beta-Amyloid induces increased release of interleukin-1 beta from lipopolysaccharide-activated human monocytes

Caspases in Alzheimer's Disease: Mechanism of Activation, Role, and Potential Treatment

With the aging of the population, treatment of conditions emerging in old age, such as neurodegenerative disorders, has become a major medical challenge. Of these, Alzheimer's disease, leading to cognitive dysfunction, is of particular interest. Neuronal loss plays an important role in the pathophysiology of this condition, and over the years, a great effort has been made to determine the role of various factors in this process. Unfortunately, until now, the exact pathomechanism of this condition remains unknown. However, the most popular theories associate AD with abnormalities in the Tau and β-amyloid (Aβ) proteins, which lead to their deposition and result in neuronal death. Neurons, like all cells, die in a variety of ways, among which pyroptosis, apoptosis, and necroptosis are associated with the activation of various caspases. It is worth mentioning that Tau and Aβ proteins are considered to be one of the caspase activators, leading to cell death. Moreover, the protease activity of caspases influences both of the previously mentioned proteins, Tau and Aβ, converting them into more toxic derivatives. Due to the variety of ways caspases impact the development of AD, drugs targeting caspases could potentially be useful in the treatment of this condition. Therefore, there is a constant need to search for novel caspase inhibitors and evaluate them in preclinical and clinical trials.

Rosiglitazone attenuates amyloid beta and glial fibrillary acidic protein in the hippocampus and neuroinflammation associated learning and memory impairments in rats

OBJECTIVE

The aim of the current study was to investigate the beneficial effects of rosiglitazone (Rosi) on amyloid beta(Aβ) and glial fibrillary acidic protein (GFAP) in the hippocampus and neuroinflammation-associated learning and memory impairments in rats.

MATERIALS AND METHODS

The rats were grouped and treated as follows: (1) Control in which saline and vehicle were administered instead of LPS and Rosi respectively. (2) Lipopolysaccharide (LPS) group in which LPS was dissolved in saline and injected (1 mg/kg) intraperitoneally. Vehicle was administered instead of Rosi in this group. (3-5) LPS+ Rosi 1, LPS+ Rosi 3, and LPS+ Rosi 5 groups in them 1, 3, or 5 mg/kg of Rosi respectively was administered 30 min before LPS. The treatments were done for two weeks. In the first week, Rosi or its vehicle was injected 30 min before LPS. In the second week, the treatments were the same as the first week and behavioral tests were also carried out in the second week. The hippocampal tissues were finally detached for biochemical assessment.

RESULTS

The results showed that Rosi reversed increased levels of Aβ, GFAP, interleukin (IL)- 6, tumor necrosis factor-α (TNF-α), nitric oxide (NO) metabolites, and malondialdehyde (MDA) due to LPS injection. Rosi also reversed attenuating effects of LPS on IL-10 and thiol concentration and activities of catalase (CAT) and superoxide dismutase (SOD). In the Morris water maze test, the LPS group had a longer latency to find the platform while spent a shorter time spent in the target quadrant in the probe trial than the control group. In the passive avoidance test, the animals of the LPS group had a shorter delay to enter the dark chamber than the animals of the control group. Treatment with Rosi reversed these parameters.

CONCLUSION

The findings showed Rosi attenuated Aβ, GFAP, and oxidative stress in the hippocampus and neuroinflammation-associated learning and memory impairments in rats.

A Function of Amyloid-β in Mediating Activity-Dependent Axon/Synapse Competition May Unify Its Roles in Brain Physiology and Pathology

Amyloid-β protein precursor (AβPP) gives rise to amyloid-β (Aβ), a peptide at the center of Alzheimer's disease (AD). AβPP, however, is also an ancient molecule dating back in evolution to some of the earliest forms of metazoans. This suggests a possible ancestral function that may have been obscured by those that evolve later. Based on literature from the functions of Aβ/AβPP in nervous system development, plasticity, and disease, to those of anti-microbial peptides (AMPs) in bacterial competition as well as mechanisms of cell competition uncovered first by Drosophila genetics, I propose that Aβ/AβPP may be part of an ancient mechanism employed in cell competition, which is subsequently co-opted during evolution for the regulation of activity-dependent neural circuit development and plasticity. This hypothesis is supported by foremost the high similarities of Aβ to AMPs, both of which possess unique, opposite (i.e., trophic versus toxic) activities as monomers and oligomers. A large body of data further suggests that the different Aβ oligomeric isoforms may serve as the protective and punishment signals long predicted to mediate activity-dependent axonal/synaptic competition in the developing nervous system and that the imbalance in their opposite regulation of innate immune and glial cells in the brain may ultimately underpin AD pathogenesis. This hypothesis can not only explain the diverse roles observed of Aβ and AβPP family molecules, but also provide a conceptual framework that can unify current hypotheses on AD. Furthermore, it may explain major clinical observations not accounted for and identify approaches for overcoming shortfalls in AD animal modeling.

Inflammatory mechanisms in neurodegeneration

This review discusses the profound connection between microglia, neuroinflammation, and Alzheimer's disease (AD). Theories have been postulated, tested, and modified over several decades. The findings have further bolstered the belief that microglia-mediated inflammation is both a product and contributor to AD pathology and progression. Distinct microglia phenotypes and their function, microglial recognition and response to protein aggregates in AD, and the overall role of microglia in AD are areas that have received considerable research attention and yielded significant results. The following article provides a historical perspective of microglia, a detailed discussion of multiple microglia phenotypes including dark microglia, and a review of a number of areas where microglia intersect with AD and other pathological neurological processes. The overall breadth of important discoveries achieved in these areas significantly strengthens the hypothesis that neuroinflammation plays a key role in AD. Future determination of the exact mechanisms by which microglia respond to, and attempt to mitigate, protein aggregation in AD may lead to new therapeutic strategies.

Can we assess severity of Guillain-Barré syndrome using absolute monocyte count?

INTRODUCTION

Guillain-Barré syndrome (GBS) is an inflammatory demyelinating autoimmune disease, associated with blood-nerve barrier breakdown, inflammatory cells infiltration, and cytokine leakage in the peripheral nervous system. Currently, it has been revealed that monocytes play key roles in the inflammatory response. Therefore, we aimed to assess the correlation between monocyte count and GBS in this study.

METHODS

Retrospective study was conducted in 114 patients with GBS and 120 age- and gender-matched individuals.

RESULTS

Absolute monocyte count in patients with GBS was higher than that in healthy controls (0.61 ± 0.24 vs 0.41 ± 0.10; P  < .001). Interestingly, monocyte count had significant positive correlations with CRP, ESR, and disease severity of GBS (r = .244, P = .009; r = .269, P = .004; r = .322, P < .001). A cutoff value of 0.515 for monocyte count was observed in patients with GBS (areas under the curve = 0.808, 95% confidence interval = 0.749-0.868, P  < .001). Meanwhile, absolute monocyte count was independently associated with GBS in logistic regression analysis (odds ratio = 2.291, 95% confidence interval = 3.557-27.493, P < .001).

CONCLUSION

Our findings demonstrated that elevated monocyte count is independently associated with GBS patients, and suggested monocyte count is positively associated with disease severity of GBS.

Lactuca capensis reverses memory deficits in Aβ1-42-induced an animal model of Alzheimer's disease

We investigated the neuropharmacological effects of the methanolic extract from Lactuca capensis Thunb. leaves (100 and 200 mg/kg) for 21 days on memory impairment in an Alzheimer's disease (AD) rat model produced by direct intraventricular delivery of amyloid‐β1‐42 (Aβ1‐42). Behavioural assays such as Y‐maze and radial arm maze test were used for assessing memory performance. Aβ1‐42 decreased cognitive performance in the behavioural tests which were ameliorated by pre‐treatment with the methanolic extract. Acetylcholinesterase activity and oxidant–antioxidant balance in the rat hippocampus were abnormally altered by Aβ1‐42 treatment while these deficits were recovered by pre‐treatment with the methanolic extract. In addition, rats were given Aβ1‐42 exhibited in the hippocampus decreased brain‐derived neurotrophic factor (BDNF) mRNA copy number and increased IL‐1β mRNA copy number which was reversed by the methanolic extract administration. These findings suggest that the methanolic extract could be a potent neuropharmacological agent against dementia via modulating cholinergic activity, increasing of BDNF levels and promoting antioxidant action in the rat hippocampus.

