Protective effects of 5-HT1A receptor antagonist and 5-HT2A receptor agonist on the biochemical and histological features in a rat model of Alzheimer’s disease

An Expanded Narrative Review of Neurotransmitters on Alzheimer's Disease: The Role of Therapeutic Interventions on Neurotransmission

Alzheimer's disease (AD) is a progressive neurodegenerative disease. The accumulation of amyloid-β (Aβ) plaques and tau neurofibrillary tangles are the key players responsible for the pathogenesis of the disease. The accumulation of Aβ plaques and tau affect the balance in chemical neurotransmitters in the brain. Thus, the current review examined the role of neurotransmitters in the pathogenesis of Alzheimer's disease and discusses the alterations in the neurochemical activity and cross talk with their receptors and transporters. In the presence of Aβ plaques and neurofibrillary tangles, changes may occur in the expression of neuronal receptors which in turn triggers excessive release of glutamate into the synaptic cleft contributing to cell death and neuronal damage. The GABAergic system may also be affected by AD pathology in a similar way. In addition, decreased receptors in the cholinergic system and dysfunction in the dopamine neurotransmission of AD pathology may also contribute to the damage to cognitive function. Moreover, the presence of deficiencies in noradrenergic neurons within the locus coeruleus in AD suggests that noradrenergic stimulation could be useful in addressing its pathophysiology. The regulation of melatonin, known for its effectiveness in enhancing cognitive function and preventing Aβ accumulation, along with the involvement of the serotonergic system and histaminergic system in cognition and memory, becomes remarkable for promoting neurotransmission in AD. Additionally, nitric oxide and adenosine-based therapeutic approaches play a protective role in AD by preventing neuroinflammation. Overall, neurotransmitter-based therapeutic strategies emerge as pivotal for addressing neurotransmitter homeostasis and neurotransmission in the context of AD. This review discussed the potential for neurotransmitter-based drugs to be effective in slowing and correcting the neurodegenerative processes in AD by targeting the neurochemical imbalance in the brain. Therefore, neurotransmitter-based drugs could serve as a future therapeutic strategy to tackle AD.

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.

Rosavin thwarts amyloid-β-induced macromolecular damages and neurotoxicity, exhibiting anti-Alzheimer's disease activity in Wister rat model

Lately, interest surrounding the utilization of plant-derived compounds as a viable beneficial approach for treating Alzheimer's disease (AD) has significantly increased. This study aimed to assess the defensive properties of rosavin against Alzheimer's disease induced by amyloid-β, utilizing experimental models. We found that rosavin exhibited anti-aggregation and disaggregation properties, suggesting its potential to prevent the gathering of Aβ-aggregates. In vitro experiments revealed that rosavin effectively mitigated the neurotoxicity induced by Aβ in Neuro-2a cells, showcasing its protective potential. Rosavin significantly improved the Aβ-induced cognitive deficits in Wistar rats, particularly in spatial memory. Which the pathophysiology of AD includes oxidative damage, which negatively impacts biological macromolecules. Triggers the apoptotic process, causing macromolecular destruction. Interestingly, rosavin attenuated Aβ-induced macromolecular damages, thereby preserving neuronal integrity. Furthermore, the activation of antioxidative defense enzymes by rosavin inhibited oxidative damage. The positive outcomes associated with rosavin were primarily attributed to its capacity to enhance acetylcholine-mediated effects. Finally, rosavin has the potential to alleviate Aβ-induced neurotoxicity and macromolecular damages, ultimately resulting in enhanced memorial and reasoning function in Wistar rats, offering promising prospects for the treatment of AD.

Psychedelics for acquired brain injury: a review of molecular mechanisms and therapeutic potential

Acquired brain injury (ABI), such as traumatic brain injury and stroke, is a leading cause of disability worldwide, resulting in debilitating acute and chronic symptoms, as well as an increased risk of developing neurological and neurodegenerative disorders. These symptoms can stem from various neurophysiological insults, including neuroinflammation, oxidative stress, imbalances in neurotransmission, and impaired neuroplasticity. Despite advancements in medical technology and treatment interventions, managing ABI remains a significant challenge. Emerging evidence suggests that psychedelics may rapidly improve neurobehavioral outcomes in patients with various disorders that share physiological similarities with ABI. However, research specifically focussed on psychedelics for ABI is limited. This narrative literature review explores the neurochemical properties of psychedelics as a therapeutic intervention for ABI, with a focus on serotonin receptors, sigma-1 receptors, and neurotrophic signalling associated with neuroprotection, neuroplasticity, and neuroinflammation. The promotion of neuronal growth, cell survival, and anti-inflammatory properties exhibited by psychedelics strongly supports their potential benefit in managing ABI. Further research and translational efforts are required to elucidate their therapeutic mechanisms of action and to evaluate their effectiveness in treating the acute and chronic phases of ABI.

