Neuroprotective effect of cyclooxygenase inhibitors in ICV-STZ induced sporadic Alzheimer's disease in rats

Selected Natural Products in Neuroprotective Strategies for Alzheimer's Disease-A Non-Systematic Review

Neurodegenerative disorders such as Alzheimer’s disease (AD) are distinguished by the irreversible degeneration of central nervous system function and structure. AD is characterized by several different neuropathologies—among others, it interferes with neuropsychiatrical controls and cognitive functions. This disease is the number one neurodegenerative disorder; however, its treatment options are few and, unfortunately, ineffective. In the new strategies devised for AD prevention and treatment, the application of plant-based natural products is especially popular due to lesser side effects associated with their taking. Moreover, their neuroprotective activities target different pathological mechanisms. The current review presents the anti-AD properties of several natural plant substances. The paper throws light on products under in vitro and in vivo trials and compiles information on their mechanism of actions. Knowledge of the properties of such plant compounds and their combinations will surely lead to discovering new potent medicines for the treatment of AD with lesser side effects than the currently available pharmacological proceedings.

Role of Monoamine Oxidase Activity in Alzheimer's Disease: An Insight into the Therapeutic Potential of Inhibitors

Despite not being utilized as considerably as other antidepressants in the therapy of depression, the monoamine oxidase inhibitors (MAOIs) proceed to hold a place in neurodegeneration and to have a somewhat broad spectrum in respect of the treatment of neurological and psychiatric conditions. Preclinical and clinical studies on MAOIs have been developing in recent times, especially on account of rousing discoveries manifesting that these drugs possess neuroprotective activities. The altered brain levels of monoamine neurotransmitters due to monoamine oxidase (MAO) are directly associated with various neuropsychiatric conditions like Alzheimer’s disease (AD). Activated MAO induces the amyloid-beta (Aβ) deposition via abnormal cleavage of the amyloid precursor protein (APP). Additionally, activated MAO contributes to the generation of neurofibrillary tangles and cognitive impairment due to neuronal loss. No matter the attention of researchers on the participation of MAOIs in neuroprotection has been on monoamine oxidase-B (MAO-B) inhibitors, there is a developing frame of proof indicating that monoamine oxidase-A (MAO-A) inhibitors may also play a role in neuroprotection. The therapeutic potential of MAOIs alongside the complete understanding of the enzyme’s physiology may lead to the future advancement of these drugs.

Optimization of intracerebroventricular streptozotocin dose for the induction of neuroinflammation and memory impairments in rats

Intracerebroventricular (ICV) injection of streptozotocin (STZ) is a well established procedure to induce neuroinflammation leading to dementia in experimental animals. However, the optimal dose of STZ has not been determined. In the present study, rats were ICV injected with 1.5, 3 and 6 mg of STZ per kg of body weight. After 21 days, neuroinflammatory markers i.e. TNF-α, IL-1β, ROS and nitrite were quantified in the hippocampus. Memory function was assessed by the radial arm maze test after 9, 12, 15, 18, 21 days following STZ injection. STZ treatment significantly increased neuroinflammatory markers and decreased memory functions in a dose dependent manner showing optimum effects at the dose of 3 mg/kg.

Hybridization of Curcumin Analogues with Cinnamic Acid Derivatives as Multi-Target Agents Against Alzheimer's Disease Targets

The synthesis of the new hybrids followed a hybridization with the aid of hydroxy-benzotriazole (HOBT) and 1-Ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDCI.HCL) in dry DMF or thionyl chloride between curcumin analogues and cinnamic acid derivatives. IR, 1H-NMR, 13C-NMR, LC/MS ESI+, and elemental analysis were used for the confirmation of the structures of the novel hybrids. The lipophilicity values of compounds were calculated theoretically and experimentally via the reversed chromatography method as RM values. The novel derivatives were studied through in vitro experiments for their activity as antioxidant agents and as inhibitors of lipoxygenase, cyclooxygenase-2, and acetyl-cholinesterase. All the compounds showed satisfying anti-lipid peroxidation activity of linoleic acid induced by 2,2'-azobis(2-amidinopropane) hydrochloride (AAPH). Hybrid 3e was the most significant pleiotropic derivative, followed by 3a. According to the predicted results, all hybrids could be easily transported, diffused, and absorbed through the blood-brain barrier (BBB). They presented good oral bioavailability and very high absorption with the exception of 3h. No inhibition for CYP1A2, CYP2C9, CYP2C19, CYP2D6, and CYP3A4 was noticed. According to the Ames test, all the hybrids induced mutagenicity with the exception of 3d. Efforts were conducted a) to correlate the in vitro results with the most important physicochemical properties of the structural components of the molecules and b) to clarify the correlation of actions among them to propose a possible mechanism of action. Docking studies were performed on soybean lipoxygenase (LOX) and showed hydrophobic interactions with amino acids. Docking studies on acetylcholinesterase (AChE) exhibited: (a) hydrophobic interactions with TRP281, LEU282, TYR332, PHE333, and TYR336 and (b) π-stacking interactions with TYR336.

