Neuroinflammation and amyloid-beta 40 are associated with reduced serotonin transporter (SERT) activity in a transgenic model of familial Alzheimer's disease

Chronic evoked seizures in young pre-symptomatic APP/PS1 mice induce serotonin changes and accelerate onset of Alzheimer's disease-related neuropathology

OBJECTIVE

Hyperexcitability is intimately linked to Alzheimer's disease (AD) pathology, but the precise timing and contributions of neuronal hyperexcitability to disease progression is unclear. Seizure induction in rodent AD models can uncover new therapeutic targets. Further, investigator-evoked seizures can directly establish how hyperexcitability and AD-associated risk factors influence neuropathological hallmarks and disease course at presymptomatic stages.

METHODS

Corneal kindling is a well-characterized preclinical epilepsy model that allows for precise control of seizure history to pair to subsequent behavioral assessments. 2-3-month-old APP/PS1, PSEN2-N141I, and transgenic control male and female mice were thus sham or corneal kindled for 2 weeks. Seizure-induced changes in glia, serotonin pathway proteins, and amyloid β levels in hippocampus and prefrontal cortex were quantified.

RESULTS

APP/PS1 females were more susceptible to corneal kindling. However, regardless of sex, APP/PS1 mice experienced extensive seizure-induced mortality versus kindled Tg- controls. PSEN2-N141I mice were not negatively affected by corneal kindling. Mortality correlated with a marked downregulation of hippocampal tryptophan hydroxylase 2 and monoamine oxidase A protein expression versus controls; these changes were not detected in PSEN2-N141I mice. Kindled APP/PS1 mice also exhibited soluble amyloid β upregulation and glial reactivity without plaque deposition.

SIGNIFICANCE

Evoked convulsive seizures and neuronal hyperexcitability in pre-symptomatic APP/PS1 mice promoted premature mortality without pathological Aβ plaque deposition, whereas PSEN2-N141I mice were unaffected. Disruptions in serotonin pathway metabolism in APP/PS1 mice was associated with increased glial reactivity without Aβ plaque deposition, demonstrating that neuronal hyperexcitability in early AD causes pathological Aβ overexpression and worsens long-term outcomes through a serotonin-related mechanism.

Establishing an OCD Model in BALB/c Mice Using RU24969: A Molecular and Behavioural Study of Optimal Dose Selection

Obsessive-compulsive disorder (OCD) is a disabling disease characterized by distressing obsessions and repetitive compulsions. The etiology of OCD is poorly known, and mouse modeling allows to clarify the genetic and neurochemical basis of this disorder and to investigate potential treatments. This study evaluates the impact of the 5-HT1B agonist RU24969 on the induction of OCD-like behaviours in female BALB/c mice (n = 30), distributed across five groups receiving varying doses of RU24969. Behavioural assessments, including marble test, tail suspension test, sucrose preference test, forced swim test, and nestlet shredding test, were conducted. Gene expression and protein quantitation of Gabra1 and serotonin transporter in mouse brain were also performed. Marble-burying behaviour increased significantly at high doses of RU24969 (15-20 mg/kg). The forced swimming test consistently showed elevated values at the same high concentrations, compared to the control. Altered reward-seeking behaviour was indicated by the sucrose preference test, notably at 15 and 20 mg/kg doses of RU24969. Nestlet shredding results did not show statistical significance among the tested animal groups. Gene expression analysis revealed reduced Gabra1 expression with increasing doses of RU, while serotonin transporter was not related to varying doses of RU24969. Western blotting corroborated these trends. The results underscore complex interactions between the serotonin system, GABAergic signaling, and OCD-relevant behaviours and suggest the use of intraperitoneal injection of 15 mg/kg of RU24969 to induce OCD-like behaviour in BALB/c mouse models.