Converged avenues: depression and Alzheimer's disease- shared pathophysiology and novel therapeutics

Depression, a highly prevalent disorder affecting over 280 million people worldwide, is comorbid with many neurological disorders, particularly Alzheimer's disease (AD). Depression and AD share overlapping pathophysiology, and the search for accountable biological substrates made it an essential and intriguing field of research. The paper outlines the neurobiological pathways coinciding with depression and AD, including neurotrophin signalling, the hypothalamic-pituitary-adrenal axis (HPA), cellular apoptosis, neuroinflammation, and other aetiological factors. Understanding overlapping pathways is crucial in identifying common pathophysiological substrates that can be targeted for effective management of disease state. Antidepressants, particularly monoaminergic drugs (first-line therapy), are shown to have modest or no clinical benefits. Regardless of the ineffectiveness of conventional antidepressants, these drugs remain the mainstay for treating depressive symptoms in AD. To overcome the ineffectiveness of traditional pharmacological agents in treating comorbid conditions, a novel therapeutic class has been discussed in the paper. This includes neurotransmitter modulators, glutamatergic system modulators, mitochondrial modulators, antioxidant agents, HPA axis targeted therapy, inflammatory system targeted therapy, neurogenesis targeted therapy, repurposed anti-diabetic agents, and others. The primary clinical challenge is the development of therapeutic agents and the effective diagnosis of the comorbid condition for which no specific diagnosable scale is present. Hence, introducing Artificial Intelligence (AI) into the healthcare system is revolutionary. AI implemented with interdisciplinary strategies (neuroimaging, EEG, molecular biomarkers) bound to have accurate clinical interpretation of symptoms. Moreover, AI has the potential to forecast neurodegenerative and psychiatric illness much in advance before visible/observable clinical symptoms get precipitated.

Serotonin Receptors as a Potential Target in the Treatment of Alzheimer's Disease

Alzheimer's disease (AD) is the most common cause of dementia worldwide that has an increasing impact on aging societies. Besides its critical role in the control of various physiological functions and behavior, brain serotonin (5-HT) system is involved in the regulation of migration, proliferation, differentiation, maturation, and programmed death of neurons. At the same time, a growing body of evidence indicates the involvement of 5-HT neurotransmission in the formation of insoluble aggregates of β-amyloid and tau protein, the main histopathological signs of AD. The review describes the role of various 5-HT receptors and intracellular signaling cascades induced by them in the pathological processes leading to the development of AD, first of all, in protein aggregation. Changes in the functioning of certain types of 5-HT receptors or associated intracellular signaling mediators prevent accumulation of β-amyloid plaques and tau protein neurofibrillary tangles. Based on the experimental data, it can be suggested that the use of 5-HT receptors as new drug targets will not only improve cognitive performance in AD, but will be also important in treating the causes of AD-related dementia.

The role of hippocampal 5-HT1D and 5-HT1F receptors on learning and memory in rats

Serotonin is a neurotransmitter, which is involved in memory via its receptors. The 5-HT_1D and 5-HT_1F receptors mainly exist in the hippocampus, which plays an important role in memory processing. However, few studies have assessed the effect of these serotonin receptors on memory. We evaluated the effect of a 5-HT_1D receptor agonist, PNU142633, 5-HT_1D receptor antagonist, BRL15572 hydrochloride, and 5-HT1F receptor agonist, LY344864, on the recognition and avoidance memory in the hippocampus area. Fifty adult male Wistar rats weighing 200-250 g were divided into the control, sham-operated, PNU, BRL, and LY groups (n=10 per group). Bilateral guide cannulas were implanted into the dentate gyrus area of the hippocampus. The drugs were administered at the dose of 1 μg/μl before the novel object recognition (NOR) and passive avoidance learning (PAL) tests. The results showed that in the NOR test, the administration of PNU and LY had no significant effect on recognition index; however, the recognition index was increased by BRL. In the PAL test, the administration of PNU had no significant effect on recognition index, but the administration of BRL and LY increased the time spent in the dark compartment of the apparatus and decreased the step-through latency into the dark compartment apparatus. It can be concluded that the inhibition of the hippocampal 5-HT_1D receptor improved cognition memory but impaired avoidance memory. Activation of the hippocampal 5-HT_1F receptor had no effect on cognitive memory but impaired avoidance memory.