A comprehensive review of monoamine oxidase inhibitors as Anti-Alzheimer's disease agents: A review

Monoamine oxidases (MAO-A and MAO-B) are mammalian flavoenzyme, which catalyze the oxidative deamination of several neurotransmitters like norepinephrine, dopamine, tyramine, serotonin, and some other amines. The oxidative deamination produces several harmful side products like ammonia, peroxides, and aldehydes during the biochemical reaction. The concentration of biochemical neurotransmitter alteration in the brain by MAO is directly related with several neurological disorders like Alzheimer's disease and Parkinson's disease (PD). Activated MAO also contributes to the amyloid beta (Aβ) aggregation by two successive cleft β-secretase and γ-secretase of amyloid precursor protein (APP). Additionally, activated MAO is also involved in aggregation of neurofibrillary tangles and cognitive destruction through the cholinergic neuronal damage and disorder of the cholinergic system. MAO inhibition has general anti-Alzheimer's disease effect as a consequence of oxidative stress reduction prompted by MAO enzymes. In this review, we outlined and addressed recent understanding on MAO enzymes such as their structure, physiological function, catalytic mechanism, and possible therapeutic goals in AD. In addition, it also highlights the current development and discovery of potential MAO inhibitors (MAOIs) from various chemical scaffolds.

Effect of Andrographis paniculata leaves extract on neurobehavioral and biochemical indices in scopolamine-induced amnesic rats

Andrographis paniculata is a medicinal herb that is used to treat various disease conditions due to its pharmacological properties. Thus, this study sought to assess the effect of A. paniculata extract on neurobehavioral and some biochemical parameters in scopolamine-induced amnesic rats. Thirty-five male rats were divided into seven groups and treated with aqueous extract of A. paniculata (50 and 500 mg/kg) and donepezil (5 mg/kg) for 14 days before administration of scopolamine. Behavioral studies (Morris water maze and Y-maze) were carried out to evaluate cognitive dysfunction in scopolamine-induced rats. Biochemical assays such as cholinesterases (AChE and BChE), monoamine oxidase (MAO), and purinergic activities were determined. Results revealed the presence of orientin, quercetin, caffeic acid, apigenin, and gallic acid in A. paniculata. Also, findings from this study showed that aqueous extract of A. paniculata had a modulatory effect on scopolamine-induced cognitive impairment and could be used in the management of memory loss. PRACTICAL APPLICATIONS: Aqueous extract of A. paniculata characterized revealed the presence of polyphenols which are antioxidants. The inhibitory activity possessed by A. paniculata on some enzymes linked to neurodegeneration could be due to the antioxidant activity. Given this, we recommend that results gotten from this study could be used to develop treatment therapy for neurodegeneration. However, in-depth studies should be carried out on the toxic effect of A. paniculata to ascertain a safe dose for treatment.

The novel GLP-1/GIP analogue DA5-CH reduces tau phosphorylation and normalizes theta rhythm in the icv. STZ rat model of AD

INTRODUCTION

Alzheimer's disease (AD) is the most common progressive neurodegenerative disease for which there is no cure. Recent studies have shown a close link between type 2 diabetes and AD, which suggested that drugs for type 2 diabetes may be effective for AD. GLP-1 and GIP are incretin hormones that can ameliorate diabetes.

METHODS

In the present study, we tested the novel dual GLP-1/GIP receptor agonist DA5-CH in the icv. streptozotocin (STZ)-induced insulin desensitization model of AD in rats to explore the protective effects of DA5-CH.

RESULTS

The results show that DA5-CH could reverse the STZ-induced working memory impairments in a Y-maze tests, and spatial memory impairments in the water maze task, and decrease the levels of phosphorylated tauS396 protein in the hippocampus. In EEG recordings, STZ treatment diminished the power of the theta band frequency. DA5-CH was able to increase the energy of theta band activity in the hippocampal CA1 region. The drug also increased the expression of synapse-related proteins in the hippocampus. After DA5-CH treatment, mitochondrial stress was alleviated as shown by the improved ratio of Bax/Bcl-2 in the hippocampus. Growth factor signaling was also normalized as shown by the increased level of the transcription factor P-CREBS133 . In addition, we were able to show that DA5-CH can cross the blood-brain barrier at an increased rate compared with other dual GLP-1/GIP or single GLP-1 receptor agonists.

CONCLUSION

Therefore, our results demonstrate that DA5-CH has neuroprotective effects in the STZ-induced animal model and that DA5-CH has potential to treat neurodegenerative disorders such as AD.

Phosphoinositide 3-kinase inhibitor AS605240 ameliorates streptozotocin-induced Alzheimer's disease like sporadic dementia in experimental rats

The quest for chemical entities able to curb the action of the phosphoinositide 3-kinase, (PI3K)/protein kinase B (AKT) signaling pathways is evolving as a potential therapeutic strategy for the treatment and/or prevention of neurodegenerative disorders including Alzheimer's disease (AD). In this study, the effects of a PI3K inhibitor, AS605240 on cognitive dysfunction and antioxidative defense parameters against intra-cerebroventricular-streptozotocin (ICV-STZ)-induced rat model of sporadic AD was evaluated. ICV administration of a single dose of STZ (3 mg/kg) was performed to induce behavioral and biochemical changes in rats using the stereotaxic technique. Animals were administered with varying doses of AS605240 (5, 10 and 15 mg/kg) orally, 1 h before ICV-STZ on day 1 and continued once daily for four weeks. The behavioral parameters (passive avoidance and Morris water maze), antioxidative defense parameters, amyloid-beta (Aβ) protein expression by Western blotting and immunostaining technique were estimated in brain tissue. AS605240 dose-dependently and significantly (p < 0.05 and p < 0.01 and p < 0.001) improved ICV-STZ-induced cognitive impairment and attenuated the altered antioxidative related parameters including superoxide dismutase, lipid peroxidation, glutathione and nitrite levels. Further, the increased Aβ protein expression levels in brain tissue were markedly restored with AS605240 treatment. In conclusion, our study demonstrated that AS605240 exhibited immense potential in attenuating STZ-induced sporadic AD features in rats and may be developed as a therapeutic agent in the treatment and management of sporadic AD.

