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

Effect of the MAGL/FAAH Dual Inhibitor JZL-195 on Streptozotocin-Induced Alzheimer's Disease-like Sporadic Dementia in Mice with an Emphasis on Aβ, HSP-70, Neuroinflammation, and Oxidative Stress

Alzheimer's disease is identified by pathological hallmarks such as intracellular neurofibrillary tangles (NFTs) and extracellular amyloid β plaques. Several hypotheses exist to define the neurodegeneration including microglial activation associated with neuroinflammatory processes. Recently, pharmacological inhibition of endocannabinoid (eCB)-degrading enzymes, fatty acid amide hydrolase (FAAH) and monoacylglycerol lipase (MAGL), is being investigated to modulate the pathology of Alzheimer's disease. While MAGL inhibitors upregulate 2-acyl glycerol (2-AG) levels and reduce neuroinflammation, FAAH inhibitors elevate anandamide (AEA) levels and prevent the degradation of HSP-70, thereby preventing the phosphorylation of tau protein and formation of NFTs in neural cells. We investigated the possible neuroprotective potential of the dual MAGL/FAAH inhibitor JZL-195 (20 mg/kg) against ICV-STZ-induced sporadic Alzheimer's disease (SAD) in Swiss albino mice using donepezil (5 mg/kg) as the standard. The protective effects of JZL-195 were observed by the reversal of altered levels of Aβ_1-42, HSP-70, neuroinflammatory cytokines, and oxidative stress markers. However, JZL-195 expressed no cognitive improvement when assessed by spontaneous alternation behavior and Morris water maze tests and no effects on the AChE enzyme level in the hippocampal tissues of mice. Therefore, the findings of the present study indicate that although JZL-195 exhibited no improvement in cognitive deficits associated with sporadic Alzheimer's disease, it displayed significant reversal of the biochemical anomalies, thereby suggesting its therapeutic potential against the sporadic Alzheimer's disease model.

Luteolin alleviates cognitive impairment in Alzheimer's disease mouse model via inhibiting endoplasmic reticulum stress-dependent neuroinflammation

Luteolin is a flavonoid in a variety of fruits, vegetables, and herbs, which has shown anti-inflammatory, antioxidant, and anti-cancer neuroprotective activities. In this study, we investigated the potential beneficial effects of luteolin on memory deficits and neuroinflammation in a triple-transgenic mouse model of Alzheimer's disease (AD) (3 × Tg-AD). The mice were treated with luteolin (20, 40 mg · kg^-1 · d^-1, ip) for 3 weeks. We showed that luteolin treatment dose-dependently improved spatial learning, ameliorated memory deficits in 3 × Tg-AD mice, accompanied by inhibiting astrocyte overactivation (GFAP) and neuroinflammation (TNF-α, IL-1β, IL-6, NO, COX-2, and iNOS protein), and decreasing the expression of endoplasmic reticulum (ER) stress markers GRP78 and IRE1α in brain tissues. In rat C6 glioma cells, treatment with luteolin (1, 10 µM) dose-dependently inhibited LPS-induced cell proliferation, excessive release of inflammatory cytokines, and increase of ER stress marker GRP78. In conclusion, luteolin is an effective agent in the treatment of learning and memory deficits in 3 × Tg-AD mice, which may be attributable to the inhibition of ER stress in astrocytes and subsequent neuroinflammation. These results provide the experimental basis for further research and development of luteolin as a therapeutic agent for AD.

A Brain-Targeted Approach to Ameliorate Memory Disorders in a Sporadic Alzheimer's Disease Mouse Model via Intranasal Luteolin-Loaded Nanobilosomes

Impaired memory and cognitive function are the main features of Alzheimer's disease (AD). Unfortunately, currently available treatments cannot cure or delay AD progression. Moreover, the blood-brain barrier hampers effective delivery of treatment to the brain. Therefore, we aimed to evaluate the impact of intranasally delivered luteolin on AD using bile-salt-based nano-vesicles (bilosomes). Different bilosomes were prepared using 23-factorial design. The variables were defined by the concentration of surfactant, the molar ratio of cholesterol:phospholipid, and the concentration of bile salt. Results demonstrated optimized luteolin-loaded bilosomes with particle size (153.2 ± 0.98 nm), zeta potential (-42.8 ± 0.24 mV), entrapment efficiency% (70.4 ± 0.77%), and % drug released after 8 h (80.0 ± 1.10%). In vivo experiments were conducted on an AD mouse model via intracerebroventricular injection of 3 mg/kg streptozotocin. We conducted behavioral, biochemical marker, histological, and immune histochemistry assays after administering a luteolin suspension or luteolin bilosomes (50 mg/kg) intranasally for 21 consecutive days. Luteolin bilosomes improved short-term and long-term spatial memory. They also exhibited antioxidant properties and reduced levels of proinflammatory mediators. They also suppressed both amyloid β aggregation and hyperphosphorylated Tau protein levels in the hippocampus. In conclusion, luteolin bilosomes are an effective, safe, and non-invasive approach with superior cognitive function capabilities compared to luteolin suspension.

Potential Roles of Glucagon-Like Peptide-1 and Its Analogues in Dementia Targeting Impaired Insulin Secretion and Neurodegeneration

Dementia is a chronic, irreversible condition marked by memory loss, cognitive decline, and mental instability. It is clinically related to various progressive neurological diseases, including Parkinson’s disease, Alzheimer’s disease, and Huntington’s. The primary cause of neurological disorders is insulin desensitization, demyelination, oxidative stress, and neuroinflammation accompanied by various aberrant proteins such as amyloid-β deposits, Lewy bodies accumulation, tau formation leading to neurofibrillary tangles. Impaired insulin signaling is directly associated with amyloid-β and α-synuclein deposition, as well as specific signaling cascades involved in neurodegenerative diseases. Insulin dysfunction may initiate various intracellular signaling cascades, including phosphoinositide 3-kinase (PI3K), c-Jun N-terminal kinases (JNK), and mitogen-activated protein kinase (MAPK). Neuronal death, inflammation, neuronal excitation, mitochondrial malfunction, and protein deposition are all influenced by insulin. Recent research has focused on GLP-1 receptor agonists as a potential therapeutic target. They increase glucose-dependent insulin secretion and are beneficial in neurodegenerative diseases by reducing oxidative stress and cytokine production. They reduce the deposition of abnormal proteins by crossing the blood-brain barrier. The purpose of this article is to discuss the role of insulin dysfunction in the pathogenesis of neurological diseases, specifically dementia. Additionally, we reviewed the therapeutic target (GLP-1) and its receptor activators as a possible treatment of dementia.

Exosomes derived from bone-marrow mesenchymal stem cells alleviate cognitive decline in AD-like mice by improving BDNF-related neuropathology

BACKGROUND

Alzheimer's disease (AD) is a neurodegenerative disease characterized by a progressive decline in cognitive ability. Exosomes derived from bone-marrow mesenchymal stem cells (BMSC-exos) are extracellular vesicles that can execute the function of bone-marrow mesenchymal stem cells (BMSCs). Given the versatile therapeutic potential of BMSC and BMSC-exos, especially their neuroprotective effect, the aim of this study was to investigate the potential effect of BMSC-exos on AD-like behavioral dysfunction in mice and explore the possible molecular mechanism.

METHODS

BMSC-exos were extracted from the supernatant of cultured mouse BMSCs, which were isolated from the femur and tibia of adult C57BL/6 mice, purified and sorted via flow cytometry, and cultured in vitro. BMSC-exos were identified via transmission electron microscopy, and typical marker proteins of exosomes were also detected via Western blot. A sporadic AD mouse model was established by intracerebroventricular injection of streptozotocin (STZ). Six weeks later, BMSC-exos were administered via lateral ventricle injection or caudal vein injection lasting five consecutive days, and the control mice were intracerebroventricularly administered an equal volume of solvent. Behavioral performance was observed via the open field test (OFT), elevated plus maze test (EPM), novel object recognition test (NOR), Y maze test (Y-maze), and tail suspension test (TST). The mRNA and protein expression levels of IL-1β, IL-6, and TNF-α in the hippocampus were measured via quantitative polymerase chain reaction (qPCR) and Western blot, respectively. Moreover, the protein expression of Aβ1-42, BACE, IL-1β, IL-6, TNF-α, GFAP, p-Tau (Ser396), Tau5, synaptotagmin-1 (Syt-1), synapsin-1, and brain-derived neurotrophic factor (BDNF) in the hippocampus was detected using Western blot, and the expression of GFAP, IBA1, Aβ1-42 and DCX in the hippocampus was measured via immunofluorescence staining.

RESULTS

Lateral ventricle administration, but not caudal vein injection of BMSC-exos improved AD-like behaviors in the STZ-injected mouse model, as indicated by the increased number of rearing, increased frequency to the central area, and increased duration and distance traveled in the central area in the OFT, and improved preference index of the novel object in the NOR. Moreover, the hyperactivation of microglia and astrocytes in the hippocampus of the model mice was inhibited after treatment with BMSC-exos via lateral ventricle administration, accompanied by the reduced expression of IL-1β, IL-6, TNF-α, Aβ1-42, and p-Tau and upregulated protein expression of synapse-related proteins and BDNF. Furthermore, the results of the Pearson test showed that the preference index of the novel object in the NOR was positively correlated with the hippocampal expression of BDNF, but negatively correlated with the expression of GFAP, IBA1, and IL-1β. Apart from a positive correlation between the hippocampal expression of BDNF and Syt-1, BDNF abundance was found to be negatively correlated with markers of glial activation and the expression of the inflammatory cytokines, Aβ1-42, and p-Tau, which are characteristic neuropathological features of AD.

