Meserine, a novel carbamate AChE inhibitor, ameliorates scopolamine-induced dementia and alleviates amyloidogenesis of APP/PS1 transgenic mice

Recent advance on carbamate-based cholinesterase inhibitors as potential multifunctional agents against Alzheimer's disease

Alzheimer's disease (AD), as the fourth leading cause of death among the elderly worldwide, has brought enormous challenge to the society. Due to its extremely complex pathogeneses, the development of multi-target directed ligands (MTDLs) becomes the major strategy for combating AD. Carbamate moiety, as an essential building block in the development of MTDLs, exhibits structural similarity to neurotransmitter acetylcholine (ACh) and has piqued extensive attention in discovering multifunctional cholinesterase inhibitors. To date, numerous preclinical studies demonstrate that carbamate-based cholinesterase inhibitors can prominently increase the level of ACh and improve cognition impairments and behavioral deficits, providing a privileged strategy for the treatment of AD. Based on the recent research focus on the novel cholinesterase inhibitors with multiple biofunctions, this review aims at summarizing and discussing the most recent studies excavating the potential carbamate-based MTDLs with cholinesterase inhibition efficacy, to accelerate the pace of pleiotropic cholinesterase inhibitors for coping AD.

Ameliorative effect of alendronate against intracerebroventricular streptozotocin induced alteration in neurobehavioral, neuroinflammation and biochemical parameters with emphasis on Aβ and BACE-1

Alzheimer's disease (AD) is the most prevalent age related neurodegenerative disorder manifested by progressive cognitive decline and neuronal loss in the brain, yet precise etiopathology of majority of sporadic or late-onset AD cases is unknown. AD is associated with various pathological events such as Aβ deposition due to BACE-1 induced cleavage of APP, neuroinflammation, increased cholesterol synthesis, cholinergic deficit and oxidative stress. It was found that bone drug, alendronate (ALN) that cross blood brain barrier inhibits brain cholesterol synthesis and AChE enzyme activity. As cholesterol modifying agents have been supposed to alter AD like pathologies, the current study was designed to investigate the possible neuroprotective and therapeutic potential of ALN against ICV STZ induced experimental sporadic AD (SAD) in mice in a non-cholesterol dependent manner, using donepezil (5 mg/kg) as a reference standard. The preliminary study was done by molecular modelling to identify the binding affinity of ALN with BACE-1 in silico. The prevention of cognitive impairment in mice induced by ICV STZ (3 mg/kg) infused on first and third day, by ALN (1.76 mg/kg p.o.) administered for 15 consecutive days was assessed through Spontaneous Alternation Behavior (SAB) and Morris water maze (MWM) test. Additionally, the protective effect of ALN was also observed by the reversal of altered levels of Aβ_1-42, BACE-,1 neuroinflammatory cytokines, AChE activity and oxidative stress markers (except TBARS) in ICV-STZ infused mice. However, the findings of the present study imply the therapeutic potential of ALN against SAD-like complications.

AChE Inhibition-based Multi-target-directed Ligands, a Novel Pharmacological Approach for the Symptomatic and Disease-modifying Therapy of Alzheimer's Disease

Alzheimer's disease (AD) is the most common form of dementia in elder people, characterised by a progressive decline in memory as a result of an impairment of cholinergic neurotransmission. To date acetylcholinesterase inhibitors (AChEIs) have become the most prescribed drugs for the symptomatic treatment of mild to moderate AD. However, the traditional “one molecule-one target” paradigm is not sufficient and appropriate to yield the desired therapeutic efficacy since multiple factors, such as amyloid-β (Aβ) deposits, neuroinflammation, oxidative stress, and decreased levels of acetylcholine (ACh) have been thought to play significant roles in the AD pathogenesis. New generation of multi-target drugs is earnestly demanded not only for ameliorating symptoms but also for modifying the disease. Herein, we delineated the catalytic and non-catalytic functions of AChE, and summarized the works of our group and others in research and development of novel AChEI-based multi-target-directed ligands (MTDLs), such as dual binding site AChEIs and multi-target AChEIs inhibiting Aβ aggregation, regulating Aβ procession, antagonizing platelet-activating factor (PAF) receptor, scavenging oxygen radical, chelating metal ions, inhibiting monoamine oxidase B (MAO-B), blocking N-methyl-D-aspartic acid (NMDA) receptor and others.