Oral treatment with royal jelly improves memory and presents neuroprotective effects on icv-STZ rat model of sporadic Alzheimer's disease

Alzheimer's disease (AD) is a neurodegenerative disorder characterized by progressive decline in cognitive function. Intracerebroventricular injection of streptozotocin (icv-STZ) has been used as an experimental model of Sporadic AD (SAD) in rodents and represents a promising tool for etiopathogenic analysis and evaluation of new therapeutic proposals for AD. The icv-STZ model shows many aspects of SAD abnormalities, resulting in decreased brain glucose and energy metabolism, cognitive impairment, oxidative stress, neuronal loss, and amyloid angiopathy. Royal jelly (RJ), a substance produced by worker honeybees of the Apis mellifera species, has been popularly used for more than 30 years in areas related to health eating and natural medicine. Researches indicate that RJ has a several pharmacological activities, including neuroprotective and improvement of cognitive function. The objective of this study was to investigate the effects of oral treatment with royal jelly during 2 weeks in Wistar rats submitted to icv-STZ on a working memory and neuroprotection, as evaluated by neurogenesis, neurodegeneration and oxidative stress. In this study, icv-STZ injection induced deleterious effects in the hippocampus, associated with cognitive impairments, and developed marked neurodegeneration, besides the reduction of neurogenesis and increased oxidative stress. On the other hand, RJ long-term oral administration induced beneficial effects in animals injured by icv-STZ injection, increasing retention time for working spatial memory, reducing neurodegeneration and oxidative stress level and increasing the proliferation of new neurons in the hippocampus. Thus, RJ promotes beneficial effects on cognitive functions and exhibits a neuroprotective action in the STZ experimental model of SAD.

Multiple Biological Effects of an Iridoid Glucoside, Catalpol and Its Underlying Molecular Mechanisms

Catalpol, an iridoid glucoside, is widely distributed in many plant families and is primarily obtained from the root of Rehmanniaglutinosa Libosch. Rehmanniaglutinosa is a plant very commonly used in Chinese and Korean traditional medicine for various disorders, including diabetes mellitus, neuronal disorders, and inflammation. Catalpol has been studied extensively for its biological properties both in vitro and in vivo. This review aims to appraise the biological effects of catalpol and their underlying mechanisms. An extensive literature search was conducted using the keyword "Catalpol" in the public domains of Google scholar, PubMed, and Scifinder. Catalpol exhibits anti-diabetic, cardiovascular protective, neuroprotective, anticancer, hepatoprotective, anti-inflammatory, and anti-oxidant effects in experimental studies. Anti-inflammatory and antioxidant properties are mostly related for its biological effect. However, some specific mechanisms are also elucidated. Elevated serotonin and BDNF level by catalpol significantly protect against depression and neurodegeneration. Catalpol demonstrated an increased mitochondrial biogenesis and activation of PI3K/Akt pathway for insulin sensitizing effect. Further, its cardiovascular protective effect was linked to PI3K/Akt, apelin/APJ and Jak-Stat pathway. Catalpol produced a significant reduction in cell proliferation and an increase in apoptosis in different cancer conditions. Overall, catalpol demonstrated multiple biological effects due to its numerous mechanisms including anti-inflammatory and antioxidant effects.

Everolimus, a mammalian target of rapamycin inhibitor, ameliorated streptozotocin-induced learning and memory deficits via neurochemical alterations in male rats

Everolimus (EVR), as a rapamycin analog, is a selective inhibitor of the mammalian target of rapamycin (mTOR) kinase and its associated signaling pathway. mTOR is a serine/threonine protein kinase and its hyperactivity is involved in the pathophysiology of Alzheimer's disease (AD) and associated cognitive deficits. The present study evaluated the impact of EVR, on cognitive functions, hippocampal cell loss, and neurochemical parameters in the intracerebroventricular streptozotocin (icv-STZ) model of AD rats. EVR (1 and 5 mg/kg) was administered for 21 days following the single administration of STZ (3 mg/kg, icv) or for 7 days on days 21-28 post-STZ injection after establishment of cognitive dysfunction. Cognitive deficits (passive avoidance and spatial memory), oxidative stress parameters, acetylcholinesterase (AChE) activity, and percentage of cell loss were evaluated in the hippocampus. Chronic administration (1 and 5 mg/kg for 21 days from the day of surgery and icv-STZ infusion) or acute injection (5 mg/kg for 7 days after establishment of cognitive impairment) of EVR significantly attenuated cognitive dysfunction, neuronal loss, oxidative stress and AChE activity in the hippocampus of STZ-AD rats. In conclusion, our study showed that EVR could prevent or improve deteriorations in behavioral, biochemical and histopathological features of the icv-STZ rat model of AD. Therefore, inhibition of the hyperactivated mTOR may be an important therapeutic target for AD.

