Targeting neuroinflammation in Alzheimer’s disease

Almost 47 million people suffer from dementia worldwide, with an estimated new case diagnosed every 3.2 seconds. Alzheimer’s disease (AD) accounts for approximately 60%–80% of all dementia cases. Given this evidence, it is clear dementia represents one of the greatest global public health challenges. Currently used drugs alleviate the symptoms of AD but do not treat the underlying causes of dementia. Hence, a worldwide quest is under way to find new treatments to stop, slow, or even prevent AD. Besides the classic targets of the oldest therapies, represented by cholinergic and glutamatergic systems, β-amyloid (Aβ) plaques, and tau tangles, new therapeutic approaches have other targets. One of the newest and most promising strategies is the control of reactive gliosis, a multicellular response to brain injury. This phenomenon occurs as a consequence of a persistent glial activation, which leads to cellular dysfunctions and neuroinflammation. Reactive gliosis is now considered a key abnormality in the AD brain. It has been demonstrated that reactive astrocytes surround both Aβ plaques and tau tangles. In this condition, glial cells lose some of their homeostatic functions and acquire a proinflammatory phenotype amplifying neuronal damage. So, molecules that are able to restore their physiological functions and control the neuroinflammatory process offer new therapeutic opportunities for this devastating disease. In this review, we describe the role of neuroinflammation in the AD pathogenesis and progression and then provide an overview of the recent research with the aim of developing new therapies to treat this disorder

Glia-neuron interplay in health and disease: pharmacological evidence for this required teamwork

Glia is a cell population highly present in the central nervous system (CNS) with the purpose, among other functions, to support neurons. In fact, many of these cells are closely in contact with neurons, actively participating to homeostatic support and synaptic transmission. For instance, astrocytes are considered integral part of the tripartite synapse. By this way, recent discoveries made possible to change perspective regarding the neuro-centric view of chronic neurodegenerative disorders, expanding the horizon to new players involved in the physiological and/or pathologic processes that take place in CNS. Better understanding the contribution of non-neuronal cells to these processes will be crucial for the development of new therapeutic approaches to counteract neurodegeneration. Moving from these assumptions, my studies focused on evaluating the role of glial cells in inducing and triggering the inflammatory processes during neurodegeneration and, in particular, on the events that lead these cells to an activated state named reactive gliosis. Moreover, the consequences caused by these processes on neuronal survival, and in a macroscopic manner, on learning and memory, were evaluated. To achieve such goals, I worked with different preclinical models of AD, both in vitro and in vivo, attempting to recreate at best the pathological hallmarks of pathology. In addition, since the crucial role of glial cells in the maintenance of brain homeostasis and their close connection with neuronal functioning and survival, the action of different molecules on neuroinflammation, as well as on neuronal survival, were tested

Does neuroinflammation turn on the flame in Alzheimer's disease? Focus on astrocytes

Data from animal models and Alzheimer's disease (AD) subjects provide clear evidence for an activation of inflammatory pathways during the pathogenetic course of such illness. Biochemical and neuropathological studies highlighted an important cause/effect relationship between inflammation and AD progression, revealing a wide range of genetic, cellular, and molecular changes associated with the pathology. In this context, glial cells have been proved to exert a crucial role. These cells, in fact, undergo important morphological and functional changes and are now considered to be involved in the onset and progression of AD. In particular, astrocytes respond quickly to pathology with changes that have been increasingly recognized as a continuum, with potentially beneficial and/or negative consequences. Although it is now clear that activated astrocytes trigger the neuroinflammatory process, however, the precise mechanisms have not been completely elucidated. Neuroinflammation is certainly a multi-faceted and complex phenomenon and, especially in the early stages, exerts a reparative intent. However, for reasons not yet all well known, this process goes beyond the physiologic control and contributes to the exacerbation of the damage. Here we scrutinize some evidence supporting the role of astrocytes in the neuroinflammatory process and the possibility that these cells could be considered a promising target for future AD therapies

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

An animal model of Alzheimer disease based on the intrahippocampal injection of amyloid beta-peptide (Abeta)