Neuregulin-1 (Nrg1) signaling has a preventive role and is altered in the frontal cortex under the pathological conditions of Alzheimer's disease

Alzheimer's disease (AD), one of the neurodegenerative disorders that may develop in the elderly, is characterized by the deposition of β‑amyloid protein (Aβ) and extensive neuronal cell death in the brain. Neuregulin‑1 (Nrg1)‑mediated intercellular and intracellular communication via binding to ErbB receptors regulates a diverse set of biological processes involved in the development of the nervous system. In the present study, a linear correlation was identified between Nrg1 and phosphorylated ErbB (pNeu and pErbB4) receptors in a human cortical tissue microarray. In addition, increased expression levels of Nrg1, but reduced pErbB receptor levels, were detected in the frontal lobe of a patient with AD. Western blotting and immunofluorescence staining were subsequently performed to uncover the potential preventive role of Nrg1 in cortical neurons affected by the neurodegenerative processes of AD. It was observed that the expression of Nrg1 increased as the culture time of the cortical neurons progressed. In addition, H2O2 and Aβ1‑42, two inducers of oxidative stress and neuronal damage, led to a dose‑dependent decrease in Nrg1 expression. Recombinant Nrg1β, however, was revealed to exert a pivotal role in preventing oxidative stress and neuronal damage from occurring in the mouse cortical neurons. Taken together, these results suggest that changes in Nrg1 signaling may influence the pathological development of AD, and exogenous Nrg1 may serve as a potential candidate for the prevention and treatment of AD.

Dihydroquinoline Carbamate Derivatives as "Bio-oxidizable" Prodrugs for Brain Delivery of Acetylcholinesterase Inhibitors: [¹¹C] Radiosynthesis and Biological Evaluation

With the aim of improving the efficiency of marketed acetylcholinesterase (AChE) inhibitors in the symptomatic treatment of Alzheimer's disease, plagued by adverse effects arising from peripheral cholinergic activation, this work reports a biological evaluation of new central AChE inhibitors based on an original "bio-oxidizable" prodrug strategy. After peripheral injection of the prodrug 1a [IC50 > 1 mM (hAChE)] in mice, monitoring markers of central and peripheral cholinergic activation provided in vivo proof-of-concept for brain delivery of the drug 2a [IC50 = 20 nM (hAChE)] through central redox activation of 1a. Interestingly, peripheral cholinergic activation has been shown to be limited in time, likely due to the presence of a permanent positive charge in 2a promoting rapid elimination of the AChE inhibitor from the circulation of mice. To support these assumptions, the radiosynthesis with carbon-11 of prodrug 1a was developed for additional ex vivo studies in rats. Whole-body biodistribution of radioactivity revealed high accumulation in excretory organs along with moderate but rapid brain uptake. Radio-HPLC analyses of brain samples confirm rapid CNS penetration of [(11)C]1a, while identification of [(11)C]2a and [(11)C]3a both accounts for central redox activation of 1a and pseudoirreversible inhibition of AChE, respectively. Finally, Caco-2 permeability assays predicted metabolite 3a as a substrate for efflux transporters (P-gp inter alia), suggesting that metabolite 3a might possibly be actively transported out of the brain. Overall, a large body of evidence from in vivo and ex vivo studies on small animals has been collected to validate this "bio-oxidizable" prodrug approach, emerging as a very promising strategy in the rational design of selective central AChE inhibitors.

Silibinin inhibits acetylcholinesterase activity and amyloid β peptide aggregation: a dual-target drug for the treatment of Alzheimer's disease

