B₂ receptor blockage prevents Aβ-induced cognitive impairment by neuroinflammation inhibition

JNK Activation in Alzheimer's Disease Is Driven by Amyloid β and Is Associated with Tau Pathology

c-Jun N-terminal kinase 3 (JNK3) is suggested to play a key role in neurodegenerative disorders, especially in Alzheimer's disease (AD). However, it remains unclear whether JNK or amyloid β (Aβ) appears first in the disease onset. Postmortem brain tissues from four dementia subtypes of patients (frontotemporal dementia, Lewy body dementia, vascular dementia, and AD) were used to measure activated JNK (pJNK) and Aβ levels. pJNK expression is significantly increased in AD; however, similar pJNK expression was found in other dementias. Furthermore, there was a significant correlation, co-localization, and direct interaction between pJNK expression and Aβ levels in AD. Significant increased levels of pJNK were also found in Tg2576 mice, a model of AD. In this line, Aβ₄₂ intracerebroventricular injection in wild-type mice was able to induce a significant elevation of pJNK levels. JNK3 overexpression, achieved by intrahippocampal injection of an adeno-associated viral vector expressing this protein, was enough to induce cognitive deficiencies and precipitate Tau aberrant misfolding in Tg2576 mice without accelerating amyloid pathology. JNK3 overexpression may therefore be triggered by increased Aβ. The latter, together with subsequent involvement of Tau pathology, may be underlying cognitive alterations in early stages of AD.

The Therapeutic and Diagnostic Potential of Amyloid β Oligomers Selective Antibodies to Treat Alzheimer's Disease

Improvements have been made in the diagnosis of Alzheimer’s disease (AD), manifesting mostly in the development of in vivo imaging methods that allow for the detection of pathological changes in AD by magnetic resonance imaging (MRI) and positron emission tomography (PET) scans. Many of these imaging methods, however, use agents that probe amyloid fibrils and plaques–species that do not correlate well with disease progression and are not present at the earliest stages of the disease. Amyloid β oligomers (AβOs), rather, are now widely accepted as the Aβ species most germane to AD onset and progression. Here we report evidence further supporting the role of AβOs as pathological instigators of AD and introduce promising anti-AβO diagnostic probes capable of distinguishing the 5xFAD mouse model from wild type mice by PET and MRI. In a developmental study, Aβ oligomers in 5xFAD mice were found to appear at 3 months of age, just prior to the onset of memory dysfunction, and spread as memory worsened. The increase of AβOs is prominent in the subiculum and correlates with concomitant development of reactive astrocytosis. The impact of these AβOs on memory is in harmony with findings that intraventricular injection of synthetic AβOs into wild type mice induced hippocampal dependent memory dysfunction within 24 h. Compelling support for the conclusion that endogenous AβOs cause memory loss was found in experiments showing that intranasal inoculation of AβO-selective antibodies into 5xFAD mice completely restored memory function, measured 30–40 days post-inoculation. These antibodies, which were modified to give MRI and PET imaging probes, were able to distinguish 5xFAD mice from wild type littermates. These results provide strong support for the role of AβOs in instigating memory loss and salient AD neuropathology, and they demonstrate that AβO selective antibodies have potential both for therapeutics and for diagnostics.

Multifaceted Alzheimer's Disease: Building a Roadmap for Advancement of Novel Therapies

Alzheimer's disease (AD) is one of the most prevailing neurodegenerative disorders of elderly humans associated with cognitive damage. Biochemical, epigenetic, and pathophysiological factors all consider a critical role of extracellular amyloid-beta (Aß) plaques and intracellular neurofibrillary tangles (NFTs) as pathological hallmarks of AD. In an endeavor to describe the intricacy and multifaceted nature of AD, several hypotheses based on the roles of Aß accumulation, tau hyperphosphorylation, impaired cholinergic signaling, neuroinflammation, and autophagy during the initiation and advancement of the disease have been suggested. However, in no way do these theories have the potential of autonomously describing the pathophysiological alterations located in AD. The complex pathological nature of AD has hindered the recognition and authentication of successful biomarkers for the progression of its diagnosis and therapeutic strategies. There has been a significant research effort to design multi-target-directed ligands for the treatment of AD, an approach which is developed by the knowledge that AD is a composite and multifaceted disease linked with several separate but integrated molecular pathways.

