Concurrent administration of cilostazol with donepezil effectively improves cognitive dysfunction with increased neuroprotection after chronic cerebral hypoperfusion in rats

Effects of cilostazol on cognitive function and dementia risk: A systematic review and meta-analysis

BACKGROUND

Cilostazol is an antiplatelet drug and is used for stroke prevention and symptomatic peripheral vascular disease. Studies have reported the effects of cilostazol on cognitive function, but the results are inconsistent and have not been systematically assessed.

METHODS

We systematically searched the PubMed, Embase, and Cochrane databases for relevant clinical studies. The primary outcome was the change in Mini-mental State Examination (MMSE) scores from baseline to the last available follow-up. The secondary outcome was dementia risk. Mean differences and 95% confidence intervals (CIs) were calculated for combining MMSE scores, and the pooled odds ratios and 95% CIs were used to calculate the association between use of cilostazol and dementia risk.

RESULTS

Overall, 8 eligible studies met inclusion criteria were pooled in meta-analysis. Though with a trend toward favoring cilostazol, the pooled changes in MMSE scores from baseline showed no significant difference in mild cognitive impairment and dementia patients (mean differences 1.02, 95% CI -0.53 to 2.57, P = .195). For secondary outcome, cilostazol reduced the risk of dementia in patients without prior history of dementia (pooled odds ratios 0.90; 95% CI 0.87 to 0.92; P = .000).

CONCLUSION

These results suggest the potential for cilostazol treatment in the suppression of cognitive decline and prevention of progression to dementia. However, the lack of blinding in most studies is likely to cause an overestimation of the effect sizes, and further well-designed studies are also needed.

Phosphodiesterase (PDE) III inhibitor, Cilostazol, improved memory impairment in aluminum chloride-treated rats: modulation of cAMP/CREB pathway

The most prevalent type of dementia is Alzheimer's disease (AD), which is currently incurable. Existing treatments for Alzheimer's disease, such as acetylcholinesterase inhibitors, are only effective for symptom relief. Disease-modifying medications for Alzheimer's disease are desperately required, given the enormous burdens that the disease places on individuals and communities. Phosphodiesterase (PDE) inhibitors are gaining a lot of attention in the research community because of their potential in treating age-related cognitive decline. Cilostazol is a selective PDE III inhibitor used as antiplatelet agent through cAMP response element-binding (CREB) protein phosphorylation pathway (cAMP/CREB). The neuroprotective effect of cilostazol in AD-like cognitive decline in rats was investigated in this study. After 2 months of intraperitoneal administration of 10 mg/kg aluminum chloride, Morris water maze and Y-maze (behavioral tests) were performed. After that, histological and biochemical examinations of the hippocampal region were carried out. Aluminum chloride-treated rats showed histological, biochemical, and behavioral changes similar to Alzheimer's disease. Cilostazol improved rats' behavioral and histological conditions, raised neprilysin level while reduced levels of amyloid-beta protein and phosphorylated tau protein. It also decreased the hippocampal levels of tumor necrosis factor-alpha, nuclear factor-kappa B, FAS ligand, acetylcholinesterase content, and malondialdehyde. These outcomes demonstrate the protective activity of cilostazol versus aluminum-induced memory impairment.

Cilostazol, a Phosphodiesterase 3 Inhibitor, Moderately Attenuates Behaviors Depending on Sex in the Ts65Dn Mouse Model of Down Syndrome

People with Down syndrome, which is a trisomy of chromosome 21, exhibit intellectual disability from infancy and neuropathology similar to Alzheimer’s disease, such as amyloid plaques, from an early age. Recently, we showed that cilostazol, a selective inhibitor of phosphodiesterase (PDE) 3, promotes the clearance of amyloid β and rescues cognitive deficits in a mouse model of Alzheimer’s disease. The objective of the present study was to examine whether cilostazol improves behaviors in the most widely used animal model of Down syndrome, i.e., Ts65Dn mice. Mice were supplemented with cilostazol from the fetal period until young adulthood. Supplementation significantly ameliorated novel-object recognition in Ts65Dn females and partially ameliorated sensorimotor function as determined by the rotarod test in Ts65Dn females and hyperactive locomotion in Ts65Dn males. Cilostazol supplementation significantly shortened swimming distance in Ts65Dn males in the Morris water maze test, suggesting that the drug improved cognitive function, although it did not shorten swimming duration, which was due to decreased swimming speed. Thus, this study suggests that early supplementation with cilostazol partially rescues behavioral abnormalities seen in Down syndrome and indicates that the effects are sex-dependent.