CONCLUSIONS

Lateral ventricle administration, but not caudal vein injection of BMSC-exos, can improve AD-like behavioral performance in STZ-injected mice, the mechanism of which might be involved in the regulation of glial activation and its associated neuroinflammation and BDNF-related neuropathological changes in the hippocampus.

The protective role of exercise against age-related neurodegeneration

Endurance exercise is a widely accessible, low-cost intervention with a variety of benefits to multiple organ systems. Exercise improves multiple indices of physical performance and stimulates pronounced health benefits reducing a range of pathologies including metabolic, cardiovascular, and neurodegenerative disorders. Endurance exercise delays brain aging, preserves memory and cognition, and improves symptoms of neurodegenerative pathologies like Amyotrophic Lateral Sclerosis, Alzheimer's disease, Parkinson's disease, Huntington's disease, and various ataxias. Potential mechanisms underlying the beneficial effects of exercise include neuronal survival and plasticity, neurogenesis, epigenetic modifications, angiogenesis, autophagy, and the synthesis and release of neurotrophins and cytokines. In this review, we discuss shared benefits and molecular pathways driving the protective effects of endurance exercise on various neurodegenerative diseases in animal models and in humans.

Digoxin Exhibits Neuroprotective Properties in a Rat Model of Dementia

Alzheimer's disease (AD) is by far the most common cause of cognitive impairment in older adults. Current treatments are entirely focused on the symptoms of AD. A complex etiology for AD has been proposed recently, in which AD leads in elevated levels of inflammation. We previously studied digoxin's involvement in the sporadic-AD intracerebroventricular (ICV)-streptozotocin (STZ) animal model due to its anti-inflammatory and neuroprotective characteristics. 18 adult sprague-dawley rats were split into three groups: control (n = 6), STZ + Saline (n = 6), and STZ + Digoxin (n = 6). Twelve AD-induced rats were split into two groups using stereotaxy five days after STZ injection (3 mg/kg) into both lateral ventricles: one group got digoxin (0.1 mg/kg/day, i.p.) for three weeks, while the other group received saline. Following treatment, each subject was subjected to a passive avoidance learning (PAL) test, followed by brain tissue harvesting. The levels of tumor necrosis factor-alpha (TNF-α) and choline acetyl transferase (ChAT) were measured in the brain, and neurons were counted using Cresyl violet staining in cornu ammonis-1 (CA1) and cornu ammonis-3 (CA3) cornu ammonis (CA3). ICV-STZ significantly shortened PAL latency, increased brain TNF-α levels, decreased brain ChAT activity, and decreased hippocampus neuron number. On the other hand, digoxin significantly reduced all of these STZ-induced deleterious effects. Digoxin significantly rescued rats from memory loss caused by ICV-STZ by decreasing hippocampal cell death, neuroinflammation, and cholinergic deficiency. These findings suggest that digoxin may be beneficial in treating cognitive impairment and Alzheimer's disease.

Bezafibrate Exerts Neuroprotective Effects in a Rat Model of Sporadic Alzheimer’s Disease

Bezafibrate, a pan-peroxisome proliferator-activated receptor (PPAR) agonist, reportedly attenuated tau pathology in a transgenic mouse model of primary tauopathy. Since tau pathology is a neuropathological hallmark of Alzheimer’s disease (AD), bezafibrate may be a potential drug for the treatment of AD. However, no study has investigated its effects in AD models. Thus, we aimed to evaluate whether bezafibrate has neuroprotective effects in a sporadic AD model induced by streptozotocin (STZ) intracerebroventricular (ICV) injection. Rats were administered STZ-ICV (3 mg/kg) followed by bezafibrate (50 mg/kg/day, intraperitoneal) for 4 weeks. Behavior tests and positron emission tomography (PET) were performed to evaluate longitudinal changes in cognitive function, tau pathology, and cerebral glucose metabolism. Immunofluorescence staining was performed to assess neuronal survival and microglial accumulation. STZ-ICV administration induced significant cognitive impairment and substantial neuronal loss, tau pathology, glucose hypometabolism, and microgliosis in the cortex and hippocampus, while bezafibrate effectively attenuated these abnormalities. This study demonstrated that bezafibrate has long-lasting neuroprotective effects in a sporadic AD model. Our data indicate that the neuroprotective effects of bezafibrate might be associated with its ability to ameliorate tau pathology, brain glucose hypometabolism, and neuroinflammation. These findings suggest that bezafibrate is a potential multi-target drug candidate for the treatment of AD.

Dimethyl Fumarate as the Peripheral Blood Inflammatory Mediators Inhibitor in Prevention of Streptozotocin-Induced Neuroinflammation in Aged Rats

Purpose

Intracerebroventricular-(ICV)-streptozotocin-(STZ)-induced neuroinflammation is a model of Alzheimer’s disease (AD) compatible with the inflammation hypothesis of ageing (“inflammaging” state). Previously, we observed age-dependent (young vs aged) dimethyl fumarate (DMF)-induced anti-inflammatory and neuroprotective effects in the brain along with improvement in cognitive functions in rats with the ICV-STZ-induced model of AD. To evaluate whether DMF reduces neuroinflammation based on the peripheral inflammatory response inhibition, we determined peripheral inflammatory mediators in young and aged rats with the ICV-STZ-induced AD pathology following DMF therapy.

Materials and Methods

Young (4-month-old) and aged (22-month-old) rats were fed with 0.4% DMF rat chow for 21 consecutive days after ICV-STZ (3 mg/ventricle) injections. After behavioral testing, blood and spleens were collected to determine the numbers of leukocytes (WBC), lymphocytes and their subpopulations, haematological parameters, the concanavalin (Con)-A-induced production and plasma concentration of interferon (IFN)-γ, interleukin (IL)-6, IL-10 and corticosterone (COR).

Results

Age-dependent anti-inflammatory effect of the DMF treatment in rats with ICV-STZ injections manifested as decreased peripheral WBC and lymphocyte numbers, including TCD3⁺CD4⁺CD8⁻, TCD3⁺CD4⁻CD8⁺, B (CD45RA⁺) and NK (161a⁺), in aged rats. Furthermore, DMF lowered the blood and spleen lymphocyte production of pro-inflammatory IFN-γ and IL-6 in young and aged rats, whereas it enhanced the plasma level of anti-inflammatory IL-10 and lymphocyte’s ability to produce it in aged rats only. In parallel to changes in peripheral WBC numbers in the model of AD, DMF decreased the red blood cell number, haemoglobin concentration, haematocrit and mean platelet volume in aged, but not young, rats. In contrast to controls, DMF did not influence the COR response in STZ groups.

Conclusion

Besides preventing neuroinflammation, DMF acts on the pro-/anti-inflammatory balance in the periphery and causes an anti-inflammatory shift in T lymphocytes which could contribute to DMF’s therapeutic effects in the ICV-STZ-induced model of AD, in particular, in aged rats.

Quercetin Exhibits α7nAChR/Nrf2/HO-1-Mediated Neuroprotection Against STZ-Induced Mitochondrial Toxicity and Cognitive Impairments in Experimental Rodents

The objective of the present study was to investigate the α7nAChR-mediated Nrf2-dependant protective activity against streptozotocin (STZ)-induced brain mitochondrial toxicity in Alzheimer's disease (AD)-like rats. STZ (3 mg/kg) was injected through an intracerebroventricular route to induce AD-like dementia. Repeated Quercetin (50 mg/kg, i.p.) administration attenuated cognitive impairments in the STZ-challenged animals during Morris water-maze and Y-maze tests. Quercetin significantly mitigated the STZ-induced increase in cholinergic dysfunction, such as the increase in acetylcholinesterase activity, decrease in acetylcholine level, and activity of choline acetyltransferase, and increase in amyloid-beta aggregation and mitochondrial toxicity in respect of mitochondrial bioenergetics, integrity, and oxidative stress in memory-challenged rat hippocampus, prefrontal cortex and, amygdala. Further, Quercetin significantly attenuated STZ-induced reduction in the α7nAChRs and HO-1 expression levels in the selected rat brain regions. On the contrary, trigonelline (10 mg/kg, i.p.) and methyllycaconitine (2 mg/kg; i.p.) abolished the neuroprotective effects of Quercetin against STZ-induced behavioral, molecular, and biochemical alterations in the AD-like animals. Hence, Quercetin exhibits α7nAChR/Nrf2/HO-1-mediated neuroprotection against STZ-challenged AD-like animals. Thus, Quercetin could be considered as a potential therapeutic option in the management of AD.

Isoformononetin, a dietary isoflavone protects against streptozotocin induced rat model of neuroinflammation through inhibition of NLRP3/ASC/IL-1 axis activation

AIMS

Isoformononetin (IFN), a methoxyl isoflavone present in most of human dietary supplements. However, being a highly potent antioxidant and anti-inflammatory molecule, its activity against neuronal oxidative stress and neuroinflammation has not been explored till now. The present study was inquested to assess the antioxidant, anti-apoptotic and anti-inflammatory activity of IFN against streptozotocin induced neuroinflammation in different brain regions of rat.

MAIN METHODS

Four groups of animals were subjected to treatment as control, toxic control (STZ; single intracerebrovascular injection), third group (STZ + IFN; 20 mg/kg p.o.), fourth group (IFN) for 14 days. The different brain regions of rats were evaluated for inflammatory, apoptotic and biochemical antioxidant markers. The brain tissues were further assessed for gene expression, immunohistochemical and western blotting examination for localization of inflammasome cascade expression that plays a pivotal role in neuroinflammation.