Evaluation of chromane derivatives: Promising privileged scaffolds for lead discovery within Alzheimer's disease

The chromane ring system is widely distributed in nature and has proven to be a highly potent pharmacophore in medicinal chemistry, which includes the area of Alzheimer's and Parkinson's diseases. We report on the development of a gem-dimethylchroman-4-ol family that was shown to give good inhibition of equine serum butyrylcholinesterase (eqBuChE) (in the range 2.9 - 7.3 μM) and in the same range of currently used drugs. We also synthesized a small library of gem-dimethylchroman-4-amine compounds, via a simple reductive amination of the corresponding chromanone precursor, that were also selective for eqBuChE presenting inhibitions in the range 7.6 - 67 μM. Kinetic studies revealed that they were mixed inhibitors. Insights into their mechanism of action were obtained through molecular docking and STD-NMR experiments, and the most active examples showed excellent drug-likeness and pharmacological properties predicted using Swiss-ADME. We also prepared a set of propargyl gem-dimethylchromanamines, for monoamine oxidase (MAO) inhibition but they were only moderately active (the best being 28% inhibition at 1 µM on MAO-B). Overall, our compounds were found to be best suited as inhibitors for BuChE.

Understanding How Physical Exercise Improves Alzheimer’s Disease: Cholinergic and Monoaminergic Systems

Alzheimer’s disease (AD) is an age-related neurodegenerative disorder, characterized by the accumulation of proteinaceous aggregates and neurofibrillary lesions composed of β-amyloid (Aβ) peptide and hyperphosphorylated microtubule-associated protein tau, respectively. It has long been known that dysregulation of cholinergic and monoaminergic (i.e., dopaminergic, serotoninergic, and noradrenergic) systems is involved in the pathogenesis of AD. Abnormalities in neuronal activity, neurotransmitter signaling input, and receptor function exaggerate Aβ deposition and tau hyperphosphorylation. Maintenance of normal neurotransmission is essential to halt AD progression. Most neurotransmitters and neurotransmitter-related drugs modulate the pathology of AD and improve cognitive function through G protein-coupled receptors (GPCRs). Exercise therapies provide an important alternative or adjunctive intervention for AD. Cumulative evidence indicates that exercise can prevent multiple pathological features found in AD and improve cognitive function through delaying the degeneration of cholinergic and monoaminergic neurons; increasing levels of acetylcholine, norepinephrine, serotonin, and dopamine; and modulating the activity of certain neurotransmitter-related GPCRs. Emerging insights into the mechanistic links among exercise, the neurotransmitter system, and AD highlight the potential of this intervention as a therapeutic approach for AD.

The role of serotonin within the microbiota-gut-brain axis in the development of Alzheimer's disease: A narrative review

Alzheimer's disease (AD) is the most common cause of dementia, accounting for more than 50 million patients worldwide. Current evidence suggests the exact mechanism behind this devastating disease to be of multifactorial origin, which seriously complicates the quest for an effective disease-modifying therapy, as well as impedes the search for strategic preventative measures. Of interest, preclinical studies point to serotonergic alterations, either induced via selective serotonin reuptake inhibitors or serotonin receptor (ant)agonists, in mitigating AD brain neuropathology next to its clinical symptoms, the latter being supported by a handful of human intervention trials. Additionally, a substantial amount of preclinical trials highlight the potential of diet, fecal microbiota transplantations, as well as pre- and probiotics in modulating the brain's serotonergic neurotransmitter system, starting from the gut. Whether such interventions could truly prevent, reverse or slow down AD progression likewise, should be initially tested in preclinical studies with AD mouse models, including sufficient analytical measurements both in gut and brain. Thereafter, its potential therapeutic effect could be confirmed in rigorously randomized controlled trials in humans, preferentially across the Alzheimer's continuum, but especially from the prodromal up to the mild stages, where both high adherence to such therapies, as well as sufficient room for noticeable enhancement are feasible still. In the end, such studies might aid in the development of a comprehensive approach to tackle this complex multifactorial disease, since serotonin and its derivatives across the microbiota-gut-brain axis might serve as possible biomarkers of disease progression, next to forming a valuable target in AD drug development. In this narrative review, the available evidence concerning the orchestrating role of serotonin within the microbiota-gut-brain axis in the development of AD is summarized and discussed, and general considerations for future studies are highlighted.