Combining antioxidant astaxantin and cholinesterase inhibitor huperzine A boosts neuroprotection

Oxidative stress is a pathophysiological condition resulting in neurotoxicity, which is possibly associated with neurodegenerative disorders. In this study, the antioxidative effects of the antioxidant astaxanthin (AXT) in combination with huperzine A (HupA), which is used as a cholinesterase inhibitor for the treatment of Alzheimer's disease, were investigated. PC12 cells were treated with either tert-butyl hydroperoxide (TBHP), or with the toxic version of β-amyloid, Aβ_25–35, to induce oxidative stress and neurotoxicity. Cell viability, morphology, lactate dehydrogenase (LDH) release, intracellular accumulation of reactive oxygen species (ROS), superoxide dismutase (SOD) activity and malondialdehyde (MDA) content were determined, while neuroprotection was also monitored using an MTT assay. It was found that combining AXT with HupA significantly increased the viability of PC12 cells, prevented membrane damage (as measured by LDH release), attenuated intracellular ROS formation, increased SOD activity and decreased the level of MDA after TBHP exposure when compared to these drugs administered alone. Pretreatment with HupA and AXT decreased toxic damage produced by Aβ_25–35. These data indicated that combining an antioxidant with a cholinesterase inhibitor increases the degree of neuroprotection; with future investigation this could be a potential therapy used to decrease neurotoxicity in the brain.

Cerebral Small Vessel Disease (CSVD) - Lessons From the Animal Models

Cerebral small vessel disease (CSVD) refers to a spectrum of clinical and imaging findings resulting from pathological processes of various etiologies affecting cerebral arterioles, perforating arteries, capillaries, and venules. Unlike large vessels, it is a challenge to visualize small vessels in vivo, hence the difficulty to directly monitor the natural progression of the disease. CSVD might progress for many years during the early stage of the disease as it remains asymptomatic. Prevalent among elderly individuals, CSVD has been alarmingly reported as an important precursor of full-blown stroke and vascular dementia. Growing evidence has also shown a significant association between CSVD's radiological manifestation with dementia and Alzheimer's disease (AD) pathology. Although it remains contentious as to whether CSVD is a cause or sequelae of AD, it is not far-fetched to posit that effective therapeutic measures of CSVD would mitigate the overall burden of dementia. Nevertheless, the unifying theory on the pathomechanism of the disease remains elusive, hence the lack of effective therapeutic approaches. Thus, this chapter consolidates the contemporary insights from numerous experimental animal models of CSVD, to date: from the available experimental animal models of CSVD and its translational research value; the pathomechanical aspects of the disease; relevant aspects on systems biology; opportunities for early disease biomarkers; and finally, converging approaches for future therapeutic directions of CSVD.

Augmented improvement of cognition and memory by aripiprazole add-on for cilostazol treatment in the chronic cerebral hypoperfusion mouse model

Cerebrovascular dysfunction is associated with cognitive impairment in vascular dementia patients. This study aimed to explore augmented improvement of cognition and memory by aripiprazole add-on for cilostazol treatment in vascular dementia model. Male C57BL/6 mice were subjected to BCAS, and spatial probe and memory retention were examined using the Morris water maze (MWM) test. In the present study, the escape latency on the first day after 3rd week was 21.4 ± 4.0 s in sham-operated mice, and 76.3 ± 4.2 s in the vehicle-treated BCAS mice. In the spatial probe tests in the 3rd week, aripiprazole (1 mg/kg/day) showed time-dependently amelioration in spatial learning and memory impairments in contrast to 0.5 mg/kg/day. After treatment with 20 mg/kg/day of cilostazol for 3 weeks, the escape latency significantly decreased to 26.6 ± 5.8 s on the first day and further shortened to 21.6 ± 6.8 s on the fourth day. When the BCAS mice were concurrently treated with 0.5 mg/kg/day aripiprazole plus 20 mg/kg/day of cilostazol for 3 weeks, the escape latency was more shortened from 20.4 ± 1.2 s (1st day) to 14.9 ± 1.7 s on the 4th day of the 3-week trials. Furthermore, decreased spatial memory retention in BCAS mice was significantly alleviated by aripiprazole plus cilostazol cotreatment, indicating the benefit of aripiprazole add-on therapy. In line with these, significantly increased mBDNF and P-CREB levels and reduced apoptosis were identified in the BCAS mouse brain dentate gyrus by cotreatment as contrasted to each monotherapy. These results may provide the synergistic therapeutic avenues for augmented improvement of cognition and memory by cotreatment with aripiprazole plus cilostazol in cases of vascular dementia.

Efficacy of Cilostazol Administration in Alzheimer's Disease Patients with White Matter Lesions: A Positron-Emission Tomography Study

This study tested the efficacy of the phosphodiesterase type III inhibitor cilostazol in Alzheimer's disease patients with white matter lesions treated with donepezil in comparison with donepezil monotherapy using fluorodeoxyglucose (18F) positron-emission tomography (FDG PET). A 24-week, randomized, double-blind, placebo-controlled, parallel-group study was conducted. Thirty-six Alzheimer's disease patients with white matter lesions who received donepezil (n = 18 each in the cilostazol and placebo groups) were enrolled. Participants underwent pre and post FDG PET imaging scans and three rounds of clinical and neuropsychological tests. The cilostazol group did not show a significant decrease of regional glucose metabolism; however, regional glucose metabolism was significantly decreased in the parietal and frontal lobes of the placebo group. The repeated measures ANOVA measuring differences in uptake change revealed that regional glucose metabolism in the left inferior frontal gyrus was significantly more preserved in the cilostazol group than that in the placebo group (p < 0.005). Mean changes from baseline on the Mini-Mental State Exam, Alzheimer's Disease Assessment Scale-cognitive subscale, Alzheimer's Disease Cooperative Study-Activities of Daily Living Inventory, and the Clinical Dementia Rating Sum of Boxes did not differ between the two groups. In the cilostazol group, the increase of glucose metabolism correlated with the improvment of the Alzheimer's Disease Assessment Scale-cognitive score. We conclude that cilostazol treatment added to donepezil may delay the decline in regional cerebral metabolism in Alzheimer's disease with white matter lesions compared with donepezil monotherapy. In additon, our results verified the efficacy of cilostazol in improving or protecting cognitive function in Alzheimer's disease through increased glucose metabolism. However, the long-term effect of cilostazol on cognitive function and Alzheimer's disease modification must be tested in further studies with larger sample size and longer study period. Trial registration: http://clinicaltrials.gov : NCT01409564.

