The involvement of sigma1 receptors in donepezil-induced rescue of hippocampal LTP impaired by beta-amyloid peptide

Guidelines for pharmacotherapy in Alzheimer's disease - A primer on FDA-approved drugs

The growing prevalence of dementia makes it important for us to better understand its pathophysiology and treatment modalities, to improve the quality of life of patients and caregivers. Alzheimer's disease (AD), a neurodegenerative disease, is the most common form of amnestic dementia in the geriatric population. Pathophysiology of AD is widely attributed to aggregation of amyloid-beta (Aβ) plaques and hyperphosphorylation of tau proteins. Initial treatment modalities aimed to increase brain perfusion in a non-specific manner. Subsequent therapy focused on rectifying neurotransmitter imbalance in the brain. Newer drugs modify the progression of the disease by acting against aggregated Aβ plaques. However, not all drugs used in therapy of AD have been granted approval by the United States Food and Drug Administration (FDA). This review categorizes and summarizes the FDA-approved drugs in the treatment of AD in a manner that would make it a convenient reference for researchers and practicing physicians alike. Drugs that mitigate symptoms of dementia may be categorized into mitigators of Behavioral and Psychological Symptoms of Dementia (BPSD), and mitigators of cognitive decline. BPSD mitigators include brexpiprazole, an atypical antipsychotic with a once-daily dosage suited to treat agitation in dementia patients, and suvorexant, an orexin receptor antagonist used to treat sleep disturbances. Cognitive decline mitigators include cholinesterase inhibitors such as donepezil, rivastigmine, and galantamine and glutamate inhibitors such as memantine. Donepezil is the most commonly prescribed drug. It is cheap, well-tolerated, and may be prescribed orally once daily, or as a transdermal patch once weekly. It increases ACh levels, enhances oligodendrocyte differentiation and also protects against Aβ toxicity. However, regular cardiac monitoring is required due to reports of cardiac conduction side effects. Rivastigmine requires a twice-daily oral dosage or once-daily replacement of transdermal patch. It has fewer cardiac side effects than donepezil, but local application-site reactions have been noted. Galantamine, in addition to improving cognitive symptoms in a short span of time, also delays the development of BPSDs and has minimal drug-drug interactions by virtue of having multiple metabolic pathways. However, cardiac conduction disturbances must be closely monitored for. Memantine, a glutamate regulator, acts as an anti-Parkinsonian agent and an antidepressant, in addition to improving cognition and neuroprotection, and requires a once-daily dosage in the form of immediate-release or sustained-release oral tablets. Disease-modifying drugs such as aducanumab and lecanemab reduce the Aβ burden. Both act by binding with fibrillary conformations of Aβ plaques in the brain. These drugs have a risk of causing amyloid-related imaging abnormalities, especially in persons with ApoE4 gene. Aducanumab is administered once every 4 weeks and lecanemab once every 2 weeks. The decision on the choice of the drug must be made after considering the availability of drug, compliance of patient (once-daily vs. multiple doses daily), cost, specific comorbidities, and the risk-benefit ratio for the particular patient. Other non-pharmacological treatment modalities must also be adopted to have a holistic approach toward the treatment of AD.

Combined Donepezil with Astaxanthin via Nanostructured Lipid Carriers Effective Delivery to Brain for Alzheimer's Disease in Rat Model

Introduction

Donepezil (DPL), a specific acetylcholinesterase inhibitor, is used as a first-line treatment to improve cognitive deficits in Alzheimer's disease (AD) and it might have a disease modifying effect. Astaxanthin (AST) is a natural potent antioxidant with neuroprotective, anti-amyloidogenic, anti-apoptotic, and anti-inflammatory effects. This study aimed to prepare nanostructured lipid carriers (NLCs) co-loaded with donepezil and astaxanthin (DPL/AST-NLCs) and evaluate their in vivo efficacy in an AD-like rat model 30 days after daily intranasal administration.

Methods

DPL/AST-NLCs were prepared using a hot high-shear homogenization technique, in vitro examined for their physicochemical parameters and in vivo evaluated. AD induction in rats was performed by aluminum chloride. The cortex and hippocampus were isolated from the brain of rats for biochemical testing and histopathological examination.

