Targeting neuroinflammation in Alzheimer's disease

Deficient Wnt Signaling and Synaptic Vulnerability in Alzheimer's Disease: Emerging Roles for the LRP6 Receptor

Synapse dysfunction and loss represent critical early events in the pathophysiology of Alzheimer’s disease (AD). While extensive research has elucidated the direct synaptotoxic effects of Amyloid-β (Aβ) oligomers, less is known about how signaling pathways at the synapse are affected by Aβ. A better understanding of the cellular and molecular mechanisms underlying synaptic vulnerability in AD is key to illuminating the determinants of AD susceptibility and will unveil novel therapeutic avenues. Canonical Wnt signaling through the Wnt co-receptor LRP6 has a critical role in maintaining the structural and functional integrity of synaptic connections in the adult brain. Accumulating evidence suggests that deficient Wnt signaling may contribute to AD pathology. In particular, LRP6 deficiency compromises synaptic function and stability, and contributes to Aß production and plaque formation. Here, we review the role of Wnt signaling for synaptic maintenance in the adult brain and the contribution of aberrant Wnt signaling to synaptic degeneration in AD. We place a focus on emerging evidence implicating the LRP6 receptor as an important modulator of AD risk and pathology.

Neuroinflammatory Cytokines Induce Amyloid Beta Neurotoxicity through Modulating Amyloid Precursor Protein Levels/Metabolism

Neuroinflammation has been observed in association with neurodegenerative diseases including Alzheimer's disease (AD). In particular, a positive correlation has been documented between neuroinflammatory cytokine release and the progression of the AD, which suggests these cytokines are involved in AD pathophysiology. A histological hallmark of the AD is the presence of beta-amyloid (Aβ) plaques and tau neurofibrillary tangles. Beta-amyloid is generated by the sequential cleavage of beta (β) and gamma (γ) sites in the amyloid precursor protein (APP) by β- and γ-secretase enzymes and its accumulation can result from either a decreased Aβ clearance or increased metabolism of APP. Previous studies reported that neuroinflammatory cytokines reduce the efflux transport of Aβ, leading to elevated Aβ concentrations in the brain. However, less is known about the effects of neuroinflammatory mediators on APP expression and metabolism. In this article, we review the modulatory role of neuroinflammatory cytokines on APP expression and metabolism, including their effects on β- and γ-secretase enzymes.

Signaling Mechanisms of Selective PPARγ Modulators in Alzheimer's Disease

Alzheimer's disease (AD) is a chronic neurodegenerative disease characterized by abnormal protein accumulation, synaptic dysfunction, and cognitive impairment. The continuous increase in the incidence of AD with the aged population and mortality rate indicates the urgent need for establishing novel molecular targets for therapeutic potential. Peroxisome proliferator-activated receptor gamma (PPARγ) agonists such as rosiglitazone and pioglitazone reduce amyloid and tau pathologies, inhibit neuroinflammation, and improve memory impairments in several rodent models and in humans with mild-to-moderate AD. However, these agonists display poor blood brain barrier permeability resulting in inadequate bioavailability in the brain and thus requiring high dosing with chronic time frames. Furthermore, these dosing levels are associated with several adverse effects including increased incidence of weight gain, liver abnormalities, and heart failure. Therefore, there is a need for identifying novel compounds which target PPARγ more selectively in the brain and could provide therapeutic benefits without a high incidence of adverse effects. This review focuses on how PPARγ agonists influence various pathologies in AD with emphasis on development of novel selective PPARγ modulators.

Distinct microglia profile in Creutzfeldt-Jakob disease and Alzheimer's disease is independent of disease kinetics

Activated microglia represent a common pathological feature of neurodegenerative diseases. Sporadic Creutzfeldt-Jakob disease (sCJD) patients show more pronounced microglial activation than Alzheimer's disease (AD) patients. Whether these differences are due to differences in disease kinetics or represent disease-specific changes is unknown. We investigated microglial phenotypes in brains of rapidly progressive AD (rpAD) and sCJD patients matched for clinical presentation, including disease duration. We immunostained the frontal cortex, basal ganglia and cerebellum in 16 patients with rpAD and sCJD using antibodies against markers of microglia and recruited monocytes (ionized calcium-binding adaptor molecule 1, human leukocyte antigen DPQR, Cluster of Differentiation 68), an antibody unique to brain-resident microglia (transmembrane protein 119 (TMEM119)), in addition to antibodies against a marker of astrocytes (glial fibrillary acidic protein), amyloid-β (Aβ) and pathological prion protein. rpAD patients showed a distinct microglial phenotype with a high abundance of TMEM119-positive microglia in all investigated regions. Presence of Aβ deposits seen in a sCJD patient with concomitant deposition of Aβ led to increase of TMEM119-positive microglia. Our data suggest that in rpAD, activation of brain-resident microglia significantly contributes to microgliosis, whereas in sCJD the TMEM119 signature of resident microglial cells is barely detectable. This is irrespective of disease duration and may indicate disease-specific microglial reaction.

Clinical PET Imaging of Microglial Activation: Implications for Microglial Therapeutics in Alzheimer's Disease

In addition to extracellular β-amyloid plaques and intracellular neurofibrillary tangles, neuroinflammation has been identified as a key pathological characteristic of Alzheimer's disease (AD). Once activated, neuroinflammatory cells called microglia acquire different activation phenotypes. At the early stage of AD, activated microglia are mainly dominated by the neuroprotective and anti-inflammatory M2 phenotype. Conversely, in the later stage of AD, the excessive activation of microglia is considered detrimental and pro-inflammatory, turning into the M1 phenotype. Therapeutic strategies targeting the modulation of microglia may regulate their specific phenotype. Fortunately, with the rapid development of in vivo imaging methodologies, visualization of microglial activation has been well-explored. In this review, we summarize the critical role of activated microglia during the pathogenesis of AD and current studies concerning imaging of microglial activation in AD patients. We explore the possibilities for identifying activated microglial phenotypes with imaging techniques and highlight promising therapies that regulate the microglial phenotype in AD mice.