PDE3 Inhibitors Repurposed as Treatments for Age-Related Cognitive Impairment

As the population of older individuals grows worldwide, researchers have increasingly focused their attention on identifying key molecular targets of age-related cognitive impairments, with the aim of developing possible therapeutic interventions. Two such molecules are the intracellular cyclic nucleotides, cAMP and cGMP. These second messengers mediate fundamental aspects of brain function relevant to memory, learning, and cognitive function. Consequently, phosphodiesterases (PDEs), which hydrolyze cAMP and cGMP, are promising targets for the development of cognition-enhancing drugs. Inhibitors that target PDEs work by elevating intracellular cAMP. In this review, we provide an overview of different PDE inhibitors, and then we focus on pharmacological and physiological effects of PDE3 inhibitors in the CNS and peripheral tissues. Finally, we discuss findings from experimental and preliminary clinical studies and the potential beneficial effects of the PDE3 inhibitor cilostazol on age-related cognitive impairments. In the innovation pipeline of pharmaceutical development, the antiplatelet agent cilostazol has come into the spotlight as a novel treatment for mild cognitive impairment. Overall, the repurposing of cilostazol may represent a potentially promising way to treat mild cognitive impairment, Alzheimer's disease, and vascular dementia. In this review, we present a brief summary of cAMP signaling and different PDE inhibitors, followed by a discussion of the pharmacological and physiological role of PDE3 inhibitors. In this context, we discuss the repurposing of a PDE3 inhibitor, cilostazol, as a potential treatment for age-related cognitive impairment based on recent research.

Stepwise occlusion of the carotid arteries of the rat: MRI assessment of the effect of donepezil and hypoperfusion-induced brain atrophy and white matter microstructural changes

Bilateral common carotid artery occlusion (BCCAo) in the rat is a widely used animal model of vascular dementia and a valuable tool for preclinical pharmacological drug testing, although the varying degrees of acute focal ischemic lesions it induces could interfere with its translational value. Recently, a modification to the BCCAo model, the stepwise occlusion of the two carotid arteries, has been introduced. To acquire objective translatable measures, we used longitudinal multimodal magnetic resonance imaging (MRI) to assess the effects of semi-chronic (8 days) donepezil treatment in this model, with half of the Wistar rats receiving the treatment one week after the stepwise BCCAo. With an ultrahigh field MRI, we measured high-resolution anatomy, diffusion tensor imaging, cerebral blood flow measurements and functional MRI in response to whisker stimulation, to evaluate both the structural and functional effects of the donepezil treatment and stepwise BCCAo up to 5 weeks post-occlusion. While no large ischemic lesions were detected, atrophy in the striatum and in the neocortex, along with widespread white matter microstructural changes, were found. Donepezil ameliorated the transient drop in the somatosensory BOLD response in distant cortical areas, as detected 2 weeks after the occlusion but the drug had no effect on the long term structural changes. Our results demonstrate a measurable functional MRI effect of the donepezil treatment and the importance of diffusion MRI and voxel based morphometry (VBM) analysis in the translational evaluation of the rat BCCAo model.

Cilostazol Use Is Associated with Reduced Risk of Dementia: A Nationwide Cohort Study

Whether antiplatelet agents have a preventive effect on cognitive function remains unknown. We examined the potential association between the use of cilostazol, an antiplatelet agent and cyclic adenosine monophosphate phosphodiesterase 3 inhibitor, and the risk of dementia in an Asian population. Patients initiating cilostazol therapy between 1 January 2004 and 31 December 2009 without a prior history of dementia were identified from Taiwan's National Health Insurance database. Participants were stratified by age, sex, comorbidities, and comedication. The outcome of interest was all-cause dementia (ICD-9-CM codes 290.0, 290.4, 294.1, 331.0). Cox regression models were used to estimate the hazard ratio (HR) of dementia. The cumulative cilostazol dosage was stratified by quartile of defined daily doses using no cilostazol use as a reference. A total of 9148 participants 40 years of age or older and free of dementia at baseline were analyzed. Patients using cilostazol (n = 2287) had a significantly decreased risk of incident dementia compared with patients not using the drug [n = 6861; adjusted HR (aHR) 0.75; 95% confidence interval (CI) 0.61-0.92]. Notably, cilostazol use was found to have a dose-dependent association with reduced rate of dementia emergence (p for trend = 0.001). Subgroup analysis identified a decline of dementia in cilostazol users with diagnosed ischemic heart disease (aHR 0.44, 95% CI 0.24-0.83) and cerebral vascular disease (aHR 0.34, 95% CI 0.21-0.54). These observations suggest that cilostazol use may reduce the risk to develop dementia, and a high cumulative dose further decreases the risk of dementia. These findings should be examined further in randomized clinical trials.