Specialized Pro-Resolving Mediators from Omega-3 Fatty Acids Improve Amyloid-β Phagocytosis and Regulate Inflammation in Patients with Minor Cognitive Impairment

In this review we discuss the immunopathology of Alzheimer's disease (AD) and recent advances in the prevention of minor cognitive impairment (MCI) by nutritional supplementation with omega-3 fatty acids. Defective phagocytosis of amyloid-β (Aβ) and abnormal inflammatory activation of peripheral blood mononuclear cells (PBMCs) are the two key immune pathologies of MCI and AD patients. The phagocytosis of Aβ by PBMCs of MCI and AD patients is universally defective and the inflammatory gene transcription is heterogeneously deregulated in comparison to normal subjects. Recent studies have discovered a cornucopia of beneficial anti-inflammatory and pro-resolving effects of the specialized proresolving mediators (SPMs) resolvins, protectins, maresins, and their metabolic precursors. Resolvin D1 and other mediators switch macrophages from an inflammatory to a tissue protective/pro-resolving phenotype and increase phagocytosis of Aβ. In a recent study of AD and MCI patients, nutritional supplementation by omega-3 fatty acids individually increased resolvin D1, improved Aβ phagocytosis, and regulated inflammatory genes toward a physiological state, but only in MCI patients. Our studies are beginning to dissect positive factors (adherence to Mediterranean diet with omega-3 and exercise) and negative factors (high fat diet, infections, cancer, and surgeries) in each patient. The in vitro and in vivo effects of omega-3 fatty acids and SPMs suggest that defective phagocytosis and chronic inflammation are related to defective production and/or defective signaling by SPMs in immune cells.

Amyloid precursor protein mediated changes in intestinal epithelial phenotype in vitro

Background

Although APP and its proteolytic metabolites have been well examined in the central nervous system, there remains limited information of their functions outside of the brain. For example, amyloid precursor protein (APP) and amyloid beta (Aβ) immunoreactivity have both been demonstrated in intestinal epithelial cells. Based upon the critical role of these cells in absorption and secretion, we sought to determine whether APP or its metabolite amyloid β (Aβ), had a definable function in these cells.

Methodology/Principal Findings

The human colonic epithelial cell line, Caco-2 cells, were cultured to examine APP expression and Aβ secretion, uptake, and stimulation. Similar to human colonic epithelium stains, Caco-2 cells expressed APP. They also secreted Aβ 1-40 and Aβ 1-42, with LPS stimulating higher concentrations of Aβ 1-40 secretion. The cells also responded to Aβ 1-40 stimulation by increasing IL-6 cytokine secretion and decreasing cholesterol uptake. Conversely, stimulation with a sAPP-derived peptide increased cholesterol uptake. APP was associated with CD36 but not FATP4 in co-IP pull down experiments from the Caco-2 cells. Moreover, stimulation of APP with an agonist antibody acutely decreased CD36-mediated cholesterol uptake.

Conclusions/Significance

APP exists as part of a multi-protein complex with CD36 in human colonic epithelial cells where its proteolytic fragments have complex, reciprocal roles in regulating cholesterol uptake. A biologically active peptide fragment from the N-terminal derived, sAPP, potentiated cholesterol uptake while the β secretase generated product, Aβ1-40, attenuated it. These data suggest that APP is important in regulating intestinal cholesterol uptake in a fashion dependent upon specific proteolytic pathways. Moreover, this biology may be applicable to cells beyond the gastrointestinal tract.

Attenuation of microglial activation in a mouse model of Alzheimer's disease via NFAT inhibition

Background

Amyloid β (Aβ) peptide is hypothesized to stimulate microglia to acquire their characteristic proinflammatory phenotype in Alzheimer’s disease (AD) brains. The specific mechanisms by which Aβ leads to microglial activation remain an area of interest for identifying attractive molecular targets for intervention. Based upon the fact that microglia express the proinflammatory transcription factor, nuclear factor of activated T cells (NFAT), we hypothesized that NFAT activity is required for the Aβ-stimulated microgliosis that occurs during disease.

Methods

Primary murine microglia cultures were stimulated with Aβ in the absence or presence of NFAT inhibitors, FK506 and tat-VIVIT peptide, to quantify secretion of cytokines, neurotoxins, or Aβ phagocytosis. A transgenic mouse model of AD, APP/PS1, was treated subcutaneously via mini-osmotic pumps with FK506 or tat-VIVIT to quantify effects on cytokines, microgliosis, plaque load, and memory.

Results

Expression of various NFAT isoforms was verified in primary murine microglia through Western blot analysis. Microglial cultures were stimulated with Aβ fibrils in the absence or presence of the NFAT inhibitors, FK506 and tat-VIVIT, to demonstrate that NFAT activity regulated Aβ phagocytosis, neurotoxin secretion, and cytokine secretion. Delivery of FK506 and tat-VIVIT to transgenic APP/PS1 mice attenuated spleen but not brain cytokine levels. However, FK506 and tat-VIVIT significantly attenuated both microgliosis and Aβ plaque load in treated mice compared to controls. Surprisingly, this did not correlate with changes in memory performance via T-maze testing.

Conclusions

Our findings suggest that development of specific NFAT inhibitors may offer promise as an effective strategy for attenuating the microgliosis and Aβ plaque deposition that occur in AD.

Electronic supplementary material

The online version of this article (doi:10.1186/s12974-015-0255-2) contains supplementary material, which is available to authorized users.

Overexpression of mutant amyloid-β protein precursor and presenilin 1 modulates enteric nervous system

Alzheimer's disease (AD) is a neurodegenerative disorder histologically characterized by amyloid-β (Aβ) protein accumulation and activation of associated microglia. Although these features are well described in the central nervous system, the process and consequences of Aβ accumulation in the enteric nervous system have not been extensively studied. We hypothesized that Aβ also may accumulate in the enteric nervous system and lead to immune cell activation and neuronal dysfunction in the digestive tract not unlike that observed in diseased brain. To test this hypothesis, ileums of the small intestine of thirteen month old AβPP/PS1 and C57BL/6 (wild type) mice were collected and analyzed using immunohistochemistry, western blot analysis, cytokine arrays, and ELISA. AβPP/PS1 mice demonstrated no differences in intestinal motility or water absorption but elevated luminal IgA levels compared to wild type mice. They also had increased protein levels of AβPP and the proteolytic enzyme, BACE, corresponding to an increase in Aβ1-40 in the intestinal lysate as well as an increase in both Aβ1-40 and Aβ1-42 in the stool. This correlated with increased protein markers of proinflammatory and immune cell activation. Histologic analysis localized AβPP within enteric neurons but also intestinal epithelial cells with elevated Aβ immunoreactivity in the AβPP/PS1 mice. The presence of AβPP, Aβ, and CD68 immunoreactivity in the intestines of some patients with neuropathologically-confirmed AD are consistent with the findings in this mouse model. These data support the hypothesis that in AD the intestine, much like the brain, may develop proinflammatory and immune changes related to AβPP and Aβ.

Correlated inflammatory responses and neurodegeneration in peptide-injected animal models of Alzheimer's disease

Animal models of Alzheimer's disease (AD) which emphasize activation of microglia may have particular utility in correlating proinflammatory activity with neurodegeneration. This paper reviews injection of amyloid- β (A β ) into rat brain as an alternative AD animal model to the use of transgenic animals. In particular, intrahippocampal injection of Aβ 1-42 peptide demonstrates prominent microglial mobilization and activation accompanied by a significant loss of granule cell neurons. Furthermore, pharmacological inhibition of inflammatory reactivity is demonstrated by a broad spectrum of drugs with a common endpoint in conferring neuroprotection in peptide-injected animals. Peptide-injection models provide a focus on glial cell responses to direct peptide injection in rat brain and offer advantages in the study of the mechanisms underlying neuroinflammation in AD brain.