Investigating metabolic dysregulation in serum of triple transgenic Alzheimer's disease male mice: implications for pathogenesis and potential biomarkers

Alzheimer's disease (AD) is a multifactorial neurodegenerative disease that lacks convenient and accessible peripheral blood diagnostic markers and effective drugs. Metabolic dysfunction is one of AD risk factors, which leaded to alterations of various metabolites in the body. Pathological changes of the brain can be reflected in blood metabolites that are expected to explain the disease mechanisms or be candidate biomarkers. The aim of this study was to investigate the changes of targeted metabolites within peripheral blood of AD mouse model, with the purpose of exploring the disease mechanism and potential biomarkers. Targeted metabolomics was used to quantify 256 metabolites in serum of triple transgenic AD (3 × Tg-AD) male mice. Compared with controls, 49 differential metabolites represented dysregulation in purine, pyrimidine, tryptophan, cysteine and methionine and glycerophospholipid metabolism. Among them, adenosine, serotonin, N-acetyl-5-hydroxytryptamine, and acetylcholine play a key role in regulating neural transmitter network. The alteration of S-adenosine-L-homocysteine, S-adenosine-L-methionine, and trimethylamine-N-oxide in AD mice serum can served as indicator of AD risk. The results revealed the changes of metabolites in serum, suggesting that metabolic dysregulation in periphery in AD mice may be related to the disturbances in neuroinhibition, the serotonergic system, sleep function, the cholinergic system, and the gut microbiota. This study provides novel insights into the dysregulation of several key metabolites and metabolic pathways in AD, presenting potential avenues for future research and the development of peripheral biomarkers.

Mitochondrial Interaction with Serotonin in Neurobiology and Its Implication in Alzheimer's Disease

Alzheimer's disease (AD) is a lethal neurodegenerative disorder characterized by severe brain pathologies and progressive cognitive decline. While the exact cause of this disease remains unknown, emerging evidence suggests that dysregulation of neurotransmitters contributes to the development of AD pathology and symptoms. Serotonin, a critical neurotransmitter in the brain, plays a pivotal role in regulating various brain processes and is implicated in neurological and psychiatric disorders, including AD. Recent studies have shed light on the interplay between mitochondrial function and serotonin regulation in brain physiology. In AD, there is a deficiency of serotonin, along with impairments in mitochondrial function, particularly in serotoninergic neurons. Additionally, altered activity of mitochondrial enzymes, such as monoamine oxidase, may contribute to serotonin dysregulation in AD. Understanding the intricate relationship between mitochondria and serotonin provides valuable insights into the underlying mechanisms of AD and identifies potential therapeutic targets to restore serotonin homeostasis and alleviate AD symptoms. This review summarizes the recent advancements in unraveling the connection between brain mitochondria and serotonin, emphasizing their significance in AD pathogenesis and underscoring the importance of further research in this area. Elucidating the role of mitochondria in serotonin dysfunction will promote the development of therapeutic strategies for the treatment and prevention of this neurodegenerative disorder.

Stress induced exacerbation of Alzheimer's disease brain pathology is thwarted by co-administration of nanowired cerebrolysin and monoclonal amyloid beta peptide antibodies with serotonin 5-HT6 receptor antagonist SB-399885

Alzheimer's disease is one of the devastating neurodegenerative diseases affecting mankind worldwide with advancing age mainly above 65 years and above causing great misery of life. About more than 7 millions are affected with Alzheimer's disease in America in 2023 resulting in huge burden on health care system and care givers and support for the family. However, no suitable therapeutic measures are available at the moment to enhance quality of life to these patients. Development of Alzheimer's disease may reflect the stress burden of whole life inculcating the disease processes of these neurodegenerative disorders of the central nervous system. Thus, new strategies using nanodelivery of suitable drug therapy including antibodies are needed in exploring neuroprotection in Alzheimer's disease brain pathology. In this chapter role of stress in exacerbating Alzheimer's disease brain pathology is explored and treatment strategies are examined using nanotechnology based on our own investigation. Our observations clearly show that restraint stress significantly exacerbate Alzheimer's disease brain pathology and nanodelivery of a multimodal drug cerebrolysin together with monoclonal antibodies (mAb) to amyloid beta peptide (AβP) together with a serotonin 5-HT6 receptor antagonist SB399885 significantly thwarted Alzheimer's disease brain pathology exacerbated by restraint stress, not reported earlier. The possible mechanisms and future clinical significance is discussed.