Long-term cilostazol administration ameliorates memory decline in senescence-accelerated mouse prone 8 (SAMP8) through a dual effect on cAMP and blood-brain barrier

Phosphodiesterases (PDEs), which hydrolyze and inactivate 3', 5'-cyclic adenosine monophosphate (cAMP) and 3', 5'-cyclic guanosine monophosphate (cGMP), play an important role in synaptic plasticity that underlies memory. Recently, several PDE inhibitors were assessed for their possible therapeutic efficacy in treating cognitive disorders. Here, we examined how cilostazol, a selective PDE3 inhibitor, affects brain functions in senescence-accelerated mouse prone 8 (SAMP8), an animal model of age-related cognitive impairment. Long-term administration of cilostazol restored the impaired context-dependent conditioned fear memory of SAMP8 to match that in normal aging control substrain SAMR1. Cilostazol also increased the number of cells containing phosphorylated cAMP-responsive element binding protein (CREB), a downstream component of the cAMP pathway. Finally, cilostazol improves blood-brain barrier (BBB) integrity, demonstrated by reduced extravasation of 2-deoxy-2-¹⁸F-fluoro-d-glucose and Evans Blue dye in the brains of SAMP8. This improvement in BBB integrity was associated with an increased amount of zona occludens protein 1 (ZO-1) and occludin proteins, components of tight junctions integral to the BBB. The results suggest that long-term administration of cilostazol exerts its beneficial effects on age-related cognitive impairment through a dual mechanism: by enhancing the cAMP system in the brain and by maintaining or improving BBB integrity.

Update on Inflammatory Biomarkers and Treatments in Ischemic Stroke

After an acute ischemic stroke (AIS), inflammatory processes are able to concomitantly induce both beneficial and detrimental effects. In this narrative review, we updated evidence on the inflammatory pathways and mediators that are investigated as promising therapeutic targets. We searched for papers on PubMed and MEDLINE up to August 2016. The terms searched alone or in combination were: ischemic stroke, inflammation, oxidative stress, ischemia reperfusion, innate immunity, adaptive immunity, autoimmunity. Inflammation in AIS is characterized by a storm of cytokines, chemokines, and Damage-Associated Molecular Patterns (DAMPs) released by several cells contributing to exacerbate the tissue injury both in the acute and reparative phases. Interestingly, many biomarkers have been studied, but none of these reflected the complexity of systemic immune response. Reperfusion therapies showed a good efficacy in the recovery after an AIS. New therapies appear promising both in pre-clinical and clinical studies, but still need more detailed studies to be translated in the ordinary clinical practice. In spite of clinical progresses, no beneficial long-term interventions targeting inflammation are currently available. Our knowledge about cells, biomarkers, and inflammatory markers is growing and is hoped to better evaluate the impact of new treatments, such as monoclonal antibodies and cell-based therapies.

Cilostazol reduces blood brain barrier dysfunction, white matter lesion formation and motor deficits following chronic cerebral hypoperfusion

Cerebral small vessel disease (CSVD) is a pathological process leading to lacunar infarcts, leukoaraiosis and cerebral microbleeds. Dysfunction of the blood brain barrier (BBB) has been proposed as a mechanism in the progression cerebral small vessel disease. A rodent model commonly used to study some aspects of CSVD is bilateral common carotid artery occlusion (BCCAO) in the rat. In the present study it was determined that gait impairment, as determined by a tapered beam test, and BBB permeability increased following BCCAO. Cilostazol, a type III phosphodiesterase inhibitor, has been shown to have anti-apoptotic effects and prevent white matter vacuolation and rarefaction induced by BCCAO in rats. In this study the protective effect of cilostazol administration on the increase BBB permeability following BCCAO was determined as well as the effect on plasma levels of circulating microparticles (MPs), cerebral white matter rarefaction, glial activation and gait disturbance. The effect of cilostazol on in vitro endothelial barriers was also evaluated. Cilostazol treatment improved BBB permeability and reduced gait disturbance, visual impairment and microglial activation in optic tract following BCCAO in vivo. It also reduced the degree of cell death and the reduction in trans-endothelial electrical resistance (TEER) in artificial endothelial barriers in vitro induced by MP treatment of in vitro barriers.