Results

DPL/AST-NLCs showed z-average diameter 149.9 ± 3.21 nm, polydispersity index 0.224 ± 0.017, zeta potential -33.7 ± 4.71 mV, entrapment efficiency 81.25 ±1.98% (donepezil) and 93.85 ±1.75% (astaxanthin), in vitro sustained release of both donepezil and astaxanthin for 24 h, spherical morphology by transmission electron microscopy, and they were stable at 4-8 ± 2°C for six months. Differential scanning calorimetry revealed that donepezil and astaxanthin were molecularly dispersed in the NLC matrix in an amorphous state. The DPL/AST-NLC-treated rats showed significantly lower levels of nuclear factor-kappa B, malondialdehyde, β-site amyloid precursor protein cleaving enzyme-1, caspase-3, amyloid beta (Aβ1‑42), and acetylcholinesterase, and significantly higher levels of glutathione and acetylcholine in the cortex and hippocampus than the AD-like untreated rats and that treated with donepezil-NLCs. DPL/AST-NLCs showed significantly higher anti-amyloidogenic, antioxidant, anti-acetylcholinesterase, anti-inflammatory, and anti-apoptotic effects, resulting in significant improvement in the cortical and hippocampal histopathology.

Conclusion

Nose-to-brain delivery of DPL/AST-NLCs is a promising strategy for the management of AD.

Review of Alzheimer's disease drugs and their relationship with neuron-glia interaction

Alzheimer's disease (AD) is the most common cause of dementia worldwide. Because Alzheimer's disease has no known treatment, sufferers and their caregivers must concentrate on symptom management. Astrocytes and microglia are now known to play distinct physiological roles in synaptic function, the blood-brain barrier, and neurovascular coupling. Consequently, the search for drugs that can slow the degenerative process in dementia sufferers continues because existing drugs are designed to alleviate the symptoms of Alzheimer's disease. Drugs that address pathological changes without interfering with the normal function of glia, such as eliminating amyloid-beta deposits, are prospective treatments for neuroinflammatory illnesses. Because neuron-astrocytes-microglia interactions are so complex, developing effective, preventive, and therapeutic medications for AD will necessitate novel methodologies and strategic targets. This review focused on existing medications used in treating AD amongst which include Donepezil, Choline Alphoscerate, Galantamine, Dextromethorphan, palmitoylethanolamide, citalopram, resveratrol, and solanezumab. This review summarizes the effects of these drugs on neurons, astrocytes, and microglia interactions based on their pharmacokinetic properties, mechanism of action, dosing, and clinical presentations.

Efficiency of donepezil in elderly patients undergoing orthopaedic surgery due to underlying post-operative cognitive dysfunction: study protocol for a multicentre randomised controlled trial

BACKGROUND

Post-operative cognitive dysfunction (POCD) is an overarching term used to describe cognitive impairment identified in the preoperative or post-operative period. After surgical operations, older patients are particularly vulnerable to memory disturbances and other types of cognitive impairment. However, the pathogenesis of POCD remains unclear with no confirmed preventable or treatable strategy available. Our previous study demonstrated that the concentration of choline acetyl transferase in the cerebral spinal fluid was a predictive factor of POCD and that donepezil, which is an acetylcholinesterase inhibitor used in clinical settings for the treatment of Alzheimer's disease, can prevent learning and memory impairment after anaesthesia/surgery in aged mice. This study aimed to determine the critical role of donepezil in preventing cognitive impairment in elderly patients undergoing orthopaedic surgery.

METHODS

A multicentre, double-blind, placebo-controlled, crossover clinical trial will be performed to assess the efficacy of donepezil in elderly patients undergoing orthopaedic surgery. Participants (n = 360) will receive donepezil (5 mg once daily) or placebo from 1 day prior to surgery until 5 days after surgery. Neuropsychological tests will be measured at 1 day before the operation and 1 week, 1 month, 6 months and 1 year after the operation.

DISCUSSION

This research project mainly aimed to study the effects of donepezil in elderly patients undergoing orthopaedic surgery due to underlying POCD and to investigate the underlying physiological and neurobiological mechanisms of these effects. The results may provide important implications for the development of effective interfering strategies, specifically regarding cognitive dysfunction therapy using drugs.