Phloroglucinol ameliorates cognitive impairments by reducing the amyloid β peptide burden and pro-inflammatory cytokines in the hippocampus of 5XFAD mice

Among the various causative factors involved in the pathogenesis of Alzheimer's disease (AD), oxidative stress has emerged as an important factor. Phloroglucinol is a polyphenol component of phlorotannin, which is found at sufficient levels in Ecklonia cava (E. cava). Phloroglucinol has been reported to exert antioxidant activities in various tissues. Previously, we reported that the stereotaxic injection of phloroglucinol regulated synaptic plasticity in an AD mouse model. In this study, we aimed to investigate the effects of oral administration of phloroglucinol in AD. The oral administration of phloroglucinol for 2 months attenuated the impairments in cognitive function observed in 6-month-old 5X familial AD (5XFAD) mice, as assessed with the T-maze and Y-maze tests. The administration of phloroglucinol for 2 months in 5XFAD mice caused a reduction in the number of amyloid plaques and in the protein level of BACE1, a major amyloid precursor protein cleavage enzyme, together with γ-secretase. Phloroglucinol also restored the reduction in dendritic spine density and the number of mature spines in the hippocampi of 5XFAD mice. In addition, phloroglucinol-administered 5XFAD mice displayed lower protein levels of GFAP and Iba-1 and mRNA levels of TNF-α and IL-6 compared with vehicle-administered 5XFAD mice. These results demonstrated that phloroglucinol alleviated the neuropathological features and behavioral phenotypes in the 5XFAD mouse model. Taken together, our results suggest that phloroglucinol has therapeutic potential for AD treatment.

Microglia prevent peripheral immune cell invasion and promote an anti-inflammatory environment in the brain of APP-PS1 transgenic mice

Background

Undoubtedly, neuroinflammation is a major contributor to Alzheimer’s disease (AD) progression. Neuroinflammation is characterized by the activity of brain resident glial cells, in particular microglia, but also by peripheral immune cells, which infiltrate the brain at certain stages of disease progression. The specific role of microglia in shaping AD pathology is still controversially discussed. Moreover, a possible role of microglia in the interaction and recruitment of peripheral immune cells has so far been completely ignored.

Methods

We ablated microglia cells in 12-month-old WT and APP-PS1 transgenic mice for 4 weeks using the CSF1R inhibitor PLX5622 and analyzed its consequences to AD pathology and in particular to peripheral immune cell infiltration.

Results

PLX5622 treatment successfully reduced microglia numbers. Interestingly, it uncovered a treatment-resistant macrophage population (Iba1⁺/TMEM119⁻). These cells strongly expressed the phagocytosis marker CD68 and the lymphocyte activation, homing, and adhesion molecule CD44, specifically at sites of amyloid-beta plaques in the brains of APP-PS1 mice. In consequence, ablation of microglia significantly raised the number of CD3⁺/CD8⁺ T-cells and reduced the expression of anti-inflammatory genes in the brains of APP-PS1 mice.

Conclusion

We conclude that in neurodegenerative conditions, chronically activated microglia might limit CD3⁺/CD8⁺ T-cell recruitment to the brain and that local macrophages connect innate with adaptive immune responses. Investigating the role of peripheral immune cells, their interaction with microglia, and understanding the link between innate and adaptive immune responses in the brain might be a future directive in treating AD pathology.

Electronic supplementary material

The online version of this article (10.1186/s12974-018-1304-4) contains supplementary material, which is available to authorized users.

Dangguishaoyao-San attenuates LPS-induced neuroinflammation via the TLRs/NF-κB signaling pathway

INTRODUCTION

Dangguishaoyao-San (DSS) is composed of six traditional Chinese medicines, including Angelica sinensis, Paeoniae radix, Rhizoma Ligusticum, Poria cocos, Rhizoma Atractylodis Macrocephalae, and Rhizoma Alismatis. DSS has been reported to be effective in alleviating the symptoms of Alzheimer's disease (AD). The aim of this study was to investigate the mechanism of action of DSS in vitro using lipopolysaccharide (LPS)-stimulated BV-2 microglia cells.

MATERIALS AND METHODS

BV-2 cells were pretreated with 0.58-1.16 mg/mL of DSS for 2 h and then treated with 1 μg/mL LPS for 24 h. Cell viability was determined by an 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. The protein expression levels were measured by Western blots. Inflammatory factors were detected by enzyme-linked immunosorbent assays (ELISAs). The mRNA levels of inflammatory factors were analyzed by quantitative real-time PCR (qRT-PCR).

RESULTS

DSS treatment at concentrations of 0.58-1.16 mg/mL resulted in no significant cytotoxicity. DSS attenuated the release of pro-inflammatory factors, such as interleukin-1β (IL-1β), iNOS and tumor necrosis factor-α (TNF-α) in LPS-induced BV-2 cells. DSS attenuated the mRNA expression of pro-inflammatory cytokines, TLR2, and TLR4 and decreased TLR4 and TLR protein levels as well as the phosphorylation of IκB in LPS-induced BV-2 cells. DSS also down-regulated the nuclear translocation of p65.

CONCLUSION

This study demonstrated that DSS has a protective effect on neuroinflammation in LPS-induced BV-2 microglia cells through the TLRs/NF-κB signaling pathway.

