently available antidepressant treatment presents low response and remission rates. Thus, new effective antidepressants need to be developed or discovered. Aiming to give an overview of novel possible antidepressant drug targets, we summarized the molecular targets of antidepressants and the underlying neurobiology of depression. We have also addressed the multidimensional perspectives on the progress in the psychopharmacological treatment of depression and on the new potential approaches with effective drug discovery.

Sick for science: experimental endotoxemia as a translational tool to develop and test new therapies for inflammation-associated depression

Depression is one of the global leading causes of disability, but treatments remain limited and classical antidepressants were found to be ineffective in a substantial proportion of patients. Thus, novel effective therapies for the treatment of depression are urgently needed. Given the emerging role of inflammation in the etiology and pathophysiology of affective disorders, we herein illustrate how experimental endotoxemia, a translational model of systemic inflammation, could be used as a tool to develop and test new therapeutic options against depression. Our concept is based on the striking overlap of inflammatory, neural, and affective characteristics in patients with inflammation-associated depression and in endotoxin-challenged healthy subjects. Experimental administration of endotoxin in healthy volunteers is safe, well-tolerated, and without known long-term health risks. It offers a highly standardized translational approach to characterize potential targets of therapies against inflammation-associated depression, as well as to identify characteristics of patients that would benefit from these interventions, and, therefore, could contribute to improve personalization of treatment and to increase the overall rate of responders.

Systemic Regulation of Cancer Development by Neuro-Endocrine-Immune Signaling Network at Multiple Levels

The overarching view of current tumor therapies simplifies cancer to a cell-biology problem in which neoplasms are caused solely by malignant cells and the exploration of carcinogenesis and tumor progression largely focuses on somatic mutations and other genetic abnormalities of cancer cells. The limited therapeutic response indicates that cancer is driven not only by endogenous oncogenic factors and reciprocal interactions within the tumor microenvironment, but also by complex systemic processes. Homeostasis is the fundamental premise of health, and is maintained by systemic regulation of neuro-endocrine-immune axis. Cancer is also a systemic disease that manifested by dysfunction of the nervous, endocrine, and immune systems. Multiple axes of regulation exist in cancer, including central-, organ-, and microenvironment-level manipulation. At each specific regulatory level, the tridirectional communication among the nervous, endocrine, and immune factors transmit flexible signaling to induce proliferation, invasion, reprogrammed metabolism, therapeutic resistance, and other malignant phenotypes of cancer cells, resulting in the extremely poor prognosis of this lethal disease. Understanding this coordinated signaling network will enable the development of new approaches for cancer treatment via behavioral and pharmacological interventions.

Acute inflammation and psychomotor slowing: Experimental assessment using lipopolysaccharide administration in healthy humans

Data from clinical and cross-sectional studies suggest that inflammation contributes to psychomotor slowing and attentional deficits found in depressive disorder. However, experimental evidence is still lacking. The aim of this study was to clarify the effect of inflammation on psychomotor slowing using an experimental and acute model of inflammation, in which twenty-two healthy volunteers received an intravenous injection of lipopolysaccharide (LPS, dose: 0.8 ​ng/kg body weight) and of placebo, in a randomized order following a double-blind within-subject crossover design. A reaction time test and a go/no-go test were conducted 3 ​h after the LPS/placebo injection and interleukin (IL)-6 and tumor necrosis factor (TNF)-α concentrations were assessed. No effect of experimental inflammation on reaction times or errors for either test was found. However, inflammation was related to worse self-rated performance and lower effort put in the tasks. Exploratory analyses indicated that reaction time fluctuated more over time during acute inflammation. These data indicate that acute inflammation has only modest effects on psychomotor speed and attention in healthy subjects objectively, but alters the subjective evaluation of test performance. Increased variability in reaction time might be the first objective sign of altered psychomotor ability and would merit further investigation.

