Cholinergic dysfunction in Alzheimer disease: cause or effect?

Eriodictyol Attenuates LPS-Induced Neuroinflammation, Amyloidogenesis, and Cognitive Impairments via the Inhibition of NF-κB in Male C57BL/6J Mice and BV2 Microglial Cells

Eriodictyol, a natural flavonoid mainly distributed in citrus fruits and peanut, has been well-documented with possession of excellent anti-inflammatory, antioxidant, and anticancer bioactivities. This work focus on the protective effects of eriodictyol on LPS-induced neuroinflammation, amyloidogenesis, cognitive impairment, and the potential mechanisms involved. Behavioral tests and histological examinations showed that eriodictyol significantly prevented the memory and neuronal damage triggered by LPS. Consistently, eriodictyol (100 mg/kg) reduced the formation of Aβ_1-42 by 28.37 ± 16.71 pg/mL compared to the LPS group. In addition, high dose eriodictyol (100 mg/kg) also equilibrated the cholinergic system via suppressing AChE activity (0.1996 ± 0.0831 U/mgprot) and elevating ChAT activity (41.81 ± 24.72 U/g) as well as ACh level (5.093 ± 3.531 μg/mgprot) compared to the LPS group. Western blot results indicated that compared to the LPS group, eriodictyol suppressed LPS-induced glial overactivation (84.29% ± 27.21%) and regulated inflammatory mediators and cytokines by inhibiting the NF-κB and MAPK pathways. These results indicated that eriodictyol alleviated amyloidogenesis and memory impairment triggered by LPS via inhibiting TLR4, MAPKs, and PI3K/Akt, and activating Sirt1 pathways and thus blocking downstream translocation of NF-κB, which offers a potential nutritional preventive strategy for neuroinflammation diseases such as Alzheimer's disease (AD).

Altered cholinergic metabolism and muscarinic receptor linked second messenger pathways after chronic exposure to dichlorvos in rat brain

Chronic dichlorvos exposure (6mg/kg b.wt/day) for a period of 8 weeks resulted in significant reduction in body weight gain of the male Wistar rats. However, the dietary intake remained unchanged in experimental animals following dichlorvos treatment. Activity of the synthesizing enzyme of acetylcholine (ACh) ie, choline acetyltransferase, was found to be significantly increased and the activity of hydrolyzing enzyme, acetyl cholinesterase (AChE), was inhibited in all the three brain regions studied. Chronic dichlorvos treatment also caused significant reduction in both high affinity (HA) and low affinity (LA) choline uptake (CU), with maximal effect being observed in the brain stem followed by cerebellum and cerebrum. Muscarinic receptor binding was significantly decreased in brain stem and cerebellum as reflected in the decreased receptor number (Bmax), without any change in the binding affinity (Kd) of the receptors. Dichlorvos treatment caused marked inhibition in cAMP synthesis as indicated by decreased adenylate cyclase activity as well as cAMP levels in cerebrum, cerebellum and brain stem. Our study shows that organophosphates may interact with muscarinic receptor-linked second messenger system and this could be a potential mechanism for the neurotoxic effects observed after repeated exposure to low levels of organophosphates, which are unexplainable on the basis of cholinergic hyperactivity. Toxicology and Industrial Health 2007; 23: 25—37.

GSK-3β, a pivotal kinase in Alzheimer disease

Alzheimer disease (AD) is the most common form of age-related dementia. The etiology of AD is considered to be multifactorial as only a negligible percentage of cases have a familial or genetic origin. Glycogen synthase kinase-3 (GSK-3) is regarded as a critical molecular link between the two histopathological hallmarks of the disease, namely senile plaques and neurofibrillary tangles. In this review, we summarize current data regarding the involvement of this kinase in several aspects of AD development and progression, as well as key observations highlighting GSK-3 as one of the most relevant targets for AD treatment.

Plants used in Chinese and Indian traditional medicine for improvement of memory and cognitive function

In traditional practices of Ayurvedic and Chinese medicine, numerous plants have been used to treat cognitive disorders, including neurodegenerative diseases such as Alzheimer's disease (AD). An ethnopharmacological approach has provided leads to identifying potential new drugs from plant sources, including those for cognitive disorders. Many drugs currently available in Western medicine were originally isolated from plants, or are derived from templates of compounds isolated from plants. Some anticholinesterase (anti-ChE) alkaloids isolated from plants have been investigated for their potential in the treatment of AD, and are now in clinical use. Galantamine, isolated from several plants including Lycoris radiata Herb., which was used in traditional Chinese medicine (TCM), is licensed in the United Kingdom for the treatment of mild to moderate AD. Various other plant species have shown pharmacological activities relevant to the treatment of cognitive disorders, indicating potential for therapeutic use in disorders such as AD. This article reviews some of the plants and their active constituents that have been used in traditional Ayurvedic medicine and TCM for their reputed cognitive-enhancing or antiageing effects. Plants and their constituents with pharmacological activities that may be relevant for the treatment of cognitive disorders, including enhancement of cholinergic function in the central nervous system (CNS), anti-inflammatory and antioxidant activities, are discussed.