Effects of rivastigmine hydrogen tartrate and donepezil hydrochloride on the cognitive function and mental behavior of patients with Alzheimer's disease

The present study aimed to examine the effects of rivastigmine hydrogen tartrate and donepezil hydrochloride on the cognitive function and mental behavior of patients with Alzheimer's disease (AD). For this purpose, a total of 126 patients with AD admitted to Luoyang Central Hospital from January, 2018 to December, 2018 were enrolled. Patients were divided into different groups according to the treatment they selected. Patients treated with single-agent donepezil were separated into a monotherapy group (n=56), and patients receiving donepezil plus rivastigmine were placed in the combination group (n=70). Before and after treatment, the cognitive functions, mental behavior and quality of life of the patients in the two groups were respectively evaluated by the Alzheimer's Disease Assessment Scale-Cognitive Subscale (ADAS-Cog), the Mini-Mental State Examination (MMSE), the Blessed-Roth Dementia Scale (BRDS) and the QOL-AD. In addition, the serum bradykinin level was detected by enzyme-linked immunosorbent assay. Following treatment, the MMSE score, BRDS, ADAS-Cog and QOL-AD scores were improved compared with those before treatment (P<0.05). However, following treatment, the 4 scores in the combination group were significantly higher than those in the monotherapy group (P<0.05). No significant differences were observed in the incidence of adverse reactions between the 2 groups (P>0.05). Following treatment, the bradykinin level in both groups was significantly decreased (P<0.05), although the decrease in the combination group was more significant than that in the monotherapy group (P<0.05). On the whole, the findings of the present study indicate that rivastigmine hydrogen tartrate used in combination with donepezil hydrochloride relieves the symptoms and improves the quality of life of patients with AD more effectively, which may be related to the reduction of the bradykinin level in these patients.

Neuropeptides and oligopeptidases in schizophrenia

Schizophrenia (SCZ) is a complex psychiatric disorder with severe impact on patient's livelihood. In the last years, the importance of neuropeptides in SCZ and other CNS disorders has been recognized, mainly due to their ability to modulate the signaling of classical monoaminergic neurotransmitters as dopamine. In addition, a class of enzymes coined as oligopeptidases are able to cleave several of these neuropeptides, and their potential implication in SCZ was also demonstrated. Interestingly, these enzymes are able to play roles as modulators of neuropeptidergic systems, and they were also implicated in neurogenesis, neurite outgrowth, neuron migration, and therefore, in neurodevelopment and brain formation. Altered activity of oligopeptidases in SCZ was described only more recently, suggesting their possible utility as biomarkers for mental disorders diagnosis or treatment response. We provide here an updated and comprehensive review on neuropeptides and oligopeptidases involved in mental disorders, aiming to attract the attention of physicians to the potential of targeting this system for improving the therapy and for understanding the neurobiology underlying mental disorders as SCZ.

The Dual Role of Kinin/Kinin Receptors System in Alzheimer's Disease

Alzheimer’s disease (AD) is the most common neurodegenerative disease characterized by progressive spatial disorientation, learning and memory deficits, responsible for 60%–80% of all dementias. However, the pathological mechanism of AD remains unknown. Numerous studies revealed that kinin/kinin receptors system (KKS) may be involved in the pathophysiology of AD. In this review article, we summarized the roles of KKS in neuroinflammation, cerebrovascular impairment, tau phosphorylation, and amyloid β (Aβ) generation in AD. Moreover, we provide new insights into the mechanistic link between KKS and AD, and highlight the KKS as a potential therapeutic target for AD treatment.

Neuroprotective Effects of Kinin B2 Receptor in Organotypic Hippocampal Cultures of Middle-Aged Mice

Aging is a multifactorial phenomenon that results in several changes at cellular and molecular levels and is considered the main risk factor for some neurodegenerative diseases. Several evidence show the participation of the kallikrein-kinin system (KKS) in neurodegeneration and this system has been associated with inflammation and immunogenic responses in the central and peripheral systems by the activation of the B1 and B2 receptors. Previous work by our group showed that bradykinin (BK) and the B2 receptor played a possible role in neuroprotection. Therefore, the objective of this study was to evaluate the participation of B2 receptors in cell viability, neuroinflammatory response and neuroplasticity in organotypic hippocampal cultures (OHCs) of 6- and 12-month-old mice. It was observed that activation of the B2 receptor by bradykinin decreased the inflammatory response and increased plasticity in 12-month-old slices. Conversely, there was an increase in the inflammatory response and a decrease in neural plasticity in the 6-month-old slices. In both ages, an increase in cell viability was observed. This data suggests that the function of the kinin B2 receptor in the hippocampus is modulated by age, providing neuroprotective action in old age.

fMRI Reveals Mitigation of Cerebrovascular Dysfunction by Bradykinin Receptors 1 and 2 Inhibitor Noscapine in a Mouse Model of Cerebral Amyloidosis