The intrahippocampal injection of amyloid beta peptide (1-42) (Aβ(1-42)) represents one of the most useful animal models of Alzheimer disease. Since none of these available models fully represents the main pathological hallmarks of Alzheimer disease, stereotaxic Aβ(1-42) infusion provides researchers with an in vivo alternative paradigm. When performed by well-trained individuals, this model is the best-suited one for short-term studies focusing on the effects of Aβ(1-42) on a specific brain region or circuitry. Here, we describe all methodological phases of such a model

Preparation of rat hippocampal organotypic cultures and application to study amyloid beta-peptide toxicity

Hippocampal organotypic cultures constitute a very easy but delicate method widely used to study amyloid β-peptide toxicity. This ex vivo technique is performed on tissues isolated from newborn rats. Here, we describe a protocol for the preparation and culture of hippocampal organotypic slices that can be maintained for 14-21 days and their application to the study of amyloid β-peptide toxicity

Astrocyte: an innovative approach for Alzheimer's disease therapy

Alzheimer's disease is a devastating neurological illness with a high economic burden. The additional morbidity associated with social issues that arises along with the course of this disorder increases the need for a clear understanding of its etiopathogenesis thus allowing an implementation of novel pharmacological strategies. Despite astrocytes have been long described to actively participate in the regulation of brain circuits, available information is still poor. Even less information is available about their precise role in the pathogenesis of illness. Moreover, the scant knowledge about the astrocyte-neuron interplay in health and disease still hampers innovative discoveries. The focus of this review is to look for new and innovative pharmacological approaches against AD. In order to perform this, we used following keywords in PubMed search engine: astrocytes, therapy, Alzheimer’s disease, AD, treatment and glia in different combinations. With this review, we collected data available in literature describing how also astrocytes besides neurons might be new potential targets for drug discovery. Different approach currently being studied include modulation of glutamate transporters expression, astroglial genetic manipulation, free radicals inhibition, up-regulation of neurotrophins, and regulation of astrogliosis and neuroinflammation. Since several studies already demonstrated that astrocytes are definitely involved in AD pathogenesis, these cells can represent a promising new therapeutic target

Astrocyte-neuron interplay in Alzheimer's disease: evidence from an innovative and promising pharmacological manipulation in a triple transgenic model of the disease

Background: Alzheimer's disease (AD) is a serious health and economic challenge of the modern age. Current treatments provide only symptomatic relief, making necessary a multitargeted approach against the several pathological processes underlying such disease. In particular, beta-amyloid deposition, tauopathy, astrocyte dysfunction, neuroinflammation and glutamate unbalance recently became promising targets to develop new therapies. In this context, it has been shown that palmitoylethanolamide (PEA) is a multitargeted treatment strategy that provides a novel potential adjunct therapy. Methods: Here, we tested the effects of a 3-months treatment with ultramicronized PEA (um-PEA), a formulation that improves PEA bioavailability, in young (6-month-old) and adult (12-month-old) 3xTg-AD mice, compared to their age-matched Non-Tg mice. Via a subcutaneous delivery system, the treatment mimicked the clinic use with a chronic daily administration. At the end of the treatments, potential neuropathological mechanisms were assessed by western blot, reverse transcription - polymerase chain reaction (RT-PCR), and immunofluorescence in the hippocampal tissues. Results: Our finding revealed that um-PEA normalizes astrocytic functionality, rebalances the astrocyte glutamate regulating system, reduces Aβ formation and tau hyperphosphorylation, restrains neuroinflammation and promotes neuronal survival in 3xTg-AD mice. Interestingly, PEA effects where more pronounced in young mice suggesting its potential as an early treatment. Conclusions: um-PEA is a novel potential treatment whose multitargeted efficacy is powerful especially in early and asymptomatic phases of AD, suggesting its application as a precocious approach. Since PEA is already licenced for use in humans, displaying a high tolerability and safety profile, it would be an ideal candidate for a long-term use lasting several years, as potential AD treatment requires

Reactive astrogliosis and neuronal impairment: in vitro and in vivo evidence on palmitoylethanolamide effects in a triple transgenic model of Alzheimer’s disease