A Brief Review on the Potential of Psychedelics for Treating Alzheimer's Disease and Related Depression

Alzheimer's disease (AD), the most common form of senile dementia, is poised to place an even greater societal and healthcare burden as the population ages. With few treatment options for the symptomatic relief of the disease and its unknown etiopathology, more research into AD is urgently needed. Psychedelic drugs target AD-related psychological pathology and symptoms such as depression. Using microdosing, psychedelic drugs may prove to help combat this devastating disease by eliciting psychiatric benefits via acting through various mechanisms of action such as serotonin and dopamine pathways. Herein, we review the studied benefits of a few psychedelic compounds that may show promise in treating AD and attenuating its related depressive symptoms. We used the listed keywords to search through PubMed for relevant preclinical, clinical research, and review articles. The putative mechanism of action (MOA) for psychedelics is that they act mainly as serotonin receptor agonists and induce potential beneficial effects for treating AD and related depression.

Elucidation of Pharmacological Mechanism Underlying the Anti-Alzheimer's Disease Effects of Evodia rutaecarpa and Discovery of Novel Lead Molecules: An In Silico Study

Alzheimer's disease (AD) is a brain disease with a peculiarity of multiformity and an insidious onset. Multiple-target drugs, especially Chinese traditional medicine, have achieved a measure of success in AD treatment. Evodia rutaecarpa (Juss.) Benth. (Wuzhuyu, WZY, i.e., E. rutaecarpa), a traditional Chinese herb, has been identified as an effective drug to cure migraines. To our surprise, our in silico study showed that rather than migraines, Alzheimer's disease was the primary disease to which the E. rutaecarpa active compounds were targeted. Correspondingly, a behavioral experiment showed that E. rutaecarpa extract could improve impairments in learning and memory in AD model mice. However, the mechanism underlying the way that E. rutaecarpa compounds target AD is still not clear. For this purpose, we employed methods of pharmacology networking and molecular docking to explore this mechanism. We found that E. rutaecarpa showed significant AD-targeting characteristics, and alkaloids of E. rutaecarpa played the main role in binding to the key nodes of AD. Our research detected that E. rutaecarpa affects the pathologic development of AD through the serotonergic synapse signaling pathway (SLC6A4), hormones (PTGS2, ESR1, AR), anti-neuroinflammation (SRC, TNF, NOS3), transcription regulation (NR3C1), and molecular chaperones (HSP90AA1), especially in the key nodes of PTGS2, AR, SLCA64, and SRC. Graveoline, 5-methoxy-N, N-dimethyltryptamine, dehydroevodiamine, and goshuyuamide II in E. rutaecarpa show stronger binding affinities to these key proteins than currently known preclinical and clinical drugs, showing a great potential to be developed as lead molecules for treating AD.

Chronic evoked seizures in young pre-symptomatic APP/PS1 mice induce serotonin changes and accelerate onset on Alzheimer's disease-related neurpathology

OBJECTIVE

People with early-onset Alzheimer's disease (AD) are at elevated seizure risk. Further, chronic seizures in pre-symptomatic stages may disrupt serotonin pathway-related protein expression, precipitating the onset of AD-related pathology and burden of neuropsychiatric comorbidities.

METHODS

2-3-month-old APP/PS1, PSEN2-N141I, and transgenic control mice were sham or corneal kindled for 2 weeks to model chronic seizures. Seizure-induced changes in glia, serotonin pathway proteins, and amyloid beta; levels in hippocampus and prefrontal cortex were quantified.

RESULTS

APP/PS1 mice experienced worsened mortality versus kindled Tg- controls. APP/PS1 females were also more susceptible to chronic kindled seizures. These changes correlated with a marked downregulation of hippocampal tryptophan hydroxylase 2 and monoamine oxidase A protein expression compared to controls; these changes were not detected in PSEN2-N141I mice. Kindled APP/PS1 mice exhibited amyloid beta; overexpression and glial overactivity without plaque deposition. PSEN2 protein expression was AD model-dependent.

SIGNIFICANCE

Seizures evoked in pre-symptomatic APP/PS1 mice promotes premature mortality in the absence of pathological amyloid deposition. Disruptions in serotonin pathway metabolism are associated with increased glial reactivity and PSEN2 downregulation without amyloid beta; deposition. This study provides the first direct evidence that seizures occurring prior to amyloid beta, plaque accumulation worsen disease burden in an AD genotype-specific manner.