KEY FINDINGS

The modulation in oxidant/antioxidant status after exposure of STZ was significantly balanced after administration of IFN to rats. Further, IFN was also found to be an apoptotic agent as it modulates the apoptotic gene (Bax) and anti-apoptotic gene (BcL₂) expression. IFN significantly curtailed the augmented protein expression of NLRP3, NLRP2, ASC, NFκBP65, IL-1β and caspase-1 due to STZ administration in cortex and hippocampus rat brain regions.

SIGNIFICANCE

The aforementioned results proclaim the neuroprotective functioning of IFN against STZ induced inflammation. IFN significantly prevents the neuroinflammation by decreasing the generation of ROS that reduces the activation of NLRP3/ASC/IL-1 axis thereby exerting neuroprotection as evidenced in rat model of STZ induced neuroninflammation.

Tau Cleavage Contributes to Cognitive Dysfunction in Strepto-Zotocin-Induced Sporadic Alzheimer's Disease (sAD) Mouse Model

Tau cleavage plays a crucial role in the onset and progression of Alzheimer’s Disease (AD), a widespread neurodegenerative disease whose incidence is expected to increase in the next years. While genetic and familial forms of AD (fAD) occurring early in life represent less than 1%, the sporadic and late-onset ones (sAD) are the most common, with ageing being an important risk factor. Intracerebroventricular (ICV) infusion of streptozotocin (STZ)—a compound used in the systemic induction of diabetes due to its ability to damage the pancreatic β cells and to induce insulin resistance—mimics in rodents several behavioral, molecular and histopathological hallmarks of sAD, including memory/learning disturbance, amyloid-β (Aβ) accumulation, tau hyperphosphorylation, oxidative stress and brain glucose hypometabolism. We have demonstrated that pathological truncation of tau at its N-terminal domain occurs into hippocampi from two well-established transgenic lines of fAD animal models, such as Tg2576 and 3xTg mice, and that it’s in vivo neutralization via intravenous (i.v.) administration of the cleavage-specific anti-tau 12A12 monoclonal antibody (mAb) is strongly neuroprotective. Here, we report the therapeutic efficacy of 12A12mAb in STZ-infused mice after 14 days (short-term immunization, STIR) and 21 days (long-term immunization regimen, LTIR) of i.v. delivery. A virtually complete recovery was detected after three weeks of 12A12mAb immunization in both novel object recognition test (NORT) and object place recognition task (OPRT). Consistently, three weeks of this immunization regimen relieved in hippocampi from ICV-STZ mice the AD-like up-regulation of amyloid precursor protein (APP), the tau hyperphosphorylation and neuroinflammation, likely due to modulation of the PI3K/AKT/GSK3-β axis and the AMP-activated protein kinase (AMPK) activities. Cerebral oxidative stress, mitochondrial impairment, synaptic and histological alterations occurring in STZ-infused mice were also strongly attenuated by 12A12mAb delivery. These results further strengthen the causal role of N-terminal tau cleavage in AD pathogenesis and indicate that its specific neutralization by non-invasive administration of 12A12mAb can be a therapeutic option for both fAD and sAD patients, as well as for those showing type 2 diabetes as a comorbidity.

Activation of PPARα enhances astroglial uptake and degradation of β-amyloid

[Figure: see text].

Streptozotocin-Induced Astrocyte Mitochondrial Dysfunction Is Ameliorated by FTO Inhibitor MO-I-500

The pathogenesis of Alzheimer's disease (AD), the most prevalent form of dementia, remains unclear. Over the past few years, evidence has accumulated indicating that perturbed cerebral bioenergetics and neuroinflammation may compromise cognitive functions and precedes the onset of AD and that impaired function of glial cells can likely contribute to the development of the disease. Recently, N6-methyladenosine (m6A) modification of RNA has been implicated in the regulation of different processes in the brain and to play a potential role in neurodegeneration. In the present study, we investigated the potential role of the m6A machinery enzymes in a streptozotocin (STZ) model of AD in human astrocytoma CCF-STTG1 cells. We observed that STZ-treated astrocytes expressed significantly higher levels of m6A demethylase fat mass and obesity-associated protein (FTO) and m6A reader YTHDF1 (YTH domain-containing family protein 1). Our experiments revealed that MO-I-500, a novel pharmacological inhibitor of FTO, can strongly reduce the adverse effects of STZ. Inhibition of FTO enhanced the survival of cells exposed to STZ and suppressed oxidative stress, apoptosis, elevated expression of glial fibrillary acidic protein, mitochondrial dysfunction, and bioenergetic disturbances induced by this compound. Overall, the results of this study indicate that perturbed m6A signaling may be contributing to AD pathogenesis, likely by compromising astrocyte bioenergetics.

Neuroprotective Potential of Mung Bean (Vigna radiata L.) Polyphenols in Alzheimer's Disease: A Review

Mung bean contains various neuroprotective polyphenols, so it might be a healthy food for Alzheimer's disease (AD) prevention. Totally, 19 major phenolic compounds were quantified in mung bean, including 10 phenolic acids and 9 flavonoids. After summarizing their contents and effective doses in rodent AD models, it was speculated that vitexin, isovitexin, sinapic acid, and ferulic acid might be the major bioactive compounds for mung bean-mediated neuroprotection. The mechanisms involved inhibition of β-amyloidogenesis, tau hyperphosphorylation, oxidative stress, and neuroinflammation, and promotion of autophagy and acetylcholinesterase enzyme activity. Notably, the neuroprotective phenolic profile in mung bean changed after germination, with decreased vitexin and isovitexin, and increased rutin, isoquercitrin, isorhamnetin, and caffeic acid detected. However, only studies of individual phenolic compounds in mung bean are published at present. Hence, further studies are needed to elucidate the neuroprotective activities and mechanisms of extractions of mung bean seeds and sprouts, and the synergism between different phenolic compounds.

Oxidative stress, the immune response, synaptic plasticity, and cognition in transgenic models of Alzheimer disease

INTRODUCTION

Worldwide, approximately 50 million people have dementia, with Alzheimer disease (AD) being the most common type, accounting for 60%-70% of cases. Given its high incidence, it is imperative to design studies to expand our knowledge about its onset and development, and to develop early diagnosis strategies and/or possible treatments. One methodological strategy is the use of transgenic mouse models for the study of the factors involved in AD aetiology, which include oxidative stress and the immune response.

DEVELOPMENT

We searched the PubMed, Scopus, and Google Scholar databases for original articles and reviews published between 2013 and 2019. In this review, we address 2 factors that have been studied independently, oxidative stress and the immune response, in transgenic models of AD, and discuss the relationship between these factors and their impact on the loss of synaptic and structural plasticity, resulting in cognitive impairment.

CONCLUSION

This review describes possible mechanisms by which oxidative stress and the immune response participate in the molecular, cellular, and behavioural effects of AD, observing a close relationship between these factors, which lead to cognitive impairment.

Brain energy metabolism in intracerebroventricularly administered streptozotocin mouse model of Alzheimer's disease: A 1H-[13C]-NMR study

Alzheimer's disease (AD) is a very common neurodegenerative disorder. Although a majority of the AD cases are sporadic, most of the studies are conducted using transgenic models. Intracerebroventricular (ICV) administered streptozotocin (STZ) animals have been used to explore mechanisms in sporadic AD. In this study, we have investigated memory and neurometabolism of ICV-STZ-administered C57BL6/J mice. The neuronal and astroglial metabolic activity was measured in ¹H-[¹³C]-NMR spectrum of cortical and hippocampal tissue extracts of mice infused with [1,6-¹³C₂]glucose and [2-¹³C]acetate, respectively. STZ-administered mice exhibited reduced (p = 0.00002) recognition index for memory. The levels of creatine, GABA, glutamate and NAA were reduced (p ≤ 0.04), while that of myo-inositol was increased (p < 0.05) in STZ-treated mice. There was a significant (p ≤ 0.014) reduction in aspartate-C3, glutamate-C4/C3, GABA-C2 and glutamine-C4 labeling from [1,6-¹³C₂]glucose. This resulted in decreased rate of glucose oxidation in the cerebral cortex (0.64 ± 0.05 vs. 0.77 ± 0.05 µmol/g/min, p = 0.0008) and hippocampus (0.60 ± 0.04 vs. 0.73 ± 0.07 µmol/g/min, p = 0.001) of STZ-treated mice, due to similar reductions of glucose oxidation in glutamatergic and GABAergic neurons. Additionally, reduced glutamine-C4 labeling points towards compromised synaptic neurotransmission in STZ-treated mice. These data suggest that the ICV-STZ model exhibits neurometabolic deficits typically observed in AD, and its utility in understanding the mechanism of sporadic AD.

Pseudoginsenoside-F11 attenuates cognitive dysfunction and tau phosphorylation in sporadic Alzheimer's disease rat model

We previously reported that pseudoginsenoside-F11 (PF11), an ocotillol-type saponin, significantly ameliorated Alzheimer's disease (AD)-associated cognitive defects in APP/PS1 and SAMP8 mice by inhibiting Aβ aggregation and tau hyperphosphorylation, suggesting a potential therapeutic effect of PF11 in the treatment of AD. In the present study we further evaluated the therapeutic effects of PF11 on relieving cognitive impairment in a rat model of sporadic AD (SAD). SAD was induced in rats by bilateral icv infusion of streptozotocin (STZ, 3 mg/kg). The rats were treated with PF11 (2, 4, 8 mg·kg^-1·d^-1, ig) or a positive control drug donepezil (5 mg·kg^-1·d^-1, ig) for 4 weeks. Their cognitive function was assessed in the nest building, Y-maze, and Morris water maze tests. We showed that STZ icv infusion significantly affected the cognitive function, tau phosphorylation, and insulin signaling pathway in the hippocampus. Furthermore, STZ icv infusion resulted in significant upregulation of the calpain I/cyclin-dependent protein kinase 5 (CDK5) signaling pathway in the hippocampus. Oral administration of PF11 dose-dependently ameliorated STZ-induced learning and memory defects. In addition, PF11 treatment markedly reduced the neuronal loss, protected the synapse structure, and modulated STZ-induced expression of tau phosphorylation by regulating the insulin signaling pathway and calpain I/CDK5 signaling pathway in the hippocampus. Donepezil treatment exerted similar beneficial effects in STZ-infused rats as the high dose of PF11 did. This study highlights the excellent therapeutic potential of PF11 in managing AD.