Targeting central β2 receptors ameliorates streptozotocin-induced neuroinflammation via inhibition of glycogen synthase kinase3 pathway in mice

Alzheimer's disease (AD) is portrayed by progressive cognitive decline and pathological deposition of amyloid plaques as well as neurofibrillary tangles. Most of AD cases are sporadic, resulting from overlap of various environmental and genetic factors. Intra-cerebroventricular injection of streptozotocin (STZ) leads to insulin resistance brain state accompanied by memory decline, oxidative stress, and neuro-degeneration which mimic the pathologies associated with sporadic Alzheimer's disease (SAD). In the current study, protective effects of formoterol in STZ-induced SAD were studied. Formoterol-induced improvement in cognition was confirmed using Morris water maze and Y maze together with histopathological evidences. Moreover, prominent declines in oxidative stress, neuro-inflammation, and apoptotic parameters were recorded upon its injection in STZ-induced SAD mouse model. This was manifested by the decrement of malondialdehyde, hydrogen peroxide, interleukin-1β, interleukin-6, tumor necrosis factor-α, and caspase-3levels contrary to reduced glutathione and interleukin-10 increments. Formoterol also reversed STZ-induced alteration in acetylcholine and glutamate levels. Furthermore, it could be concluded that formoterol was capable of combating STZ-induced neuro-inflammation and retarding the development of the main pathological hallmarks of AD through glycogen synthase kinase-3 deactivation.

Inosine improves cognitive function and decreases aging-induced oxidative stress and neuroinflammation in aged female rats

In the present study, the effect of inosine was evaluated on learning and memory of 18 months old aged female rats. Inosine (50, 100 and 200 mg/kg; i.p.) was administered to separate groups of rats for 15 successive days. Donepezil (1 mg/kg; i.p.), an acetylcholinesterase inhibitor, was used as a standard drug. Behavioral models such as Morris water maze and elevated plus maze were used to evaluate the effect of drugs on learning and memory of rats. After behavioral studies, animals were killed and their brain was isolated and further processed for estimation of various biochemical parameters such as acetylcholinesterase activity, oxidative stress markers, proinflammatory marker and histological examinations. Inosine (100 and 200 mg/kg) significantly improved learning and memory of aged rats. Further, inosine significantly reduced lipid peroxidation and nitrite, and increased the levels of reduced glutathione and superoxide dismutase. However, no significant difference in AChEs activity was observed in inosine-treated rats as compared to aged control rats. TNF-α level was found to be ameliorated in aged rats by inosine. Histopathological evaluation showed that inosine-treated aged rats have less number of pyknotic neurons in hippocampal CA1 region as compared to aged control rats. In conclusion, inosine significantly improved learning and memory of aged female rats possibly through its antioxidant as well as anti-inflammatory effect and improvement of neuronal survival in the hippocampal CA1 region. However, additional studies are required to further explore the downstream signaling pathways involved in the neuroprotective effect of inosine in aged animals.

Protective effects of gingerol on streptozotocin-induced sporadic Alzheimer's disease: emphasis on inhibition of β-amyloid, COX-2, alpha-, beta - secretases and APH1a

Gingerol is a major dietary compound that occurs in several plants belonging to the Zingiberaceae family. In the current study, the protective effect of gingerol on STZ-induced sporadic Alzheimer's disease (SAD) was determined. Gingerol was isolated from the seeds of Aframomum melegueta K. Schum and tested at doses of 10 and 20 mg/kgbwt for its possible effect on the SAD model in mice, using celecoxib (30 mg/kg bwt) as a reference standard. The curative effects of gingerol were assessed through measurement of β-amyloid (Aβ-42), α-, β- secretases, APH1a and COX-2 levels. In addition, improvement in the cognitive deficit in mice after treatment was confirmed using the water maze and Y-maze with intra-maze cues. Gingerol improved the cognitive and behavioral impairment and AD-like pathology in streptozotocin model mice. These beneficial effects occurred with an increase in α-secretase activity and a decrease in cerebral Aβ-42, β- secretase, APH1a activity and COX-2-linked neuro-inflammation.

Protective effect of valproic acid in streptozotocin-induced sporadic Alzheimer's disease mouse model: possible involvement of the cholinergic system

Sporadic Alzheimer's disease (SAD) is a slowly progressive neurological disorder that is the most common form of dementia. Cholinergic system dysfunction and amyloid beta formation are the two main underlying pathological mechanisms for the disease development. In recent studies, insulin receptor desensitization and disturbances in the downstream effects of insulin receptor signaling were observed in the brains of Alzheimer's patients. Currently, intracereberoventricular (ICV) injection of streptozotocin (STZ) is found to induce behavioral, neurochemical, and structural alterations in animals resembling those found in SAD patients. Valproic acid (VPA), a histone deacetylase inhibitor (HDACi), was recently shown to regulate the transcription of several genes in both in vivo and in vitro models of Alzheimer's disease. The aim of the current study is to investigate the potential effect of different doses of valproic acid, in an ICV-STZ-induced animal model of SAD. Streptozotocin-injected mice showed cognitive and spatial memory dysfunction in the Y-maze, object recognition test, and Morris water maze (MWM) neurobehavioral tests. The mice also exhibited a decrease in acetylcholine (ACh) and neprilysin (NEP) levels accompanied by an increase in acetylcholinesterase (AChE) activity. For the first time to our knowledge, our findings have shown that VPA is capable of restoring ACh levels in ICV-STZ-injected mice, as well as normalizing both NEP levels and AChE activity. Via this mechanism, an enhancement of cognitive functions is observed. Thus, VPA is suggested to be a promising therapeutic approach against SAD.