Serotonin Degeneration and Amyloid-β Deposition in Mild Cognitive Impairment: Relationship to Cognitive Deficits

BACKGROUND

Neuropathological and neuroimaging studies have demonstrated degeneration of the serotonin system in Alzheimer's disease (AD). Neuroimaging studies have extended these observations to the preclinical stages of AD, mild cognitive impairment (MCI). Serotonin degeneration has been observed also in transgenic amyloid mouse models, prior to widespread cortical distribution of amyloid-β (Aβ).

OBJECTIVE

The present study evaluated the regional distribution of the serotonin transporter (5-HTT) and of Aβ in individuals with MCI and healthy older controls, as well as the contribution of 5-HTT and Aβ to cognitive deficits.

METHODS

Forty-nine MCI participants and 45 healthy older controls underwent positron emission tomography (PET) imaging of 5-HTT and Aβ, structural magnetic resonance imaging and neuropsychological assessments.

RESULTS

Lower cortical, striatal, and limbic 5-HTT and higher cortical Aβ was observed in MCIs relative to healthy controls. Lower 5-HTT, mainly in limbic regions, was correlated with greater deficits in auditory-verbal and visual-spatial memory and semantic, not phonemic fluency. Higher cortical A β was associated with greater deficits in auditory-verbal and visual-spatial memory and in semantic, not phonemic fluency. When modeling the association between cognition, gray matter volumes and Aβ, inclusion of 5-HTT in limbic and in select cortical regions significantly improved model fit for auditory-verbal and visual-spatial memory and semantic, but not phonemic fluency.

CONCLUSIONS

These results support the role of serotonin degeneration in the memory and semantic fluency deficits observed in MCI.

Comparative efficacy and safety of antidepressant therapy for the agitation of dementia: A systematic review and network meta-analysis

Background

Dementia is a clinical syndrome commonly seen in the elderly individuals. With the prevalence of dementia, the incidence of neuropsychiatric symptoms in dementia patients is increasing annually. Agitation, as one of the neuropsychiatric symptoms, has a serious impact on the quality of life of patients with dementia. Several antidepressant drugs have been shown to be effective for treating agitated behavior symptoms in patients with dementia, but there are no direct comparisons among those drugs. Therefore, we carried out a network meta-analysis (NMA) to examine the efficacy and safety of those antidepressant drugs.

Methods

We searched eight databases (PubMed, Cochrane Library, Web of Science, Embase, Wanfang Database, China National Knowledge Infrastructure, VIP Database and China biomedical literature service) from their inception to 6 November 2022. Randomized controlled trials (RCTs) reporting the efficacy and safety of antidepressant drugs in treating agitated behavior symptoms in patients with dementia were included in our analysis. The quality assessment was carried out by two researchers individually and the analysis was based on the frequency method.

Results

Twelve articles with 1,146 participants were included in our analysis. Based on the outcome of the agitation score, treatment with citalopram (standardized mean difference, SMD = -0.44, 95% confidence interval, 95% CI = -0.72 to -0.16) showed significant benefits over the placebo group. Treatment with trazodone (odds ratio, OR = 4.58, 95% CI = 1.12-18.69) was associated with a higher risk of total adverse events compared with a placebo treatment.

Conclusion

Among the antidepressant drugs included in this study, treatment with citalopram was probably the only optimal intervention, when considering the improvement from baseline to the end of the intervention, and there was not a statistically significant difference in safety when compared with a placebo treatment.

Systematic review registration

https://www.crd.york.ac.uk/prospero/#recordDetails, identifier: PROSPERO, CRD42022320932.

Alterations in Peripheral Metabolites as Key Actors in Alzheimer's Disease

Growing evidence supports that Alzheimer's disease (AD) could be regarded as a metabolic disease, accompanying central and peripheral metabolic disturbance. Nowadays, exploring novel and potentially alternative hallmarks for AD is needed. Peripheral metabolites based on blood and gut may provide new biochemical insights about disease mechanisms. These metabolites can influence brain energy homeostasis, maintain gut mucosal integrity, and regulate the host immune system, which may further play a key role in modulating the cognitive function and behavior of AD. Recently, metabolomics has been used to identify key AD-related metabolic changes and define metabolic changes during AD disease trajectory. This review aims to summarize the key blood- and microbial-derived metabolites that are altered in AD and identify the potential metabolic biomarkers of AD, which will provide future targets for precision therapeutic modulation.