Amyloid-β peptides activate α1-adrenergic cardiovascular receptors

Alzheimer disease features amyloid-β (Aβ) peptide deposition in brain and blood vessels and is associated with hypertension. Aβ peptide can cause vasoconstriction and endothelial dysfunction. We observed that Aβ peptides exert a chronotropic effect in neonatal cardiomyocytes, similar to α1-adrenergic receptor autoantibodies that we described earlier. Recently, it was shown that α1-adrenergic receptor could impair blood-brain flow. We hypothesized that Aβ peptides might elicit a signal transduction pathway in vascular cells, induced by α1-adrenergic receptor activation. Aβ (25-35) and Aβ (10-35) induced a positive chronotropic effect in the cardiac contraction assay (28.75±1.15 and 29.40±0.98 bpm), which was attenuated by α1-adrenergic receptor blockers (urapidil, 1.53±1.17 bpm; prazosin, 0.30±0.96 bpm). Both Aβ peptides induced an intracellular calcium release in vascular smooth muscle cells. Chronotropic activity and calcium response elicited by Aβ (25-35) were blocked with peptides corresponding to the first extracellular loop of the α1-adrenergic receptor. We observed an induction of extracellular-regulated kinase 1/2 phosphorylation by Aβ (25-35) in Chinese hamster ovary cells overexpressing α1-adrenergic receptor, vascular smooth muscle cells, and cardiomyocytes. We generated an activation-state-sensitive α1-adrenergic receptor antibody and visualized activation of the α1-adrenergic receptor by Aβ peptide. Aβ (25-35) induced vasoconstriction of mouse aortic rings and in coronary arteries in Langendorff-perfused rat hearts that resulted in decreased coronary flow. Both effects could be reversed by α1-adrenergic receptor blockade. Our data are relevant to the association between Alzheimer disease and hypertension. They may explain impairment of vascular responses by Aβ and could have therapeutic implications.

Nimodipine inhibits IL-1β release stimulated by amyloid β from microglia

BACKGROUND AND PURPOSE

There is growing evidence that inflammation plays a major role in the pathogenesis of neural damage caused by deposition of amyloid β (Aβ) in the brain. Nimodipine has received attention as a drug that might improve learning and reduce cognitive deficits in Alzheimer's disease, but the mechanism of action is poorly known. In this study, we tested the hypothesis that nimodipine inhibited Aβ-stimulated IL-1β release from microglia.

EXPERIMENTAL APPROACH

Cultures of N13 microglia cells or primary mouse microglia were treated with nimodipine, and intracellular accumulation and release of IL-1β in response to Aβ or to the P2 receptor agonists ATP and benzoyl ATP (BzATP) were measured. Accumulation of IL-1β was measured in vivo after intrahippocampal inoculation of Aβ in the absence or presence of nimodipine. The effect of nimodipine on Aβ-triggered cytotoxicity was also investigated.

KEY RESULTS

We show here that nimodipine dose-dependently inhibited Aβ-stimulated IL-1β synthesis and release from primary microglia and microglia cell lines. Furthermore, nimodipine also inhibited Aβ-induced IL-1βin vivo accumulation at concentrations known to be reached in the CNS. Finally, nimodipine protected microglia from Aβ-dependent cytotoxicity.

CONCLUSION AND IMPLICATIONS

These data suggest that alleviation of symptoms of Alzheimer's disease following nimodipine administration might be due to an anti-inflammatory effect and point to a novel role for nimodipine as a centrally acting anti-inflammatory drug.

Inflammation and the pathophysiology of Alzheimer's disease

There is increasing evidence that a chronic inflammatory response in the brain in Alzheimer's disease (AD) ultimately leads to neuronal injury and cognitive decline. Microglia, the primary immune effector cells of the brain, are thought to be key to this process. This paper discusses the evidence for inflammation in AD, and describes the mechanism whereby microglia generate neurotoxic cytokines, reactive oxygen species, and nitric oxide. Evidence that the cytokine macrophage colony-stimulating factor (M-CSF) is an important cofactor in microglial activation in AD is presented. Ongoing work using organotypic hippocampal expiant cultures to model the inflammatory process in the AD brain is also discussed. Potential avenues for therapeutic intervention are outlined.

Human Cytokine Response to ex vivo Amyloid-β Stimulation is Mediated by Genetic Factors

Through its ability to induce the enhanced release and production of cytokines, amyloid-β is responsible for the chronic inflammatory response that contributes to Alzheimer's disease (AD). Determining whether the response of monocytes to amyloid-β stimulation is under genetic control may help understand the basis of why some people are more prone to develop neuronal degeneration than others. In the current study we investigated the heritability of the cytokine (IL-10, IL-6, IL-1β, IL-1ra, TNF-[.alpha]) production capacity upon ex vivo stimulation with amyloid-β in whole blood samples of 222 twins and 85 singleton siblings from 139 extended twin families. It was found that individual differences in amyloid-β-induced cytokine production capacity are to a large extent of genetic origin, with heritability estimates ranging from 55% (IL-1β) to 68% (IL-6). We conclude that genes influencing amyloid-β-induced cytokine response may provide clues to the progression of AD pathology.

Amyloid precursor protein and proinflammatory changes are regulated in brain and adipose tissue in a murine model of high fat diet-induced obesity

Background

Middle age obesity is recognized as a risk factor for Alzheimer's disease (AD) although a mechanistic linkage remains unclear. Based upon the fact that obese adipose tissue and AD brains are both areas of proinflammatory change, a possible common event is chronic inflammation. Since an autosomal dominant form of AD is associated with mutations in the gene coding for the ubiquitously expressed transmembrane protein, amyloid precursor protein (APP) and recent evidence demonstrates increased APP levels in adipose tissue during obesity it is feasible that APP serves some function in both disease conditions.

Methodology/Principal Findings

To determine whether diet-induced obesity produced proinflammatory changes and altered APP expression in brain versus adipose tissue, 6 week old C57BL6/J mice were maintained on a control or high fat diet for 22 weeks. Protein levels and cell-specific APP expression along with markers of inflammation and immune cell activation were compared between hippocampus, abdominal subcutaneous fat and visceral pericardial fat. APP stimulation-dependent changes in macrophage and adipocyte culture phenotype were examined for comparison to the in vivo changes.

Conclusions/Significance

Adipose tissue and brain from high fat diet fed animals demonstrated increased TNF-α and microglial and macrophage activation. Both brains and adipose tissue also had elevated APP levels localizing to neurons and macrophage/adipocytes, respectively. APP agonist antibody stimulation of macrophage cultures increased specific cytokine secretion with no obvious effects on adipocyte culture phenotype. These data support the hypothesis that high fat diet-dependent obesity results in concomitant pro-inflammatory changes in brain and adipose tissue that is characterized, in part, by increased levels of APP that may be contributing specifically to inflammatory changes that occur.

Flipping the switches: CD40 and CD45 modulation of microglial activation states in HIV associated dementia (HAD)

Microglial dysfunction is associated with the pathogenesis and progression of a number of neurodegenerative disorders including HIV associated dementia (HAD). HIV promotion of an M1 antigen presenting cell (APC) - like microglial phenotype, through the promotion of CD40 activity, may impair endogenous mechanisms important for amyloid- beta (Aβ) protein clearance. Further, a chronic pro-inflammatory cycle is established in this manner. CD45 is a protein tyrosine phosphatase receptor which negatively regulates CD40L-CD40-induced microglial M1 activation; an effect leading to the promotion of an M2 phenotype better suited to phagocytose and clear Aβ. Moreover, this CD45 mediated activation state appears to dampen harmful cytokine production. As such, this property of microglial CD45 as a regulatory "off switch" for a CD40-promoted M1, APC-type microglia activation phenotype may represent a critical therapeutic target for the prevention and treatment of neurodegeneration, as well as microglial dysfunction, found in patients with HAD.