Local Drug-Drug Interaction of Donepezil with Cilostazol at Breast Cancer Resistance Protein (ABCG2) Increases Drug Accumulation in Heart

Clinical reports indicate that cardiotoxicity due to donepezil can occur after coadministration with cilostazol. We speculated that the concentration of donepezil in heart tissue might be increased as a result of interaction with cilostazol at efflux transporters such as P-glycoprotein (P-gp, ABCB1) and breast cancer resistance protein (BCRP, ABCG2), which are expressed in many tissues including the heart, and our study tested this hypothesis. First, donepezil was confirmed to be a substrate of both BCRP and P-glycoprotein in transporter-transfected cells in vitro. Cilostazol inhibited BCRP and P-glycoprotein with half-inhibitory concentrations of 130 nM and 12.7 μM, respectively. Considering the clinically achievable unbound plasma concentration of cilostazol (about 200 nM), it is plausible that BCRP-mediated transport of donepezil would be affected by cilostazol in vivo. Indeed, in an in vivo rat study, we found that coadministration of cilostazol significantly increased the concentrations of donepezil in the heart and brain, where BCRP functions as a part of the blood-tissue barrier, whereas the plasma concentration of donepezil was unaffected. In addition, in vitro accumulation of donepezil in heart tissue slices of rats was significantly increased in the presence of cilostazol. These results indicate that donepezil-cilostazol interaction at BCRP may be clinically relevant in heart and brain tissues. In other words, the tissue distribution of drugs can be influenced by drug-drug interaction (DDI) at efflux transporters in certain tissues (local DDI) without any apparent change in plasma concentration (systemic DDI).

Phase II anti-inflammatory and immune-modulating drugs for acute ischaemic stroke

INTRODUCTION

Stroke is the second leading cause of death worldwide and the leading cause of adult neurological disability. Despite advances in stroke unit care, and increasing use of thrombolysis, there remains an urgent need for safe and effective treatments for acute ischaemic stroke. However, this is against a backdrop of multiple failures in translational drug development. Cerebral ischaemia initiates a complex cascade of immune and inflammatory pathways in the brain microvasculature and periphery, which contribute to the evolution of cerebral injury, resolution and repair. Targeting specific inflammatory or immune pathways, therefore, represents an attractive treatment strategy in acute ischaemic stroke. Although anti-inflammatory drugs have already failed in clinical trial development, several are currently at the Phase II developmental stage.

AREAS COVERED

The authors highlight several candidate drugs, which modulate a range of inflammatory and immune pathways, and have been investigated in pre-clinical and Phase II studies to date.

EXPERT OPINION

Drugs targeting inflammatory and immune pathways offer theoretical advantages including potentially longer therapeutic time windows and effects complementary to thrombolysis (ameliorating reperfusion injury). Fundamental changes in the approach to pre-clinical and clinical drug development are required to facilitate successful translation of promising candidate drugs into clinical practice.

Diabetes augments cognitive dysfunction in chronic cerebral hypoperfusion by increasing neuronal cell death: implication of cilostazol for diabetes mellitus-induced dementia

Many patients with diabetes are at increased risk of cognitive dysfunction and dementia. Diabetes mellitus is a vascular risk factor that may increase the risk of dementia through its associations with vascular dementia. We tested whether cognitive impairment could be exacerbated in combined injury using a rat model of chronic cerebral hypoperfusion with diabetes. We also determined whether a potent inhibitor of type III phosphodiesterase could prevent the cognitive decline caused by this combined injury. We used Otsuka Long-Evans Tokushima Fatty (OLETF) rats as a model of type II diabetes (T2DM) and Long-Evans Tokushima Otsuka (LETO) rats as a control. Chronic cerebral hypoperfusion was modeled by permanent bilateral common carotid artery occlusion (BCCAO). At 24weeks, the non-diabetic and T2DM rats were randomly assigned into groups for the following experiments: analysis I (1) sham non-diabetic rats (n=8); (2) hypoperfused non-diabetic rats (n=9); (3) sham T2DM rats (n=8); (4) hypoperfused T2DM rats (n=9); analysis II- (1) sham T2DM rats without treatment (n=8); (2) cilostazol-treated T2DM rats (n=8); (3) hypoperfused T2DM rats (n=9); and (4) hypoperfused T2DM rats and cilostazol treatment (n=9). The rats were orally administered cilostazol (50mg/kg) or vehicle once a day for 2weeks after 24weeks. Rats performed Morris water maze tasks, and neuronal cell death and neuroinflammation were investigated via Western blots and histological investigation. Spatial memory impairment was exacerbated synergistically in the hypoperfused T2DM group compared with the hypoperfused non-diabetic group and sham T2DBM group (P<0.05). Compared with the control group, neuronal cell death was increased in the hippocampus of the hypoperfused T2DM group. Cilostazol, a PDE-3 inhibitor, improved the memory impairments through inhibition of neuronal cell death, activation of CREB phosphorylation and BDNF expression in the hypoperfused T2DM group. Our experimental results support the hypothesis that there are deleterious interactions between chronic cerebral hypoperfusion and T2DM. That is, metabolic diseases such as diabetes may exacerbate cognitive impairment in a rat model of vascular dementia. We also suggest that surprisingly, the phosphodiesterase III inhibitor, cilostazol may be useful for the treatment of cognitive impairment in diabetes mellitus-induced dementia. In conclusion, diabetes can aggravate cognitive dysfunction in vascular dementia, and PDE-3 inhibitors, such as cilostazol, may form the basis of a novel therapeutic strategy for diabetes-associated cognitive impairment or vascular dementia.

