Ameliorative effects of azaindolizinone derivative ZSET845 on scopolamine-induced deficits in passive avoidance and radial-arm maze learning in the rat

Scutellarein suppresses Aβ-induced memory impairment via inhibition of the NF-κB pathway in vivo and in vitro

The flavonoid compound scutellarin (Scu) is a traditional Chinese medicine used to treat a variety of diseases; however, the use of scutellarein (Scue), the hydrolysate of Scu, and its mechanisms of action in Alzheimer's disease (AD) have not been fully elucidated. In the present study, the effects of Scue on amyloid β (Aβ)-induced AD-like pathology were investigated. An in vitro model of inflammation and an aged rat model were used to confirm the effects of Scue. In vitro MTT assays and flow cytometry were used to assess the effects of Scue on cell viability and apoptosis, respectively. A Morris water maze was used to evaluate spatial learning and memory, and the levels of Aβ deposition, superoxide dismutase, malondialdehyde, apoptosis, neuro-inflammatory factors and nuclear factor-κB (NF-κB) activation in hippocampal tissues in vivo were measured to determine the effect of Scue in AD. Scue may be protective, as it decreased the apoptosis of hippocampal cells in vitro, inhibited Aβ-induced cognitive impairment, suppressed hippocampal neuro-inflammation and suppressed activation of NF-κB in vivo. Therefore, Scue may be a useful agent for the treatment of Aβ-associated pathology in the central nervous system through inhibition of the protein kinase B/NF-κB signaling pathway and thus, future studies are required to investigate the efficacy of Scue in patients with AD.

Anti-dementia drugs and hippocampal-dependent memory in rodents

Abnormalities in hippocampal structure and function are characteristics of early Alzheimer's disease (AD). Behavioral tests measuring hippocampal-dependent memory in rodents are often used to evaluate novel treatments for AD and other dementias. In this study, we review the effects of drugs marketed for the treatment of AD, such as the acetylcholinesterase inhibitors, donepezil, rivastigmine, galantamine and the N-methyl-D-aspartic acid antagonist, memantine, in rodent models of memory impairment. We also briefly describe the effects of novel treatments for cognitive impairment in rodent models of memory impairment, and discuss issues concerning the selection of the animal model and behavioral tests. Suggestions for future research are offered.

In vivo investigations on the cholinesterase-inhibiting effects of tricyclic quinazolinimines: Scopolamine-induced cognitive impairments in rats are attenuated at low dosage and reinforced at higher dosage

Tricyclic quinazolinimines as a novel class of potent inhibitors of cholinesterases in vitro are micro- and sub-micromolar inhibitors with activities at both acetyl- (AChE) and butyrylcholinesterase (BChE) or at BChE only. To further establish the antiamnesic properties of this class of compounds, an in vivo test system has been established. Cognitive impairment in rats was reversibly induced by scopolamine (0.05 mg/100 g body weight) and evaluated in an eight-arm radial maze. A representative quinazolinimine (MD212) showed attenuation of cognitive deficits at a low dosage (0.01 mg/100 g body weight), whereas at a high dosage (>0.1 mg/100 g body weight) the effect of scopolamine is markedly reinforced. As MD212 applied alone does not influence rat's cognition at all, the reinforcement of scopolamine effect has to be due to the amplification of scopolamine action possibly by (1) inhibition of scopolamine metabolism, (2) influence of scopolamine on MD212 metabolism or (3) allosteric modulation of mACh receptors. Receptor-binding studies proved hypothesis (3): MD212 stabilizes [3H]N-methylscopolamine binding to muscarinic receptors allosterically.

Donepezil primarily attenuates scopolamine-induced deficits in psychomotor function, with moderate effects on simple conditioning and attention, and small effects on working memory and spatial mapping

RATIONALE

Alzheimer's dementia (AD) patients have profound deficits in cognitive and social functions, mediated in part by a decline in cholinergic function. Acetylcholinesterase inhibitors (AChEI) are the most commonly prescribed treatment for the cognitive deficits in AD patients, but their therapeutic effects are small, and it is still not clear if they primarily affect attention, memory, or some other cognitive/behavioral functions.

OBJECTIVES

The objective of the present experiments was to explore the effects of donepezil (Aricepttrade mark), an AChEI, on behavioral deficits related exclusively to cholinergic dysfunction.

MATERIALS AND METHODS

The effects of donepezil were assessed in Sprague-Dawley rats with scopolamine-induced deficits in a battery of cognitive/behavioral tests.

RESULTS

Scopolamine produced deficits in contextual and cued fear conditioning, the 5-choice serial reaction time test, delayed nonmatching to position, the radial arm maze, and the Morris water maze. Analyses of the pattern and size of the effects revealed that donepezil produced very large effects on scopolamine-induced deficits in psychomotor function (approximately 20-50% of the variance), moderate-sized effects on scopolamine-induced deficits in simple conditioning and attention (approximately 3-10% of the variance), but only small effects on scopolamine-induced deficits in higher cognitive functions of working memory and spatial mapping (approximately 1% of the variance).