Characterization of Cerebral Damage in a Monkey Model of Alzheimer's Disease Induced by Intracerebroventricular Injection of Streptozotocin

In line with recent findings showing Alzheimer's disease (AD) as an insulin-resistant brain state, a non-transgenic animal model with intracerebroventricular streptozotocin (icv-STZ) administration has been proposed as a representative experimental model of AD. Although icv-STZ rodent models of AD have been increasingly researched, studies in non-human primate models are very limited. In this study, we aimed to characterize the cerebral damage caused by icv-STZ in non-human primates; to achieve this, three cynomolgus monkeys (Macaca fascicularis) were administered four dosages of STZ (2 mg/kg) dissolved in artificial cerebrospinal fluid and another three controls were injected with only artificial cerebrospinal fluid at the cerebellomedullary cistern. In vivo neuroimaging was performed with clinical 3.0 T MRI, followed by quantitative analysis with FSL for evaluation of structural changes of the brain. Immunohistochemistry was performed to evaluate cerebral histopathology. We showed that icv-STZ caused severe ventricular enlargement and parenchymal atrophy, accompanying amyloid-β deposition, hippocampal cell loss, tauopathy, ependymal cell loss, astrogliosis, and microglial activation, which are observed in human aged or AD brain. The findings suggest that the icv-STZ monkey model would be a valuable resource to study the mechanisms and consequences of a variety of cerebral pathologies including major pathological hallmarks of AD. Furthermore, the study of icv-STZ monkeys could contribute to the development of treatments for age- or AD-associated cerebral changes.

Warburg effect linked to cognitive-executive deficits in FMR1 premutation

A 55-200 CGG repeat expansion in the 5'-UTR of the fragile X mental retardation 1 (FMR1) gene is known as a premutation. Some carriers are affected by the neurodegenerative disorder fragile X-associated tremor/ataxia syndrome (FXTAS), primary ovarian insufficiency, and neurobehavioral impairments. Based on the mitochondrial dysfunction observed in fibroblasts and brain samples from carriers, as well as in neurons and brains from a mouse model of the premutation, we evaluated the presence of the Warburg effect in peripheral blood mononuclear cells (PBMCs) from 30 premutation carriers with either a rebalance of the metabolism [increasing glycolysis while decreasing oxidative phosphorylation (oxphos)] or a metabolic amplification (increasing glycolysis while maintaining/increasing oxphos). Deficits in oxphos-more pronounced in FXTAS-affected subjects-were accompanied by a shift toward glycolysis, suggesting increased glycolysis despite aerobic conditions. Differential proteomics extended these findings, unveiling a decreased antioxidant response, translation, and disrupted extracellular matrix and cytoskeleton organization with activation of prosenescence pathways. Lower bioenergetics segregated with increased incidence of low executive function, tremors, below-average IQ, and FXTAS. The combination of functional and proteomic data unveiled new mechanisms related to energy production in the premutation, showing the potential of being applicable to other psychiatric disorders to identify endophenotype-specific responses relevant to neurobiology.-Napoli, E., Song, G., Schneider, A., Hagerman, R., Eldeeb, M. A. A. A., Azarang, A., Tassone, F., Giulivi, C. Warburg effect linked to cognitive-executive deficits in FMR1 premutation.

Role of cox-2 mediated neuroinflammation on the neurodegeneration and cognitive impairments in colchicine induced rat model of Alzheimer's Disease

The neurodegeneration in colchicine induced AD (cAD) rats is linked with neuroinflammation. The inducible cox-2 present in the brain may participate in the neuroinflammatory process related to progressive neurodegeneration in cAD rats. The aim of this study is to investigate the role of cox-2 in the neurodegeneration and cognitive impairments in cAD rats. The parameters of memory (working and reference memory), inflammatory markers [IL-1β, TNF-α, prostaglandin E2 (PGE2), cox-2 level] and histopathology of hippocampus were measured after 21-day of i.c.v. colchicine injection in rats and compared with that of control and sham operated rats. These parameters were also measured in these 3 different groups of rats after p.o. administration of 3 different doses of etoricoxib, a cox 2 inhibitor. The impairments of working and reference memory were associated with neuroinflammation and neurodegeneration in the hippocampus and increased cox-2 and PGE2 levels in hippocampus in cAD. Administration of etoricoxib in cAD rats resulted in recovery of memory impairments, neurodegeneration and neuroinflammation in hippocampus and inhibition of cox-2 and PGE2 levels in hippocampus. It appears from the results that activation of cox-2 in cAD is related to neuroinflammation involved in neurodegeneration. Colchicine induced initial neurodegeneration may trigger cascade of events for a progressive neurodegeneration where cox-2 activation plays a critical role. Moreover, this cox-2 mediated neurodegeneration is related to impairments of memory parameters. Thus, the present study showed that the impairments of memory and neurodegeneration in the hippocampus of cAD in 21-day study are mediated by cox-2 induced neuroinflammation.