Cilostazol improves hippocampus-dependent long-term memory in mice

RATIONALE

Phosphodiesterases (PDEs) play an important role in the regulation of intracellular signaling mediated by cyclic adenosine monophosphate (cAMP). Recently, several PDE inhibitors were assessed for their possible cognitive enhancing properties. However, little is known about the effect of PDE3 inhibitors on memory function.

OBJECTIVES

We examined how the PDE3 inhibitor cilostazol affects C57BL/6 J mice as they perform various behavioral tasks. After behavioral assessment, brains of the mice were analyzed immunohistochemically to quantify the phosphorylation of cAMP-responsive element binding protein (CREB), a downstream component of the cAMP pathway.

RESULTS

Oral administration of cilostazol significantly enhanced recollection of the exact platform location in the Morris water maze probe test. Cilostazol also improved context-dependent long-term fear memory, without affecting short-term memory. No apparent effect was observed in cue-dependent fear memory. The results suggest that cilostazol selectively improves hippocampus-dependent long-term memory in these tasks. Cilostazol also significantly increased the number of phosphorylated-CREB-positive cells in hippocampal dentate gyrus.

CONCLUSIONS

These results suggest that cilostazol may exert its beneficial effects on learning and memory by enhancing the cAMP system in hippocampus, where it increases intracellular cAMP activity.

Standardized Extract of Bacopa monniera Attenuates Okadaic Acid Induced Memory Dysfunction in Rats: Effect on Nrf2 Pathway

The aim of the present study is to investigate the effect of standardized extract of Bacopa monnieri (memory enhancer) and Melatonin (an antioxidant) on nuclear factor erythroid 2 related factor 2 (Nrf2) pathway in Okadaic acid induced memory impaired rats. OKA (200 ng) was administered intracerebroventricularly (ICV) to induce memory impairment in rats. Bacopa monnieri (BM-40 and 80 mg/kg) and Melatonin (20 mg/kg) were administered 1 hr before OKA injection and continued daily up to day 13. Memory functions were assessed by Morris water maze test on days 13–15. Rats were sacrificed for biochemical estimations of oxidative stress, neuroinflammation, apoptosis, and molecular studies of Nrf2, HO1, and GCLC expressions in cerebral cortex and hippocampus brain regions. OKA caused a significant memory deficit with oxidative stress, neuroinflammation, and neuronal loss which was concomitant with attenuated expression of Nrf2, HO1, and GCLC. Treatment with BM and Melatonin significantly improved memory dysfunction in OKA rats as shown by decreased latency time and path length. The treatments also restored Nrf2, HO1, and GCLC expressions and decreased oxidative stress, neuroinflammation, and neuronal loss. Thus strengthening the endogenous defense through Nrf2 modulation plays a key role in the protective effect of BM and Melatonin in OKA induced memory impairment in rats.

Synergistic effect of acetylcholinesterase inhibition (donepezil) and 5-HT(4) receptor activation (RS67333) on object recognition in mice

Facing inefficiency of current treatments to cure Alzheimer disease (AD), a pharmacological approach is now emerging on the assumption that a single compound may be able to hit multiple targets, namely Multi-Target-Directed Ligands (MTDLs). Displaying numerous advantages, several MTDL for AD have been recently described but none associating an inhibition of AChE and an activation of 5-HT(4)R. The aim of this study was to validate the concept of a synergistic action of these two targets on episodic-like memory performances in mice. Among potent molecules, RS67333, a reference 5-HT(4)R agonist and donepezil (DNPZ), a reference acetylcholinesterase inhibitor, have been particularly chosen because of their close chemical structure. Administered separately, RS67333 (0.3 and 1mg/kg) and DNPZ (1mg/kg) improved recognition performances compared to saline treated animals but not with lower doses. Co-administration of subactive doses of RS67333 (0.1mg/kg) and DNPZ (0.3mg/kg) improved memory, moreover, this improvement is prevented if a 5-HT(4)R antagonist (GR125487, 10mg/kg) is also administered. Activation of 5-HT(4)R combined with inhibition of AChE with subactive doses of RS67333 and of DNPZ has synergistic effects on memory performances in mice. These molecules having close chemical structures, the synergistic effect of their combination affords new hope to chemist for the synthesis of MTDL.

Isoflurane-induced spatial memory impairment in mice is prevented by the acetylcholinesterase inhibitor donepezil

Although many studies have shown that isoflurane exposure impairs spatial memory in aged animals, there are no clinical treatments available to prevent this memory deficit. The anticholinergic properties of volatile anesthetics are a biologically plausible cause of cognitive dysfunction in elderly subjects. We hypothesized that pretreatment with the acetylcholinesterase inhibitor donepezil, which has been approved by the Food and Drug Administration (FDA) for the treatment of Alzheimer's disease, prevents isoflurane-induced spatial memory impairment in aged mice. In present study, eighteen-month-old mice were administered donepezil (5 mg/kg) or an equal volume of saline by oral gavage with a feeding needle for four weeks. Then the mice were exposed to isoflurane (1.2%) for six hours. Two weeks later, mice were subjected to the Morris water maze to examine the impairment of spatial memory after exposure to isoflurane. After the behavioral test, the mice were sacrificed, and the protein expression level of acetylcholinesterase (AChE), choline acetylase (ChAT) and α7 nicotinic receptor (α7-nAChR) were measured in the brain. Each group consisted of 12 mice. We found that isoflurane exposure for six hours impaired the spatial memory of the mice. Compared with the control group, isoflurane exposure dramatically decreased the protein level of ChAT, but not AChE or α7-nAChR. Donepezil prevented isoflurane-induced spatial memory impairments and increased ChAT levels, which were downregulated by isoflurane. In conclusions, pretreatment with the AChE inhibitor donepezil prevented isoflurane-induced spatial memory impairment in aged mice. The mechanism was associated with the upregulation of ChAT, which was decreased by isoflurane.