Elucidating vulnerability to inflammation-induced hyperalgesia: Predictors of increased musculoskeletal pain sensitivity during experimental endotoxemia

Despite broad clinical implications, the mechanisms linking inflammation and pain remain incompletely understood. Using human experimental endotoxemia as a translational model of systemic inflammation, we aimed to elucidate putative vulnerability factors of inflammation-induced musculoskeletal hyperalgesia. We pooled data from three published randomized controlled trials, resulting in a sample of N = 98 healthy volunteers who received either low-dose endotoxin (lipopolysaccharide) or vehicle (saline) intravenously. As measure of musculoskeletal pain sensitivity, pressure pain thresholds (PPTs) were assessed at baseline and 3 h post injection with a handheld algometer for the low back (erector spinae muscle), calf (gastrocnemius muscle), and shoulder region (deltoid muscle). Implementing multiple regression models, we tested the contribution of putative vulnerability factors on musculoskeletal hyperalgesia during systemic inflammation, including acute changes in pro-inflammatory cytokines, state anxiety and mood, as well as pre-existing symptoms of anxiety and depression. Endotoxin application led to significant increases in plasma cytokines, state anxiety, and negative mood, and significantly decreased PPTs for all muscle groups. Regression models revealed that greater M. erector spinae PPT changes were predicted by higher HADS-anxiety scores. Higher TNF-α concentration emerged as predictor for M. gastrocnemius PPT changes, and more pronounced TNF-α increase and higher HADS-anxiety were predictive for M. deltoideus PPTs. HADS scores emerged as predictor for a mean PPT score (computed across all body sites). Together, our results indicate that musculoskeletal hyperalgesia during systemic inflammation is related to pro-inflammatory cytokines, specifically TNF-α. Importantly, subclinical anxiety symptoms (even though in a low and normal range in this cohort of healthy volunteers) may contribute to inflammation-induced hyperalgesia, making individuals more vulnerable to the detrimental effects of systemic inflammation.

Immunological and behavioral responses to in vivo lipopolysaccharide administration in young and healthy obese and normal-weight humans

Obesity is associated with an increase prevalence of neuropsychiatric symptoms and diseases, such as depression. Based on the facts that pro-inflammatory cytokines are able to modulate behavior, and that obesity is characterized by a chronic low-grade inflammatory state, inflammation has been hypothesized to contribute to the neuropsychiatric comorbidity in obese individuals. However, a causal link between inflammation and the development of neuropsychiatric symptoms is hard to establish in humans. Here, we used an inflammatory stimulus, i.e. the intravenous injection of lipopolysaccharide (LPS), in a double-blind placebo-controlled design, to determine the vulnerability of obese individuals to inflammation-induced behavioral changes. The hypothesis was that obese individuals would show heightened behavioral response compared to normal-weight subjects for the same inflammatory stimulus, reflecting an increased sensitivity to the behavioral effects of pro-inflammatory cytokines. LPS (dose 0.8 ng/kg body weight, adjusted for estimated blood volume in obese subjects) and placebo (saline) were intravenously injected in 14 obese healthy subjects and 23 normal-weight healthy subjects in a within-subject, randomized, crossover design. LPS administration induced, in both groups, an acute increase in blood concentrations of cytokines (interleukin-6, tumor necrosis factor-α, and IL-10), as well as in body temperature, cortisol, norepinephrine, sickness symptoms, fatigue, negative mood, and state anxiety. There were little differences in the immune and behavioral responses to LPS between obese and normal-weight subjects, but the cortisol response to LPS was strongly attenuated in obese individuals. Higher percentage of body fat was related to a lower cortisol response to LPS. Taken together, the population of young and healthy obese individuals in this study did not exhibit an increased behavioral sensitivity to cytokines, but an attenuated cortisol response to the immune challenge. Future studies will need to determine whether additional physiological and psychological factors interact with the state of obesity to increase the risk for inflammation-induced neuropsychiatric symptoms.