The location discrimination reversal task in mice is sensitive to deficits in performance caused by aging, pharmacological and other challenges

Deficits in hippocampal-mediated pattern separation are one aspect of cognitive function affected in schizophrenia (SZ) or Alzheimer's disease (AD). To develop novel therapies, it is beneficial to explore this specific aspect of cognition preclinically. The location discrimination reversal (LDR) task is a hippocampal-dependent operant paradigm that evaluates spatial learning and cognitive flexibility using touchscreens. Here we assessed baseline performance as well as multimodal disease-relevant manipulations in mice. Mice were trained to discriminate between the locations of two images where the degree of separation impacted performance. Administration of putative pro-cognitive agents was unable to improve performance at narrow separation. Furthermore, a range of disease-relevant manipulations were characterized to assess whether performance could be impaired and restored. Pertinent to the cholinergic loss in AD, scopolamine (0.1 mg/kg) produced a disruption in LDR, which was attenuated by donepezil (1 mg/kg). Consistent with NMDA hypofunction in cognitive impairment associated with SZ, MK-801 (0.1 mg/kg) also disrupted performance; however, this deficit was not modified by rolipram. Microdeletion of genes associated with SZ (22q11) resulted in impaired performance, which was restored by rolipram (0.032 mg/kg). Since aging and inflammation affect cognition and are risk factors for AD, these aspects were also evaluated. Aged mice were slower to acquire the task than young mice and did not reach the same level of performance. A systemic inflammatory challenge (lipopolysaccharide (LPS), 1 mg/kg) produced prolonged (7 days) deficits in the LDR task. These data suggest that LDR task is a valuable platform for evaluating disease-relevant deficits in pattern separation and offers potential for identifying novel therapies.

Lewis-Acid-Mediated Union of Epoxy-Carvone Diastereomers with Anisole Derivatives: Mechanistic Insight and Application to the Synthesis of Non-natural CBD Analogues

The use of trimethylsilyl trifluoromethanesulfonate as a mild means to unite epoxy-carvone silyl ethers with anisole derivatives to yield products that are structurally similar to the CBD scaffold is reported. Importantly, unlike related methods, this process can utilize both epoxy-carvone diastereomers and does not require the use of air/moisture-sensitive organometallic reagents. Several examples of aryl nucleophiles as well as mechanistic insight based on in silico computational analysis are presented.

The anti-parkinsonian drug zonisamide reduces neuroinflammation: Role of microglial Nav 1.6

Parkinson's disease (PD), the second most common age-related progressive neurodegenerative disorder, is characterized by dopamine depletion and the loss of dopaminergic (DA) neurons with accompanying neuroinflammation. Zonisamide is an-anti-convulsant drug that has recently been shown to improve clinical symptoms of PD through its inhibition of monoamine oxidase B (MAO-B). However, zonisamide has additional targets, including voltage-gated sodium channels (Na_v), which may contribute to its reported neuroprotective role in preclinical models of PD. Here, we report that Na_v1.6 is highly expressed in microglia of post-mortem PD brain and of mice treated with the parkinsonism-inducing neurotoxin MPTP. Administration of zonisamide (20 mg/kg, i.p. every 4 h × 3) following a single injection of MPTP (12.5 mg/kg, s.c.) reduced microglial Na_v 1.6 and microglial activation in the striatum, as indicated by Iba-1 staining and mRNA expression of F4/80. MPTP increased the levels of the pro-inflammatory cytokine TNF-α and gp91^phox, and this was significantly reduced by zonisamide. Together, these findings suggest that zonisamide may reduce neuroinflammation through the down-regulation of microglial Na_v 1.6. Thus, in addition to its effects on parkinsonian symptoms through inhibition of MAO-B, zonisamide may have disease modifying potential through the inhibition of Na_v 1.6 and neuroinflammation.

The Gut Microbiome Alterations and Inflammation-Driven Pathogenesis of Alzheimer's Disease-a Critical Review

One of the most important scientific discoveries of recent years was the disclosure that the intestinal microflora takes part in bidirectional communication between the gut and the brain. Scientists suggest that human gut microflora may even act as the “second brain” and be responsible for neurodegenerative disorders like Alzheimer’s disease (AD). Although human-associated microbial communities are generally stable, they can be altered by common human actions and experiences. Enteric bacteria, commensal, and pathogenic microorganisms, may have a major impact on immune system, brain development, and behavior, as they are able to produce several neurotransmitters and neuromodulators like serotonin, kynurenine, catecholamine, etc., as well as amyloids. However, brain destructive mechanisms, that can lead to dementia and AD, start with the intestinal microbiome dysbiosis, development of local and systemic inflammation, and dysregulation of the gut-brain axis. Increased permeability of the gut epithelial barrier results in invasion of different bacteria, viruses, and their neuroactive products that support neuroinflammatory reactions in the brain. It seems that, inflammatory-infectious hypothesis of AD, with the great role of the gut microbiome, starts to gently push into the shadow the amyloid cascade hypothesis that has dominated for decades. It is strongly postulated that AD may begin in the gut, and is closely related to the imbalance of gut microbiota. This is promising area for therapeutic intervention. Modulation of gut microbiota through personalized diet or beneficial microbiota intervention, alter microbial partners and their products including amyloid protein, will probably become a new treatment for AD.

Naringin Dihydrochalcone Ameliorates Cognitive Deficits and Neuropathology in APP/PS1 Transgenic Mice

Alzheimer’s disease (AD) is a multi-factorial neurodegenerative disorder with abnormal accumulation of amyloid-β (Aβ) plaques, neuroinflammation and impaired neurogenesis. Mounting evidences suggest that single-target drugs have limited effects on clinical treatment and alternative or multiple targets are required. In recent decades, natural compounds and their derivatives have gained increasing attention in AD drug discovery due to their inherently enormous chemical and structural diversity. In this study, we demonstrated that naringin dihydrochalcone (NDC), a widely used dietary sweetener with strong antioxidant activity, improved the cognitive function of transgenic AD mice. Pathologically, NDC attenuated Aβ deposition in AD mouse brain. Furthermore, NDC reduced periplaque activated microglia and astrocytes, indicating the inhibition of neuroinflammation. It also enhanced neurogenesis as investigated by BrdU/NeuN double labeling. Additionally, the inhibition of Aβ level and neuroinflammation by NDC treatment was also observed in an AD cell model or a microglia cell line. Taken together, our study indicated that NDC might be a potential therapeutic agent for the treatment of AD against multiple targets that include Aβ pathology, neuroinflammation and neurogenesis.