Psychedelics and Anti-inflammatory Activity in Animal Models

The serotonin (5-hydroxytryptamine, 5-HT) 2A receptor is most well known as the common target for classic psychedelic compounds. Interestingly, the 5-HT_2A receptor is the most widely expressed mammalian serotonin receptor and is found in nearly every examined tissue type including neural, endocrine, endothelial, immune, and muscle, suggesting it could be a novel and pharmacological target for several types of disorders. Despite this, the bulk of research on the 5-HT_2A receptor is focused on its role in the central nervous system (CNS). Recently, activation of 5-HT_2A receptors has emerged as a new anti-inflammatory strategy. This review will describe recent findings regarding psychedelics as anti-inflammatory compounds, as well as parse out differences in functional selectivity and immune regulation that exist between a number of well-known hallucinogenic compounds.

Role of Receptors in Relation to Plaques and Tangles in Alzheimer's Disease Pathology

Despite the identification of Aβ plaques and NFTs as biomarkers for Alzheimer’s disease (AD) pathology, therapeutic interventions remain elusive, with neither an absolute prophylactic nor a curative medication available to impede the progression of AD presently available. Current approaches focus on symptomatic treatments to maintain AD patients’ mental stability and behavioral symptoms by decreasing neuronal degeneration; however, the complexity of AD pathology requires a wide range of therapeutic approaches for both preventive and curative treatments. In this regard, this review summarizes the role of receptors as a potential target for treating AD and focuses on the path of major receptors which are responsible for AD progression. This review gives an overall idea centering on major receptors, their agonist and antagonist and future prospects of viral mimicry in AD pathology. This article aims to provide researchers and developers a comprehensive idea about the different receptors involved in AD pathogenesis that may lead to finding a new therapeutic strategy to treat AD.

Cannabidiol - A phytocannabinoid that widely affects sphingolipid metabolism under conditions of brain insulin resistance

Obesity-related insulin resistance (IR) and attenuated brain insulin signaling are significant risk factors for neurodegenerative disorders, e.g., Alzheimer's disease. IR and type 2 diabetes correlate with an increased concentration of sphingolipids, a class of lipids that play an essential structural role in cellular membranes and cell signaling pathways. Cannabidiol (CBD) is a nonpsychoactive constituent of Cannabis sativa plant that interacts with the endocannabinoidome. Despite known positive effects of CBD on improvement in diabetes and its aftermath, e.g., anti-inflammatory and anti-oxidant effects, there are no studies evaluating the effect of phytocannabinoids on the brain insulin resistance and sphingolipid metabolism. Our experiment was carried out on Wistar rats that received a high-fat diet and/or intraperitoneal CBD injections. In our study, we indicated inhibition of de novo synthesis and salvage pathways, which resulted in significant changes in the concentration of sphingolipids, e.g., ceramide and sphingomyelin. Furthermore, we observed reduced brain IR and decreased tau protein phosphorylation what might be protective against neuropathologies development. We believe that our research will concern a new possible therapeutic approach with Cannabis -plant derived compounds and within a few years, cannabinoids would be considered as prominent substances for targeting both metabolic and neurodegenerative pathologies.

5-HT1A Partial Agonist Tandospirone for Behavioral and Psychological Symptoms in Oldest-old Patients with Dementia at a Special Elderly Nursing Home

OBJECTIVE

To investigate the efficacy of tandospirone, an azapirone anxiolytic similar to buspirone that is used in Japan, for behavioral and psychological symptoms of dementia (BPSD), especially in oldest-old patients.

METHODS

This was an open-label observational study involving residents with BPSD in a special elderly nursing home between August 2013 and August 2018. The severity of dementia was assessed using the Clinical Dementia Rating (CDR) scale; as the main outcomes, the severity of BPSD was assessed using the Clinical Global Impressions-Severity scale (CGI-S) and Neuropsychiatric Inventory-12 (NPI-12) at baseline and 4 weeks after the maintenance dose of tandospirone was reached. The administration of tandospirone started at 30 mg, divided into three doses per day. Two weeks later, if the efficacy was sufficient based on the clinical nursing record, that dose was continued; if the efficacy was insufficient, the daily dose was increased from 40 mg/day to a maximum dose of 60 mg/day.

RESULTS

Thirty-three participants (25 females [76%], mean age 87.1 ± 5.4 years) completed the study. Twenty-three participants (70%) were oldest-old (18 females [78%], mean age 89.9 ± 3.4 years). The mean CDR score was 2.9 ± 0.3 in all participants. Tandospirone treatment showed few or no obvious adverse effects and significantly improved CGI-S scores, as well as total scores and many subscale scores on the NPI-12, in both the sample at large and the oldest-old participants.

CONCLUSION

This study demonstrated the efficacy and safety of tandospirone for BPSD in oldest-old participants.

