Loss Of Cholinergic Neurotransmission Research Articles

Synthesis, in vitro biological evaluation and molecular modelling of new 2-chloro-3-hydrazinopyrazine derivatives as potent acetylcholinesterase inhibitors\u200f on PC12 cells

BackgroundThe loss of cholinergic neurotransmission in Alzheimer's disease (AD) patients' brain is accompanied by a reduced concentration of Acetylcholine (ACh) within synaptic clefts. Thus, the use of acetylcholinesterase inhibitors (AChEIs) to block the cholinergic degradation of ACh is a promising approach for AD treatment. In the present study, a series of 2-chloro-3-hydrazinopyrazine derivatives (CHP1-5) were designed, synthesized, and biologically evaluated as potential multifunctional anti-AD agents.MethodsIn addition, the chemical structures and purity of the synthesized compounds were elucidated through using IR, 1H and 13C NMR, and elemental analyses. Further, the intended compounds were assessed in vitro for their AChE inhibitory and neuroprotective effects. Furthermore, DPPH, FRAP and ABTS assays were utilized to determine their antioxidant activity. The statistical analysis was performed using one-way ANOVA.ResultsBased on the results, CHP4 and CHP5 exhibited strong AChE inhibitory effects with the IC50 values of 3.76 and 4.2 µM compared to the donepezil (0.53 µM), respectively. The study examined the effect and molecular mechanism of CHP4 on the Ab1–42-induced cytotoxicity in differentiated PC12 cells. At concentrations of 0–100 μM, CHP4 was non-toxic in PC12. Additionally, Ab1–42 significantly stimulated tau hyperphosphorylation and induced differentiated PC12 cell death. Further, CHP4 resulted in diminishing the Ab1–42-induced toxicity in PC12 cell significantly. CHP4 at 30 μM concentration significantly increased the Ab1–42-induced HSP70 expression and decreased tau hyperphosphorylation.ConclusionsAccording to the results of our studies CHP4 can be considered as safe and efficient AChEI and employed as a potential multifunctional anti-AD agent.

Alzheimer’s Disease: Development of Disease-Modifying Treatments Is the Challenge for Our Generation

Welcome to our first thematic collection that crosses-over with the Journal of Medicinal Chemistry and ACS Medicinal Chemistry Letters to highlight advances in the pharmacology, medicinal chemistry, and therapeutic strategies currently under development for Alzheimer’s disease (AD)—the most challenging and important disease facing our generation. While the 1970s heralded a “war on cancer” and the 1980s and 1990s witnessed a monumental effort to vanquish the death sentence of AIDs with novel therapeutics targeting multiple aspects of the viral machinery, the challenge of this millennium is the development of disease-modifying treatments for AD. Unfortunately, even after several decades of research, there are few approved drugs for AD; moreover, the available drugs only attenuate symptoms, show little to no effect on slowing disease progression, and have no effect on the behavioral disturbances associated with AD.1−4 Current estimates indicate that approximately 5.4 million Americans are suffering from AD at an annual cost to the United States healthcare system of over $200 billion.1−4 While staggering, the situation grows more desperate as the 76 million baby boomers advance in age. This is based on the likelihood of developing AD doubles every 5 years after age 65, and after age 85 the risk of developing AD climbs to ∼50%. Importantly, if no disease-modifying therapies are developed, the number of AD patients may climb as high as 13.5 million by 2050, resulting in over $1 trillion in patient care costs.1−4 An even more sobering statistic focuses on mortality and AD. Between 2000 and 2008, there was a 66% increase in deaths directly related to AD; in contrast, during the same time period, deaths from HIV decreased 29%, deaths from stroke decreased 20%, deaths from heart disease decreased 13%, and deaths from several cancers also declined significantly.1−4 Early neuropathology of AD is characterized by the loss of basal forebrain cholinergic neurons and loss of cholinergic neurotransmission. Current approved drugs for AD target cholinergic and glutamatergic transmission thereby improving cognitive symptoms in some patients; however, these agents are not disease-modifying, nor do they slow disease progression. Current approved therapies include cholinesterase inhibitors (tacrine (Cognex), donepezil (Aricept), rivastigmine (Exelon), and galanatamine (Razadyne)) and the glutamate modulator memantine (Namenda).1−4 The other major hallmarks of AD include plaques and neurofibrillary tangles in the brain which led to the amyloid hypothesis and tau hypothesis in 1991 and 2004, respectively, as fundamental causes of AD. Drug development efforts have pursued these hypotheses via multiple approaches.1−4 The amyloid hypothesis of AD initiated major drug discovery efforts across the pharmaceutical industry, with novel small molecules targeting Aβ peptide production. Aβ is produced by the proteolytic cleavage of APP by γ- and β-secretases leading to Aβ1–40 and Aβ1–42 peptides which aggregate and form toxic oligomers.1−4 The amyloid hypothesis has undergone many revisions and refinements since 1991, and with multiple failures of both small molecules and biologic approaches that diminish Aβ load, there is growing debate that targeting Aβ may be questionable as an AD therapeutic approach.1−5 However, others argue that the hypothesis is still valid and that the issues were with inferior molecules, biologics, the “sink” approach and/or trial design. Numerous BACE1 inhibitors are in phase I trials, where compounds such as MK-8931, lowered Aβ up to 90%, and efficacy in phase II are eagerly awaited.6 PhRMA reports in their 2012 Medicines in Development Report for AD4 that there are currently 93 medicines in various stages of development, both small molecule and biologic. In general, all 93 compounds fall into one of the following therapeutic strategies: (1) agents targeting neurotransmission, (2) agents targeting Aβ production, (3) agents targeting Aβ aggregation, (4) agents targeting Aβ clearance, (5) agents increasing brain resistance to Aβ, (6) agents targeting tau protein, and (7) agents targeting neurotrophins and agents modulating synaptic plasticity and nerve growth.1−4 Significant advances have been, and continue to be made, in the development of imaging agents, for example, Amyvid,1−4 for amyloid imaging biomarkers for disease. Overall, new therapeutic agents must address multiple stages of disease progression, from Aβ/tau accumulation to mild cognitive impairment to late stage dementia and behavioral (psychotic) symptoms, the latter of which are more difficult for caregivers than the dementia. In this Special Issue on AD, we present 17 outstanding papers (both reviews and primary scientific studies) encompassing basic neuropathology, novel therapeutic strategies, novel small molecules, and genetic studies relevant to understanding and treating AD. We at ACS Chemical Neuroscience thank all of the contributors to this special issue on AD and encourage our readers to take advantage of our first thematic collection that crosses-over with the Journal of Medicinal Chemistry and ACS Medicinal Chemistry Letters and check out the outstanding papers in these Journals on AD.