Molecular and functional interaction between GPR18 and cannabinoid CB2 G-protein-coupled receptors. Relevance in neurodegenerative diseases

GPR18, still considered an orphan receptor, may respond to endocannabinoids, whose canonical receptors are CB₁ and CB₂. GPR18 and CB₂ receptors share a role in peripheral immune response regulation and are co-expressed in microglia, which are immunocompetent cells in the central nervous system (CNS). We aimed at identifying heteroreceptor complexes formed by GPR18 and CB₁R or CB₂R in resting and activated microglia. Receptor-receptor interaction was assessed using energy-transfer approaches, and receptor function by determining cAMP levels and ERK1/2 phosphorylation in heterologous cells and primary cultures of microglia. Heteroreceptor identification in primary cultures of microglia was achieved by in situ proximity ligation assays. Energy transfer results showed interaction of GPR18 with CB₂R but not with CB₁R. CB₂-GPR18 heteroreceptor complexes displayed particular functional properties (heteromer prints) often consisting of negative cross-talk (activation of one receptor reduces signaling arising from the partner receptor) and cross-antagonism (the response of one of the receptors is blocked by a selective antagonist of the partner receptor). Activated microglia showed the heteromer print (negative cross-talk and bidirectional cross-antagonism) and increased expression of CB₂R and GPR18. Due to the important role of CB₂R in neuroprotection, we further investigated heteroreceptor occurrence in primary cultures of microglia from transgenic mice overexpressing human APP_Sw,Ind, an Alzheimer's disease model. Microglial cells from transgenic mice showed the heteromer print and functional interactions that were similar to those found in cells from wild-type animals that were activated by treatment with lipopolysaccharide and interferon-γ. Our results suggest that GPR18 and its heteromers may play important roles in neurodegenerative processes.

Emerging Biosensing Technologies for Neuroinflammatory and Neurodegenerative Disease Diagnostics

Neuroinflammation plays a critical role in the onset and progression of many neurological disorders, including Multiple Sclerosis, Alzheimer's and Parkinson's diseases. In these clinical conditions the underlying neuroinflammatory processes are significantly heterogeneous. Nevertheless, a common link is the chronic activation of innate immune responses and imbalanced secretion of pro and anti-inflammatory mediators. In light of this, the discovery of robust biomarkers is crucial for screening, early diagnosis, and monitoring of neurological diseases. However, the difficulty to investigate biochemical processes directly in the central nervous system (CNS) is challenging. In recent years, biomarkers of CNS inflammatory responses have been identified in different body fluids, such as blood, cerebrospinal fluid, and tears. In addition, progress in micro and nanotechnology has enabled the development of biosensing platforms capable of detecting in real-time, multiple biomarkers in clinically relevant samples. Biosensing technologies are approaching maturity where they will become deployed in community settings, at which point screening programs and personalized medicine will become a reality. In this multidisciplinary review, our goal is to highlight both clinical and recent technological advances toward the development of multiplex-based solutions for effective neuroinflammatory and neurodegenerative disease diagnostics and monitoring.

TNF alpha inhibitors in Alzheimer's disease: A systematic review

OBJECTIVES

The objective of this study was to evaluate the effect of tumour necrosis factor-alpha inhibitors (TNF-αI) on Alzheimer's disease-associated pathology.

DESIGN

A literature search of PubMed, Embase, PsychINFO, Web of Science, Scopus, and the Cochrane Library databases for human and animal studies that evaluated the use of TNF-αI was performed on 26 October 2016.

RESULTS

The main outcomes assessed were cognition and behaviour, reduction in brain tissue mass, presence of plaques and tangles, and synaptic function. Risk of bias was assessed regarding blinding, statistical model, outcome reporting, and other biases. Sixteen studies were included, 13 of which were animal studies and 3 of which were human. All animal studies found that treatment with TNF-αI leads to an improvement in cognition and behaviour. None of the studies measured change in brain tissue mass. The majority of studies documented a beneficial effect in other areas, including the presence of plaques and tangles and synaptic function. The amount of data from human studies was limited. Two out of 3 studies concluded that TNF-αI are beneficial in Alzheimer's disease patients, with one being an observational study and the latter being a small pilot study, with a high risk of bias.

CONCLUSION

It was concluded that a large-scale randomized controlled trial assessing the effectiveness of TNF-αI on humans is warranted.

Beneficial Effects of Exercise Pretreatment in a Sporadic Alzheimer's Rat Model

PURPOSE

This study aimed to examine the effects of swimming exercise pretreatment on a streptozotocin (STZ)-induced sporadic Alzheimer's disease (AD) rat model and provide an initial understanding of related molecular mechanisms.

METHODS

Male 2.5-month-old Sprague-Dawley rats were divided into the following four groups: (a) control, (b) swim + vehicle, (c) STZ without swim, and (d) swim + STZ. The Barnes maze task and novel object recognition test were used to measure hippocampus-dependent spatial learning and working memory, respectively. Immunofluorescence staining, Western blot analysis, enzyme-linked immunosorbent assay (ELISA) analysis, and related assay kits were used to assess synaptic proteins, inflammatory cytokines, total antioxidant capacity, antioxidant enzymes, amyloid-beta production, and tau hyperphosphorylation.

RESULTS

Behavioral tests revealed that exercise pretreatment could significantly inhibit STZ-induced cognitive dysfunction (P < 0.05). STZ animals displayed significant loss of presynaptic/postsynaptic markers in the hippocampal CA1 that was reversed by exercise pretreatment (P < 0.05). STZ rats also displayed increased reactive gliosis, release of proinflammatory cytokines, and oxidative damage, effects attenuated by preexercise (P < 0.05, between-treatment changes). Likewise, preexercise significantly induced protein expression (P < 0.001) and DNA-binding activity (P = 0.015) of Nrf2 and downstream antioxidant gene expression in the hippocampal CA1 region (P < 0.05). STZ rats had increased levels of amyloid-beta (1-42) and tau hyperphosphorylation that were significantly ameliorated by exercise (P < 0.05). Histological studies showed that exercise imparted substantial neuroprotection (P < 0.001), suppressing neuronal apoptosis-like cell death in the hippocampal CA1 compared with the STZ control group (P < 0.001).

CONCLUSIONS

Exercise pretraining exerts multifactorial benefits on AD that support its use as a promising new therapeutic option for prevention of neurodegeneration in the elderly and/or AD population.