[Immunopsychiatry and SARS-CoV-2 pandemic: Links and possible consequences]

OBJECTIVE

The SARS-CoV-2 (or COVID-19) pandemic has been propagating since December 2019, inducing a drastic increase in the prevalence of anxious and depressive disorders in the general population. Psychological trauma can partly explain these disorders. However, since psychiatric disorders also have an immuno-inflammatory component, the direct effects of the virus on the host's immune system, with a marked inflammatory response, but also the secondary inflammation to these psychosocial stressors, may cause the apparition or the worsening of psychiatric disorders. We describe here the probable immunopsychiatric consequences of the SARS-CoV-2 pandemic, to delineate possible screening actions and care that could be planned.

METHOD

Data from previous pandemics, and existing data on the psychopathological consequences of the SARS-CoV-2 pandemic, allowed us to review the possible immunopsychiatric consequences of the SARS-CoV-2 pandemic, on the gestational environment, with the risk of consecutive neurodevelopmental disorders for the fetus on one hand, on the children and adults directly infected being at increased risks of psychiatric disorders on the other hand.

RESULTS

As in previous pandemics, the activation of the immune system due to psychological stress and/or to infection during pregnancy, might lead to an increased risk of neurodevelopmental disorders for the fetus (schizophrenia and autism spectrum disorders). Furthermore, in individuals exposed to psychological trauma and/or infected by the virus, the risk of psychiatric disorders, especially mood disorders, is probably increased.

CONCLUSION

In this context, preventive measures and specialized care are necessary. Thus, it is important to propose a close follow-up to the individuals who have been infected by the virus, in order to set up the earliest care possible. Likewise, in pregnant women, screening of mood disorders during the pregnancy or the postpartum period must be facilitated. The follow-up of the babies born during the pandemic must be strengthened to screen and care for possible neurodevelopmental disorders.

Systemic immunization with altered myelin basic protein peptide produces sustained antidepressant-like effects

Immune dysregulation, specifically of inflammatory processes, has been linked to behavioral symptoms of depression in both human and rodent studies. Here, we evaluated the antidepressant effects of immunization with altered peptide ligands of myelin basic protein (MBP)-MBP_87-99[A⁹¹, A⁹⁶], MBP_87-99[A⁹¹], and MBP_87-99[R⁹¹, A⁹⁶]-in different models of depression and examined the mechanism by which these peptides protect against stress-induced depression. We found that a single dose of subcutaneously administered MBP_87-99[A⁹¹, A⁹⁶] produced antidepressant-like effects by decreasing immobility in the forced swim test and by reducing the escape latency and escape failures in the learned helplessness paradigm. Moreover, immunization with MBP_87-99[A⁹¹, A⁹⁶] prevented and reversed depressive-like and anxiety-like behaviors that were induced by chronic unpredictable stress (CUS). However, MBP_87-99[R⁹¹, A⁹⁶] tended to aggravate CUS-induced anxiety-like behavior. Chronic stress increased the production of peripheral and central proinflammatory cytokines and induced the activation of microglia in the prelimbic cortex (PrL), which was blocked by MBP_87-99[A⁹¹, A⁹⁶]. Immunization with MBP-derived altered peptide ligands also rescued chronic stress-induced deficits in p11, phosphorylated cyclic adenosine monophosphate response element binding protein, and brain-derived neurotrophic factor expression. Moreover, microinjections of recombinant proinflammatory cytokines and the knockdown of p11 in the PrL blunted the antidepressant-like behavioral response to MBP_87-99[A⁹¹, A⁹⁶]. Altogether, these findings indicate that immunization with altered MBP peptide produces prolonged antidepressant-like effects in rats, and the behavioral response is mediated by inflammatory factors (particularly interleukin-6), and p11 signaling in the PrL. Immune-neural interactions may impact central nervous system function and alter an individual's response to stress.

