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

Psilocybin for dementia prevention? The potential role of psilocybin to alter mechanisms associated with major depression and neurodegenerative diseases

Major depression is an established risk factor for subsequent dementia, and depression in late life may also represent a prodromal state of dementia. Considering current challenges in the clinical development of disease modifying therapies for dementia, the focus of research is shifting towards prevention and modification of risk factors to alter the neurodegenerative disease trajectory. Understanding mechanistic commonalities underlying affective symptoms and cognitive decline may reveal biomarkers to aid early identification of those at risk of progressing to dementia during the preclinical phase of disease, thus allowing for timely intervention. Adult hippocampal neurogenesis (AHN) is a phenomenon that describes the birth of new neurons in the dentate gyrus throughout life and it is associated with spatial learning, memory and mood regulation. Microglia are innate immune system macrophages in the central nervous system that carefully regulate AHN via multiple mechanisms. Disruption in AHN is associated with both dementia and major depression and microgliosis is a hallmark of several neurodegenerative diseases. Emerging evidence suggests that psychedelics promote neuroplasticity, including neurogenesis, and may also be immunomodulatory. In this context, psilocybin, a serotonergic agonist with rapid-acting antidepressant properties has the potential to ameliorate intersecting pathophysiological processes relevant for both major depression and neurodegenerative diseases. In this narrative review, we focus on the evidence base for the effects of psilocybin on adult hippocampal neurogenesis and microglial form and function; which may suggest that psilocybin has the potential to modulate multiple mechanisms of action, and may have implications in altering the progression from major depression to dementia in those at risk.

Serum amyloid A-dependent inflammasome activation and acute injury in a mouse model of experimental stroke

Serum amyloid A (SAA) proteins increase dramatically in the blood following inflammation. Recently, SAAs are increased in humans following stroke and in ischemic animal models. However, the impact of SAAs on whether this signal is critical in the ischemic brain remains unknown. Therefore, we investigated the role of SAA and SAA signaling in the ischemic brain. Wildtype and SAA deficient mice were exposed to middle cerebral artery occlusion and reperfusion, examined for the impact of infarct volumes, behavioral changes, inflammatory markers, TUNEL staining, and BBB changes. The underlying mechanisms were investigated using SAA deficient mice, transgenic mice and viral vectors. SAA levels were significantly increase following MCAo and mice deficient in SAAs showed reduced infarct volumes and improved behavioral outcomes. SAA deficient mice showed a reduction in TUNEL staining, inflammation and decreased glial activation. Mice lacking acute phase SAAs demonstrated a reduction in expression of the NLRP3 inflammasome and SAA/NLRP3 KO mice showed improvement. Restoration of SAA expression via SAA tg mice or adenoviral expression reestablished the detrimental effects of SAA. A reduction in BBB permeability was seen in the SAA KO mice and anti-SAA antibody treatment reduced the effects on ischemic injury. SAA signaling plays a critical role in regulating NLRP3-induced inflammation and glial activation in the ischemic brain. Blocking this signal will be a promising approach for treating ischemic stroke.

Association between thyroid function and comorbid anxiety in first-episode and drug naïve patients with major depressive disorder

OBJECTIVE

Existing studies have shown that thyroid dysfunction is associated with depression. However, its role in major depressive disorder (MDD) with comorbid anxiety remains unclear. The main purpose of this study was to compare thyroid function in a large sample of first episode drug naïve (FEDN) MDD patients with and without anxiety.

METHODS

This cross-sectional study examined 1718 outpatients who were drug-naïve and diagnosed as MDD at first episode. Socio-demographic and clinical data, as well as thyroid function-related parameters, including free thyroxine (FT4), free triiodothyronine (FT3), thyroid-stimulating hormone (TSH), thyroid peroxidase antibodies (TPOAb) and anti-thyroglobulin (TGAb), were evaluated. The Hamilton Depression Rating Scale (HAMD), Hamilton Anxiety Rating Scale (HAMA) and the positive subscale of the Positive and Negative Syndrome Scale (PANSS) were used to evaluate depressive, anxiety and psychotic symptoms, respectively.