Streptozotocin Intracerebroventricular-Induced Neurotoxicity and Brain Insulin Resistance: a Therapeutic Intervention for Treatment of Sporadic Alzheimer's Disease (sAD)-Like Pathology

Alzheimer's disease (AD) is a neurodegenerative disorder that is remarkably characterized by pathological hallmarks which include amyloid plaques, neurofibrillary tangles, neuronal loss, and progressive cognitive loss. Several well-known genetic mutations which are being used for the development of a transgenic model of AD lead to an early onset familial AD (fAD)-like condition. However, these settings are only reasons for a small percentage of the total AD cases. The large majorities of AD cases are considered as a sporadic in origin and are less influenced by a single mutation of a gene. The etiology of sporadic Alzheimer's disease (sAD) remains unclear, but numerous risk factors have been identified that increase the chance of developing AD. Among these risk factors are insulin desensitization/resistance state, oxidative stress, neuroinflammation, synapse dysfunction, tau hyperphosphorylation, and deposition of Aβ in the brain. Subsequently, these risk factors lead to development of sAD. However, the underlying molecular mechanism is not so clear. Streptozotocin (STZ) produces similar characteristic pathology of sAD such as altered glucose metabolism, insulin signaling, synaptic dysfunction, protein kinases such as protein kinase B/C, glycogen synthase-3β (GSK-3β) activation, tau hyperphosphorylation, Aβ deposition, and neuronal apoptosis. Further, STZ also leads to inhibition of Akt/PKB, insulin receptor (IR) signaling molecule, and insulin resistance in brain. These alterations mediated by STZ can be used to explore the underlying molecular and pathophysiological mechanism of AD (especially sAD) and their therapeutic intervention for drug development against AD pathology.

BDNF and COX-2 participate in anti-depressive mechanisms of catalpol in rats undergoing chronic unpredictable mild stress

Catalpol, a major compound in Rehmannia glutinosa with both medicinal and nutritional values, has been previously confirmed to shorten the duration of immobility in mice exposed to tail suspension and forced swimming tests. This study attempted to examine the anti-depressive mechanisms of catalpol in rats undergoing chronic unpredictable mild stress (CUMS) by involving brain-derived neurotrophic factor (BDNF) and cyclooxygenase-2 (COX-2). CUMS-exposed rats were given catalpol daily (5, 10, and 20mg/kg, ig) or a reference drug, fluoxetine hydrochloride (FH, 10mg/kg, ig), at 5 weeks after starting the CUMS procedure. Sucrose preference test was performed to observe depression-like behavior, and serum and brain tissues were used for neurochemical and fluorescent quantitative reverse transcription PCR analysis. CUMS induced depression-like behavior, whereas catalpol and FH administration attenuated this symptom. Moreover, CUMS caused excessively elevated levels of serum corticosterone, an index of hypothalamic-pituitary-adrenal (HPA) axis hyperactivation, in a manner attenuated by catalpol and FH administration. Catalpol administration also further decreased BDNF activities, downregulated the mRNA expression of BDNF and tropomyosin-related kinase B (TrkB), and reversed the excessive elevation in the activities and mRNA expression levels of COX-2 and prostaglandin E2 (PGE2) in the hippocampus and frontal cortex of rats undergoing CUMS. Results indicate that catalpol can ameliorate CUMS-induced depression-like behavior, and suggest its mechanisms may partially be ascribed to restoring HPA axis dysfunctions, upregulating BDNF expression and its cognate receptor TrkB, and downregulating COX-2 expression, thereby reducing PGE2 levels in the brain.

Rodent models of neuroinflammation for Alzheimer's disease

Alzheimer's disease remains incurable, and the failures of current disease-modifying strategies for Alzheimer's disease could be attributed to a lack of in vivo models that recapitulate the underlying etiology of late-onset Alzheimer's disease. The etiology of late-onset Alzheimer's disease is not based on mutations related to amyloid-β (Aβ) or tau production which are currently the basis of in vivo models of Alzheimer's disease. It has recently been suggested that mechanisms like chronic neuroinflammation may occur prior to amyloid-β and tau pathologies in late-onset Alzheimer's disease. The aim of this study is to analyze the characteristics of rodent models of neuroinflammation in late-onset Alzheimer's disease. Our search criteria were based on characteristics of an idealistic disease model that should recapitulate causes, symptoms, and lesions in a chronological order similar to the actual disease. Therefore, a model based on the inflammation hypothesis of late-onset Alzheimer's disease should include the following features: (i) primary chronic neuroinflammation, (ii) manifestations of memory and cognitive impairment, and (iii) late development of tau and Aβ pathologies. The following models fit the pre-defined criteria: lipopolysaccharide- and PolyI:C-induced models of immune challenge; streptozotocin-, okadaic acid-, and colchicine neurotoxin-induced neuroinflammation models, as well as interleukin-1β, anti-nerve growth factor and p25 transgenic models. Among these models, streptozotocin, PolyI:C-induced, and p25 neuroinflammation models are compatible with the inflammation hypothesis of Alzheimer's disease.