Effects of Zuojin pill on depressive behavior and gastrointestinal function in rats with chronic unpredictable mild stress: Role of the brain-gut axis

ETHNOPHARMACOLOGICAL RELEVANCE

Zoujin pill (ZJP), a medication used to treat gastrointestinal disorders since the 15th Century in China, have been reported to exert anti-depressant effects in various models.

STUDY AIM

To assess the effects of ZJP on gastrointestinal function and depressive behavior in rats under chronic unpredictable mild stress (CUMS), and to examine the underlying mechanisms related to brain-gut axis.

METHODS

The rats suffered the stressor once daily for 5 weeks. ZJP (0.6 and 1.2 g/kg) and fluoxetine (15 mg/kg) as positive control were administered to the rats through gastric intubation once daily for 5 consecutive weeks. The anti-depression effects were compared by performing sucrose preference tests and open field tests. Gastrointestinal motility was investigated by determining the gastrointestinal transit rate and by electrogastrogram. The serum levels of the gastrointestinal hormone (GAS, MOT, VIP, SP), inflammatory cytokine (IL-1β, IL-6; , TNFα) and glucagon-like peptide-1 (GLP-1) were assayed by enzyme-linked immunosorbent assay. For monoamine neurotransmitters (NE, 5-HT, DA), the levels were determined by high-performance liquid chromatography and electrochemical detection in conjunction, which was applied on the samples taken from the hypothalamus, hippocampus, and striatum.

RESULTS

The depression-like symptoms among rats under CUMS were significantly relieved by ZJP administration (0.6 and 1.2 g/kg). Gastrointestinal motility was also improved by restoring gastric electrical rhythm and promoting gastrointestinal propulsion. The ZJP at 0.6 g/kg dosage obviously up-regulated 5-HT and DA levels in hippocampus. The ZJP at 1.2 g/kg dosage could increase 5-HT and DA levels in hypothalamus, striatum, and hippocampus, while down-regulated the NE level in hypothalamus and hippocampus. ZJP also reversed the alterations in serum gastrointestinal hormones. Furthermore, treatment with ZJP significantly reduced levels of IL-1β, IL-6 and TNF-α and increased serum GLP-1 compared with the CUMS group. Fluoxetine also exerted similar anti-depressant effects in the absence of effects on gastrointestinal motility and the levels of serum hormone, inflammatory cytokine and GLP-1.

CONCLUSION

ZJP imposed anti-depressant and gastrointestinal regulating functions in rats under CUMS, suggesting potential clinical application. .

Comparison of bacterial lipopolysaccharide-induced sickness behavior in rodents and humans: Relevance for symptoms of anxiety and depression

Increasing evidence from animal and human studies suggests that inflammation may be involved in mood disorders. Sickness behavior and emotional changes induced by experimental inflammatory stimuli have been extensively studied in humans and rodents to better understand the mechanisms underlying inflammation-driven mood alterations. However, research in animals and humans have remained compartmentalized and a comprehensive comparison of inflammation-induced sickness and depressive-like behavior between rodents and humans is lacking. Thus, here, we highlight similarities and differences in the effects of bacterial lipopolysaccharide administration on the physiological (fever and cytokines), behavioral and emotional components of the sickness response in rodents and humans, and discuss the translational challenges involved. We also emphasize the differences between observable sickness behavior and subjective sickness reports, and advocate for the need to obtain both subjective reports and objective measurements of sickness behavior in humans. We aim to provide complementary insights for translational clinical and experimental research on inflammation-induced behavioral and emotional changes, and their relevance for mood disorders such as depression.