Nanodelivery of oxiracetam enhances memory, functional recovery and induces neuroprotection following concussive head injury

Military personnel are the most susceptible to concussive head injury (CHI) caused by explosion, blast or missile or blunt head trauma. Mild to moderate CHI could induce lifetime functional and cognitive disturbances causing significant decrease in quality of life. Severe CHI leads to instant death and lifetime paralysis. Thus, further exploration of novel therapeutic agents or new features of known pharmacological agents are needed to enhance quality of life of CHI victims. Previous reports from our laboratory showed that mild CHI induced by weight drop technique causing an impact of 0.224N results in profound progressive functional deficit, memory impairment and brain pathology from 5h after trauma that continued over several weeks of injury. In this investigation we report that TiO2 nanowired delivery of oxiracetam (50mg/kg, i.p.) daily for 5 days after CHI resulted in significant improvement of functional deficit on the 8th day. This was observed using Rota Rod treadmill, memory improvement assessed by the time spent in finding hidden platform under water. The motor function improvement is seen in oxiracetam treated CHI group by placing forepaw on an inclined mesh walking and foot print analysis for stride length and distance between hind feet. TiO2-nanowired oxiracetam also induced marked improvements in the cerebral blood flow, reduction in the BBB breakdown and edema formation as well as neuroprotection of neuronal, glial and myelin damages caused by CHI at light and electron microscopy on the 7th day after 5 days TiO2 oxiracetam treatment. Adverse biochemical events such as upregulation of CSF nitrite and nitrate, IL-6, TNF-a and p-Tau are also reduced significantly in oxiracetam treated CHI group. On the other hand post treatment of 100mg/kg dose of normal oxiracetam in identical conditions after CHI is needed to show slight but significant neuroprotection together with mild recovery of memory function and functional deficits on the 8th day. These observations are the first to point out that nanowired delivery of oxiracetam has superior neuroprotective ability in CHI. These results indicate a promising clinical future of TiO2 oxiracetam in treating CHI patients for better quality of life and neurorehabilitation, not reported earlier.

Insulin-like growth factor 1 gene transfer for sporadic Alzheimer's disease: New evidence for trophic factor mediated hippocampal neuronal and synaptic recovery-based behavior improvement

Sporadic Alzheimer's disease (sAD) is the most prevalent neurodegenerative disorder with no cure. Patients typically suffer from cognitive impairment imprinted by irreversible neocortex and hippocampal degeneration with overt synaptic and neuron dysfunction. Insulin-like growth factor 1 (IGF1) has proven to be a potent neuroprotective molecule in animal models of age-related neurodegeneration. In this regard, adenoviral gene transfer aiming at IGF1 brain overexpression has been hitherto an underexplored approach for the sAD treatment. We postulated enhanced IGF1 signaling in the brain as a restorative means in the diseased brain to revert cognitive deficit and restore hippocampal function. We implemented recombinant adenovirus mediated intracerebroventricular IGF1 gene transfer on the streptozotocin (STZ) induced sAD rat model, using 3-month-old male Sprague Dawley rats. This approach enhanced IGF1 signaling in the hippocampus and dampened sAD phosphorylated Tau. We found a remarkable short-term improvement in species-typical behavior, recognition memory, spatial memory, and depressive-like behavior. Histological analysis revealed a significant recovery of immature hippocampal neurons. We additionally recorded an increase in hippocampal microglial cells, which we suggest to exert anti-inflammatory effects. Finally, we found decreased levels of pre- and postsynaptic proteins in the hippocampus of STZ animals. Interestingly, IGF1 gene transfer increased the levels of PSD95 and GAD65/67 synaptic markers, indicating that the treatment enhanced the synaptic plasticity. We conclude that exogenous activation of IGF1 signaling pathway, 1 week after intracerebroventricular STZ administration, protects hippocampal immature neurons, dampens phosphorylated Tau levels, improves synaptic function and therefore performs therapeutically on the sAD STZ model. Hence, this study provides strong evidence for the use of this trophic factor to treat AD and age-related neurodegeneration.

DRD1 agonist A-68930 improves mitochondrial dysfunction and cognitive deficits in a streptozotocin-induced mouse model

Alzheimer's disease (AD) is the most prevalent neurodegenerative disorder characterized by irreversible cognitive deficits and memory dysfunction. Dopamine is the most abundant catecholaminergic neurotransmitter in the brain which regulates motivation, reward, movement, and cognition. Recently, increasing evidences have shown that dopaminergic system is disturbed in AD conditions, and pharmacological interventions targeting dopamine D1 receptor (DRD1) exhibit certain therapeutic benefits in AD models. However, the underlying link between DRD1 and AD remains elusive. This study sought to test whether the selective DRD1 agonist A-68930 could improve streptozotocin (STZ)-induced cognitive impairment in mice. Here we found that A-68930 treatment through intraperitoneal injection efficiently alleviated STZ-induced cognitive deficits in mice. Moreover, our mechanism researches revealed that the DRD1 signaling induced by A-68930 significantly rescued STZ-induced mitochondrial biogenesis deficit, mitochondrial dysfunction, Aβ overexpression, and tau phosphorylation in mice hippocampus and cortex and SH-SY5Y cells, which may be mediated through stimulating AMPK/PGC-1α pathway. This study indicates that DRD1 agonist A-68930 can improve STZ-induced cognitive deficits and mitochondrial dysfunction in vivo and in vitro, and DRD1 may represent an appropriate target candidate for AD drug development.

Verapamil Prevents Development of Cognitive Impairment in an Aged Mouse Model of Sporadic Alzheimer's Disease

Currently, dementia is the only leading cause of death that is still on the rise, with total costs already exceeding those of cancer and heart disease and projected to increase even further in the coming years. Unfortunately, there are no satisfactory treatments and attempts to develop novel, more effective treatments have been extremely costly, albeit unsuccessful thus far. This has led us to investigate the use of established drugs, licensed for other therapeutic indications, for their potential application in cognitive disorders. This strategy, referred to as "drug repositioning," has been successful in many other areas including cancer and cardiovascular diseases. To our knowledge, this is the first study to investigate the effects of long-term treatment with verapamil, a calcium channel blocker commonly prescribed for various cardiovascular conditions and recently applied for prevention of cluster headaches, on the development of cognitive impairment in aged animals. Verapamil was studied at a low dose (1mg/kg/d) in a mouse model of sporadic Alzheimer's disease (sAD). Oral treatment with verapamil or vehicle was started, 24 h post-intracerebroventricular (ICV) streptozotocin/(STZ), in 12-month-old animals and continued for 3 months. Cognitive function was assessed using established tests for spatial learning, short-term/working memory, and long-term/reference memory. Our findings demonstrate that long-term low-dose verapamil effectively prevents development of ICV/STZ-induced cognitive impairment. It mitigates the astrogliosis and synaptic toxicity otherwise induced by ICV/STZ in the hippocampus of aged animals. These findings indicate that long-term, low-dose verapamil may delay progression of sAD in susceptible subjects of advanced age.

Survival Bias and Crosstalk between Chronological and Behavioral Age: Age- and Genotype-Sensitivity Tests Define Behavioral Signatures in Middle-Aged, Old, and Long-Lived Mice with Normal and AD-Associated Aging

New evidence refers to a high degree of heterogeneity in normal but also Alzheimer's disease (AD) clinical and temporal patterns, increased mortality, and the need to find specific end-of-life prognosticators. This heterogeneity is scarcely explored in very old male AD mice models due to their reduced survival. In the present work, using 915 (432 APP23 and 483 C57BL/6 littermates) mice, we confirmed the better survival curves in male than female APP23 mice and respective wildtypes, providing the chance to characterize behavioral signatures in middle-aged, old, and long-lived male animals. The sensitivity of a battery of seven paradigms for comprehensive screening of motor (activity and gait analysis), neuropsychiatric and cognitive symptoms was analyzed using a cohort of 56 animals, composed of 12-, 18- and 24-month-old male APP23 mice and wildtype littermates. Most variables analyzed detected age-related differences. However, variables related to coping with stress, thigmotaxis, frailty, gait, and poor cognition better discriminated the behavioral phenotype of male APP23 mice through the three old ages compared with controls. Most importantly, non-linear age- and genotype-dependent behavioral signatures were found in long-lived animals, suggesting crosstalk between chronological and biological/behavioral ages useful to study underlying mechanisms and distinct compensations through physiological and AD-associated aging.