CONCLUSIONS

These results are consistent with the limited efficacy of donepezil on higher cognitive function in AD patients, and suggest that preclinical behavioral models could be used not only to determine if novel treatments have some therapeutic potential, but also to predict more precisely what the pattern and size of the effects might be.

Effects of a Novel Cognitive Enhancer, Spiro[imidazo-[1,2-a]pyridine-3,2-indan]-2(3H)-one (ZSET1446), on Learning Impairments Induced by Amyloid-β1–40 in the Rat

We have previously shown that intracerebroventricular (i.c.v.) infusion of amyloid-beta (Abeta)1-40 produces oxidative stress and cholinergic dysfunction, as well as learning and memory deficits, in rats. In the present study, effects of a newly synthesized azaindolizinone derivative, spiro[imidazo[1,2-a]pyridine-3,2-indan]-2(3H)-one (ZSET1446), were assessed in rats with learning deficits induced by Abeta1-40 or scopolamine. The i.c.v. infusion of Abeta1-40 caused impairments in spontaneous alternation behavior in a Y-maze task, spatial reference and short-term memory in a water-maze task, and retention of passive-avoidance learning. Abeta1-40-infused rats also showed reduction in choline acetyltransferase (ChAT) activity in the medial septum and hippocampus, but not in the basal forebrain and cortex, and a decrease in glutathione S-transferase (GST)-like immunoreactivity in the cortex. Nicotine-stimulated acetylcholine (ACh) release in Abeta1-40-infused rats was lower than that in vehicle-infused rats. Oral administration of ZSET1446 at the dose range of 0.01 to 1 mg/kg ameliorated Abeta1-40-induced learning impairment in Y-maze, water-maze, and passive-avoidance tasks. ZSET1446 reversed the decrease of ChAT activity in the medial septum and hippocampus, GST-like immunoreactivity in the cortex, and nicotine-stimulated ACh release of Abeta1-40-treated rats to the levels of vehicle-infused control rats. Furthermore, 0.001 to 0.1 mg/kg ZSET1446 showed ameliorative effects on learning impairments caused by scopolamine in a passive-avoidance task. These results suggest that ZSET1446 may be a potential candidate for development as a therapeutic agent to manage cognitive impairment associated with conditions such as Alzheimer's disease.

Acteoside of Callicarpa dichotoma Attenuates Scopolamine-Induced Memory Impairments

We previously reported that ten phenylethanoid glycosides including acteoside isolated from the leaves and twigs of Callicarpa dichotoma significantly attenuated glutamate-induced neurotoxicity. In the present study, we examined anti-amnesic activity of acteoside using scopolamine-induced (1 mg/kg body weight, s.c.) amnesic mice with both passive avoidance and Morris water maze tests. Acute oral treatment (single administration prior to scopolamine treatment) of mice with acteoside (1.0, 2.5 mg/kg body weight) significantly mitigated scopolamine-induced memory deficits in the passive avoidance test. It is interesting to note that prolonged oral daily treatment of mice with much lower amount (0.1 mg/kg body weight) of acteoside for 10 d reversed the scopolamine-induced memory deficits. In the Morris water maze, prolonged oral treatment with acteoside (prolonged daily administration of 1.0 mg/kg body weight for 10 d) significantly ameliorated scopolamine-induced memory deficits showing the formation of long-term and/or short-term spatial memory. We suggest, therefore, that acteoside has anti-amnesic activity that may ultimately hold significant therapeutic value in alleviating certain memory impairment observed in Alzheimer's disease.

Antiamnesic effects of azaindolizinone derivative ZSET845 on impaired learning and decreased ChAT activity induced by amyloid-beta 25-35 in the rat

Antiamnesic effects of a newly synthesized azaindolizinone derivative ZSET845 were assessed in rats made learning ability deficient by amyloid-beta (Abeta)25-35 treatment. Intracerebroventricular injection of Abeta25-35 induced a marked decrease in step-through latency in passive avoidance task and reduction in choline acetyltransferase (ChAT) activity in the medial septum and hippocampus, but not in the basal forebrain and cortex. The number of ChAT-immunoreactive cells was decreased in the medial septum. Oral administration of ZSET845 at a dose of 1 or 10 mg/kg ameliorated learning impairment in passive avoidance task and enhanced ChAT activity in the basal forebrain, medial septum and hippocampus, and increased in the number of ChAT-immunoreactive cells in the medial septum in Abeta-treated rats to the levels of vehicle-injected control rats. These results suggest that ZSET845 is worth testing for further preclinical study aimed for the treatment of senile dementia such as Alzheimer's disease.