Solid lipid curcumin particles provide greater anti-amyloid, anti-inflammatory and neuroprotective effects than curcumin in the 5xFAD mouse model of Alzheimer's disease

BACKGROUND

Neuroinflammation and the presence of amyloid beta protein (Aβ) and neurofibrillary tangles are key pathologies in Alzheimer's disease (AD). As a potent anti-amyloid and anti-inflammatory natural polyphenol, curcumin (Cur) could be potential therapies for AD. Unfortunately, poor solubility, instability in physiological fluids, and low bioavailability limit its clinical utility. Recently, different lipid modifications in the formulae of Cur have been developed that would enhance its therapeutic potential. For example, we have reported greater permeability and neuroprotection with solid lipid curcumin particles (SLCP) than with natural Cur in an in vitro model of AD. In the present study, we compared the Aβ aggregation inhibition, anti-amyloid, anti-inflammatory responses of Cur and or SLCP in both in vitro and in vivo models of AD. One-year-old 5xFAD-and age-matched wild-type mice were given intraperitoneal injections of Cur or SLCP (50 mg/kg body weight) for 2- or 5-days. Levels of Aβ aggregation, including oligomers and fibril formation, were assessed by dot blot assay, while Aβ plaque load and neuronal morphology in the pre-frontal cortex (PFC) and hippocampus were assayed by immunolabeling with Aβ-specific antibody and cresyl violet staining, respectively. In addition, neuroinflammation was assessed the immunoreactivity (IR) of activated astrocytes (GFAP) and microglia (Iba-1) in different brain areas. Finally, comparisons of solubility and permeability of Cur and SLCP were made in cultured N2a cells and in primary hippocampal neurons derived from E16 pups of 5xFAD mice.

RESULTS

We observed that relative to Cur, SLCP was more permeable, labeled Aβ plaques more effectively, and produced a larger decrease in Aβ plaque loads in PFC and dentate gyrus (DG) of hippocampus. Similarly, relative to Cur, SLCP produced a larger decrease of pyknotic, or tangle-like, neurons in PFC, CA1, and CA3 areas of hippocampus after 5 days of treatment. Both Cur and or SLCP significantly reduced GFAP-IR and Iba-1-IR in PFC, in the striatum as well as CA1, CA3, DG, subicular complex of hippocampus, and the entorhinal cortex in the 5xFAD mice after 5 days of treatment.

CONCLUSIONS

The use of SLCP provides more anti-amyloid, anti-inflammatory, and neuroprotective outcomes than does Cur in the 5xFAD mouse model of AD.

Atorvastatin Attenuates Cognitive Deficits and Neuroinflammation Induced by Aβ1-42 Involving Modulation of TLR4/TRAF6/NF-κB Pathway

Inflammatory damage aggravates the progression of Alzheimer's disease (AD) and the mechanism of inflammatory damage may provide a new therapeutic window for the treatment of AD. Toll-like receptor 4 (TLR4)-mediated signaling can regulate the inflammatory process. However, changes in TLR4 signaling pathway induced by beta-amyloid (Aβ) have not been well characterized in brain, especially in the hippocampus. In the present study, we explored the changes of TLR4 signaling pathway induced by Aβ in the hippocampus and the role of atorvastatin in modulating this signal pathway and neurotoxicity induced by Aβ. Experimental AD rats were induced by intrahippocampal injection of Aβ_1-42, and the rats were treated with atorvastatin by oral gavage from 3 weeks before to 6 days after injections of Aβ_1-42. To determine the spatial learning and memory ability of rats in the AD models, Morris water maze (MWM) was performed. The expression of the glial fibrillary acidic protein (GFAP), ionized calcium binding adapter molecule-1 (Iba-1), TLR4, tumor necrosis factor receptor-associated factor 6 (TRAF6), and nuclear transcription factor (NF)-κB (NF-κB) protein in the hippocampus was detected by immunohistochemistry and Western blot. Compared to the control group, increased expression of TLR4, TRAF6, and NF-κB was observed in the hippocampus at 7 days post-injection of Aβ (P < 0.01). Furthermore, atorvastatin treatment significantly ameliorated cognitive deficits of rats, attenuated microglia and astrocyte activation, inhibited apoptosis, and down-regulated the expression of TLR4, TRAF6, and NF-κB, both at the mRNA and protein levels (P < 0.01). TLR4 signaling pathway is thus actively involved in Aβ-induced neuroinflammation and atorvastatin treatment can exert the therapeutic benefits for AD via the TLR4 signaling pathway.

Dietary Total Prenylflavonoids from the Fruits of Psoralea corylifolia L. Prevents Age-Related Cognitive Deficits and Down-Regulates Alzheimer's Markers in SAMP8 Mice

Alzheimer's disease (AD) is a serious threat for the aging society. In this study, we examined the preventive effect of the total prenylflavonoids (TPFB) prepared from the dried fruits of Psoralea corylifolia L., using an age-related AD mouse model SAMP8. We found that long-term dietary TPFB at 50 mg/kg·day significantly improved cognitive performance of the SAMP8 mice in Morris water maze tests, similar to 150 mg/kg·day of resveratrol, a popular neuro-protective compound. Furthermore, TPFB treatment showed significant improvements in various AD markers in SAMP8 brains, which were restored to near control levels of the normal mice, SAMR1. TPFB significantly reduced the level of amyloid β-peptide 42 (Aβ42), inhibited hyperphosphorylation of the microtubule-associated protein Tau, induced phosphorylation of Ser9 of the glycogen synthase kinase 3β (GSK-3β), and decreased the expression of the proinflammatory cytokines TNFα, IL-6, and IL-1β. Finally, TPFB also markedly reduced the level of serum derivatives of reactive oxygen metabolites (d-ROMs), a biomarker of oxidative stress in vivo. These results showed that dietary TPFB could effectively prevent age-related cognitive deficits and AD-like neurobiochemical changes, and may have a potential role in the prevention of Alzheimer's disease.