Protection of streptozotocin induced insulin receptor dysfunction, neuroinflammation and amyloidogenesis in astrocytes by insulin

Impaired insulin signaling, amyloid pathology and neuroinflammation are closely associated with neurodegenerative disorder like Alzheimer's disease (AD). Our earlier studies showed that intracerebroventricular streptozotocin (STZ) induces insulin receptor (IR) signaling defect in the hippocampus, which is associated with memory impairment in rats. Astrocytes are the most abundant cells in the brain and play a major role in neuroinflammation. However, involvement of astrocytes in STZ induced IR dysfunction has not received much attention. Therefore, the present study was planned to explore the effect of STZ on IR signaling, proinflammatory markers and amyloidogenesis in rat astrocytoma cell line, (C6). STZ (100 μM) treatment in astrocytes (n = 3) for 24 h, resulted significant decrease in IR mRNA and protein expression, phosphorylation of IRS-1, Akt, GSK-3α and GSK-3β (p < 0.01). Further STZ induced amyloidogenic protein expression as evidenced by the increase in APP, BACE-1 and Aβ1-42 expression (p < 0.05) in astrocytes. STZ also significantly induced astrocytes activation as evidenced by increased expression of GFAP and p-P38 MAPK (p < 0.05). STZ treatment caused enhanced translocation of p65 NF-kB, triggered over expression of TNF-α, IL-1β, COX-2, oxidative/nitrosative stress and caspase activation (p < 0.05) in astrocytes. Insulin (25-100 nM) pretreatment (n = 3) significantly prevented changes in IR signaling, amyloidogenic protein expression and levels of proinflammatory markers (p < 0.05) in STZ treated astroglial cells. In the present study, the protective effect of insulin suggests that, IR dysfunction along with amyloidogenesis and neuroinflammation may have played a major role in STZ induced toxicity in astrocytes which are relevant to AD pathology.

Monoamine oxidase inhibitors: promising therapeutic agents for Alzheimer's disease (Review)

Activated monoamine oxidase (MAO) has a critical role in the pathogenesis of Alzheimer's disease (AD), including the formation of amyloid plaques from amyloid β peptide (Aβ) production and accumulation, formation of neurofibrillary tangles, and cognitive impairment via the destruction of cholinergic neurons and disorder of the cholinergic system. Several studies have indicated that MAO inhibitors improve cognitive deficits and reverse Aβ pathology by modulating proteolytic cleavage of amyloid precursor protein and decreasing Aβ protein fragments. Thus, MAO inhibitors may be considered as promising therapeutic agents for AD.

Geniposide ameliorates learning memory deficits, reduces tau phosphorylation and decreases apoptosis via GSK3β pathway in streptozotocin-induced alzheimer rat model

Intracerebral-ventricular (ICV) injection of streptozotocin (STZ) induces an insulin-resistant brain state that may underlie the neural pathogenesis of sporadic Alzheimer disease (AD). Our previous work showed that prior ICV treatment of glucagon-like peptide-1 (GLP-1) could prevent STZ-induced learning memory impairment and tau hyperphosphorylation in the rat brain. The Chinese herbal medicine geniposide is known to relieve symptoms of type 2 diabetes. Because geniposide is thought to act as a GLP-1 receptor agonist, we investigated the potential therapeutic effect of geniposide on STZ-induced AD model in rats. Our result showed that a single injection of geniposide (50 μM, 10 μL) to the lateral ventricle prevented STZ-induced spatial learning deficit by about 40% and reduced tau phosphorylation by about 30% with Morris water maze test and quantitative immunohistochemical analysis, respectively. It has been known that tau protein can be phosphorylated by glycogen synthase kinase-3 (GSK3) and STZ can increase the activity of GSK3β. Our result with Western blot analysis showed that central administration of geniposide resulted in an elevated expression of GSK3β(pS-9) but suppressed GSK3β(pY-216) indicating that geniposide reduced STZ-induced GSK3β hyperactivity. In addition, ultrastructure analysis showed that geniposide averted STZ-induced neural pathology, including paired helical filament (PHF)-like structures, accumulation of vesicles in synaptic terminal, abnormalities of endoplasmic reticulum (ER) and early stage of apoptosis. In summary, our study suggests that the water soluble and orally active monomer of Chinese herbal medicine geniposide may serve as a novel therapeutic agent for the treatment of sporadic AD.

Pharmacogenomics of Alzheimer's disease: novel therapeutic strategies for drug development

Alzheimer's disease (AD) is a major problem of health and disability, with a relevant economic impact on our society. Despite important advances in pathogenesis, diagnosis, and treatment, its primary causes still remain elusive, accurate biomarkers are not well characterized, and the available pharmacological treatments are not cost-effective. As a complex disorder, AD is a polygenic and multifactorial clinical entity in which hundreds of defective genes distributed across the human genome may contribute to its pathogenesis. Diverse environmental factors, cerebrovascular dysfunction, and epigenetic phenomena, together with structural and functional genomic dysfunctions, lead to amyloid deposition, neurofibrillary tangle formation, and premature neuronal death, the major neuropathological hallmarks of AD. Future perspectives for the global management of AD predict that genomics and proteomics may help in the search for reliable biomarkers. In practical terms, the therapeutic response to conventional drugs (cholinesterase inhibitors, multifactorial strategies) is genotype-specific. Genomic factors potentially involved in AD pharmacogenomics include at least five categories of gene clusters: (1) genes associated with disease pathogenesis; (2) genes associated with the mechanism of action of drugs; (3) genes associated with drug metabolism (phase I and II reactions); (4) genes associated with drug transporters; and (5) pleiotropic genes involved in multifaceted cascades and metabolic reactions. The implementation of pharmacogenomic strategies will contribute to optimize drug development and therapeutics in AD and related disorders.