Vanillic acid attenuates amyloid β1-40-induced long-term potentiation deficit in male rats: an in vivo investigation

Objectives: Alzheimer disease (AD) is a neurodegenerative disorderliness that involves deductible progressive cognition function caused by amyloid-beta (Aβ) peptide accumulation in the interstitial space. The increase of Aβ stimulates all kinds of active oxygen and causes oxidative stress and apoptosis. In this investigation, we researched the neuroprotective impacts of vanillic acid (VA) on the Aβ-induced (Aβ1-40) long-term potentiation (LTP) of the hippocampus - a commonly probed synaptic plasticity model that happens at the same time as memory and learning - in the AD rats.Methods: Forty-five male Wistar rats were categorized into five groups (n = 8 rats/group, 200-220 g), and studied as control (standard diet), sham (vehicle), VA (50 mg/kg), Aβ and Aβ + VA (50 mg/kg) groups. In vivo electrophysiological recordings were implemented after the stereotaxic surgery to gauge the excitatory postsynaptic potential (EPSP) slope and population spike (PS) amplitude in the dentate gyrus of the hippocampus. By the stimulation at high-frequency of the perforate pathway, long-term potentiation (LTP) was induced. To assess the plasma levels of malondialdehyde (MDA) and total thiol group (TTG), blood samples were garnered.Results: In the Aβ-injected rats, EPSP slope, and PS amplitude were significantly reduced after the induction of LTP. Thus, the findings demonstrate that VA decreases the impacts of Aβ on LTP; also, the treatments through VA neuroprotective against the negative effects of Aβ on the synaptic plasticity of the hippocampus can decrease the MDA levels and also increase the TTG levels significantly.Discussion: Therefore, based on this experiment on male rats, VA has neuroprotective effects and antioxidants benefits against the Aβ-mediated inhibition of long-term potentiation.

Opportunities for multiscale computational modelling of serotonergic drug effects in Alzheimer's disease

Alzheimer's disease (AD) is an age-specific neurodegenerative disease that compromises cognitive functioning and impacts the quality of life of an individual. Pathologically, AD is characterised by abnormal accumulation of beta-amyloid (Aβ) and hyperphosphorylated tau protein. Despite research advances over the last few decades, there is currently still no cure for AD. Although, medications are available to control some behavioural symptoms and slow the disease's progression, most prescribed medications are based on cholinesterase inhibitors. Over the last decade, there has been increased attention towards novel drugs, targeting alternative neurotransmitter pathways, particularly those targeting serotonergic (5-HT) system. In this review, we focused on 5-HT receptor (5-HTR) mediated signalling and drugs that target these receptors. These pathways regulate key proteins and kinases such as GSK-3 that are associated with abnormal levels of Aβ and tau in AD. We then review computational studies related to 5-HT signalling pathways with the potential for providing deeper understanding of AD pathologies. In particular, we suggest that multiscale and multilevel modelling approaches could potentially provide new insights into AD mechanisms, and towards discovering novel 5-HTR based therapeutic targets.

Ebselen reversed peripheral oxidative stress induced by a mouse model of sporadic Alzheimer's disease

Intracerebroventricular streptozotocin injection (icv STZ) is a well established sporadic Alzheimer's disease (AD) model in rodents. AD is characterized by neuronal degeneration accompanied by central oxidative stress. Studies also indicate peripheral oxidative damage in AD, but if the icv STZ model of sporadic AD mimics this feature is an open question. This study aimed to investigate if icv STZ administration induces peripheral oxidative stress and the antioxidant action of Ebselen, compared to the reference drug (donepezil), in this sporadic AD model. Male adult Swiss mice received icv STZ (days 1 and 3). Mice received Ebselen (10 mg/kg, i.p) or Donepezil (5 mg/kg, i.p) for 14 days. Mice were killed and the kidney and liver were excised to determine parameters of oxidative stress and toxicity markers. The mice icv STZ-injected showed peripheral oxidative stress. Ebselen reversed renal lipid peroxidation in the icv STZ administered mice by modulating NPSH levels, SOD and CAT activities, whereas Donepezil, modulated only NPSH levels. Ebselen and Donepezil counteracted hepatic lipid peroxidation in STZ-injected mice by modulating NPSH levels and CAT activity. The δ-ALA-D activity was inhibited in the kidney, but not in the liver, whereas the icv STZ-injected mice had an increase in the GST activity in both tissues. Ebselen reversed the increase in the hepatic GST activity of the STZ-injected mice. Donepezil increased renal GST activity in the control mice. In conclusion, this study demonstrates that the icv STZ administration induced peripheral oxidative stress. Ebselen, similar to Donepezil, was effective against peripheral oxidative stress in a mouse model of sporadic AD.