RESULTS

Compared to MDD patients without anxiety, MDD patients with anxiety were more likely to have more suicide attempts and psychotic symptoms, as well as higher serum levels of TSH, TPOAb and TGAb (all p < 0.001). Among patients with abnormally elevated serum TSH, TPOAb, and TGAb, 83.5% (872/1044), 89.3% (391/438) and 89.6% (266/297) had comorbid anxiety disorders, respectively. The odds ratio between patients with comorbid and without comorbid anxiety was 1.657 (95% CI 1.304-2.105) for elevated TSH levels, 1.943 (95% CI 1.444-2.613) for elevated TGAb levels, and 2.448 (95% CI 1.760-3.403) for elevated TPOAb levels. Furthermore, multivariable linear analysis showed that elevated TSH and TGAb were significant predictors of anxiety in MDD patients.

CONCLUSIONS

Our results suggest that comorbid anxiety in FEDN MDD patients is positively associated with elevated TSH and TGAb levels, which may be promising biomarkers of comorbid anxiety in MDD patients. Clinical treatment of impaired thyroid function may be useful for comorbid anxiety in MDD patients.

Multimorbidity burden and developmental trajectory in relation to later‐life dementia: A prospective study

INTRODUCTION

This study assessed the associations of multimorbidity burden and its developmental trajectory with later-life dementia.

METHODS

Among 5923 Health and Retirement Study participants, major chronic conditions including hypertension, diabetes mellitus, cancer, lung diseases, heart disease, stroke, psychological disorders, and arthritis were self- or proxy-reported in 1994-2008. Dementia diagnosis was self- or proxy-reported in 2008-2018. We used Cox regression to assess the associations of multimorbidity with incident dementia.

RESULTS

During follow-up (median = 8 years), 701 participants developed dementia. Each additional chronic condition in 2008 was related to 15% (confidence interval: 9% to 22%) higher hazard of dementia. Multimorbidity trajectories in 1994-2008 were classified as "rapid growth", "steady growth", "slow growth", and "no new condition" by the group-based trajectory modelling methods. Compared to "no new condition", the "rapid growth" trajectory was related to 32% (3% to 69%) higher dementia risk.

CONCLUSIONS

Both multimorbidity burden and its developmental trajectory were prospectively associated with risk of dementia.

Prevalence of Comorbid Dementia in Late-life Depression and Bipolar Disorder: A Retrospective Inpatient Study

Background:

Dementia in patients with late-life mood disorders is clinically important.

Objective:

We aimed to investigate the prevalence of dementia in patients with late-life major depressive disorder (MDD) or bipolar disorder (BD) and to clarify the clinical characteristics associated with the diagnosis of dementia.

Methods:

The prevalence of dementia at hospital discharge and the clinical characteristics at hospitalization who are diagnosed with MDD or BD over 65 years of age, from the medical records of 684 patients who had been admitted from 2015 to 2020 were investigated.

Results:

A total of 66 patients with MDD (n = 50) and BD (n = 16) were analyzed. The prevalence of dementia was significantly higher in MDD than in BD (24.0% versus 0%; p = 0.026). The mean age at onset of MDD was significantly older in the MDD with dementia group than in the MDD without (76.9±6.3 years versus 62.2±14.0 years; p < 0.001). The rate of first depressive episode at this admission was significantly higher in the MDD with dementia group (91.7% versus 30.3%; p < 0.001). The diagnosis of dementia was significantly associated with lower scores for “insomnia early” (p = 0.019) and higher scores for “insight” (p = 0.049) on the 17-item Hamilton Depression Rating (HAMD-17) subscales and lower scores for “recall” (p = 0.003) on the MMSE subscales.

Conclusion:

The older age of first onset of depression, “insomnia early”, “insight” and “recall” may be useful indicators for a diagnosis of dementia in late-life depression.

Serum metabolomics of end-stage renal disease patients with depression: potential biomarkers for diagnosis

Background

End-stage renal disease (ESRD) is the final stage during the development of renal failure. Depression is the most common psychiatric disorder in patients with ESRD, which in turn aggravates the progression of renal failure, however, its underlying mechanism remains unclear. This study aimed to reveal the pathogenesis and to discover novel peripheral biomarkers for ESRD patients with depression through metabolomic analysis.

Methods

Ultra-high-performance liquid chromatography coupled with mass spectrometry (UPLC-MS) was used to explore changes of serum metabolites among healthy controls, ESRD patients with or without depression. The differential metabolites between groups were subjected to clustering analysis, pathway analysis, receiver operating characteristic (ROC) curve analysis.