Amyloid-beta(1-42) fibrillar precursors are optimal for inducing tumor necrosis factor-alpha production in the THP-1 human monocytic cell line

Pathological studies have determined that fibrillar forms of amyloid-beta protein (Abeta) comprise the characteristic neuritic plaques in Alzheimer's disease (AD). These studies have also revealed significant inflammatory markers such as activated microglia and cytokines surrounding the plaques. Although the plaques are a hallmark of AD, they are only part of an array of Abeta aggregate morphologies observed in vivo. Interestingly, not all of these Abeta deposits provoke an inflammatory response. Since structural polymorphism is a prominent feature of Abeta aggregation both in vitro and in vivo, we sought to clarify which Abeta morphology or aggregation species induces the strongest proinflammatory response using human THP-1 monocytes as a model system. An aliquot of freshly reconstituted Abeta(1-42) in sterile water (100 microM, pH 3.6) did not effectively stimulate the cells at a final Abeta concentration of 15 microM. However, quiescent incubation of the peptide at 4 degrees C for 48-96 h greatly enhanced its ability to induce tumor necrosis factor-alpha (TNFalpha) production, the level of which surprisingly declined upon further aggregation. Imaging of the Abeta(1-42) aggregation solutions with atomic force microscopy indicated that the best cellular response coincided with the appearance of fibrillar structures, yet conditions that accelerated or increased the level of Abeta(1-42) fibril formation such as peptide concentration, temperature, or reconstitution in NaOH/PBS at pH 7.4 diminished its ability to stimulate the cells. Finally, depletion of the Abeta(1-42) solution with an antibody that recognizes fibrillar oligomers dramatically weakened the ability to induce TNFalpha production, and size-exclusion separation of the Abeta(1-42) solution provided further characterization of an aggregated species with proinflammatory activity. The findings suggested that an intermediate stage Abeta(1-42) fibrillar precursor is optimal for inducing a proinflammatory response in THP-1 monocytes.

Peripheral inflammatory cytokines as biomarkers in Alzheimer's disease and mild cognitive impairment

BACKGROUND

Several lines of evidence in the literature have shown that inflammation is involved in the pathogenesis of Alzheimer's disease (AD). However, the results from the evaluation of serum inflammatory markers in AD patients have been controversial.

OBJECTIVE

To determine if any differences exist in the monocytic secretion pattern of IL-1beta, IL-6, IL-12 and TNF-alpha from mild cognitive impairment (MCI) and AD patients, when compared with healthy age-matched controls.

METHODS

To evaluate the percentage of peripheral monocytes secreting IL-1beta, IL-6, IL-12 and TNF-alpha along with the relative levels of these proteins, a cytofluorimetric analysis was conducted under basal conditions and after lipopolysaccharide-induced cell activation.

RESULTS

We found, in AD and MCI patients, a significant raise in the percentage of monocytes producing the studied cytokines (under basal conditions and after the exposure to an inflammatory stimulus), as well as a decreased competence of these cells to respond to inflammatory challenges, when compared with controls.

CONCLUSIONS

These results agree with a persistent inflammatory status in AD, reinforcing the hypothesis of a progressive impairment of the immune response in this disorder and suggesting that monocytes may be good targets to study the progression from MCI to AD.

Suppressive Effects of Melatonin on Amyloid-β-induced Glial Activation in Rat Hippocampus

BACKGROUND

Growing evidence indicates that activated glia, as a result of chronic inflammation, are associated with amyloid-beta peptide (Abeta) deposits in the brain of Alzheimer's disease (AD) patients. The purpose of the present study was to investigate, in vivo, the effects of melatonin on glia activation, which may contribute to improved learning and memory in amnesic rats induced by amyloid-beta peptide 25-35 (Abeta25-35).

METHODS

We examined cognitive function using the Morris water maze test. Expression of interleukin 1alpha (IL-1alpha) or complement 1q (C1q) in rat hippocampal tissue was determined by immunohistochemistry.

RESULTS

It was found that Abeta25-35 injected into rat hippocampus induced an impairment in learning and memory and a marked increase of positive glial cells expressing IL-1alpha and C1q in hippocampus, compared with the controls. This suggests that glial activation triggered by Abeta25-35 parallels the dysfunction of learning and memory. Melatonin, at doses of 0.01, 0.1, and 1 mg/kg (i.g. for 10 days), improved learning and memory of rats treated with Abeta25-35. Cells expressing IL-1alpha and C1q were significantly decreased in hippocampus by pretreatment with melatonin at doses of 0.1 mg/kg and 1 mg/kg, but not at the dose of 0.01 mg/kg.

CONCLUSIONS

Our data indicate that melatonin inhibited expressions of proinflammatory factors, which may contribute to improvement of learning and memory function in AD.

Amyloid precursor protein cross-linking stimulates beta amyloid production and pro-inflammatory cytokine release in monocytic lineage cells

Beta amyloid peptide-containing neuritic plaques are a defining feature of Alzheimer's disease pathology. Beta amyloid are 38-43 residue peptides derived by proteolytic cleavage of amyloid precursor protein. Although much attention has focused on the proteolytic events leading to beta amyloid generation, the function of amyloid precursor protein remains poorly described. Previously, we reported that amyloid precursor protein functions as a pro-inflammatory receptor on monocytic lineage cells and defined a role for amyloid precursor protein in adhesion by demonstrating that beta(1) integrin-mediated pro-inflammatory activation of monocytes is amyloid precursor protein dependent. We demonstrated that antibody-induced cross-linking of amyloid precursor protein in human THP-1 monocytes and primary mouse microglia stimulates a tyrosine kinase-based pro-inflammatory signaling response leading to acquisition of a reactive phenotype. Here, we have identified pro-inflammatory mediators released upon amyloid precursor protein-dependent activation of monocytes and microglia. We show that amyloid precursor protein cross-linking stimulated tyrosine kinase-dependent increases in pro-inflammatory cytokine release and a tyrosine kinase-independent increase in beta amyloid 1-42 generation. These data provide much needed insight into the function of amyloid precursor protein and provide potential therapeutic targets to limit inflammatory changes associated with the progression of Alzheimer's disease.

Beta-amyloid protein structure determines the nature of cytokine release from rat microglia

Activated microglia represent a major source of inflammatory factors in Alzheimer's disease and a possible source of cytotoxic factors. beta-Amyloid (Abeta) peptide, the predominant component in amyloid plaques, has been shown to activate microglia and stimulate their production of inflammatory factors. The present study was performed to analyze the responses of microglia to different forms of Abeta, with regard to release of the proinflammatory cytokines interleukin-1alpha (IL-1alpha), IL-1beta, tumor necrosis factor-alpha (TNF-alpha), IL-6, and interferon-gamma (IFN-gamma), as well as the IL-1 receptor antagonist (IL-1ra). Primary cultures of microglia from rat neonatal cerebral cortex were incubated with freshly dissolved Abeta1-40 or Abeta1-42, Abeta1-40 fibrils, Abeta1-40 betaamy balls, or vehicle. Abeta1-40 fibrils did not significantly stimulate any of these cytokines. Freshly dissolved Abeta1-40 resulted in a marked increase in the release of IL-1beta, and freshly dissolved Abeta1-42 significantly stimulated both IL-1alpha and IFN-gamma secretion. The Abeta1-40 betaamy balls stimulated the secretion of IL-1alpha and IL-1beta. Incubation with Abeta peptides did not affect the secretion of IL-1ra, IL-6, or TNF-alpha. In the case of IL-1beta, the response is correlated with the presence of Abeta peptide as monomers and oligomers.

Ginger extract inhibits beta-amyloid peptide-induced cytokine and chemokine expression in cultured THP-1 monocytes

INTRODUCTION

Neuritic plaques, a neuropathologic hallmark of Alzheimer's disease, are extracellular deposits of beta-amyloid peptides (Abeta). In the central nervous system neuritic plaques are surrounded by activated microglial cells expressing proinflammatory cytokines, chemokines, and neurotoxic mediators. Long-term activation of microglial cells is suspected to contribute to the neuron loss in Alzheimer's disease.