Intracerebroventricularly Injected Streptozotocin Exerts Subtle Effects on the Cognitive Performance of Long-Evans Rats

Intracerebroventricularly injected streptozotocin (STZ)-induced learning impairment has been an increasingly used rat model of Alzheimer disease. The evoked pathological changes involve many symptoms of the human disease (cognitive decline, increase in β-amyloid and phospho-tau level, amyloid plaque-like deposits). However, the model has predominantly been used with Wistar rats in the literature. The objective of the current study was to transfer it to Long-Evans rats with the ulterior aim to integrate it in a complex cognitive test battery where we use this strain because of its superior cognitive capabilities. We performed two experiments (EXP1, EXP2) with three months old male animals. At EXP1, rats were treated with 2 × 1.5 mg/kg STZ (based on the literature) or citrate buffer vehicle injected bilaterally into the lateral ventricles on days 1 and 3. At EXP2 animals were treated with 3 × 1.5 mg/kg STZ or citrate buffer vehicle injected in the same way as in EXP1 at days 1, 3, and 5. Learning and memory capabilities of the rats were then tested in the following paradigms: five choice serial reaction time test (daily training, started from week 2 or 8 post surgery in Exp1 or Exp2, respectively, and lasting until the end of the experiment); novel object recognition (NOR) test (at week 8 or 14), passive avoidance (at week 11 or 6) and Morris water-maze (at week 14 or 6). 15 or 14 weeks after the STZ treatment animals were sacrificed and brain phospho-tau/tau protein ratio and β -amyloid level were determined by western blot technique. In EXP1 we could not find any significant difference between the treated and the control groups in any of the assays. In EXP2 we found significant impairment in the NOR test and elevated β-amyloid level in the STZ treated group in addition to slower learning of the five-choice paradigm and a trend for increased phospho-tau/tau ratio. Altogether our findings suggest that the Long-Evans strain may be less sensitive to the STZ treatment than the Wistar rats and higher doses may be needed to trigger pathological changes in these animals. The results also highlight the importance of strain diversity in modelling human diseases.

Spatial Memory and Gut Microbiota Alterations Are Already Present in Early Adulthood in a Pre-clinical Transgenic Model of Alzheimer's Disease

The irreversible and progressive neurodegenerative Alzheimer’s disease (AD) is characterized by cognitive decline, extracellular β-amyloid peptide accumulation, and tau neurofibrillary tangles in the cortex and hippocampus. The triple-transgenic (3xTg) mouse model of AD presents memory impairment in several behavioral paradigms and histopathological alterations from 6 to 16 months old. Additionally, it seems that dysbiotic gut microbiota is present in both mouse models and patients of AD at the cognitive symptomatic stage. The present study aimed to assess spatial learning, memory retention, and gut microbiota alterations in an early adult stage of the 3xTg-AD mice as well as to explore its sexual dimorphism. We evaluated motor activity, novel-object localization training, and retention test as well as collected fecal samples to characterize relative abundance, alpha- and beta-diversity, and linear discriminant analysis (LDA) effect size (LEfSe) analysis in gut microbiota in both female and male 3xTg-AD mice, and controls [non-transgenic mice (NoTg)], at 3 and 5 months old. We found spatial memory deficits in female and male 3xTg-AD but no alteration neither during training nor in motor activity. Importantly, already at 3 months old, we observed decreased relative abundances of Actinobacteria and TM7 in 3xTg-AD compared to NoTg mice, while the beta diversity of gut microbiota was different in female and male 3xTg-AD mice in comparison to NoTg. Our results suggest that gut microbiota modifications in 3xTg-AD mice anticipate and thus could be causally related to cognitive decline already at the early adult age of AD. We propose that microbiota alterations may be used as an early and non-invasive diagnostic biomarker of AD.

Myelin Repair: From Animal Models to Humans

It is widely thought that brain repair does not occur, but myelin regeneration provides clear evidence to the contrary. Spontaneous remyelination may occur after injury or in multiple sclerosis (MS). However, the efficiency of remyelination varies considerably between MS patients and between the lesions of each patient. Myelin repair is essential for optimal functional recovery, so a profound understanding of the cells and mechanisms involved in this process is required for the development of new therapeutic strategies. In this review, we describe how animal models and modern cell tracing and imaging methods have helped to identify the cell types involved in myelin regeneration. In addition to the oligodendrocyte progenitor cells identified in the 1990s as the principal source of remyelinating cells in the central nervous system (CNS), other cell populations, including subventricular zone-derived neural progenitors, Schwann cells, and even spared mature oligodendrocytes, have more recently emerged as potential contributors to CNS remyelination. We will also highlight the conditions known to limit endogenous repair, such as aging, chronic inflammation, and the production of extracellular matrix proteins, and the role of astrocytes and microglia in these processes. Finally, we will present the discrepancies between observations in humans and in rodents, discussing the relationship of findings in experimental models to myelin repair in humans. These considerations are particularly important from a therapeutic standpoint.

The Potential Role of Herpes Simplex Virus Type 1 and Neuroinflammation in the Pathogenesis of Alzheimer's Disease

Alzheimer's disease (AD) is a neurodegenerative disease affecting ~50 million people worldwide. To date, there is no cure and current therapies have not been effective in delaying disease progression. Therefore, there is an urgent need for better understanding of the pathogenesis of AD and to rethink possible therapies. Herpes simplex virus type 1 (HSV1) has recently received growing attention for its potential role in sporadic AD. The virus is a ubiquitous human pathogen that infects mucosal epithelia and invades the peripheral nervous system (PNS) of its host to establish a reactivable, latent infection. Upon reactivation, HSV1 spreads back to the epithelium and initiates a new infection, causing epithelial lesions. Occasionally, the virus spreads from the PNS to the brain after reactivation. In this review, we discuss current work on the pathogenesis of AD and summarize research results that support a potential role for HSV1 in the infectious hypothesis of AD. We also highlight recent findings on the neuroinflammatory response, which has been proposed to be the main driving force of AD, starting early in the course of the disease. Relevant rodent models to study neuroinflammation in AD and novel therapeutic approaches are also discussed. Throughout this review, we focus on several aspects of HSV1 pathogenesis, including its primary role as an invader of the PNS, that should be considered in the etiology of AD. We also point out some of the contradictory data and remaining knowledge gaps that require further research to finally fully understand the cause of AD in humans.

Thiamme2-G, a Novel O-GlcNAcase Inhibitor, Reduces Tau Hyperphosphorylation and Rescues Cognitive Impairment in Mice

BACKGROUND

Abnormal hyperphosphorylation of microtubule-associated protein tau plays a pivotal role in Alzheimer's disease (AD). We previously found that O-GlcNAcylation inversely correlates to hyperphosphorylation of tau in AD brain, and downregulation of brain O-GlcNAcylation promotes tau hyperphosphorylation and AD-like neurodegeneration in mice.

OBJECTIVE

Herein we investigated the effect of increasing O-GlcNAcylation by using intermittent dosing with low doses of a potent novel O-GlcNAcase (OGA) inhibitor on AD-like brain changes and cognitive function in a mouse model of sporadic AD (sAD) induced by intracerebroventricular (ICV) injection of streptozotocin (STZ).

METHODS

STZ was injected into the lateral ventricle of C57BL/6J mice. From the second day, Thiamme2-G (TM2G) or saline, as a vehicle control, was orally administered to the ICV-STZ mice three times per week for five weeks. A separate group of ICV-saline mice treated with saline was used as a baseline control. Behavioral tests, including open field and novel object recognition, were conducted three weeks after the first dose of the TM2G or saline. Protein O-GlcNAcylation, tau hyperphosphorylation, synaptic proteins, and neuroinflammation in the mouse brain were assessed by western blotting.

RESULTS

ICV-STZ caused decreased protein O-GlcNAcylation. Enhancement of O-GlcNAcylation to moderate levels by using low-dose OGA inhibitor in ICV-STZ mice prevented STZ-induced body weight loss, rescued cognitive impairments, and restored AD-like pathologies, including hyperphosphorylation of tau and abnormalities in synaptic proteins and neuroinflammation.

CONCLUSION

These findings suggest that moderately increasing protein O-GlcNAcylation by using low doses of OGA inhibitor may be a suitable therapeutic strategy for sAD.

A New Approach to Model Sporadic Alzheimer's Disease by Intracerebroventricular Streptozotocin Injection in APP/PS1 Mice

Alzheimer's disease (AD) is the most common cause of dementia among elderly people. Majority of AD cases are sporadic (SAD) with unknown cause. Transgenic animal models closely reflect the familial (genetic) aspect of the disease but not the sporadic type. However, most new drug candidates which are tested positive in transgenic animal models failed in clinical studies so far. Herein, we aim to develop an AD animal model that combines most of the neuropathological features seen in sporadic AD in humans with amyloid plaques observed in transgenic mice. Four-month-old wild-type and APP/PS1 AD mice were given a single intracerebroventricular (ICV) injection of 3 mg/kg streptozotocin (STZ), a diabetogenic agent. Three weeks later, their cognitive behavior was assessed, and their brain tissues were collected for biochemical and histological analysis. STZ produced cognitive deficits in both non-transgenic mice and AD mice. Biochemical analysis showed a severe decline in synaptic proteins, increase in tau phosphorylation, oxidative stress, disturbed brain insulin signaling with extensive neuroinflammation, and cell death. Significant increase was also observed in the level of the soluble beta amyloid precursor protein (APP) fragments and robust accumulation of amyloid plaques in AD mice compared to the control. These results suggest that STZ ICV treatment causes disturbance in multiple metabolic and cell signaling pathways in the brain that facilitated amyloid plaque accumulation and tau phosphorylation. Therefore, this animal model can be used to evaluate new AD therapeutic agents for clinical translation.