Therapeutic role of yoga in neuropsychological disorders

Yoga is considered a widely-used approach for health conservation and can be adopted as a treatment modality for a plethora of medical conditions, including neurological and psychological disorders. Hence, we reviewed relevant articles entailing various neurological and psychological disorders and gathered data on how yoga exerts positive impacts on patients with a diverse range of disorders, including its modulatory effects on brain bioelectrical activities, neurotransmitters, and synaptic plasticity. The role of yoga practice as an element of the treatment of several neuropsychological diseases was evaluated based on these findings.

Is the Exposome Involved in Brain Disorders through the Serotoninergic System?

Serotonin (5-hydroxytryptamine, 5-HT) is a biogenic monoamine acting as a neurotransmitter in the central nervous system (CNS), local mediator in the gut, and vasoactive agent in the blood. It has been linked to a variety of CNS functions and is implicated in many CNS and psychiatric disorders. The high comorbidity between some neuropathies can be partially understood by the fact that these diseases share a common etiology involving the serotoninergic system. In addition to its well-known functions, serotonin has been shown to be a mitogenic factor for a wide range of normal and tumor cells, including glioma cells, in vitro. The developing CNS of fetus and newborn is particularly susceptible to the deleterious effects of neurotoxic substances in our environment, and perinatal exposure could result in the later development of diseases, a hypothesis known as the developmental origin of health and disease. Some of these substances affect the serotoninergic system and could therefore be the source of a silent pandemic of neurodevelopmental toxicity. This review presents the available data that are contributing to the appreciation of the effects of the exposome on the serotoninergic system and their potential link with brain pathologies (neurodevelopmental, neurodegenerative, neurobehavioral disorders, and glioblastoma).

Positron emission tomography imaging of serotonin degeneration and beta-amyloid deposition in late-life depression evaluated with multi-modal partial least squares

Depression in late-life is associated with increased risk of cognitive decline and development of all-cause dementia. The neurobiology of late-life depression (LLD) may involve both neurochemical and neurodegenerative mechanisms that are common to depression and dementia. Transgenic amyloid mouse models show evidence of early degeneration of monoamine systems. Informed by these preclinical data, the hypotheses were tested that a spatial covariance pattern of higher beta-amyloid (Aβ) and lower serotonin transporter availability (5-HTT) in frontal, temporal, and parietal cortical regions would distinguish LLD patients from healthy controls and the expression of this pattern would be associated with greater depressive symptoms. Twenty un-medicated LLD patients who met DSM-V criteria for major depression and 20 healthy controls underwent PET imaging with radiotracers for Aβ ([11C]-PiB) and 5-HTT ([11C]-DASB). A voxel-based multi-modal partial least squares (mmPLS) algorithm was applied to the parametric PET images to determine the spatial covariance pattern between the two radiotracers. A spatial covariance pattern was identified, including higher Aβ in temporal, parietal and occipital cortices associated with lower 5-HTT in putamen, thalamus, amygdala, hippocampus and raphe nuclei (dorsal, medial and pontine), which distinguished LLD patients from controls. Greater expression of this pattern, reflected in summary 5-HTT/Aβ mmPLS subject scores, was associated with higher levels of depressive symptoms. The mmPLS method is a powerful approach to evaluate the synaptic changes associated with AD pathology. This spatial covariance pattern should be evaluated further to determine whether it represents a biological marker of antidepressant treatment response and/or cognitive decline in LLD patients.

Highlighting Immune System and Stress in Major Depressive Disorder, Parkinson's, and Alzheimer's Diseases, with a Connection with Serotonin

There is recognition that both stress and immune responses are important factors in a variety of neurological disorders. Moreover, there is an important role of several neurotransmitters that connect these factors to several neurological diseases, with a special focus in this paper on serotonin. Accordingly, it is known that imbalances in stressors can promote a variety of neuropsychiatric or neurodegenerative pathologies. Here, we discuss some facts that link major depressive disorder, Alzheimer’s, and Parkinson’s to the stress and immune responses, as well as the connection between these responses and serotonergic signaling. These are important topics of investigation which may lead to new or better treatments, improving the life quality of patients that suffer from these conditions.

Efficacy of serotonergic antidepressant treatment for the neuropsychiatric symptoms and agitation in dementia: A systematic review and meta-analysis

OBJECTIVE

Serotonergic dysfunction may be involved in the etiology of overall neuropsychiatric symptoms (NPS) and agitation in patients with dementia; therefore, we aim to perform a systematic review and meta-analysis to investigate the efficacy of serotonergic antidepressants in such populations.