OBJECTIVE

This study was conducted to determine whether a ginger (Zingiber officinale and Alpinia galanga) extract (GE) can dampen the activation of THP-1 cells by lipopolysaccharide, proinflammatory cytokines, and fibrillar amyloid peptide Abeta(1-42), a major component of neuritic plaques.

METHODS

THP-1 cells, a human monocytic cell line with properties similar to human microglial cells, were incubated with GE or control medium alone for 1 hour, and then with reincubated lipopolysaccharide (LPS), tumor necrosis factor-alpha (TNF-alpha), interleukin-1beta (IL-1beta) or fibrillar Abeta(1-42) for an additional hour. The extent of THP-1 cell activation was determined by measuring mRNA levels of TNF-alpha and IL-1beta, cyclooxygenase-2 (COX-2), macrophage inflammatory protein 1alpha (MIP-1alpha), monocyte chemoattractant protein-1 (MCP-1), and interferon-gamma inducible protein 10 (IP-10).

RESULTS

The results document that the GE used in this study inhibits LPS, cytokine, and amyloid Abeta peptide-induced expression of the proinflammatory genes TNF-alpha, IL-1beta, COX-2, MIP-alpha, MCP-1, and IP-10. The data provide experimental evidence that ginger can inhibit the activation of human monocytic THP-1 cells by different proinflammatory stimuli and reduce the expression of a wide range of inflammation-related genes in these microglial-like cells.

CONCLUSIONS

The findings suggest that GE may be useful in delaying the onset and the progression of neurodegenerative disorders involving chronically activated microglial cells in the central nervous system.

Alzheimer patients treated with an AchE inhibitor show higher IL-4 and lower IL-1 beta levels and expression in peripheral blood mononuclear cells

The study evaluates the expression and production of cytokines in peripheral blood mononuclear cells of patients with Alzheimer disease treated or not treated with acetylcholinesterase inhibitor, which enhances neuronal transmission. Cytokines associated with brain inflammation such as interleukin (IL)-1beta, IL-6, and tumor necrosis factor-alpha have been implicated in the regulation of amyloid peptide protein synthesis. The anti-inflammatory cytokine, IL-4, may suppress the activity of IL-1beta. Patients were assessed for clinical and immunologic features at baseline and after 1 month of treatment with Donepezil, an acetylcholinesterase inhibitor. Peripheral blood mononuclear cells were cultured with and without phytohemagglutinin stimulation. IL-1beta and IL-4 levels were measured by enzyme-linked immunosorbent assay. Reverse transcriptase-polymerase chain reaction was used to determine the expression of cytokines in peripheral mononuclear cells. Compared with untreated patients and healthy control subjects, IL-1beta levels and expression decreased in Alzheimer disease patients treated with Donepezil (P < 0.001). In contrast, IL-4 levels and expression were significantly higher in Alzheimer patients treated with the acetylcholinesterase inhibitor. This increment was observed in both unstimulated and phytohemagglutinin-stimulated peripheral blood mononuclear cells.

A proline-rich polypeptide complex (PRP) from ovine colostrum. Studies on the effect of PRP on nitric oxide (NO) production induced by LPS in THP-1 cells

A proline-rich polypeptide complex (PRP) isolated from ovine colostrum shows immunoregulatory activity. Similar activity was observed when PRP was replaced with a nonapeptide (NP) isolated from chymotryptic digest of PRP. The polypeptide complex also shows procognitive activity. In the form of orally administered tablets called Colostrinin, containing 100 microg of PRP, it improves the outcome of Alzheimer's disease (AD) patients. The mechanism of action of PRP/Colostrinin in AD is not yet clarified. Microglial cells involvement in AD has been related to amyloid beta (Abeta) internalization, the release of inflammatory cytokines, overproduction of nitrogen oxide (NO) and superoxide anion (O2-), and the development of neuritic plaques. It has been previously found in our laboratory that PRP regulates the secretion of an array of cytokines. It also was shown, in preliminary experiments using human blood cells and murine macrophages, that PRP inhibits production of NO and O2- induced by LPS. In the present work, to study the effect of PRP and NP on the release of NO and O2-induced by LPS we applied THP-1 cells. The human monocyte/macrophage THP-1 cell line has been widely used as a model of human microglial cells. The results obtained showed that THP-1 cells release NO when activated with LPS. However, neither PRP nor NP induced production of NO. Although the nonapeptide, at higher concentration (100 microg/mL), showed an inhibitory activity on the release of NO induced by LPS, no inhibition was observed when PRP was used. THP-1 cells treated with LPS, PRP or NP did not release O2-.

P2X7 receptor modulation of beta-amyloid- and LPS-induced cytokine secretion from human macrophages and microglia

To test whether extracellular ATP can play a role in the neuroimmunopathology of Alzheimer's disease (AD), we evaluated the capacity of the ATP-binding purinoreceptor, P2X7, to modulate cytokine secretion on cultured human macrophages and microglia pre-activated 24 h with the 42 amino acid beta-amyloid peptide (Abeta(1-42)) or lipopolysaccharide. Thirty minutes of exposure to the selective P2X7 agonist 2'-3'-O-(4-benzoylbenzoyl)adenosine 5'-triphosphate (BzATP) resulted in the secretion of IL-1beta after either Abeta(1-42) or LPS stimulation of human macrophages that was dependent on the concentration of the stimulus used to pre-activate the cells. Further tests on human microglia treated with BzATP (300 microM) resulted in a 1.5- and 3.5-fold enhancement of IL-1alpha and IL-1beta secretion, respectively, from cells pre-activated by 10 microM Abeta(1-42) and a 1.6- and 3.9-fold enhancement of IL-1alpha and IL-1beta secretion, respectively, from cells pre-activated by 1 microg/ml LPS. BzATP induction of IL-1alpha and IL-1beta secretion from microglia was completely reversed by pre-incubation of the cells with the P2X7 antagonist, adenosine 5'-triphosphate 2',3'-acyclic dialcohol (oxidized ATP). In contrast to its effects on IL-1alpha and IL-1beta secretion, BzATP induced TNF-alpha after LPS stimulation, but not after stimulation with Abeta(1-42), induced IL-18 secretion regardless of whether microglia were pre-activated and attenuated IL-6 secretion after either LPS or Abeta(1-42) pre-activation. These results demonstrate that extracellular ATP can modulate Abeta-induced cytokine secretion from human macrophages and microglia and thus may play a role in the neuroimmunopathology of AD.

Interleukin-6 in the aging brain

Astrocytes, microglia, and neurons express the cytokine interleukin-6 (IL-6), which in the brain has been suggested to reduce food intake, inhibit memory and learning, cause neurodegeneration, and exacerbate sickness behavior induced by other cytokines. Recent evidence indicates IL-6 levels are increased in brain of healthy aged animals, thus it may play a role in the neurophysiological manifestations of old age. The purpose of this brief report is to discuss the new evidence that suggests an age-related increase in brain IL-6 and the impact this inflammatory cytokine may have on "successful" aging.

Identification of Cathepsin B as a Mediator of Neuronal Death Induced by Aβ-activated Microglial Cells Using a Functional Genomics Approach

Alzheimer's disease is a progressive neurodegenerative disease characterized by senile plaques, neurofibrillary tangles, dystrophic neurites, and reactive glial cells. Activated microglia are found to be intimately associated with senile plaques and may play a central role in mediating chronic inflammatory conditions in Alzheimer's disease. Activation of cultured murine microglial BV2 cells by freshly sonicated Abeta42 results in the secretion of neurotoxic factors that kill primary cultured neurons. To understand molecular pathways underlying Abeta-induced microglial activation, we analyzed the expression levels of transcripts isolated from Abeta42-activated BV2 cells using high density filter arrays. The analysis of these arrays identified 554 genes that are transcriptionally up-regulated by Abeta42 in a statistically significant manner. Quantitative reverse transcription-PCR was used to confirm the regulation of a subset of genes, including cysteine proteases cathepsin B and cathepsin L, tissue inhibitor of matrix metalloproteinase 2, cytochrome c oxidase, and allograft inflammatory factor 1. Small interfering RNA-mediated silencing of the cathepsin B gene in Abeta-activated BV2 cells diminished the microglial activation-mediated neurotoxicity. Moreover, CA-074, a specific cathepsin B inhibitor, also abolished the neurotoxic effects caused by Abeta42-activated BV2 cells. Our results suggest an essential role for secreted cathepsin B in neuronal death mediated by Abeta-activated inflammatory response.