Role of Interleukin-6 in Depressive Disorder

Major depressive disorder (MDD), which is a leading psychiatric illness across the world, severely affects quality of life and causes an increased incidence of suicide. Evidence from animal as well as clinical studies have indicated that increased peripheral or central cytokine interleukin-6 (IL-6) levels play an important role in stress reaction and depressive disorder, especially physical disorders comorbid with depression. Increased release of IL-6 in MDD has been found to be a factor associated with MDD prognosis and therapeutic response, and may affect a wide range of depressive symptomatology. However, study results of the IL6 genetic effects in MDD are controversial. Increased IL-6 activity may cause depression through activation of hypothalamic-pituitary-adrenal axis or influence of the neurotransmitter metabolism. The important role of neuroinflammation in MDD pathogenesis has created a new perspective that the combining of blood IL-6 and other depression-related cytokine levels may help to classify MDD biological subtypes, which may allow physicians to identify the optimal treatment for MDD patients. To modulate the IL-6 activity by IL-6-related agents, current antidepressive agents, herb medication, pre-/probiotics or non-pharmacological interventions may hold great promise for the MDD patients with inflammatory features.

Stress and the brain-gut axis in functional and chronic-inflammatory gastrointestinal diseases: A transdisciplinary challenge

The broad role of stress in the brain-gut axis is widely acknowledged, with implications for multiple prevalent health conditions that are characterized by chronic gastrointestinal symptoms. These include the functional gastrointestinal disorders (FGID), such as irritable bowel syndrome and functional dyspepsia, as well as inflammatory bowel diseases (IBD) like ulcerative colitis and Crohn's disease. Although the afferent and efferent pathways linking the gut and the brain are modulated by stress, the fields of neurogastroenterology and psychoneuroendocrinology (PNE)/ psychoneuroimmunology (PNI) remain only loosely connected. We aim to contribute to bringing these fields closer together by drawing attention to a fascinating, evolving research area, targeting an audience with a strong interest in the role of stress in health and disease. To this end, this review introduces the concept of the brain-gut axis and its major pathways, and provides a brief introduction to epidemiological and clinical aspects of FGIDs and IBD. From an interdisciplinary PNE/PNI perspective, we then detail current knowledge regarding the role of chronic and acute stress in the pathophysiology of FGID and IBD. We provide an overview of evidence regarding non-pharmacological treatment approaches that target central or peripheral stress mechanisms, and conclude with future directions, particularly those arising from recent advances in the neurosciences and discoveries surrounding the gut microbiota.

Fatigue and sleepiness responses to experimental inflammation and exploratory analysis of the effect of baseline inflammation in healthy humans

Inflammation is believed to be a central mechanism in the pathophysiology of fatigue. While it is likely that dynamic of the fatigue response after an immune challenge relates to the corresponding cytokine release, this lacks evidence. Although both fatigue and sleepiness are strong signals to rest, they constitute distinct symptoms which are not necessarily associated, and sleepiness in relation to inflammation has been rarely investigated. Here, we have assessed the effect of an experimental immune challenge (administration of lipopolysaccharide, LPS) on the development of both fatigue and sleepiness, and the associations between increases in cytokine concentrations, fatigue and sleepiness, in healthy volunteers. In addition, because chronic-low grade inflammation may represent a risk factor for fatigue, we tested whether higher baseline levels of inflammation result in a more pronounced development of cytokine-induced fatigue and sleepiness. Data from four experimental studies was combined, giving a total of 120 subjects (LPS N = 79, 18 (23%) women; Placebo N = 69, 12 (17%) women). Administration of LPS resulted in a stronger increase in fatigue and sleepiness compared to the placebo condition, and the development of both fatigue and sleepiness closely paralleled the cytokine responses. Individuals with stronger increases in cytokine concentrations after LPS administration also suffered more from fatigue and sleepiness (N = 75), independent of gender. However, there was no support for the hypothesis that higher baseline inflammatory markers moderated the responses in fatigue or sleepiness after an inflammatory challenge. The results demonstrate a tight connection between the acute inflammatory response and development of both fatigue and sleepiness, and motivates further investigation of the involvement of inflammation in the pathophysiology of central fatigue.