Acetylcholinesterase Inhibitors as a Starting Point Towards Improved Alzheimers Disease Therapeutics

The knowledge about the pathogenesis and the development of the neurodegeneration associated with Alzheimer's disease (AD) has been organised throughout the years into two theories, namely the cholinergic and the amyloid hypotheses. The loss of cholinergic neurotransmission and the abnormal aggregation and deposition of the amyloid-beta peptide (A beta) in the brain are retained as the central events by the two theories, respectively. These phenomena and their pathological consequences are the main targets of the drug discovery strategies based on each hypothesis. However, the two paradigms share some common aspects as shown by several experimental evidences, such that they might even fit into a unifying scenario of neuropathology and neurodegeneration. In this context, in a perspective of drug discovery, the enzyme acetylcholinesterase (AChE) holds a key position, as it is a main target for cholinomimetic AD drugs being responsible for the breakdown of the neurotransmitter, and it is also involved in the aggregation of A beta and the formation of the neurotoxic fibrils. Following this view, in recent years, a drug design strategy has emerged, directed to finding molecules able to inhibit both of these actions exerted by AChE. In this review, we will briefly introduce the biological basis of this strategy, and then will account for the early results obtained in this field in our and in other laboratories. The main focus will be on potential lead compounds for which some experimental evidence exists supporting the hypothesis of their dual action, as AChE inhibitors and blockers of the AChE-induced A beta aggregation.

Cortical cholinergic dysfunction after human head injury.

Loss of cholinergic neurotransmission is implicated in memory impairment and cognitive dysfunction after head injury. The aim of the present study was to investigate presynaptic markers, particularly in relation to cholinergic neurotransmission in human postmortem brain from patients who died following a head injury and age-matched controls. Choline acetyltransferase activity and high-affinity nicotinic receptor binding sites were assayed in the inferior temporal gyrus, cingulate gyrus, and superior parietal cortex of 16 head-injured patients and 8 controls. Synaptophysin immunoreactivity was determined in the left cingulate gyrus from the same patient groups. In the head-injured group, choline acetyltransferase activity was consistently reduced in each cortical region compared to control subjects. The presence of a subdural haematoma and a prolonged survival period after head injury tended to be associated with lower choline acetyltransferase activity. In contrast to the marked reduction in choline acetyltransferase activity, nicotine receptor binding was unchanged in head-injured compared to control patients. Synaptophysin immunoreactivity in the cingulate gyrus was reduced by approximately 30% (p < 0.05) in the head-injured group compared to controls. Correlation of choline acetyltransferase activity with synaptophysin immunoreactivity indicated there is a deficit of cholinergic presynaptic terminals in postmortem human brain following head injury.

Serotonin influences the behavioral recovery of rats following nucleus basalis lesions

The present study investigated the effects of serotonergic depletion upon the performance of rats with lesions of the nucleus basalis magnocellularis (NBM) in a nonspatial memory task. NBM lesions were made by injections of ibotenic acid. Serotonin was depleted by systemic injections of p-chloroamphetamine (PCA). After four weeks of testing, the choice accuracy of PCA rats was not different from that of control rats (CON), while the choice accuracy of NBM rats and rats with combined treatment (NBM + PCA) was significantly lower than CON rats, but not different from each other. After prolonged testing, performance improved in NBM rats, but not in NBM + PCA rats indicating that simultaneous loss of both cholinergic and serotonergic neurotransmission produced a significantly longer lasting behavioral deficit than the loss of cholinergic neurotransmission alone.