Peripheral cytokine release in Alzheimer patients: correlation with disease severity

Various studies suggested that inflammation is involved in the pathogenesis of Alzheimer's disease (AD). We investigated cytokine release from LPS-stimulated blood cells of 32 AD patients, with different disease severity, compared to 16 age-related controls. A significant decrease of IL-1beta and IL-6 secretion was observed in severely demented patients; TNF-alpha release was also decreased, but not significantly. By contrast, mild and moderate patients showed a cytokine release similar to controls. IL-1beta, IL-6 and TNF-alpha secretion was negatively correlated with the severity of dementia, quantified by the MMSE. Our data suggest that alterations of the immune profile are associated with AD progression.

Reduction of human monocytic cell neurotoxicity and cytokine secretion by ligands of the cannabinoid-type CB2 receptor

1 Two cannabinoid receptors, CB1 and CB2, have been identified. The CB1 receptor is preferentially expressed in brain, and the CB2 receptor in cells of leukocyte lineage. We identified the mRNA for the CB1 receptor in human neuroblastoma SH-SY5Y cells, and the mRNA and protein for the CB2 receptor in human microglia and THP-1 cells. 2 Delta(9)-and Delta(8)-tetrahydrocannabinol (THC) were toxic when added directly to SH-SY5Y neuroblastoma cells. The toxicity of Delta(9)- THC was inhibited by the CB1 receptor antagonist SR141716A but not by the CB2 receptor antagonist SR144528. The endogenous ligand anandamide was also toxic, and this toxicity was enhanced by inhibitors of its enzymatic hydrolysis. 3 The selective CB2 receptor ligands JWH-015 and indomethacin morpholinylamide (BML-190), when added to THP-1 cells before stimulation with lipopolysaccharide (LPS) and IFN-gamma, reduced the toxicity of their culture supernatants to SH-SY5Y cells. JWH-015 was more effective against neurotoxicity of human microglia than THP-1 cells. The antineurotoxic activity of JWH-015 was blocked by the selective CB2 receptor antagonist SR144528, but not by the CB1 receptor antagonist SR141716A. This activity of JWH-015 was synergistic with that of the 5-lipoxygenase (5-LOX) inhibitor REV 5901. 4 Cannabinoids inhibited secretion of IL-1beta and tumor necrosis factor-alpha (TNF-alpha) by stimulated THP-1 cells, but these effects could not be directly correlated with their antineurotoxic activity. 5 Specific CB2 receptor ligands could be useful anti-inflammatory agents, while avoiding the neurotoxic and psychoactive effects of CB1 receptor ligands such as Delta(9)-THC.

A cell surface receptor complex for fibrillar beta-amyloid mediates microglial activation

Senile plaques found in the Alzheimer's disease brain are foci of local inflammatory reactions mediated by plaque-associated microglia. The interaction of microglia with compacted deposits of beta-amyloid (Abeta) fibrils results in the stimulation of intracellular Tyr kinase-based signaling cascades and cellular activation, leading to the secretion of proinflammatory molecules. This study identifies a cell surface receptor complex that mediates the binding of microglia to Abeta fibrils and the subsequent activation of intracellular signaling pathways leading to a proinflammatory response. The receptor complex includes the B-class scavenger receptor CD36, the integrin-associated protein/CD47, and the alpha(6)beta(1)-integrin. Antagonists of scavenger receptors, CD36, CD47, and alpha(6)beta(1) inhibited the adhesion of THP-1 monocytes to Abeta fibrils. In addition, peptide competitors of Abeta fibril interactions with CD36, scavenger receptors, CD47, and the alpha(6)beta(1)-integrin inhibited Abeta stimulation of Tyr kinase-based signaling cascades in both THP-1 monocytes and murine microglia as well as interleukin 1beta production. A scavenger receptor antagonist and antibodies specific for CD36 and the beta(1)-integrin subunit also inhibited the Abeta-stimulated generation of reactive oxygen species. Importantly, the principal components of this receptor complex are shared with those for other fibrillar proteins and thus represent general elements through which myeloid lineage cells recognize complex fibrillar proteins. Identification of the cell surface molecules that interact with Abeta fibrils and mediate their activation of intracellular signaling cascades represents a potential intervention point in the treatment of Alzheimer's disease.

Toxicity of human monocytic THP-1 cells and microglia toward SH-SY5Y neuroblastoma cells is reduced by inhibitors of 5-lipoxygenase and its activating protein FLAP

To explore whether the proinflammatory products of the 5-lipoxygenase (5-LOX) pathway are involved in microglia-mediated toxicity toward neuronal cells, we evaluated the effects of 5-LOX inhibitors using an in vitro assay system where human neuronal SH-SY5Y cells are exposed to toxic secretions from THP-1 monocytic cells or human microglia. The specific 5-LOX inhibitors, REV 5901, zileuton, and 5-hydroxyeicosatetraenoic acid lactone; the nonselective LOX inhibitors, phenidone and dapsone; the dual 5-LOX/cyclooxygenase inhibitor, tepoxalin; and the selective inhibitor of the 5-LOX-activating protein (FLAP), MK-886, inhibited such toxicity. The toxicity was enhanced by the 5-LOX product leukotriene (LT)D(4) and reduced by the selective cysteinyl LT receptor (CysLT(1)) antagonist MK-571. The mRNAs for 5-LOX and FLAP were detected in THP-1 cells and human microglia but not in SH-SY5Y cells. The data suggest that inhibition of proinflammatory LT production by 5-LOX inhibition could selectively reduce toxicity of microglial cells and thus be beneficial in neuroinflammatory diseases.

The role of macrophage/microglia and astrocytes in the pathogenesis of three neurologic disorders: HIV-associated dementia, Alzheimer disease, and multiple sclerosis

Macrophage/microglia (M phi) are the principal immune cells in the central nervous system (CNS) concomitant with inflammatory brain disease and play a significant role in the host defense against invading microorganisms. Astrocytes, as a significant component of the blood-brain barrier, behave as one of the immune effector cells in the CNS as well. However, both cell types may play a dual role, amplifying the effects of inflammation and mediating cellular damage as well as protecting the CNS. Interactions of the immune system, M phi, and astrocytes result in altered production of neurotoxins and neurotrophins by these cells. These effects alter the neuronal structure and function during pathogenesis of HIV-1-associated dementia (HAD), Alzheimer disease (AD), and multiple sclerosis (MS). HAD primarily involves subcortical gray matter, and both HAD and MS affect sub-cortical white matter. AD is a cortical disease. The process of M phi and astrocytes activation leading to neurotoxicity share similarities among the three diseases. Human Immunodeficiency Virus (HIV)-1-infected M phi are involved in the pathogenesis of HAD and produce toxic molecules including cytokines, chemokines, and nitric oxide (NO). In AD, M phis produce these molecules and are activated by beta-amyloid proteins and related oligopeptides. Demyelination in MS involves M phi that become lipid laden, spurred by several possible antigens. In these three diseases, cytokine/chemokine communications between M phi and astrocytes occur and are involved in the balance of protective and destructive actions by these cells. This review describes the role of M phi and astrocytes in the pathogenesis of these three progressive neurological diseases, examining both beneficent and deleterious effects in each disease.