Protriptyline improves spatial memory and reduces oxidative damage by regulating NFκB-BDNF/CREB signaling axis in streptozotocin-induced rat model of Alzheimer's disease

Antidepressants are well known to exert their role via upregulation of brain derived neurotrophic factor (BDNF). BDNF has been reported to exerts its neuroprotective effect in rodent and primate models as well as in patients of Alzheimer's disease (AD). The aim of our study was to evaluate the effect of protriptyline (PRT), a tricyclic antidepressant, in streptozotocin (STZ)- induced rat model of AD. Total 10 µl of STZ was injected into each ventricle (1 mg/kg). PRT (10 mg/kg, i.p.) treatment was started 3-day post STZ administration and continued till 21 days. We found that STZ treatment significantly increased pTau, Aβ42 and BACE-1 expression, oxidative stress and neurodegeneration in hippocampus and cortex of adult rats. STZ induced impairment in spatial learning and retention memory was associated with increased NFκB and reduced CREB and BDNF expression in cortex and hippocampus. Interestingly, PRT treatment significantly reduced pTau, Aβ42 and BACE-1 levels, neurodegeneration, oxidative stress and glial activation, contributing to the improved spatial learning and retention memory in STZ treated rats. Moreover, PRT treatment significantly improved p-ERK/ERK ratio and enhanced BDNF and CREB levels by reducing NFκB and GFAP expression in STZ treated rats. Our data suggest that impaired NFκB and CREB signaling potentially contribute in AD pathogenesis by elevating oxidative stress and neuroinflammation mediated neurodegeneration. Our study has established protriptyline as a multi target molecule in pre-clinical model of AD and further investigations on PRT like molecules could pave way for further development of effective new treatments in neurodegenerative disorders.

A Neonatal Mild Defect in Brain Insulin Signaling Predisposes a Subclinical Model of Sporadic Alzheimer's to Develop the Disease

Brain insulin system dysfunction has been proposed as a key player in the pathogenesis of sporadic Alzheimer's disease (sAD). Given this fact, an adult rat model for sAD has been developed by intracerebroventricular injection of a subdiabetogenic streptozotocin dosage (icv-STZ). A low dose of icv-STZ in adult rats leads to a subclinical model of Alzheimer's disease. According to the brain developmental origin for sAD occurrence, the present study evaluated the effect of neonatal injection of icv-STZ on the development and progression of Alzheimer's disease later in the adult animals treated with a low dose of icv-STZ. Although no alteration was observed in the rats receiving an adult low dose of icv-STZ, these animals displayed cognitive deficits if they were also treated neonatally with icv-STZ. These impairments were associated with altered gene expression of insulin receptor, tau and choline acetyltransferase, along with increased astrocyte and dark neuron densities in the hippocampus. This study highlights neonatal brain insulin system dysfunction in the programming of brain insulin signaling sensitivity and provides more evidence for the developmental origin of sAD.

Liraglutide Has Anti-Inflammatory and Anti-Amyloid Properties in Streptozotocin-Induced and 5xFAD Mouse Models of Alzheimer's Disease

Recent clinical and epidemiological studies support the contention that diabetes mellitus (DM) is a strong risk factor for the development of Alzheimer’s disease (AD). The use of insulin cell toxin, streptozotocin (STZ), when injected into the lateral ventricles, develops an insulin resistant brain state (IRBS) and represents a non-transgenic, or sporadic AD model (SAD), with several AD-like neuropathological features. The present study explored the effects of an anti-diabetic drug, liraglutide (LIR), in reversing major pathological hallmarks in the prodromal disease stage of both the 5xFAD transgenic and SAD mouse models of AD. Three-month-old 5xFAD and age-matched wild type mice were given a single intracerebroventricular (i.c.v) injection of STZ or vehicle (saline) and were subsequently treated with LIR, intraperitoneally (IP), once a day for 30 days. The extent of neurodegeneration, Aβ plaque load, and key proteins associated with the insulin signaling pathways were measured using Western blot and neuroinflammation (via immunohistological assays) in the cortical and hippocampal regions of the brain were assessed following a series of behavioral tests used to measure cognitive function after LIR or vehicle treatments. Our results indicated that STZ significantly increased neuroinflammation, Aβ plaque deposition and disrupted insulin signaling pathway, while 25 nmol/kg LIR, when injected IP, significantly decreased neuroinflammatory responses in both SAD and 5xFAD mice before significant cognitive changes were observed, suggesting LIR can reduce early neuropathology markers prior to the emergence of overt memory deficits. Our results indicate that LIR has neuroprotective effects and has the potential to serve as an anti-inflammatory and anti-amyloid prophylactic therapy in the prodromal stages of AD.

Grape seed proanthocyanidins improves depression-like behavior by alleviating oxidative stress and NLRP3 activation in the hippocampus of prenatally-stressed female offspring rats

Over several decades, there is a growing evidence, which has shown that prenatal stress (PS) contributes to depression in offspring. Grape seed proanthocyanidins (GSPs), which contain dimers, trimers, oligomers of catechin and epicatechin, are known to possess antidepressant effects. The present study aimed to investigate the mechanism of antidepressant effects of GSPs on female juvenile prenatally stressed offspring rats. The results showed that the female juvenile offspring rats exposed to PS exhibited depression-like behavior manifested as longer immobility time and lesser consumption of sucrose solution. Prenatal stress reduced the number of hippocampal neurons and increased the level of the reactive oxygen species (ROS) in the hippocampus of the female juvenile offspring rats. Furthermore, the expression of PYD domains-containing protein 3 (NLRP3) and its downstream cytokines, Caspase-1, and interleukin-1β (IL-1β), were increased in the hippocampus of the female juvenile offspring rats exposed to PS. Administration of GSPs not only improved depression-like behavior and enhanced the number of hippocampal neurons, but also abated excessive ROS generation and inhibited the activation of the NLRP3-Caspase-1 signaling pathway. Taken together, GSPs counteract PS-induced hippocampal neuron loss and depression-like behavior by alleviating oxidative stress and NLRP3 activation. The present study provides a new insight for GSPs as an effective therapeutic agent for adolescent depression.

Mitochondrial Transfer Ameliorates Cognitive Deficits, Neuronal Loss, and Gliosis in Alzheimer's Disease Mice

Pathogenesis of neurodegenerative diseases involves dysfunction of mitochondria, one of the most important cell organelles in the brain, with its most prominent roles in producing energy and regulating cellular metabolism. Here we investigated the effect of transferring active intact mitochondria as a potential therapy for Alzheimer's disease (AD), in order to correct as many mitochondrial functions as possible, rather than a mono-drug related therapy. For this purpose, AD-mice (amyloid-β intracerebroventricularly injected) were treated intravenously (IV) with fresh human isolated mitochondria. One to two weeks later, a significantly better cognitive performance was noticed in the mitochondria treated AD-mice relative to vehicle treated AD-mice, approaching the performance of non-AD mice. We also detected a significant decrease in neuronal loss and reduced gliosis in the hippocampus of treated mice relative to untreated AD-mice. An amelioration of the mitochondrial dysfunction in brain was noticed by the increase of citrate-synthase and cytochrome c oxidase activities relative to untreated AD-mice, reaching activity levels of non-AD-mice. Increased mitochondrial activity was also detected in the liver of mitochondria treated mice. No treatment-related toxicity was noted. Thus, IV mitochondrial transfer may possibly offer a novel therapeutic approach for AD.

p47phox deficiency improves cognitive impairment and attenuates tau hyperphosphorylation in mouse models of AD

Background

Alzheimer’s disease (AD) is characterized by progressive memory loss and cognitive impairment. The aggregation of amyloid β (Aβ) and hyperphosphorylated tau protein are two major pathological features of AD. Nicotinamide adenine dinucleotide phosphate oxidase (NADPH oxidase, NOX) has been indicated in Aβ pathology; however, whether and how it affects tau pathology are not yet clear.

Methods

The role of NOX2 in cognitive function, amyloid plaque formation, and tau hyperphosphorylation were examined in APP/PS1 transgenic mice mated with p47^phox-deficient mice (with deletion of the gene of neutrophil cytosolic factor 1, Ncf1) and/or in p47^phox-deficient mice receiving intracerebroventricular (ICV) injection of streptozotocin (STZ). The cognitive and non-cognitive functions in these mice were assessed by Morris water maze, Rotarod test, open field, and elevated plus maze. Aβ levels, amyloid plaques, p47^phox expression, and astrocyte activation were evaluated using immunofluorescence staining, ELISA, and/or Western blotting. Cultured primary neuronal cells were treated with okadaic acid or conditioned media (CM) from high glucose-stimulated primary astrocytes. The alteration in tau pathology was determined using Western blotting and immunofluorescence staining.

Results

Deletion of the gene coding for p47^phox, the organizer subunit of NOX2, significantly attenuated cognitive impairment and tau pathology in these mice. p47^phox deficiency decreased the activation of astrocytes but had no effect on Aβ levels and amyloid plaque formation in the brains of aged APP/PS1 mice, which displayed markedly increased expression of p47^phox in neurons and astrocytes. Cell culture studies found that neuronal p47^phox deletion attenuated okadaic acid-induced tau hyperphosphorylation at specific sites in primary cultures of neurons. CM from high glucose-treated WT astrocytes increased tau hyperphosphorylation in primary neurons, whereas this effect was absent from p47^phox-deficient astrocytes.

Conclusions

These results suggest that p47^phox is associated with cognitive function and tau pathology in AD. p47^phox expressed in neurons contributes to tau hyperphosphorylation directly, while p47^phox in astrocytes affect tau hyperphosphorylation by activating astrocytes indirectly. Our results provide new insights into the role of NOX2 in AD and indicate that targeted inhibition of p47^phox may be a new strategy for the treatment of AD.