Cilostazol prevents amyloid β peptide(25-35)-induced memory impairment and oxidative stress in mice

BACKGROUND AND PURPOSE

Cilostazol may be effective in dementia associated with a cerebral ischaemia. In this study, we examined whether it exerts beneficial effects on learning and/or memory impairment induced by Aβ(25-35) in mice, and compared its effects with those of aspirin.

EXPERIMENTAL APPROACH

Aβ(25-35) (9 nmol) was administered to mice i.c.v. Learning and memory behaviour were evaluated by measuring spontaneous alternation in a Y-maze and a step-down type passive avoidance test, on the 5th and 8th days after injection respectively. Levels of lipid peroxidation (malondialdehyde) and cytokines in the frontal cortex and hippocampus were measured 2, 3, 5 and 7 days after the Aβ(25-35) injection. The effects of repeated administration of cilostazol and aspirin (both at 30 and 100 mg·kg(-1), p.o.) on any changes induced by Aβ(25-35) were evaluated.

KEY RESULTS

Repeated administration of cilostazol significantly attenuated the impairment of spontaneous alternation and the shortened step-down latency induced by Aβ(25-35) . Aspirin did not show any beneficial effect. A significant increase in the levels of malondialdehyde (MDA) and IL-1β (only measured in hippocampus) was observed 2, 3 and 5 days after the Aβ(25-35) injection in the frontal cortex and hippocampus. Repeated administration of cilostazol (100 mg·kg(-1)) completely prevented the increase in MDA levels but failed to antagonize the increase in the expression of IL-1β induced by Aβ(25-35).

CONCLUSIONS AND IMPLICATIONS

These results suggest that the protective effect of cilostazol on Aβ(25-35)-induced memory impairment may be related to oxidative stress in the frontal cortex and the hippocampus.

Enhanced dendritic spine number of neurons of the prefrontal cortex, hippocampus, and nucleus accumbens in old rats after chronic donepezil administration

In Alzheimer's disease brains, morphological changes in the dendrites of pyramidal neurons of the prefrontal cortex (PFC) and hippocampus have been observed. These changes are particularly reflected in the decrement of both the dendritic tree and spine number. Donepezil is a potent and selective acetylcholinesterase inhibitor used in the treatment of Alzheimer's disease. We have studied the effect of oral administration of this drug on the morphology of neuronal cells from the brain of aged rats. We examined dendrites of pyramidal neurons of the PFC, dorsal or ventral hippocampus (VH), and medium spiny neurons of the nucleus accumbens (NAcc). Donepezil (1 mg/kg, vo) was administrated every day for 60 days to rats aged 10 and 18 months. Dendritic morphology was studied by the Golgi-Cox stain procedure followed by Sholl analysis at 12 and 20 months ages, respectively. In all Donepezil-treated rats, a significant increment of the dendritic spines number in pyramidal neurons of the PFC and dorsal hippocampus was observed. However, pyramidal neurons of the VH and medium spiny cells of the NAcc only showed an increase in the number of their spines in 12-month-old rats. Our results suggest that Donepezil prevents the alterations of the neuronal dendrite morphology caused by aging.

Microglia signaling as a target of donepezil

Donepezil is a reversible and noncompetitive cholinesterase inhibitor. The drug is considered as a first-line treatment in patients with mild to moderate Alzheimer's disease. Recently, anti-inflammatory and neuroprotective effects of the drug have been reported. "Cholinergic anti-inflammation pathway" has major implications in these effects. Here, we present evidence that donepezil at 5-20 microM directly acts on microglial cells to inhibit their inflammatory activation. Our conclusion is based on the measurement of nitric oxide and proinflammatory mediators using purified microglia cultures and microglia cell lines: donepezil attenuated microglial production of nitric oxide and tumor necrosis factor (TNF)-alpha, and suppressed the gene expression of inducible nitric oxide synthase, interleukin-1 beta, and TNF-alpha. Subsequent studies showed that donepezil inhibited a canonical inflammatory NF-kappaB signaling. Microglia/neuroblastoma coculture and animal experiments supported the anti-inflammatory effects of donepezil. Based on the studies using nicotinic acetylcholine receptor antagonists, the donepezil inhibition of microglial activation was independent of acetylcholine and its receptor. Thus, inflammatory activation signaling of microglia may be one of the direct targets of donepezil in the central nervous system. It should be noted, however, that there is a large gap between the therapeutic dose of the drug used clinically and the concentration of the drug that exerts the direct action on microglial cells.