Results

A total of 57 significant serum differential metabolites were identified between ESRD patients with or without depression, which were involved in 19 metabolic pathways, such as energy metabolism, glycerolipid metabolism, and glutamate-centered metabolism. Moreover, the area under the ROC curve of gentisic acid, uric acid, 5-hydroxytryptamine, 2-phosphoglyceric acid, leucyl-phenylalanine, propenyl carnitine, naloxone, pregnenolone, 6-thioxanthene 5'-monophosphate, hydroxyl ansoprazole, zileuton O-glucuronide, cabergoline, PA(34:2), PG(36:1), probucol and their combination was greater than 0.90.

Conclusions

Inflammation, oxidative stress and energy metabolism abnormalities, glycerolipid metabolism, and glutamate-centered metabolism are associated with the pathogenesis of ESRD with depression, which may be promising targets for therapy. Furthermore, the identified differential metabolites may serve as biomarkers for the diagnosis of ESRD patients with depression.

Creation of a gene expression portrait of depression and its application for identifying potential treatments

Depression is a complex mental health disorder and the goal here was to identify a consistent underlying portrait of expression that ranks all genes from most to least dysregulated and indicates direction of change relative to controls. Using large-scale neural gene expression depression datasets, a combined portrait (for men and women) was created along with one for men and one for women only. The depressed brain was characterized by a "hypo" state, that included downregulation of activity-related genes, including EGR1, FOS, and ARC, and indications of a lower brain temperature and sleep-like state. MAP kinase and BDNF pathways were enriched with overlapping genes. Expression patterns suggested decreased signaling for GABA and for neuropeptides, CRH, SST, and CCK. GWAS depression genes were among depression portrait genes and common genes of interest included SPRY2 and PSEN2. The portraits were used with the drug repurposing approach of signature matching to identify treatments that could reverse depression gene expression patterns. Exercise was identified as the top treatment for depression for the combined and male portraits. Other non-traditional treatments that scored well were: curcumin, creatine, and albiflorin. Fluoxetine scored best among typical antidepressants. The creation of the portraits of depression provides new insights into the complex landscape of depression and a novel platform for evaluating and identifying potential new treatments.

Total Plasma Homocysteine and Depressive Symptoms in Older Hispanics

BACKGROUND

Very few studies have investigated the association between total plasma homocysteine (tHcy) and depressive symptoms in older Hispanics.

OBJECTIVE

To test the hypothesis that high tHcy associates with depressive symptoms in older Hispanics.

METHODS

A total of 1,418 participants .55 years old from the Maracaibo Aging Study (MAS) underwent standardized neurological, neuropsychiatric, and cardiovascular assessments. The Neuropsychiatric Inventory Depression Subscale (NPId) was used to assess the burden of depressive symptoms. The tHcy levels and other biochemical parameters in blood samples were measured. Univariate and multivariate logistic regression models were applied.

RESULTS

Participants with depressive symptoms had higher levels of tHcy than those without (15.1 versus 13.9 µmol/L; p = 0.009). Elevated tHcy levels were associated with depressive symptoms after adjusting for age, sex, education, smoking, diabetes, hypertension, alcohol intake, stroke, and dementia (OR = 1.58; 95% CI, 1.18-2.12).

CONCLUSION

Elevated levels of tHcy were associated with depressive symptoms in older Hispanics living under the nutritional and environmental conditions of a developing country.

Immune dysregulation in depression: Evidence from genome-wide association

A strong body of evidence supports a role for immune dysregulation across many psychiatric disorders including depression, the leading cause of global disability. Recent progress in the search for genetic variants associated with depression provides the opportunity to strengthen our current understanding of etiological factors contributing to depression and generate novel hypotheses. Here, we provide an overview of the literature demonstrating a role for immune dysregulation in depression, followed by a detailed discussion of the immune-related genes identified by the most recent genome-wide meta-analysis of depression. These genes represent strong evidence-based targets for future basic and translational research which aims to understand the role of the immune system in depression pathology and identify novel points for therapeutic intervention.

Incidence and Risk Factors for Dementia in Type 2 Diabetes Mellitus: A Nationwide Population-Based Study in Korea

BACKGROUND

Diabetes mellitus is associated with an increased risk of dementia. We aimed to comprehensively analyze the incidence and risk factors for dementia and young-onset dementia (YOD) in diabetic patients in Korea using the National Health Insurance Service data.

METHODS

Between January 1, 2009 and December 31, 2012, a total of 1,917,702 participants with diabetes were included and followed until the date of dementia diagnosis or until December 31, 2015. We evaluated the incidence and risk factors for all dementia, Alzheimer's disease (AD), and vascular dementia (VaD) by Cox proportional hazards analyses. We also compared the impact of risk factors on the occurrence of YOD and late-onset dementia (LOD).