Inhibitor Kappa B Kinase β, Modulated by DJ-1/p-VHL, Reduces Phosphorylated Tau (p-Tau) Accumulation via Autophagy in Alzheimer's Disease Model

It has been demonstrated Inhibitor Kappa B Kinase β (IKKβ) facilitates autophagy, which in turn mediates p-Tau protein clearance. However, the specific regulatory mechanism in Alzheimer's disease (AD) remains unclear. Firstly, AD model was generated by the intracerebroventricular (ICV) injection of the Β-amyloid 1-42 (Aβ_1-42) peptide. Subsequently, mice were injected with shRNA adenoviral transduction particles designed to target DJ-1 or Aβ_1-42 or Aβ_1-42 + shNC or Aβ_1-42 + shRNA against DJ-1. shRNA against DJ-1 were injected into hippocampus of mice (8 × 10⁴ viral particles for each mice) for seven consecutive days. Immunohistochemistry was performed to detect the accumulation of Aβ in the hippocampus of mice, and Hematoxylin-Eosin (HE) staining assay was carried to detect pathological changes in the hippocampus of mice. Further, sh-IKKβ, shDJ-1, pcDNA-IKKβ and pcDNA-DJ-1 plasmids were transfected into HT-22 cells, MTT assay, TUNEL staining and Hoechst staining were performed to detect cell viability and apoptosis, respectively. Western blotting was carried to measure the relative expression of proteins. Findings indicated that Aβ_1-42 inhibited autophagy and up-regulated p-Tau protein expression; Overexpression of IKKβ and DJ-1 all rescued the autophagy inhibited by Aβ_1-42 and down-regulated p-Tau protein expression induced by Aβ_1-42; DJ-1 up-regulated IKKβ via p-VHL, further promoted autophagy and reduced the expression of p-Tau protein; DJ-1 knockdown inhibited autophagy and up-regulated p-Tau protein expression, resulting in delayed behavior in mice. In conclusion, IKKβ, modulated by DJ-1/p-VHL, reduces p-Tau accumulation via autophagy in AD's disease model. This study may provide theoretical basis for the treatment of AD.

miR-132 improves the cognitive function of rats with Alzheimer's disease by inhibiting the MAPK1 signal pathway

Alzheimer's disease (AD) is a common worldwide progressive neurodegenerative disease. The dysregulation of miRNA is crucial in neurodegenerative diseases and neuron apoptosis during AD and is closely associated with the MAPK pathway. By bioinformatic website, we found that there was target inhibiting relationship between microRNA (miR)-132 and MAPK1. Therefore, the current study speculated that miR-132 could improve the cognitive function of rats with AD by inhibiting MAPK1 expression. To verify our hypothesis, 10 normal rats and 60 rats with AD were selected and divided into model, Ad-miR-132 negative control (NC), Ad-miR-132, Ad-small interfering (si)MAPK1 NC, Ad-siMAPK1 and Ad-miR-132 + Ad-MAPK1 groups. Rats were evaluated for learning by performing morris water maze tests and pathological changes of the hippocampus were assessed via HE staining. Additionally, hippocampus cell apoptosis was determined using a TUNEL assay and levels of acetylcholinesterase (AChE), reactive oxygen species (ROS), malondialdehyde (MDA), superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px) were evaluated in sera via ELISA. The mRNA and protein expression of miR-132, iNOS, MAPK1 and phosphorylated (p)-MAPK1 was determined in hippocampus tissues via reverse transcription-quantitative PCR and western blotting, respectively. Compared with normal mice, rats with AD had significantly decreased learning abilities, increased cell apoptosis rates, increased levels of AChE, iNOS, ROS, MDA, MAPK1 and p-MAPK1 and decreased levels of SOD, GSH-Px and miR-132. Upregulation of miR-132 group improved the above indictors and silencing MAKP1 worsened the condition of rats. miR-132 upregulation therefore reversed the negative effects caused by MAPK1 silencing in rats with AD. In conclusion, miR-132 inhibited hippocampal iNOS expression and oxidative stress by inhibiting MAPK1expression to improve the cognitive function of rats with AD.

Effects of a Nutritional Formulation Containing Caprylic and Capric Acid, Phosphatidylserine, and Docosahexaenoic Acid in Streptozotocin-Lesioned Rats

Background

It has been studied that nutrition can influence Alzheimer's disease (AD) onset and progression. Some studies on rodents using intraventricular streptozotocin (STZ) injection showed that this toxin changes cerebral glucose metabolism and insulin signaling pathways.

Objective

The aim of the present study was to evaluate whether a nutritional formulation could reduce cognitive impairment in STZ-induced animals.

Methods

The rats were randomly divided into two groups: sham and STZ. The STZ group received a single bilateral STZ-ICV injection (1 mg/kg). The sham group received a bilateral ICV injection of 0.9% saline solution. The animals were treated with AZ1 formulation (Instanth^® NEO, Prodiet Medical Nutrition) (1 g/kg, PO) or its vehicle (saline solution) for 30 days, once a day starting one day after the stereotaxic surgery (n = 6-10). The rats were evaluated using the open field test to evaluate locomotor activity at day 27 after surgery. Cognitive performance was evaluated at day 28 using the object recognition test and the spatial version of the Y-maze test. At day 30, the rats were anesthetized with chloral hydrate (400 mg/kg, i.p) and euthanized in order to evaluate IBA1 in the hippocampus. The differences were analyzed using one-way ANOVA with Bonferroni's or Kruskal Wallis with Dunn's post-hoc test.

Results/Conclusion

STZ-lesioned rats present memory impairment besides the increased microglial activation. The treatment with AZ1 formulation reversed the memory impairment observed in the object recognition test and Y-maze and also reduced IBA1 in CA1 and DG.

The Chemokine-like Receptor 1 Deficiency Improves Cognitive Deficits of AD Mice and Attenuates Tau Hyperphosphorylation via Regulating Tau Seeding

Pathologic features of Alzheimer's disease (AD) include accumulation of amyloid β (Aβ) and hyperphosphorylated tau protein. We have shown previously that the chemokine-like receptor 1 (CMKLR1) is a functional receptor for Aβ, and CMKLR1 contributes to the uptake of Aβ. However, it is unclear whether CMKLR1 ameliorates or aggravates the process of AD. Here, we show that deletion of the gene coding for CMKLR1 significantly increased Aβ deposits in brains of both male and female amyloid β precursor protein/presenilin-1 mice. However, it markedly decreased the mortality of these mice. Behavioral studies found that CMKLR1 deficiency improved cognitive impairment of male and female amyloid β precursor protein/presenilin-1 mice and intracerebroventricular-streptozotocin injection AD mice. We further explored the effect of CMKLR1 on tau pathology. We found that CMKLR1 deficiency or inhibition attenuated the hyperphosphorylation of tau in brains of AD mice in vivo and in the neuronal cells in vitro The expression of CMKLR1 on the neurons affected tau phosphorylation by participating in tau seeding. Together, these results uncover a novel mechanism of CMKLR1 in the pathologic process of AD and suggest that inhibiting the promotion effect of CMKLR1 on tau seeding may provide a new strategy for the treatment of AD.SIGNIFICANCE STATEMENT Evidence suggests that inflammation is involved in the pathologic progression of AD. The chemokine-like receptor 1 (CMKLR1), belonging to the family of GPCRs, is able to bind and uptake amyloid β. We show here, for the first time, that, although CMKLR1 deficiency increased amyloid β deposits in AD mice, it reduced the mortality and improved the cognitive deficits of AD mice. We furthermore show that CMKLR1 deficiency or inhibition attenuated tau hyperphosphorylation in brains of AD model mice in vivo and in neuronal cells in vitro Finally, we first discovered that the expression of CMKLR1 on neurons affected tau phosphorylation by participating in tau seeding. These findings suggest that inhibition of CMKLR1 may provide a new strategy for the treatment of AD.

Streptozotocin Induces Alzheimer's Disease-Like Pathology in Hippocampal Neuronal Cells via CDK5/Drp1-Mediated Mitochondrial Fragmentation

Aberrant brain insulin signaling plays a critical role in the pathology of Alzheimer’s disease (AD). Mitochondrial dysfunction plays a role in the progression of AD, with excessive mitochondrial fission in the hippocampus being one of the pathological mechanisms of AD. However, the molecular mechanisms underlying the progression of AD and mitochondrial fragmentation induced by aberrant brain insulin signaling in the hippocampal neurons are poorly understood. Therefore, we investigated the molecular mechanistic signaling associated with mitochondrial dynamics using streptozotocin (STZ), a diabetogenic compound, in the hippocampus cell line, HT-22 cells. In this metabolic dysfunctional cellular model, hallmarks of AD such as neuronal apoptosis, synaptic loss, and tau hyper-phosphorylation are induced by STZ. We found that in the mitochondrial fission protein Drp1, phosphorylation is increased in STZ-treated HT-22 cells. We also determined that inhibition of mitochondrial fragmentation suppresses STZ-induced AD-like pathology. Furthermore, we found that phosphorylation of Drp1 was induced by CDK5, and inhibition of CDK5 suppresses STZ-induced mitochondrial fragmentation and AD-like pathology. Therefore, these findings indicate that mitochondrial morphology and functional regulation may be a strategy of potential therapeutic for treating abnormal metabolic functions associated with the pathogenesis of AD.