TRIAL REGISTRATION

ClinicalTrials.gov NCT04423276 . Registered on 14 June 2020.

Effect of Water Extract of Mangosteen Pericarp on Donepezil Pharmacokinetics in Mice

The pharmacokinetic (PK) change in a drug by co-administered herbal products can alter the efficacy and toxicity. In the circumstances that herb-drug combinations have been increasingly attempted to alleviate Alzheimer's disease (AD), the PK evaluation of herb-drug interaction (HDI) is necessary. The change in systemic exposure as well as target tissue distribution of the drug have been issued in HDIs. Recently, the memory-enhancing effects of water extract of mangosteen pericarp (WMP) has been reported, suggesting a potential for the combination of WMP and donepezil (DNP) for AD treatment. Thus, it was evaluated how WMP affects the PK change of donepezil, including systemic exposure and tissue distribution in mice after simultaneous oral administration of DNP with WMP. Firstly, co-treatment of WMP and donepezil showed a stronger inhibitory effect (by 23.0%) on the neurotoxicity induced by Aβ_(25-35) in SH-SY5Y neuroblastoma cells than donepezil alone, suggesting that the combination of WMP and donepezil may be more effective in moderating neurotoxicity than donepezil alone. In PK interaction, WMP increased donepezil concentration in the brain at 4 h (by 63.6%) after administration without affecting systemic exposure of donepezil. Taken together, our results suggest that WMP might be used in combination with DNP as a therapy for AD.

Significant effects of cholinesterase inhibitors on tau pathology in the Alzheimer's disease continuum: An in vivo positron emission tomography study

OBJECTIVES

No prior study has assessed the effects of cholinesterase inhibitors (ChEIs) on tau pathology in the brains of patients with Alzheimer's disease (AD). Using positron emission tomography, this study aimed to investigate whether ChEIs reduce tau aggregation in amyloid-positive participants.

METHODS

We analyzed datasets from the Alzheimer's Disease Neuroimaging Initiative and included amyloid-positive participants who had undergone baseline and 1- or 2-year follow-up AV-1451 positron emission tomography scans. We included participants treated with and without ChEIs (ChEIs group: n = 15, No-ChEIs group, n = 45). The annual change in tau aggregation was calculated as the difference in AV-1451- standardized uptake value ratio (SUVR) between the two scans divided by the time between scans. Group differences in annual AV-1451-SUVR change were examined.

RESULTS

We found a significantly lower annual change in AV-1451-SUVR in the Braak 1/2 regions (entorhinal cortex and hippocampus) of participants taking ChEIs. Increased AV-1451-SUVR between the first and second examinations were observed in 22 of 45 participants not taking ChEIs and 2 of 15 participants taking ChEIs. Fisher's exact test showed a significant difference in the ratio of participants with increased AV-1451-SUVR between the groups.

CONCLUSIONS

The findings of this positron emission tomography study suggest that the administration of ChEIs has some neuroprotective effects in patients of the AD continuum, at least in the early stage of the disease progression. This in vivo effect may be mediated via tau, preventing amyloid β-induced neurotoxicity.

The emerging role of the sigma-1 receptor in autophagy: hand-in-hand targets for the treatment of Alzheimer's

INTRODUCTION

Autophagy is a cellular catabolic mechanism that helps clear damaged cellular components and is essential for normal cellular and tissue function. The sigma-1 receptor (σ-1R) is a chaperone protein involved in signal transduction, neurite outgrowth, and plasticity, improving memory, and neuroprotection. Recent evidence shows that σ-1R can promote autophagy. Autophagy activation by the σ-1Rs along with other neuroprotective effects makes it an interesting target for the treatment of Alzheimer's disease. AF710B, T-817 MA, and ANAVEX2-73 are some of the σ-1R agonists which have shown promising results and have entered clinical trials. These molecules have also been found to induce autophagy and show cytoprotective effects in cellular models.

AREAS COVERED

This review provides insight into the current understanding of σ-1R functions related to autophagy and their role in alleviating AD.

EXPERT OPINION

We propose a mechanism through which the activation of σ-1R and autophagy could alter amyloid precursor protein processing to inhibit amyloid-β production by reconstituting cholesterol and gangliosides in the lipid raft to offer neuroprotection against AD. Future AD treatment could involve the combined targeting of the σ-1R and autophagy activation. We suggest that future studies investigate the link between autophagy the σ-1R and AD.