Palmitoylethanolamide Dampens Reactive Astrogliosis and Improves Neuronal Trophic Support in a Triple Transgenic Model of Alzheimer's Disease: In Vitro and In Vivo Evidence

Alzheimer's disease (AD) is a neurodegenerative disorder responsible for the majority of dementia cases in elderly people. It is widely accepted that the main hallmarks of AD are not only senile plaques and neurofibrillary tangles but also reactive astrogliosis, which often precedes detrimental deposits and neuronal atrophy. Such phenomenon facilitates the regeneration of neural networks; however, under some circumstances, like in AD, reactive astrogliosis is detrimental, depriving neurons of the homeostatic support, thus contributing to neuronal loss. We investigated the presence of reactive astrogliosis in 3×Tg-AD mice and the effects of palmitoylethanolamide (PEA), a well-documented anti-inflammatory molecule, by in vitro and in vivo studies. In vitro results revealed a basal reactive state in primary cortical 3×Tg-AD-derived astrocytes and the ability of PEA to counteract such phenomenon and improve viability of 3×Tg-AD-derived neurons. In vivo observations, performed using ultramicronized- (um-) PEA, a formulation endowed with best bioavailability, confirmed the efficacy of this compound. Moreover, the schedule of treatment, mimicking the clinic use (chronic daily administration), revealed its beneficial pharmacological properties in dampening reactive astrogliosis and promoting the glial neurosupportive function. Collectively, our results encourage further investigation on PEA effects, suggesting it as an alternative or adjunct treatment approach for innovative AD therapy.

Receptor-heteromer mediated regulation of endocannabinoid signaling in activated microglia. Role of CB1 and CB2 receptors and relevance for Alzheimer's disease and levodopa-induced dyskinesia

Endocannabinoids are important regulators of neurotransmission and, acting on activated microglia, they are postulated as neuroprotective agents. Endocannabinoid action is mediated by CB₁ and CB₂ receptors, which may form heteromeric complexes (CB₁-CB₂Hets) with unknown function in microglia. We aimed at establishing the expression and signaling properties of cannabinoid receptors in resting and LPS/IFN-γ-activated microglia. In activated microglia mRNA transcripts increased (2 fold for CB₁ and circa 20 fold for CB₂), whereas receptor levels were similar for CB₁ and markedly upregulated for CB₂; CB₁-CB₂Hets were also upregulated. Unlike in resting cells, CB₂ receptors became robustly coupled to G_i in activated cells, in which CB₁-CB₂Hets mediated a potentiation effect. Hence, resting cells were refractory while activated cells were highly responsive to cannabinoids. Interestingly, similar results were obtained in cultures treated with ß-amyloid (Aß_1-42). Microglial activation markers were detected in the striatum of a Parkinson's disease (PD) model and, remarkably, in primary microglia cultures from the hippocampus of mutant β-amyloid precursor protein (APP_Sw,Ind) mice, a transgenic Alzheimer's disease (AD) model. Also of note was the similar cannabinoid receptor signaling found in primary cultures of microglia from APP_Sw,Ind and in cells from control animals activated using LPS plus IFN-γ. Expression of CB₁-CB₂Hets was increased in the striatum from rats rendered dyskinetic by chronic levodopa treatment. In summary, our results showed sensitivity of activated microglial cells to cannabinoids, increased CB₁-CB₂Het expression in activated microglia and in microglia from the hippocampus of an AD model, and a correlation between levodopa-induced dyskinesia and striatal microglial activation in a PD model. Cannabinoid receptors and the CB₁-CB₂ heteroreceptor complex in activated microglia have potential as targets in the treatment of neurodegenerative diseases.

Involvement of Astrocytes in Alzheimer's Disease from a Neuroinflammatory and Oxidative Stress Perspective

Alzheimer disease (AD) is a frequent and devastating neurodegenerative disease in humans, but still no curative treatment has been developed. Although many explicative theories have been proposed, precise pathophysiological mechanisms are unknown. Due to the importance of astrocytes in brain homeostasis they have become interesting targets for the study of AD. Changes in astrocyte function have been observed in brains from individuals with AD, as well as in AD in vitro and in vivo animal models. The presence of amyloid beta (Aβ) has been shown to disrupt gliotransmission, neurotransmitter uptake, and alter calcium signaling in astrocytes. Furthermore, astrocytes express apolipoprotein E and are involved in the production, degradation and removal of Aβ. As well, changes in astrocytes that precede other pathological characteristics observed in AD, point to an early contribution of astroglia in this disease. Astrocytes participate in the inflammatory/immune responses of the central nervous system. The presence of Aβ activates different cell receptors and intracellular signaling pathways, mainly the advanced glycation end products receptor/nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) pathway, responsible for the transcription of pro-inflammatory cytokines and chemokines in astrocytes. The release of these pro-inflammatory agents may induce cellular damage or even stimulate the production of Aβ in astrocytes. Additionally, Aβ induces the appearance of oxidative stress (OS) and production of reactive oxygen species and reactive nitrogen species in astrocytes, affecting among others, intracellular calcium levels, NADPH oxidase (NOX), NF-κB signaling, glutamate uptake (increasing the risk of excitotoxicity) and mitochondrial function. Excessive neuroinflammation and OS are observed in AD, and astrocytes seem to be involved in both. The Aβ/NF-κB interaction in astrocytes may play a central role in these inflammatory and OS changes present in AD. In this paper, we also discuss therapeutic measures highlighting the importance of astrocytes in AD pathology. Several new therapeutic approaches involving phenols (curcumin), phytoestrogens (genistein), neuroesteroids and other natural phytochemicals have been explored in astrocytes, obtaining some promising results regarding cognitive improvements and attenuation of neuroinflammation. Novel strategies comprising astrocytes and aimed to reduce OS in AD have also been proposed. These include estrogen receptor agonists (pelargonidin), Bambusae concretio Salicea, Monascin, and various antioxidatives such as resveratrol, tocotrienol, anthocyanins, and epicatechin, showing beneficial effects in AD models.