Effects of nefiracetam on deficits in active avoidance response and hippocampal cholinergic and monoaminergic dysfunctions induced by AF64A in mice

The effects of nefiracetam [DM-9384; N-(2,6-dimethyl-phenyl)-2-(2-oxo-pyrrolidinyl)acetamide] and of phosphatidylcholine on a step-up active avoidance response, locomotor activities and regional brain cholinergic and monoaminergic neurotransmitters in AF64A-treated mice were investigated. Intracerebroventricular (i.c.v.) injection of AF64A (ethylcholine mustard aziridinium ion; 8 nmol/ventricle) impaired acquisition and retention of the avoidance task, and increased vertical and horizontal locomotor activities. Regional levels of acetylcholine, noradrenaline, 3-methoxy-4-hydroxyphenylglycol (MHPG), 5-hydroxytryptamine (5-HT) and 5-hydroxyindoleacetic acid (5-HIAA) were significantly decreased and homovanillic acid (HVA) levels were increased in the hippocampus but not in the septum, cerebral cortex or striatum of AF64A-treated animals. Administration of nefiracetam (3 mg/kg, p.o.) twice daily for 9 days to AF64A-treated animals ameliorated the deficit in active avoidance response in addition to attenuating the increase in locomotor activities. In parallel with these behavioural effects, nefiracetam reversed AF64A-induced alterations in the hippocampal profiles of cholinergic and monoaminergic neurotransmitters and their metabolites. In contrast, administration of phosphatidylcholine (30 mg/kg, p.o.) twice daily for 9 days had no significant effect on the deficit in active avoidance response, despite significantly reversing the decrease in acetylcholine levels in the hippocampus. These results indicate that the effects of nefiracetam on AF64A-induced behavioural deficits are probably due to its ability to facilitate both cholinergic and monoaminergic neurotransmitter systems.

MKC-231, a choline uptake enhancer, ameliorates working memory deficits and decreased hippocampal acetylcholine induced by ethylcholine aziridinium ion in mice

The effects of acute and chronic administration of MKC-231, a new choline uptake enhancer, and two other nootropic agents, linopiridine (Dup 996) and tetrahydroaminoacridine (THA) on working memory deficits and decreased hippocampal acetylcholine (ACh) content were studied in a delayed non-matching to sample task, using a T-maze, in ethylcholine aziridinium ion (AF64A)-treated mice. Treatment with AF64A (3.5 nmol, i.c.v.) produced memory deficits and decreased hippocampal ACh content. In acute behavioral experiments, MKC-231 and THA had no significant effect on AF64A-induced memory deficits at any doses tested (0.3, 1.0 and 3.0 mg/kg), whereas Dup 996, at a dose of 1.0 mg/kg, significantly improved memory deficits. In chronic experiments, MKC-231 improved memory deficit at all doses tested (0.3, 1.0, or 3.0 mg/kg p.o., once daily for 11 days) and Dup 996 did so only at a dose of 3.0 mg/kg, whereas THA did not improve memory deficit at any doses tested. In acute neurochemical experiments, MKC-231 and THA did not reverse the AF64A-induced hippocampal ACh depletion. Dup 996, however, further decreased hippocampal ACh content compared to that in the AF64A-treated group. In chronic experiments, MKC-231 significantly reversed hippocampal ACh depletion at doses of 0.3 and 1.0 mg/kg, whereas neither Dup 996 nor THA reversed hippocampal ACh depletion at any doses tested. These results indicate that MKC-231 improved the AF64A-induced working memory deficit and hippocampal ACh depletion, probably by recovering reduced high-affinity choline uptake and ACh release.

Reversal effect of DM-9384 on scopolamine-induced acetylcholine depletion in certain regions of the mouse brain

The effect of a new cognition enhancer, DM-9384, N-(2,6-dimethylphenyl)-2-(2-oxo-1-pyrrolidinyl) acetamide, on regional acetylcholine (ACh) levels and against scopolamine-induced ACh depletion was examined in mouse brain. In addition, the effects of DM-9384 were compared with those of oxiracetam, physostigmine and tacrine. Independent administration of DM-9384 (1, 3, 10 or 30 mg/kg, PO) or oxiracetam (10 or 50 mg/kg, PO) to mice had no effect on the ACh level in the hippocampus, frontal cortex, amygdala and striatum. Nevertheless, in all brain regions, pretreatment with DM-9384 significantly reduced the depletion of ACh induced by scopolamine (0.5 mg/kg, IP) in a nondose-related bell-shaped manner. By contrast, oxiracetam attenuated the effect of scopolamine in the hippocampus, frontal cortex and striatum but not in the amygdala. Physostigmine (0.2 mg/kg, SC) significantly increased ACh levels and reversed the scopolamine-induced ACh depletion in all brain regions. Unlike physostigmine, tacrine (10 mg/kg, PO) increased ACh levels in the striatum but not in the other regions. Tacrine reversed the effect of scopolamine in the hippocampus, amygdala and striatum, but not in the frontal cortex. In the present study, DM-9384 more effectively inhibited scopolamine-induced depletion of ACh levels than the other agents tested. The results obtained indicate that the protective action of DM-9384 against scopolamine-induced amnesia is due to its ability to reverse the ACh depletion.