Grape seed proanthocyanidins ameliorate neuronal oxidative damage by inhibiting GSK-3β-dependent mitochondrial permeability transition pore opening in an experimental model of sporadic Alzheimer's disease

Mitochondria-associated oxidative stress plays a crucial role in Alzheimer’s disease (AD). Grape seed proanthocyanidins (GSPs) have been reported to prevent oxidative stress. In this study, we investigated the underlying mechanisms of GSPs in protecting neurons against oxidative injury in an experimental model of sporadic AD. Primary mouse cortical neurons were subjected to streptozotocin (STZ) to mimic neuronal oxidative damage in vitro, and mice were subjected to intracerebroventricular (ICV) injection of STZ as an in vivo sporadic AD model. GSPs not only significantly ameliorated neuron loss and mitochondrial dysfunction in mouse cortical neurons pretreated of STZ, but also reduced cognitive impairments, apoptosis and mitochondrial oxidative stress in the cerebral cortex and hippocampus of sporadic AD mice. Moreover, GSPs increased phosphorylation levels of phosphatidylinositol 3-kinase (PI3K), Akt and glycogen synthase kinase 3β (GSK-3β) at its Ser9. Notably, GSPs inhibited STZ-induced mitochondrial permeability transition pore (mPTP) opening via enhancing phosphorylated GSK-3β (p-GSK-3β) binds to adenine nucleotide translocator (ANT), thereby reducing the formation of the complex ANT-cyclophilin D (CypD). In conclusion, GSPs ameliorate neuronal oxidative damage and cognitive impairment by inhibiting GSK-3β-dependent mPTP opening in AD. Our study provides new insights into that GSPs may be a new therapeutic candidate for treatment of AD.

Inhibition of complex I-III activity of brain mitochondria after intracerebroventricular administration of streptozotocin in rats is possibly related to loss of body weight

The effects of streptozotocin (STZ) on the brain after intracerebroventricular (ICV) administration in rodents have been suggested to mimic the pathogenesis of sporadic Alzheimer's disease (AD). Oxidative damage, decreased glucose utilization, mitochondrial bioenergetic changes, neuroinflammation and behavioral impairment have been reported in rodents after ICV-STZ administration. However, the molecular mechanisms of STZ effects on brain after ICV administration remain highly controversial. In this study we re-examined several bioenergetic parameters of rat brain mitochondria on day 15 following ICV-STZ treatment. We observed only a moderate but statistically significant decrease in complex I-III activity in brain mitochondria from streptozotocin-treated rats. There were no changes in complex II-III activity or phosphorylation capacity of brain mitochondria after streptozotocin treatment. More importantly, it was observed that ICV-STZ treatment caused variable degrees of body-weight loss in rats, and complex I-III activity was decreased only in those rats showing a significant (more than 10%-35%) loss in body-weights.

Apelin attenuates streptozotocin-induced learning and memory impairment by modulating necroptosis signaling pathway

Apelin is a neuropeptide that plays an important role in neuronal protection. In this study, we investigated the effects of apelin intracerebroventricular administration on spatial learning and memory-related behaviors, and necroptosis signaling pathways in the hippocampus of streptozotocin (STZ) -injected rats. Apelin treatment was implemented following STZ-induced dementia for 15 days. After conducting a behavioral test (Morris Water Maze), the cellular and molecular aspects were examined to detect the apelin effect on the necroptosis signaling pathway. We demonstrated that STZ administration significantly slowed down the learning capability. However apelin treatment notably reversed this neuroinflammation induced behavioral impairment. Furthermore, molecular investigations showed that apelin treatment reduced the hippocampal RIP1, RIP3, and TNF-α level. Our results suggest that apelin treatment attenuates STZ-induced dementia. This effect may be mediated by inhibition of the necroptosis signaling pathway which seems to be associated with the ability of apelin to reduce central TNF-α level. This data provides evidence of the neuroprotective effect of apelin on STZ-induced learning and memory impairment and characterize some of the underlying mechanisms.

Inhibition of mTORC1 improves STZ-induced AD-like impairments in mice

Alzheimer's disease (AD) and type 2 diabetes mellitus (T2DM) share some pathological features, including tau hyperphosphorylation and deficits in insulin signaling, but the underlying mechanism and effective drugs for treating AD are unknown. The AD-like brain impairments are almost same in both of mouse type 2 DM models induced by the multiple low-dose intraperitoneal (i.p.) streptozotocin (STZ) injection and twice intracerebroventricular (i.c.v.) STZ injection. We found that memory disorders, impairment of insulin signaling, and AD-like tauopathies were exhibited in two different STZ-induced mouse models and that the level of Advanced Glycation End Products (AGEs) was increased in two STZ mouse models. Inhibition of mTORC1 with rapamycin reversed the deficits of insulin signaling associated kinases activity, decreased levels of AGEs and AD-like tau phosphorylation, and also improved memory deficit in both STZ mice. Rapamycin attenuated HG-induced tau hyperphosphorylation via the AKT/AMPK/GSK-3β pathways and p70S6K in SH-SY5Y cells. Taken together, these data demonstrated that rapamycin improved STZ-induced AD-like tauopathies and memory deficit in mice via improving p70S6K and AKT/AMPK/GSK-3β signaling and decreasing AGEs. Therefore, regulating insulin signaling via mTORC1 is a new strategy for preventing T2DM-associated AD, and mTORC1 is a potential drug target.

Xanthotoxin and umbelliferone attenuate cognitive dysfunction in a streptozotocin-induced rat model of sporadic Alzheimer's disease: The role of JAK2/STAT3 and Nrf2/HO-1 signalling pathway modulation

The aim of the present study was to assess the neuroprotective effects of xanthotoxin and umbelliferone in streptozotocin (STZ)-induced cognitive dysfunction in rats. Animals were injected intracerebroventricularly (ICV) with STZ (3 mg/kg) once to induce a sporadic Alzheimer's disease (SAD)-like condition. Xanthotoxin or umbelliferone (15 mg/kg, i.p.) were administered 5 hr after ICV-STZ and daily for 20 consecutive days. Xanthotoxin or umbelliferone prevented cognitive deficits in the Morris water maze and object recognition tests. In parallel, xanthotoxin or umbelliferone reduced hippocampal acetylcholinestrase activity and malondialdehyde level. Moreover, xanthotoxin or umbelliferone increased glutathione content. These coumarins also modulated neuronal cell death by reducing the level of proinflammatory cytokines (tumour necrosis factor-alpha and interleukin-6), inhibiting the overexpression of inflammatory markers (nuclear factor κB [NF-κB] and cyclooxygenase II), and upregulating the expression of NF-κB inhibitor (IκB-α). Interestingly, xanthotoxin diminished phosphorylated JAK2 and phosphorylated STAT3 protein expression, while umbelliferone markedly replenished nuclear factor erythroid-derived 2-like 2 (Nrf2) and haem oxygenase-1 (HO-1) levels. The current study provides evidence for the protective effect of xanthotoxin and umbelliferone in STZ-induced cognitive dysfunction in rats. This effect may be attributed, at least in part, to inhibiting acetylcholinestrase and attenuating oxidative stress, neuroinflammation and neuronal loss.

Formyl Peptide Receptor 2 Deficiency Improves Cognition and Attenuates Tau Hyperphosphorylation and Astrogliosis in a Mouse Model of Alzheimer's Disease

Alzheimer's disease (AD) is characterized by progressive loss of memory and other cognitive functions. Accumulation of amyloid-β (Aβ) and hyperphosphorylated tau are two major neuropathological features of AD. Formyl peptide receptor 2 (FPR2), contributing to innate immunity and inflammation, has been implicated in the uptake and clearance of Aβ. It remains unclear whether FPR2 affects cognition and tau phosphorylation. The effects of FPR2 in cognition and tau phosphorylation were examined using FPR2 knock-out (Fpr2-/-) mice receiving intracerebroventricular (ICV) injection of streptozotocin (STZ). The general behaviors and cognitive functions were evaluated using rotarod, open field test, and Morris water maze test. The alteration in tau hyperphosphorylation and activation of astrocytes were determined by using western blotting and/or immunofluorescence staining. ICV injection of STZ impaired spatial learning and memory of mice in Morris water maze. FPR2 deficiency improved spatial learning and memory of ICV-STZ mice. In the hippocampus and cortex of ICV-STZ mice, a marked increase was observed in tau phosphorylation at Ser199, Thr205, and Ser396 compared with ICV-saline control mice. However, FPR2 deficiency attenuated the hyperphosphorylation of tau at Ser199 and Ser396. In addition, the expression of GFAP was significantly increased in hippocampus and cortex of ICV-STZ mice. FPR2 deletion reduced the increase of GFAP expression induced by ICV injection of STZ. These results indicate that FPR2 deficiency is associate with improved cognition, reduced tau hyperphosphorylation, and activation of astrocytes in the mouse AD model tested. FPR2 may be a potential target in AD prevention and therapy.

Effect of amyloid toxicity or chronic cerebral hypoperfusion on brain insulin resistance in a rat model with intracerebroventricular streptozotocin

Sporadic Alzheimer's disease (AD) is a multifactorial neurodegenerative disorder affected by amyloid and vascular pathogenesis. Brain insulin resistance (BIR) has been suggested as one of the pathomechanisms of sporadic AD. We investigated how the amyloid and vascular pathogenesis of AD interacts with BIR. We examined experimental groups mimicking amyloid pathogenesis following intracerebroventriculr (icv) injection of amyloid β or vascular pathogenesis following permanent ligation of the bilateral common carotid arteries in Wistar rats that had undergone icv injection of streptozotocin. Behavioral tests and pathologic studies were performed. Cognitive impairments were induced by BIR superimposed by amyloid or vascular pathogenesis. Neuroinflammation in the white matter and hippocampus was aggravated by an interaction between BIR and vascular pathogenesis. Amyloid-associated pathology in the white matter was enhanced by BIR and vascular pathogenesis. Tau-associated pathology in the hippocampus was altered by BIR in a relation with amyloid or vascular pathogenesis. Our study may provide useful experimental insights based on an integrated approach to the influence of amyloid and vascular pathogenesis on BIR, permitting better understanding of the heterogeneous pathogenesis of sporadic AD. Pathologic responses in sporadic AD may differ depending on amyloid and vascular pathogenesis and may sometimes be synergistically aggravated when combined with BIR.