Cografting astrocytes improves cell therapeutic outcomes in a Parkinson's disease model

Transplantation of neural progenitor cells (NPCs) is a potential therapy for treating neurodegenerative disorders, but this approach has faced many challenges and limited success, primarily because of inhospitable host brain environments that interfere with enriched neuron engraftment and function. Astrocytes play neurotrophic roles in the developing and adult brain, making them potential candidates for helping with modification of hostile brain environments. In this study, we examined whether astrocytic function could be utilized to overcome the current limitations of cell-based therapies in a murine model of Parkinson's disease (PD) that is characterized by dopamine (DA) neuron degeneration in the midbrain. We show here that cografting astrocytes, especially those derived from the midbrain, remarkably enhanced NPC-based cell therapeutic outcomes along with robust DA neuron engraftment in PD rats for at least 6 months after transplantation. We further show that engineering of donor astrocytes with Nurr1 and Foxa2, transcription factors that were recently reported to polarize harmful immunogenic glia into the neuroprotective form, further promoted the neurotrophic actions of grafted astrocytes in the cell therapeutic approach. Collectively, these findings suggest that cografting astrocytes could be a potential strategy for successful cell therapeutic outcomes in neurodegenerative disorders.

Soluble epoxide hydrolase as a therapeutic target for pain, inflammatory and neurodegenerative diseases

Eicosanoids are biologically active lipid signaling molecules derived from polyunsaturated fatty acids. Many of the actions of eicosanoid metabolites formed by cyclooxygenase and lipoxygenase enzymes have been characterized, however, the epoxy-fatty acids (EpFAs) formed by cytochrome P450 enzymes are newly described by comparison. The EpFA metabolites modulate a diverse set of physiologic functions that include inflammation and nociception among others. Regulation of EpFAs occurs primarily via release, biosynthesis and enzymatic transformation by the soluble epoxide hydrolase (sEH). Targeting sEH with small molecule inhibitors has enabled observation of the biological activity of the EpFAs in vivo in animal models, greatly contributing to the overall understanding of their role in the inflammatory response. Their role in modulating inflammation has been demonstrated in disease models including cardiovascular pathology and inflammatory pain, but extends to neuroinflammation and neuroinflammatory disease. Moreover, while EpFAs demonstrate activity against inflammatory pain, interestingly, this action extends to blocking chronic neuropathic pain as well. This review outlines the role of modulating sEH and the biological action of EpFAs in models of pain and inflammatory diseases.

Neuroprotective effect of berberine against environmental heavy metals-induced neurotoxicity and Alzheimer's-like disease in rats

Heavy metals are reported as neurodegenerative disorders progenitor. They play a role in the precipitation of abnormal β-amyloid protein and hyper-phosphorylated tau, the main hallmarks of Alzheimer's disease (AD). The present study aimed to validate the heavy metals-induced Alzheimer's-like disease in rats as an experimental model of AD and explore the therapeutic effect of berberine via tracking its effect on the oxidative stress-inflammatory pathway. Alzheimer's-like disease was induced in rats orally by a mixture of aluminium, cadmium and fluoride for three months, followed by berberine treatment for another one month. Berberine significantly improved the cognitive behaviors in Morris water maze test and offered a protective effect against heavy metals-induced memory impairment. Docking results showed that berberine inhibited AChE, COX-2 and TACE. Matching with in silico study, berberine downregulated the AChE expression and inhibited its activity in the brain tissues. Also, it normalized the production of TNF- α, IL-12, IL-6 and IL-1β. Moreover, it evoked the production of antioxidant Aβ40 and inhibited the formation of Aβ42, responsible for the aggregations of amyloid-β plaques. Histopathological examination confirmed the neuroprotective effect of berberine. The present data advocate the possible beneficial effect of berberine as therapeutic modality for Alzheimer's disease via its antiinflammatory/antioxidant mechanism.

Sex differences in the phagocytic and migratory activity of microglia and their impairment by palmitic acid

Sex differences in the incidence, clinical manifestation, disease course, and prognosis of neurological diseases, such as autism spectrum disorders or Alzheimer's disease, have been reported. Obesity has been postulated as a risk factor for cognitive decline and Alzheimer's disease and, during pregnancy, increases the risk of autism spectrum disorders in the offspring. Obesity is associated with increased serum and brain levels of free fatty acids, such as palmitic acid, which activate microglial cells triggering a potent inflammatory cascade. In this study, we have determined the effect of palmitic acid in the inflammatory profile, motility, and phagocytosis of primary male and female microglia, both in basal conditions and in the presence of a pro-inflammatory stimulus (interferon-γ). Male microglia in vitro showed higher migration than female microglia under basal and stimulated conditions. In contrast, female microglia had higher basal and stimulated phagocytic activity than male microglia. Palmitic acid did not affect basal migration or phagocytosis, but abolished the migration and phagocytic activity of male and female microglia in response to interferon-γ. These findings extend previous observations of sex differences in microglia and suggest that palmitic acid impairs the protective responses of these cells.

Anserine (beta-alanyl-3-methyl-L-histidine) improves neurovascular-unit dysfunction and spatial memory in aged AβPPswe/PSEN1dE9 Alzheimer's-model mice

Anserine/carnosine supplementation improves cerebral blood flow and verbal episodic memory in elderly people, as we previously reported. Anserine’s buffering activity is superior to that of carnosine at neutral pH. In human sera, carnosine but not anserine is rapidly cleaved by carnosinase, limiting its effectiveness. This study examined the effects of anserine on AβPPswe/PSEN1dE9 Alzheimer’s disease (AD) model mice over 18-months old, an age at which these mice exhibit detectable memory deficits. We found that 8 weeks of anserine treatment completely recovered the memory deficits, improved pericyte coverage on endothelial cells in the brain, and diminished chronic glial neuroinflammatory reactions in these mice. These results suggest that anserine (beta-alanyl-3-methyl-L-histidine) supplementation improved memory functions in AD-model mice by exerting a protective effect on the neurovascular units, which are composed of endothelial cells, pericytes, and supporting glial cells.