Alzheimer's disease (AD) is characterized by amyloid β (Aβ) peptide aggregation and cholinergic neurodegeneration. Therefore, in this paper, we examined silibinin, a flavonoid extracted from Silybum marianum, to determine its potential as a dual inhibitor of acetylcholinesterase (AChE) and Aβ peptide aggregation for AD treatment. To achieve this, we used molecular docking and molecular dynamics simulations to examine the affinity of silibinin with Aβ and AChE in silico. Next, we used circular dichroism and transmission electron microscopy to study the anti-Aβ aggregation capability of silibinin in vitro. Moreover, a Morris Water Maze test, enzyme-linked immunosorbent assay, immunohistochemistry, 5-bromo-2-deoxyuridine double labeling, and a gene gun experiment were performed on silibinin-treated APP/PS1 transgenic mice. In molecular dynamics simulations, silibinin interacted with Aβ and AChE to form different stable complexes. After the administration of silibinin, AChE activity and Aβ aggregations were down-regulated, and the quantity of AChE also decreased. In addition, silibinin-treated APP/PS1 transgenic mice had greater scores in the Morris Water Maze. Moreover, silibinin could increase the number of newly generated microglia, astrocytes, neurons, and neuronal precursor cells. Taken together, these data suggest that silibinin could act as a dual inhibitor of AChE and Aβ peptide aggregation, therefore suggesting a therapeutic strategy for AD treatment.

Determination of Meserine, a new candidate for Alzheimer's disease in mice brain by liquid chromatography-tandem mass spectrometry and its application to a pharmacokinetic and tissue distribution study

A rapid and sensitive liquid chromatography-tandem mass spectrometry (LC-MS/MS) method for determination of Meserine ((-)-meptazinol phenylcarbamate), a novel potent inhibitor of acetylcholinesterase (AChE), was developed, validated, and applied to a pharmacokinetic study in mice brain. The lower limit of quantification (LLOQ) was 1 ng mL(-1) and the linear range was 1-1,000 ng mL(-1). The analyte was eluted on a Zorbax SB-Aq column (2.1 × 100 mm, 3.5 μm) with the mobile phase composed of methanol and water (70:30, v/v, aqueous phase contained 10 mM ammonium formate and 0.3% formic acid) using isocratic elution, and monitored by positive electrospray ionization in multiple reaction monitoring (MRM) mode. The flow rate was 0.25 mL min(-1). The injection volume was 5 μL and total run time was 4 min. The relative standard deviation (RSD) of intraday and interday variation was 2.49-7.81 and 3.01-7.67%, respectively. All analytes were stable after 4 h at room temperature and 6 h in autosampler. The extraction recoveries of Meserine in brain homogenate were over 90%. The main brain pharmacokinetic parameters obtained after intranasal administration were T max = 0.05 h, C max = 462.0 ± 39.7 ng g(-1), T 1/2 = 0.4 h, and AUC(0-∞) = 283.1 ± 9.1 ng h g(-1). Moreover, Meserine was distributed rapidly and widely into brain, heart, liver, spleen, lung, and kidney tissue. The method is validated and could be applied to the pharmacokinetic and tissue distribution study of Meserine in mice.

Protocatechuic acid improves cognitive deficits and attenuates amyloid deposits, inflammatory response in aged AβPP/PS1 double transgenic mice

Protocatechuic acid (PCA), a phenolic compound of Radix Salviae Miltiorrhizae (RSM), has been found to have a protective effect on improving cognitive deficits in STZ-induced AD rats. The present study aimed to evaluate the potential protection activity of PCA on improving cognitive deficits and attenuating Aβ deposition and inflammatory responses in aged AβPP/PS1 double transgenic AD-model mice. The results of Morris water maze test showed that PCA (100mg/kg) significantly prolonged the mean latency time and the path length of AβPP/PS1 mice. PCA could significantly reduce the number of Aβ positive expressions in the hippocampus and cerebral cortex of AβPP/PS1 mice by immunocytochemical assay with Congo red staining and decrease remarkably APP expression level by Western blot analysis (P<0.01). The results from ELISA and Western blot analysis showed that the levels of inflammatory cytokines including TNF-α, IL-1β, IL-6 and IL-8 decreased remarkably by the treatment with PCA (P<0.01). Further, there was a substantial increase of brain derived neurotrophic factor (BDNF) in the hippocampus and cerebral cortex of AβPP/PS1 mice treated with PCA (P<0.01). The present study provided confirmatory evidence that PCA significantly decreased Aβ deposits, APP and inflammatory response, whereas increased learning and memory ability, as well as enhanced BDNF level. Our findings indicated that PCA is an effective neuroprotective agent for AD therapy. It might be associated with the attenuation on Aβ deposits and inflammation responses involved in the process.