More than 60-80% of dementia cases worldwide in elderly people is caused by Alzheimer’s disease (AD) (Alzheimer’s disease Facts and Figures, 2017). Histopathologically, AD is characterized by the aggregation of extracellular neuritic β-amyloid peptide that leads to the creation of senile plaques, and the production of intracellular neurofibrillary tangles caused by tau protein hyperphosphorylation (Braak et al., 1988; Merz et al., 1983). Recently, abnormally activated glial cells, previously considered only space-filling and supporting cells of the central nervous system, were recognized as another crucial feature of AD brains (Rodriguez et al., 2009). This phenomenon, accompanied by an intense inflammation, is defined reactive astrogliosis (Verkhratsky et al., 2010; 2012). Physiologically, it has a defensive intent aimed at removing injurious stimuli, but if prolonged and unstopped, as in the case of AD, it causes neuronal dysfunction and death (Brown et al., 2003). Considering these evidence, an early combination of neuroprotective and anti-inflammatory treatments may represent an efficacious approach to counteract AD. In this context, palmitoylethanolamide (PEA), an endogenous lipid mediator, already tested in a surgical model of AD (Scuderi et al., 2011; 2014; Tomasini et al., 2015), is an excellent candidate. We investigated the presence of reactive astrogliosis in a triple transgenic model of AD (3×Tg-AD) and the effects of PEA by in vitro and in vivo studies. In vitro results revealed a basal reactive state in primary cortical 3xTg-AD-derived astrocytes and the ability of PEA in counteracting this phenomenon. PEA also improved the viability of 3xTg-AD-derived primary neurons. In vivo experiments, conducted using ultramicronized-PEA, a formulation that improves its bioavailability, revealed the efficacy of this compound in dampening reactive astrogliosis and promoting the glial neurosupportive function. Considering that the safety and efficacy of PEA have been already proven also in human (Nestmann et al., 2017), our results impel towards a possible translation of these data into the clinical practice

Effect of ultramicronized-palmytoilethanolamide on astrocyte dysfunction in a triple transgenic model of Alzheimer’s disease

Alzheimer's disease (AD) is one of the most economically burdensome health conditions in current society that leads patients to functional disabilities. The main features of the disease are β-amyloid plaques (SPs) and neurofibrillary tangles (NFTs) creation which causes neuronal and synaptic loss (Braak et al., 1988; Merz et al., 1983). During last decades, also astrocyte dysfunction and the presence of an intense inflammatory state have been considered further hallmarks of AD. Indeed, abnormally activated microglia and dysfunctional astrocytes are closely associated with amyloid deposits in brain parenchyma (Akiyama et al., 2000). According to these events, it is reasonable to assume that a combination of neuroprotective and anti-inflammatory treatments may represent an appropriate approach to tackle AD. In this context, the endogenous lipid mediator palmitoylethanolamide (PEA), abundant in the central nervous system and produced also by glial cells, seems to fulfill the criteria of a multi-factorial approach. The aim of this work was to investigate the effect of a chronic treatment with ultramicronized (um)-PEA (subcutaneously administered by a depot delivery system) in 6-month-old 3xTg-AD mice. In particular, we investigated the effect of um-PEA on glial dysfunction and neuroinflammation during the mild stage of AD pathology. We studied both glial fibrillary acidic protein (GFAP) and S100B as markers for astrocyte functioning, and cyclooxygenase (COX)-2, inducible nitric oxide synthase (iNOS), NF-kB transcriptional factor, and the main proinflammatory cytokines to explore the inflammatory state. Results revealed a mild astrocyte dysfunction in the 3xTg-AD mice when compared with their Non-Tg littermates. Such a dysfunction was rescued by um-PEA chronic treatment. Moreover, we found that 6-month-old 3xTg-AD mice are characterized by an intense pro-inflammatory state. Um-PEA chronic treatment was able to normalize these alterations. By virtue of its high tolerability and safety (Petrosino et al., 2016), also demonstrated in humans, in their entirety, these results suggest um-PEA as a valid tool in the therapeutic strategy against AD