Structure-function relationship exists for ginsenosides in reducing cell proliferation and inducing apoptosis in the human leukemia (THP-1) cell line

Ginsenosides of the 20(S)-protopanaxadiol and 20(S)-protopanaxatriol classifications including the aglycones, protopanaxadiol (PD), protopanaxatriol (PT), and ginsenosides Rh2 and Rh1 were shown to posses characteristic effects on the proliferation of human leukemia cells (THP-1). A similar efficacy was not apparent for ginsenoside Rg3. The concentrations to inhibit 50% of cells (LC50) for PD, Rh2, PT, and Rh1 were 13, 15, 19, and 210 microg/mL, respectively. PD and PT induced DNA fragmentation at the LC50 after 72 h of treatment, compared to Rh2, Rh1, dexamethasone, and untreated cells. Cell-cycle analysis confirmed apoptosis with PD and PT treatment of THP-1 cells resulting in a buildup of sub-G1 cells after 24, 48, and 72 h of treatment. Rh2 and dexamethasone treatments also increased apoptotic cells after 24 h, whereas Rh1 did not. After 48 and 72 h, Rh2, Rh1, and dexamethasone similarly increased apoptosis, but these effects were significantly (P<0.05) lower than those observed for both PD and PT treatments. Furthermore, treatments that produced the largest buildup of apoptotic cells were also found to have the largest release of lactate dehydrogenase. It can be concluded from these studies that the presence of sugars in PD and PT aglycone structures reduces the potency to induce apoptosis, and alternately alter membrane integrity. These cytotoxic effects were different to THP-1 cells than dexamethasone.

Amyloid-beta-induced chemokine production in primary human macrophages and astrocytes

In Alzheimer's disease (AD), chemotaxis might be responsible for attracting glial cells towards the neuritic plaque. Using primary monocyte-derived macrophages and primary adult astrocytes as a model, amyloid-beta (Abeta) (1-42) was able to stimulate the production, as measured by RT-PCR, of MIP-1alpha and MIP-1beta mRNA in macrophages and MCP-1 in astrocytes. Cocultures showed in unstimulated as well as in Abeta-stimulated cells an increase in MIP-1alpha, MIP-1beta and MCP-1 mRNA. ELISAs of supernatant samples of stimulated macrophages and astrocytes also showed an increase in MIP-1alpha and MIP-1beta in macrophages and MCP-1 in astrocytes. Stimulated cocultures showed an increase in MIP-1alpha, MIP-1beta and MCP-1 protein levels in contrast to unstimulated cocultures.

Endogenous brain cytokine mRNA and inflammatory responses to lipopolysaccharide are elevated in the Tg2576 transgenic mouse model of Alzheimer's disease

Beta-amyloid (Abeta) plaques have been shown to induce inflammatory changes in Alzheimer's disease brains. Cortical, but not cerebellar tissue from 16-month-old Tg2576 (Tg+) mice showed significant increases in interleukin (IL)-1alpha (2.2-fold), IL-1beta (3.4-fold), tumor necrosis factor-alpha (3.9-fold), and monocyte chemoattractant protein-1 (2.5-fold) mRNA levels compared to controls (Tg-). These changes were not apparent in 6-month-old Tg+ mice except for TNF-alpha. mRNA levels of glial fibrillary acidic protein and complement components, C1qA and C3 were also elevated in aged mice. Lipopolysaccharide (LPS) (25 microg/mouse, i.v.) induced a significantly greater production of IL-1beta protein in the cortices and hippocampi of Tg+ vs. Tg- mice at 1, 2, 4, and 6 h. Experiments in 6-month-old mice showed that not only was there less cytokine produced compared to 16-month-old mice, but the exacerbated cytokine response to LPS in Tg+ mice was not apparent. Higher levels of Abeta1-40 were measured in the cortices of 6- and 16-month-old Tg+ mice at 4-6 h after LPS, which returned to baseline after 18 h. We demonstrate that Abeta plaques elicit inflammatory responses in Tg2576 mice that are further exacerbated when challenged by an exogenous inflammatory insult, which may serve to amplify degenerative processes.

Gangliosides inhibit the release of interleukin-1beta in amyloid beta-protein-treated human monocytic cells

Amyloid-beta protein (A beta) is known to induce microglial activation with concomitant release of cytokines. Gangliosides have documented neuritogenic and neurotrophic properties. We determined the effects of A beta on the release of interleukin-1beta (IL-1beta) from the human monocytic cell line, THP-1 cells. A beta 1-42 significantly induced the release of IL-1beta from the cells. A beta 1-40, A beta 40-1, A beta 1-38, and A beta precursor protein (beta-APP) analogs also released a small amount of IL-1beta. A beta 1-42-activated cells demonstrated approx an 18-fold higher IL-1beta release than that for control cells or A beta 1-40 (soluble; S) treated cells. The release of IL-1beta from A beta 1-42-activated cells was significantly inhibited (33-48% of activated cells; p < 0.05 for the control value) by addition of gangliosides, suggesting that gangliosides inhibit the continuous cycle of the IL-1beta production in THP-1 cells.

Inflammatory cytokine levels are influenced by interactions between THP-1 monocytic, U-373 MG astrocytic, and SH-SY5Y neuronal cell lines of human origin

We measured the secretion of interleukin (IL)1beta, IL-6 and tumor necrosis factor-alpha (TNF-alpha) from human monocytic (THP-1), astrocytic (U-373 MG) and neuronal (SH-SY5Y) cell lines alone and in co-culture, with and without stimulation by a combination of lipopolysaccharide (LPS) plus interferon-gamma (IFN-gamma) or amyloid beta peptide 1-40 (Abeta). LPS+IFN-gamma stimulation increased IL-1beta secretion 16-fold from THP-1 cells. It increased IL-6 secretion 23-fold from THP-1 cells and 2.5-fold from U-373 MG cells. It increased TNF-alpha secretion 3.4-fold from THP-1 cells, but did not influence its secretion from U-373 MG cells. It did not affect the secretion of any of the cytokines from SH-SY5Y cells. Abeta stimulation increased IL-6 secretion 2.3-fold from U-373 MG cells but did not influence secretion of IL-1beta or TNF-alpha. Abeta stimulation also failed to influence secretion of any of the cytokines from THP-1 or SH-SY5Y cells. When THP-1 and U-373 MG cells were cocultured, IL-1beta and IL-6 secretion, but not TNF-alpha secretion, were significantly reduced from the levels obtained in independent cultures, suggesting that a mutual suppressive action may occur between microglia and astrocytes.

Immunological aspects of microglia: relevance to Alzheimer's disease

Alzheimer's disease (AD) is a progressive dementing neurologic illness, and the most frequent cause of dementia in the elderly. Neuritic plaques are one of the main neuropathological findings in AD, and the major protein component is the beta-amyloid protein (A beta). Another striking feature of neuritic plaques is the presence of activated microglia, cytokines, and complement components, suggestive of "inflammatory foci" within AD brain. In this review, we will examine the mechanisms by which microglia become activated in AD, emphasizing the role in the A beta protein and proinflammatory cytokines. As well, pathways for suppression of microglial activation by immunosuppressive cytokines will be described. Inflammation mediated by activated microglia is an important component of AD pathophysiology, and strategies to control this response could provide new therapeutic approaches for the treatment of AD.

Microglial signalling cascades in neurodegenerative disease

Activated microglia release a number of substances, the specific cocktail released depending on the stimulus. Many of the substances released by microglia also serve to activate them, suggesting the presence of a number of autocrine/paracrine loops. Because of the low density of microglia present in the normal brain, such autocrine/paracrine loops may not be significant but during the initiation and ongoing states of neurodegeneration, the increased concentrations of microglia may allow the activation and escalated stimulation of these feedback pathways. The activation of p38 MAPK by A beta and cytokines may be part of a microglial autocrine loop which results in the fueling of the microglial inflammatory response. A novel class of cytokine suppressive anti-inflammatory drugs (CSAIDs) inhibit the activation of p38 kinase (Bhat et al., 1998) suggesting this kinase plays a key role in transducing microglial responses to activation stimuli (Badger et al., 1996).