Donepezil attenuates the development of morphine tolerance in rats with cancer-induced bone pain: The role of cortical N-methyl-D-aspartate receptors

Cancer-induced bone pain (CIBP), which is associated with poor quality of life, is most commonly treated using opioids. However, long-term use of morphine for analgesia induces tolerance and can diminish the treatment's effectiveness. The mechanisms that underlie morphine tolerance have been reported to be related to the inflammation of the nervous system and hyperactivation of N-methyl-D-aspartate receptors (NMDARs). Donepezil is an anti-inflammatory and neuroprotective drug that is thought to alleviate morphine tolerance. In this study, we aimed to investigate the effect of three different dosages of donepezil (1, 1.5 and 2 mg/kg) on morphine tolerance in rats with CIBP, and the possible involvement of donepezil-mediated NMDAR subunit 1 (NR1). We found that donepezil can prolong the analgesic efficacy of morphine and delay the development of chronic morphine tolerance. Furthermore, continuous morphine injection increased the expression of NR1, and this was suppressed by co-administration with donepezil using both western blotting and immunofluorescence. Our findings demonstrate that donepezil has the potential to attenuate morphine tolerance, possibly by inhibiting NR1 activity in the cortex.

PRE-084 as a tool to uncover potential therapeutic applications for selective sigma-1 receptor activation

The discovery of a highly selective putative sigma-1 (σ1) receptor agonist, PRE-084, has revealed the numerous potential uses of this receptor subtype as a therapeutic target. While much work has been devoted to determining the role of σ1 receptors in normal and pathophysiological states in the nervous system, recent work suggests that σ1 receptors may be important for modulating functions of other tissues. These discoveries have provided novel insights into σ1 receptor structure, function, and importance in multiple intracellular signaling mechanisms. These discoveries were made possible by σ1 receptor-selective agonists such as PRE-084. The chemical properties and pharmacological actions of PRE-084 will be reviewed here, along with the expanding list of potential therapeutic applications for selective activation of σ1 receptors.

Donepezil, a drug for Alzheimer's disease, promotes oligodendrocyte generation and remyelination

Myelin sheaths play important roles in neuronal functions. In the central nervous system (CNS), the myelin is formed by oligodendrocytes (OLs), which are differentiated from oligodendrocyte precursor cells (OPCs). In CNS demyelinating disorders such as multiple sclerosis (MS), the myelin sheaths are damaged and the remyelination process is hindered. Small molecule drugs that promote OPC to OL differentiation and remyelination may provide a new way to treat these demyelinating diseases. Here we report that donepezil, an acetylcholinesterase inhibitor (AChEI) developed for the treatment of Alzheimer's disease (AD), significantly promotes OPC to OL differentiation. Interestingly, other AChEIs, including huperzine A, rivastigmine, and tacrine, have no such effect, indicating that donepezil's effect in promoting OPC differentiation is not dependent on the inhibition of AChE. Donepezil also facilitates the formation of myelin sheaths in OPC-DRG neuron co-culture. More interestingly, donepezil also promotes the repair of the myelin sheaths in vivo and provides significant therapeutic effect in a cuprizone-mediated demyelination animal model. Donepezil is a drug that has been used to treat AD safely for many years; our findings suggest that it might be repurposed to treat CNS demyelinating diseases such as MS by promoting OPC to OL differentiation and remyelination.

Beyond symptomatic effects: potential of donepezil as a neuroprotective agent and disease modifier in Alzheimer's disease

Alzheimer's disease (AD) is associated with neurodegenerative changes resulting clinically in progressive cognitive and functional deficits. The only therapies are the cholinesterase inhibitors donepezil, galantamine and rivastigmine and the N-methyl-D-aspartate-receptor antagonist memantine. Donepezil acts primarily on the cholinergic system as a symptomatic treatment, but it also has potential for disease modification and may reduce the rate of progression of AD. This review explores the potential for disease modifying effects of donepezil. Several neuroprotective mechanisms that are independent of cholinesterase inhibition, are suggested. Donepezil has demonstrated a range of effects, including protecting against amyloid β, ischaemia and glutamate toxicity; slowing of progression of hippocampal atrophy; and up-regulation of nicotinic acetylcholine receptors. Clinically, early and continuous treatment with donepezil is considered to preserve cognitive function more effectively than delayed treatment. The possible neuroprotective effects of donepezil and the potential for disease pathway modification highlight the importance of early diagnosis and treatment initiation in AD.