Sevoflurane preconditioning reverses impairment of hippocampal long-term potentiation induced by myocardial ischaemia-reperfusion injury

BACKGROUND AND OBJECTIVE

We sought to test whether a transient myocardial ischaemia can induce impairment of hippocampal long-term potentiation (LTP) and whether sevoflurane preconditioning can provide robust protective effects on this neurological impairment.

METHODS

Wistar rats were subjected to a transient coronary artery occlusion for 30 min. Sevoflurane preconditioning was performed by exposure to 1.0 minimum alveolar concentration of sevoflurane for 1 h and washout for 30 min before myocardial ischaemia. Hippocampal LTP was evaluated during a 7-day observation period. The expressions of haem oxygenase-1 mRNA, tumour necrosis factor-alpha mRNA and interleukin-1beta mRNA in the hippocampus were analysed by quantitative reverse transcription-PCR.

RESULTS

LTP was significantly inhibited 1 and 3 days after the transient myocardial ischaemia in the control group when compared with the animals subjected to a sham operation without coronary occlusion, and the LTP recovered to a normal magnitude 7 days later. Sevoflurane preconditioning remarkably reversed the transient inhibition of LTP observed at 1 and 3 days after myocardial ischaemia. Compared with the sham animals, the expressions of haem oxygenase-1 mRNA, tumour necrosis factor-alpha mRNA and interleukin-1beta mRNA in the hippocampus of the control rats were significantly increased during the early stage after myocardial ischaemia (1-3 days), and the increases of these cytokines were attenuated by sevoflurane pretreatment.

CONCLUSION

Sevoflurane preconditioning induced neuroprotection against impairment of hippocampal LTP resulting from myocardial ischaemia and reperfusion.

Cilostazol improves cognitive function in mice by increasing the production of insulin-like growth factor-I in the hippocampus

Insulin-like growth factor I (IGF-I) exerts beneficial effects on cognitive function by inducing angiogenesis and neurogenesis in the hippocampus. We demonstrated that stimulation of sensory neurons in the gastrointestinal tract increased IGF-I production in the hippocampus, and thereby improved cognitive function in mice. Since cAMP plays a critical role in stimulation of sensory neurons, the type III phosphodiesterase (PDE3) inhibitor cilostazol might increase IGF-I production in the hippocampus by stimulating sensory neurons and thus improve cognitive function in mice. We tested this hypothesis in the present study. Cilostazol increased the release of calcitonin gene-related peptide (CGRP) and levels of cAMP in dorsal root ganglion (DRG) neurons isolated from wild-type (WT) mice. Tissue levels of cAMP in the DRG and hippocampus and those of CGRP, IGF-I, and IGF-I mRNA in the hippocampus were increased after 4-week oral administration of cilostazol to WT mice. Levels of expression of c-fos in the spinal dorsal horns, parabrachial nuclei, the solitary tract nucleus, and the hippocampus were also increased in these animals. Significant enhancement of angiogenesis and neurogenesis was observed in the dentate gyrus of the hippocampus after cilostazol administration in WT mice. Significant improvement of spatial learning was also observed in WT mice administered cilostazol. However, none of these effects in WT mice were observed in CGRP-knockout mice. These observations suggest that cilostazol may improve cognitive function in mice by increasing the hippocampal production of IGF-I through stimulation of sensory neurons.

Methylthioninium chloride reverses cognitive deficits induced by scopolamine: comparison with rivastigmine

RATIONALE

The cholinergic system is involved in cognition as well as in age-related cognitive decline and Alzheimer disease (AD). Cholinergic enhancers ameliorate AD symptoms and represent the main current therapy for AD. MTC (Methylthioninium chloride), an antioxidant with metabolism-enhancing properties may be a novel candidate with pro-cognitive capacities.

OBJECTIVES

This study was performed: (1) to assess the pro-cognitive efficacy of MTC and establish its dose-response; (2) to compare the efficacy of MTC with rivastigmine and (3) to determine the potential for combination therapy by co-administration of MTC and rivastigmine.

METHODS

Spatial cognition of female NMRI mice was tested in a reference memory water maze task. Subjects received intra-peritoneal injections of scopolamine (0.5 mg/kg) followed by vehicle, and/or MTC and/or rivastigmine (0.15-4 mg/kg MTC; 0.1-0.5 mg/kg rivastigmine) in mono or combination treatment.

RESULTS

Scopolamine treatment prevented spatial learning in NMRI female mice and the deficit was reversed by both rivastigmine and MTC in a dose-dependent manner. Mono-therapy with high doses of rivastigmine (>0.5 mg/kg) caused severe side effects but MTC was safe up to 4 mg/kg. Co-administration of sub-effective doses of both drugs acted synergistically in reversing learning deficits and scopolamine-induced memory impairments.

CONCLUSIONS

In our model, MTC reversed the spatial learning impairment. When combined with the ChEI rivastigmine, the effect of MTC appeared to be amplified indicating that combination therapy could potentially improve not only symptoms but also contribute beneficially to neuronal metabolism by minimising side effects at lower doses.