Activation of human macrophages by amyloid-beta is attenuated by astrocytes

In Alzheimer's disease, neuritic amyloid-beta plaques along with surrounding activated microglia and astrocytes are thought to play an important role in the inflammatory events leading to neurodegeneration. Studies have indicated that amyloid-beta can be directly neurotoxic by activating these glial cells to produce oxygen radicals and proinflammatory cytokines. This report shows that, using primary human monocyte-derived macrophages as model cells for microglia, amyloid-beta(1-42) stimulate these macrophages to the production of superoxide anions and TNF-alpha. In contrast, astrocytes do not produce both inflammatory mediators when stimulated with amyloid-beta(1-42). In cocultures with astrocytes and amyloid-beta(1-42)-stimulated macrophages, decreased levels of both superoxide anion and TNF-alpha were detected. These decreased levels of potential neurotoxins were due to binding of amyloid-beta(1-42) to astrocytes since FACScan analysis demonstrated binding of FITC-labeled amyloid-beta(1-42) to astrocytoma cells and pretreatment of astrocytes with amyloid-beta(1-16) prevented the decrease of superoxide anion in cocultures of human astrocytes and amyloid-beta(1-42)-stimulated macrophages. To elucidate an intracellular pathway involved in TNF-alpha secretion, the activation state of NF-kappaB was investigated in macrophages and astrocytoma cells after amyloid-beta(1-42) treatment. Interestingly, although activation of NF-kappaB could not be detected in amyloid-beta-stimulated macrophages, it was readily detected in astrocytoma cells. These results not only demonstrate that amyloid-beta stimulation of astrocytes and macrophages result in different intracellular pathway activation but also indicate that astrocytes attenuate the immune response of macrophages to amyloid-beta(1-42) by interfering with amyloid-beta(1-42) binding to macrophages.

Overexpression of macrophage colony-stimulating factor receptor on microglial cells induces an inflammatory response

Microglia are important in the inflammatory response in Alzheimer's disease (AD). We showed previously that macrophage colony-stimulating factor receptor (M-CSFR), encoded by the c-fms protooncogene, is overexpressed on microglia surrounding amyloid beta (Abeta) deposits in the APP(V717F) mouse model for AD. The M-CSFR is also increased on microglia after experimental brain injury and in AD. To determine the relevance of these findings, we transiently expressed M-CSFR on murine BV-2 and human SV-A3 microglial cell lines using an SV40-promoted c-fms construct. M-CSFR overexpression resulted in microglial proliferation and increased expression of inducible nitric-oxide synthase, the proinflammatory cytokines interleukin-1alpha, macrophage inflammatory protein 1-alpha, and interleukin-6 and of macrophage colony-stimulating factor (M-CSF) itself. Antibody neutralization of M-CSF showed that the M-CSFR-induced proinflammatory response was dependent on M-CSF in the culture media. By using a co-culture of c-fms-transfected murine microglia and rat organotypic hippocampal slices and a species-specific real time reverse transcriptase-polymerase chain reaction assay and enzyme-linked immunosorbent assay, we showed that M-CSFR overexpression on exogenous microglia induced expression of interleukin-1alpha by the organotypic culture. These results show that increased M-CSFR expression induces microglial proliferation, cytokine expression, and a paracrine inflammatory response, suggesting that in APP(V717F) mice increased M-CSFR on microglia could be an important factor in Abeta-induced inflammatory response.

Microglial interaction with beta-amyloid: implications for the pathogenesis of Alzheimer's disease

The etiology of Alzheimer's disease (AD) involves a significant inflammatory component as evidenced by the presence of elevated levels of a diverse range of proinflammatory molecules in the AD brain. These inflammatory molecules are produced principally by activated microglia, which are found to be clustered within and adjacent to the senile plaque. Moreover, long-term treatment of patients with non-steroidal anti-inflammatory drugs has been shown to reduce risk and incidence of AD and delay disease progression. The microglia respond to beta-amyloid (Abeta) deposition in the brain through the interaction of fibrillar forms of amyloid with cell surface receptors, leading to the activation of intracellular signal transduction cascades. The activation of multiple independent signaling pathways ultimately leads to the induction of proinflammatory gene expression and production of reactive oxygen and nitrogen species. These microglial inflammatory products act in concert to produce neuronal toxicity and death. Therapeutic approaches focused on inhibition of the microglial-mediated local inflammatory response in the AD brain offer new opportunities to intervene in the disease.

Inflammatory repertoire of Alzheimer's disease and nondemented elderly microglia in vitro

We have previously developed and characterized isolated microglia and astrocyte cultures from rapid (<4 h) brain autopsies of Alzheimer's disease (AD) and nondemented elderly control (ND) patients. In the present study, we evaluate the inflammatory repertoire of AD and ND microglia cultured from white matter (corpus callosum) and gray matter (superior frontal gyrus) with respect to three major proinflammatory cytokines, three chemokines, a classical pathway complement component, a scavenger cell growth factor, and a reactive nitrogen intermediate. Significant, dose-dependent increases in the production of pro-interleukin-1beta (pro-IL-1beta), interleukin-6 (IL-6), tumor necrosis factor-alpha (TNF-alpha), monocyte chemoattractant protein-1 (MCP-1), macrophage inflammatory peptide-1alpha (MIP-1alpha), IL-8, and macrophage colony-stimulating factor (M-CSF) were observed after exposure to pre-aggregated amyloid beta peptide (1-42) (Abeta1-42). Across constitutive and Abeta-stimulated conditions, secretion of complement component C1q, a reactive nitrogen intermediate, and M-CSF was significantly higher in AD compared with ND microglia. Taken together with previous in situ hybridization findings, these results demonstrate unequivocally that elderly human microglia provide a brain endogenous source for a wide range of inflammatory mediators.

beta-Amyloid stimulation of microglia and monocytes results in TNFalpha-dependent expression of inducible nitric oxide synthase and neuronal apoptosis

Reactive microglia associated with the beta-amyloid plaques in Alzheimer's disease (AD) brains initiate a sequence of inflammatory events integral to the disease process. We have observed that fibrillar beta-amyloid peptides activate a tyrosine kinase-based signaling response in primary mouse microglia and the human monocytic cell line, THP-1, resulting in production of neurotoxic secretory products, proinflammatory cytokines, and reactive oxygen species. We report that most of the amyloid-induced tyrosine kinase activity was stimulated after activation of Src family members such as Lyn. However, transduction of the signaling response required for increased production of the cytokines TNFalpha and IL1-beta was mediated by the nonreceptor tyrosine kinase, Syk. Additionally, beta-amyloid stimulated an NFkappaB-dependent pathway in parallel that was required for cytokine production. Importantly, TNFalpha generated by the monocytes and microglia was responsible for the majority of the neuorotoxic activity secreted by these cells after beta-amyloid stimulation but must act in concert with other factors elaborated by microglia to elicit neuronal death. Moreover, we observed that the neuronal loss was apoptotic in nature and involved increased neuronal expression of inducible nitric oxide synthase and subsequent peroxynitrite production. Selective inhibitors of inducible nitric oxide synthase effectively protected cells from toxicity associated with the microglial and monocytic secretory products. This study demonstrates a functional linkage between beta-amyloid-dependent activation of microglia and several characteristic markers of neuronal death occurring in Alzheimer's disease brains.

Age- and concentration-dependent neuroprotection and toxicity by TNF in cortical neurons from beta-amyloid

The induction of an inflammatory response and release of cytokines such as TNF may be involved in the age-related etiology of Alzheimer disease (AD). In the brain, microglia have been shown to produce a wide variety of immune mediators, including the pro-inflammatory cytokine tumor necrosis factor (TNF). We hypothesize that with age there is increased ability of microglia to produce TNF or that age decreases the neuroprotective effect of TNF against beta-amyloid (Abeta) toxicity in neurons. We investigated the effects of Abeta(1-40) on TNF secretion from forebrain cultures of microglia from embryonic, middle-age (9-month) and old (36-month) rats. Over the first 12 hr of exposure to 10 microM Abeta (1-40), microglia from embryonic and old rats increase TNF secretion, although microglia from middle-age rats did not produce detectable levels of TNF. When low concentrations of TNF are added to neurons together with Abeta (1-40) in the absence of exogenous antioxidants, neuroprotection for old neurons is significantly less than neuroprotection for middle-age neurons. In neurons from old rats, high levels of TNF together with Abeta are more toxic than in neurons from middle-age or embryonic rats. These results are discussed in relation to neuroprotection and toxicity of the age-related pathology of AD.