The Anti-dementia Effects of Donepezil Involve miR-206-3p in the Hippocampus and Cortex

Alzheimer's disease (AD) is a most serious age-related neurodegenerative disorder accompanied with significant memory impairments in this world. Recently, microRNAs (miRNAs) have been reported to be invlolved in the pathophysiology of AD. Previous studies have shown that miRNA-206 (miR-206) is implicated in the pathogenesis of AD via suppressing the expression of brain-derived neurotrophic factor (BDNF) in the brain. Here, we examined the miR-206-3p and miR-206-5p expression in the hippocampus and cortex of Abeta precursor protein (APP)/presenilin-1 (PS1) transgenic mice treated with donepezil, a drug approved for treating AD in clinic. We found that the expression of miR-206-3p was significantly up-regulated in the hippocampus and cortex of APP/PS1 mice, while donepezil administration significantly reversed this dysfunction. In addition, enhancing the miR-206-3p level by the usage of AgomiR-206-3p significantly attenuated the anti-dementia effects of donepezil in APP/PS1 mice. Together, these results suggested that miR-206-3p is involved in the anti-dementia effects of donepezil, and could be a novel pharmacological target for treating AD.

Protection by sigma-1 receptor agonists is synergic with donepezil, but not with memantine, in a mouse model of amyloid-induced memory impairments

Drugs activating the sigma-1 (σ1) chaperone protein are anti-amnesic and neuroprotective in neurodegenerative pathologies like Alzheimer's disease (AD). Since these so-called σ1 receptor (σ1R) agonists modulate cholinergic and glutamatergic systems in a variety of physiological responses, we addressed their putative additive/synergistic action in combination with cholinergic or glutamatergic drugs. The selective σ1 agonist PRE-084, or the non-selective σ1 drug ANAVEX2-73 was combined with the acetylcholinesterase inhibitor donepezil or the NMDA receptor antagonist memantine in the nontransgenic mouse model of AD-like memory impairments induced by intracerebroventricular injection of oligomeric Aβ25-35 peptide. Two behavioral tests, spontaneous alternation and passive avoidance response, were used in parallel and both protective and symptomatic effects were examined. After determination of the minimally active doses for each compound, the combinations were tested and the combination index (CI) calculated. Combinations between the σ1 agonists and donepezil showed a synergic protective effect, with CI<1, whereas the combinations with memantine showed an antagonist effect, with CI>1. Symptomatic effects appeared only additive for all combinations, with CI=1. A pharmacological analysis of the PRE-084+donepezil combination revealed that the synergy could be due to an inter-related mechanism involving α7 nicotinic ACh receptors and σ1R. These results demonstrated that σ1 drugs do not only offer a protective potential alone but also in combination with other therapeutic agents. The nature of neuromodulatory molecular chaperone of the σ1R could eventually lead to synergistic combinations.

Sigma-1 receptor chaperones in neurodegenerative and psychiatric disorders

INTRODUCTION

Sigma-1 receptors (Sig-1Rs) are molecular chaperones that reside mainly in the endoplasmic reticulum (ER) but exist also in the proximity of the plasma membrane. Sig-1Rs are highly expressed in the CNS and are involved in many cellular processes including cell differentiation, neuritogenesis, microglia activation, protein quality control, calcium-mediated ER stress and ion channel modulation. Disturbance in any of the above cellular processes can accelerate the progression of many neurological disorders; therefore, the Sig-1R has been implicated in several neurological diseases.

AREAS COVERED

This review broadly covers the functions of Sig-1Rs including several neurodegenerative disorders in humans and drug addiction-associated neurological disturbance in the case of HIV infection. We discuss how several Sig-1R ligands could be utilized in therapeutic approaches to treat those disorders.

EXPERT OPINION

Emerging understanding of the cellular functions of this unique transmembrane chaperone may lead to the use of new agents or broaden the use of certain available ligands as therapeutic targets in those neurological disorders.