RESULTS

During an average of 5.1 years of follow-up, the incidence of all types of dementia, AD, or VaD was 9.5, 6.8, and 1.3/1,000 person-years, respectively, in participants with diabetes. YOD comprised 4.8% of all dementia occurrence, and the ratio of AD/VaD was 2.1 for YOD compared with 5.5 for LOD. Current smokers and subjects with lower income, plasma glucose levels, body mass index (BMI), and subjects with hypertension, dyslipidemia, vascular complications, depression, and insulin treatment developed dementia more frequently. Vascular risk factors such as smoking, hypertension, and previous cardiovascular diseases were more strongly associated with the development of VaD than AD. Low BMI and a history of stroke or depression had a stronger influence on the development of YOD than LOD.

CONCLUSION

The optimal management of modifiable risk factors may be important for preventing dementia in subjects with diabetes mellitus.

Serum Amyloid A-Mediated Inflammasome Activation of Microglial Cells in Cerebral Ischemia

Serum amyloid A (SAA) proteins are acute-phase reactant associated with high-density lipoprotein (HDL) particles and increase in the plasma 1000-fold during inflammation. Recent studies have implicated SAAs in innate immunity and various disorders; however, the precise mechanism eludes us. Previous studies have shown SAAs are elevated following stroke and cerebral ischemia, and our studies demonstrated that SAA-deficient mice reduce inflammation and infarct volumes in a mouse stroke model. Our studies demonstrate that SAA increases the cytokine interleukin-1β (IL-1β), which is mediated by Nod-like receptor protein 3 (NLRP3) inflammasome, cathepsin B, and caspase-1 and may play a role in the pathogenesis of neurological disorders. SAA induced the expression of NLRP3, which mediated IL-1β induction in murine BV-2 cells and both sex primary mouse microglial cells, in a dose- and time-dependent fashion. Inhibition or KO of the NLRP3 in microglia prevented the increase in IL-1β. N-acetyl-l-cysteine and mito-TEMPO blocked the induction of IL-1β by inhibiting ROS with SAA treatment. In addition, inhibition of cathepsin B with different drugs or microglia from CatB-deficient mice attenuated inflammasome activation. Our studies suggest that the impact of SAA on inflammasome stimulation is mediated in part by the receptor for advanced glycation endproducts and Toll-like receptor proteins 2 and 4. SAA induced inflammatory cytokines and an M1 phenotype in the microglial cells while downregulating anti-inflammation M2 phenotype. These studies suggest that brain injury to can elicit a systemic inflammatory response mediated through SAA that contributes to the pathological outcomes.SIGNIFICANCE STATEMENT In the present study, serum amyloid A can induce that activation of the inflammasome in microglial cells and give rise to IL-1β release, which can further inflammation in the brain following neurological diseases. The also presents a novel target for therapeutic approaches in stroke.

Therapeutics for dementia and Alzheimer's disease: New directions for precision medicine

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.

Linking late life depression and Alzheimer's disease: mechanisms and resilience

Purpose of Review

This review summarizes recent literature linking Alzheimer's disease (AD) and late life depression (LLD). It describes shared neurobiological features associated with both conditions, as well as factors that may increase resilience to onset and severity of cognitive decline and AD. Finally, we pose a number of future research directions toward improving detection, management, and treatment of both conditions.

Recent Findings

Epidemiological studies have consistently shown a significant relationship between LLD and AD, with support for depression as a prodromal feature of AD, a risk factor for AD, and observation of some shared risk factors underlying both disease processes. Three major neurobiological features shared by LLD and AD include neurodegeneration, disruption to cerebrovascular functioning, and increased levels of neuroinflammation. There are also potentially modifiable factors that can increase resilience to AD and LLD, including social support, physical and cognitive engagement, and cognitive reserve.

Summary

We propose that, in the context of depression, neurobiological events, such as neurodegeneration, cerebrovascular disease, and neuroinflammation result in a brain that is more vulnerable to the consequences of the pathophysiological features of AD, lowering the threshold for the onset of the behavioral presentation of AD (i.e., cognitive decline and dementia). We discuss factors that can increase resilience to AD and LLD, including social support, physical and cognitive engagement, and cognitive reserve. We conclude with a discussion of future research directions.

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.