METHODS

We systematically searched PubMed, Medline, Embase, and Cochrane Library to obtain randomized controlled trials (RCTs) from the date of their inception until December 11, 2020 to examine the effect of serotonergic antidepressants on the outcomes of interest in patients with dementia. Data were pooled using a random-effects model. Co-primary outcomes were mean changes in overall NPS and agitation as a specific symptom of NPS. Secondary outcomes were mean changes in depressive symptoms, cognition, and care burden.

RESULTS

Fourteen randomized controlled trials were eligible (n = 1,374; mean age = 76.8 years; mean proportion of female = 61.9 %). Serotonergic antidepressants significantly reduced the overall NPS (k = 12, n = 1276, Hedges' g = -0.49, 95 % confidence intervals [CIs] = -0.74 to -0.24, p < 0.001) and agitation severity (k = 9, n = 749, Hedges' g = -0.28, 95 % CIs = -0.43 to -0.14, p < 0.001), both with small effect size in patients with dementia. For secondary outcome, serotonergic antidepressants also significantly improved depressive symptoms, cognition, and care burden with small to very small effect sizes (depressive symptoms, k = 8, n = 938, Hedges' g = -0.32, 95 % CIs = -0.49 to -0.15, p < 0.001;cognition, k = 6, n = 983, Hedges' g = 0.15, 95 % CIs = 0.002 to 0.29, p = 0.046; care burden, k = 7, n = 961, Hedges' g = -0.24, 95 % CIs = -0.41 to -0.07, p = 0.005). Subgroup analysis showed that both selective serotonin reuptake inhibitors (SSRIs) and non-SSRIs significant reduced agitation and depressive symptoms (For agitation, SSRIs, k = 6, n = 605, Hedges' g = -0.25, 95 % CIs = -0.41 to -0.09, p=0.002; non-SSRIs, k = 3, n = 144, Hedges' g = -0.41, 95 % CIs = -0.74 to -0.08, p = 0.016; For depression, SSRIs, k = 6, n = 736, Hedges' g = -0.29, 95 % CIs = -0.48 to -0.09, p=0.004; non-SSRIs, k = 343, n = 144, Hedges' g = -0.43, 95 % CIs = -0.78 to -0.09, p = 0.016), whereas only SSRIs reduced overall NPS (k = 9, n = 1109, Hedges' g = -0.49, 95 % CIs = -0.78 to -0.20, p = 0.001) and care burden (k = 5, n = 740, Hedges' g = -0.29, 95 % CIs = -0.50 to -0.08, p=0.007).

CONCLUSION

The present meta-analysis indicates that serotonergic antidepressants effectively alleviate overall NPS, agitation, depressive symptoms, and care burden, and improve cognitive function.

Tumor Necrosis Factor (TNF) Is Required for Spatial Learning and Memory in Male Mice under Physiological, but Not Immune-Challenged Conditions

Increasing evidence demonstrates that inflammatory cytokines-such as tumor necrosis factor (TNF)-are produced at low levels in the brain under physiological conditions and may be crucial for synaptic plasticity, neurogenesis, learning and memory. Here, we examined the effects of developmental TNF deletion on spatial learning and memory using 11-13-month-old TNF knockout (KO) and C57BL6/J wild-type (WT) mice. The animals were tested in the Barnes maze (BM) arena under baseline conditions and 48 h following an injection of the endotoxin lipopolysaccharide (LPS), which was administered at a dose of 0.5 mg/kg. Vehicle-treated KO mice were impaired compared to WT mice during the acquisition and memory-probing phases of the BM test. No behavioral differences were observed between WT and TNF-KO mice after LPS treatment. Moreover, there were no differences in the hippocampal content of glutamate and noradrenaline between groups. The effects of TNF deletion on spatial learning and memory were observed in male, but not female mice, which were not different compared to WT mice under baseline conditions. These results indicate that TNF is required for spatial learning and memory in male mice under physiological, non-inflammatory conditions, however not following the administration of LPS. Inflammatory signalling can thereby modulate spatial cognition in male subjects, highlighting the importance of sex- and probably age-stratified analysis when examining the role of TNF in the brain.