Intranasal delivery of dexamethasone efficiently controls LPS-induced murine neuroinflammation

Neuroinflammation is the hallmark of several infectious and neurodegenerative diseases. Synthetic glucocorticoids (GCs) are the first-line immunosuppressive drugs used for controlling neuroinflammation. A delayed diffusion of GCs molecules and the high systemic doses required for brain-specific targeting lead to severe undesirable effects, particularly when lifelong treatment is required. Therefore, there is an urgent need for improving this current therapeutic approach. The intranasal (i.n.) route is being employed increasingly for drug delivery to the brain via the olfactory system. In this study, the i.n. route is compared to the intravenous (i.v.) administration of GCs with respect to their effectiveness in controlling neuroinflammation induced experimentally by systemic lipopolysaccharide (LPS) injection. A statistically significant reduction in interleukin (IL)-6 levels in the central nervous system (CNS) in the percentage of CD45⁺ /CD11b⁺ /lymphocyte antigen 6 complex locus G6D [Ly6G⁺ and in glial fibrillary acidic protein (GFAP) immunostaining was observed in mice from the i.n.-dexamethasone (DX] group compared to control and i.v.-DX-treated animals. DX treatment did not modify the percentage of microglia and perivascular macrophages as determined by ionized calcium binding adaptor molecule 1 (Iba1) immunostaining of the cortex and hippocampus. The increased accumulation of DX in brain microvasculature in DX-i.n.-treated mice compared with controls and DX-IV-treated animals may underlie the higher effectiveness in controlling neuroinflammation. Altogether, these results indicate that IN-DX administration may offer a more efficient alternative than systemic administration to control neuroinflammation in different neuropathologies.

Brain and Peripheral Atypical Inflammatory Mediators Potentiate Neuroinflammation and Neurodegeneration

Neuroinflammatory response is primarily a protective mechanism in the brain. However, excessive and chronic inflammatory responses can lead to deleterious effects involving immune cells, brain cells and signaling molecules. Neuroinflammation induces and accelerates pathogenesis of Parkinson’s disease (PD), Alzheimer’s disease (AD) and Multiple sclerosis (MS). Neuroinflammatory pathways are indicated as novel therapeutic targets for these diseases. Mast cells are immune cells of hematopoietic origin that regulate inflammation and upon activation release many proinflammatory mediators in systemic and central nervous system (CNS) inflammatory conditions. In addition, inflammatory mediators released from activated glial cells induce neurodegeneration in the brain. Systemic inflammation-derived proinflammatory cytokines/chemokines and other factors cause a breach in the blood brain-barrier (BBB) thereby allowing for the entry of immune/inflammatory cells including mast cell progenitors, mast cells and proinflammatory cytokines and chemokines into the brain. These peripheral-derived factors and intrinsically generated cytokines/chemokines, α-synuclein, corticotropin-releasing hormone (CRH), substance P (SP), beta amyloid 1–42 (Aβ1–42) peptide and amyloid precursor proteins can activate glial cells, T-cells and mast cells in the brain can induce additional release of inflammatory and neurotoxic molecules contributing to chronic neuroinflammation and neuronal death. The glia maturation factor (GMF), a proinflammatory protein discovered in our laboratory released from glia, activates mast cells to release inflammatory cytokines and chemokines. Chronic increase in the proinflammatory mediators induces neurotoxic Aβ and plaque formation in AD brains and neurodegeneration in PD brains. Glial cells, mast cells and T-cells can reactivate each other in neuroinflammatory conditions in the brain and augment neuroinflammation. Further, inflammatory mediators from the brain can also enter into the peripheral system through defective BBB, recruit immune cells into the brain, and exacerbate neuroinflammation. We suggest that mast cell-associated inflammatory mediators from systemic inflammation and brain could augment neuroinflammation and neurodegeneration in the brain. This review article addresses the role of some atypical inflammatory mediators that are associated with mast cell inflammation and their activation of glial cells to induce neurodegeneration.

Microglia-targeted stem cell therapies for Alzheimer disease: A preclinical data review

Alzheimer disease (AD) is a severe, life-threatening illness characterized by gradual memory loss. The classic histological features of AD include extracellular formation of β-amyloid plaques (Aβ), intracellular neurofibrillary tangles (NFT), and synaptic loss. Recently, accumulated evidence has confirmed the critical role of microglia in the development and exacerbation of AD. When Aβ forms deposits, microglia quickly respond to restore brain physiology by activating a series of repair mechanisms. However, prolonged microglial activation is considered detrimental and may aggravate AD progression. To date, there are no curative therapies for AD. The advent of stem cell transplantation offers novel strategies to treat AD in animal models. Furthermore, studies have reported that transplanted stem cells might ameliorate AD symptoms by regulating microglial functions, from detrimental to protective. This review focuses on the crucial functions of microglia in AD and examines the reactions of microglia to transplanted stem cells.

Intranasal BMP9 Ameliorates Alzheimer Disease-Like Pathology and Cognitive Deficits in APP/PS1 Transgenic Mice

Alzheimer’s disease (AD) is the most common type of dementia and has no effective therapies. Previous studies showed that bone morphogenetic protein 9 (BMP9), an important factor in the differentiation and phenotype maintenance of cholinergic neurons, ameliorated the cholinergic defects resulting from amyloid deposition. These findings suggest that BMP9 has potential as a therapeutic agent for AD. However, the effects of BMP9 on cognitive function in AD and its underlying mechanisms remain elusive. In the present study, BMP9 was delivered intranasally to 7-month-old APP/PS1 mice for 4 weeks. Our data showed that intranasal BMP9 administration significantly improved the spatial and associative learning and memory of APP/PS1 mice. We also found that intranasal BMP9 administration significantly reduced the amyloid β (Aβ) plaques overall, inhibited tau hyperphosphorylation, and suppressed neuroinflammation in the transgenic mouse brain. Furthermore, intranasal BMP9 administration significantly promoted the expression of low-density lipoprotein receptor-related protein 1 (LRP1), an important membrane receptor involved in the clearance of amyloid β via the blood-brain barrier (BBB), and elevated the phosphorylation levels of glycogen synthase kinase-3β (Ser9), which is considered the main kinase involved in tau hyperphosphorylation. Our results suggest that BMP9 may be a promising candidate for treating AD by targeting multiple key pathways in the disease pathogenesis.