Effects of naproxen on immune responses in a colchicine-induced rat model of Alzheimer's disease

BACKGROUND

The components of the immune system have been indicated to be linked with the neurotoxicity in Alzheimer's disease (AD). The participation of the immune system in the neurodegeneration in a rat model of colchicine-induced AD has not been explored.

METHODS

In the present study, hippocampal neurodegeneration along with reactive oxygen species (ROS), nitrite and TNF-α in the hippocampus and some systemic immune responses were measured after 15 and 21 days of intracerebroventricular colchicine injection in rats and again after oral administration of different doses of the anti-inflammatory drug naproxen in AD rats.

RESULTS

Chromatolysis and amyloid plaques were found along with higher ROS, nitrite and TNF-α levels in the hippocampus of colchicine-induced AD rats, and these changes were prevented by naproxen in a dose-dependent manner. Alterations in immunological parameters [increased phagocytic activity of white blood cells and splenic polymorphonuclear cells (PMN), increased cytotoxicity and decreased leucocyte adhesive inhibition index (LAI) of splenic mononuclear cells (MNC)] were also observed in colchicine-injected rats, which showed a dose-dependent recovery after oral administration of naproxen in AD rats. The number of plaques, chromatolysis of Nissl granules, TNF-α, nitrite and ROS levels in the hippocampus, phagocytic activity of splenic PMN and LAI of splenic MNC in AD rats showed greater changes in the 21- than in the 15-day study, and the recovery of these parameters after administration of naproxen differed between the two study durations.

CONCLUSION

The present study shows that colchicine-induced neurodegeneration is time dependent and mediated by cyclooxygenase-induced neuroinflammation, which is reflected in the systemic immunological responses.

A non-transgenic mouse model (icv-STZ mouse) of Alzheimer's disease: similarities to and differences from the transgenic model (3xTg-AD mouse)

Alzheimer's disease (AD) can be divided into sporadic AD (SAD) and familial AD (FAD). Most AD cases are sporadic and result from multiple etiologic factors, including environmental, genetic, and metabolic factors, whereas FAD is caused by mutations in the presenilins or amyloid-β (Aβ) precursor protein (APP) genes. A commonly used animal model for AD is the 3xTg-AD transgenic mouse model, which harbors mutated presenilin 1, APP, and tau genes and thus represents a model of FAD. There is an unmet need in the field to characterize animal models representing different AD mechanisms, so that potential drugs for SAD can be evaluated preclinically in these animal models. A mouse model generated by intracerebroventricular (icv) administration of streptozocin (STZ), the icv-STZ mouse, shows many aspects of SAD. In this study, we compared the non-cognitive and cognitive behaviors as well as biochemical and immunohistochemical alterations between the icv-STZ mouse and the 3xTg-AD mouse. We found that both mouse models showed increased exploratory activity as well as impaired learning and spatial memory. Both models also demonstrated neuroinflammation, altered synaptic proteins and insulin/IGF-1 (insulin-like growth factor-1) signaling, and increased hyperphosphorylated tau in the brain. The most prominent brain abnormality in the icv-STZ mouse was neuroinflammation, and in the 3xTg-AD mouse it was elevation of hyperphosphorylated tau. These observations demonstrate the behavioral and neuropathological similarities and differences between the icv-STZ mouse and the 3xTg-AD mouse models and will help guide future studies using these two mouse models for the development of AD drugs.

In vivo cross-sectional characterization of cerebral alterations induced by intracerebroventricular administration of streptozotocin

Cerebral aging is often associated with the occurrence of neurodegenerative diseases leading to dementia. Animal models are critical to elucidate mechanisms associated to dementia and to evaluate neuroprotective drugs. Rats that received intracerebroventricular injection of streptozotocin (icv-STZ) have been reported as a model of dementia. In these animals, this drug induces oxidative stress and brain glucose metabolism impairments associated to insulin signal transduction failure. These mechanisms are reported to be involved in the pathogenesis of Alzheimer's disease and other dementia. Icv-STZ rats also display memory impairments. However, little is known about the precise location of the lesions induced by STZ administration. In this context, the present study characterized the cerebral lesions induced by two-doses of icv-STZ by using high-field magnetic resonance imaging to easily and longitudinally detect cerebral abnormalities and by using immunohistochemistry to evaluate neuronal loss and neuroinflammation (astrocytosis and microgliosis). We showed that, at high doses, icv-STZ induces severe and acute neurodegenerative lesions in the septum and corpus callosum. The lesions are associated with an inflammation process. They are less severe and more progressive at low doses. The relevance of high and low doses of icv-STZ to mimic dementia and evaluate new drugs is discussed in the final part of this article.