Functional magnetic resonance imaging (fMRI) techniques can be used to assess cerebrovascular dysfunction in Alzheimer’s disease, an important and early contributor to pathology. We hypothesized that bradykinin receptor inhibition alleviates the vascular dysfunction in a transgenic arcAβ mouse model of cerebral amyloidosis and that fMRI techniques can be used to monitor the treatment response. Transgenic arcAβ mice, and non-transgenic littermates of 14 months-of-age were either treated with the bradykinin receptors 1 and 2 blocker noscapine or received normal drinking water as control over 3 months (n = 8–11/group) and all mice were assessed using fMRI at the end of the treatment period. Perfusion MRI using an arterial spin labeling technique showed regional hypoperfusion in arcAβ compared to non-transgenic controls, which was alleviated by noscapine treatment. Similarly, measuring cerebral blood volume changes upon pharmacological stimulation using vessel dilator acetazolamide revealed recovery of regional impairment of cerebral vascular reactivity in arcAβ mice upon noscapine treatment. In addition, we assessed with immunohistochemistry beta-amyloid (Aβ) and inflammation levels in brain sections. Immunohistological stainings for Aβ deposition (6E10) and related microgliosis (Iba1) in the cortex and hippocampus were found comparable between noscapine-treated and untreated arcAβ mice. In addition, levels of soluble and insoluble Aβ₃₈, Aβ₄₀, Aβ₄₂ were found to be similar in brain tissue homogenates of noscapine-treated and untreated arcAβ mice using electro-chemiluminescent based immunoassay. In summary, bradykinin receptors blockade recovered cerebral vascular dysfunction in a mouse model of cerebral amyloidosis. fMRI methods revealed the functional deficit in disease condition and were useful tools to monitor the treatment response.

A novel crosslinking protocol stabilizes amyloid β oligomers capable of inducing Alzheimer's-associated pathologies

Amyloid β oligomers (AβOs) accumulate early in Alzheimer's disease (AD) and experimentally cause memory dysfunction and the major pathologies associated with AD, for example, tau abnormalities, synapse loss, oxidative damage, and cognitive dysfunction. In order to develop the most effective AβO-targeting diagnostics and therapeutics, the AβO structures contributing to AD-associated toxicity must be elucidated. Here, we investigate the structural properties and pathogenic relevance of AβOs stabilized by the bifunctional crosslinker 1,5-difluoro-2,4-dinitrobenzene (DFDNB). We find that DFDNB stabilizes synthetic Aβ in a soluble oligomeric conformation. With DFDNB, solutions of Aβ that would otherwise convert to large aggregates instead yield solutions of stable AβOs, predominantly in the 50-300 kDa range, that are maintained for at least 12 days at 37°C. Structures were determined by biochemical and native top-down mass spectrometry analyses. Assayed in neuronal cultures and i.c.v.-injected mice, the DFDNB-stabilized AβOs were found to induce tau hyperphosphorylation, inhibit choline acetyltransferase, and provoke neuroinflammation. Most interestingly, DFDNB crosslinking was found to stabilize an AβO conformation particularly potent in inducing memory dysfunction in mice. Taken together, these data support the utility of DFDNB crosslinking as a tool for stabilizing pathogenic AβOs in structure-function studies.

Association of cerebrovascular dysfunction with the development of Alzheimer's disease-like pathology in OXYS rats

Background

Cerebrovascular dysfunction plays a critical role in the pathogenesis of Alzheimer’s disease (AD): the most common cause of dementia in the elderly. The involvement of neurovasculature disorders in the progression of AD is now increasingly appreciated, but whether they represent initial factors or late-stage pathological changes during the disease is unclear. Using senescence-accelerated OXYS rats, which simulate key characteristics of sporadic AD, we evaluated contributions of cerebrovascular alterations to the disease development. At preclinical, early, and advanced stages of AD-like pathology, in the hippocampus of OXYS and Wistar (control) rats, we evaluated (i) the blood vessel state by histological and electron-microscopic analyses; (ii) differences in gene expression according to RNA sequencing (RNA-Seq) to identify the metabolic processes and pathways associated with blood vessel function; (iii) the amount of vascular endothelial growth factor (VEGF) by western blot and immunohistochemical analysis.

Results

We observed a loss of hippocampal blood vessel density and ultrastructural changes of those blood vessels in OXYS rats at the early stage of AD-like pathology. There were significant alterations in the vessels and downregulation of VEGF with an increased amount of amyloid β_1–42 there at the advanced stage of the disease. According to RNA-Seq data analysis, major alterations in cerebrovascular processes of OXYS rats were associated with blood vessel development, circulatory system processes, the VEGF signaling pathway, and vascular smooth muscle contraction. At preclinical and early stages of the AD-like pathology, these processes were upregulated and then downregulated with age. At the advanced stage in OXYS rats, differentially expressed genes (DEGs) were associated with downregulation of cerebrovascular function as compared to Wistar rats. Among the 46 DEGs at the preclinical stage of the disease, 28 DEGs at the early stage, and among 85 DEGs at the advanced stage, using functional analysis and gene network construction, we identified genes (Nos1, P2rx4, Pla2g6, and Bdkrb2) probably playing a significant role in the development of cerebrovascular dysfunction in OXYS rats.

Conclusions

Changes in expression of the genes functionally associated with cerebrovascular processes already in the early period of life may contribute to the development of AD-like pathology in OXYS rats.

Electronic supplementary material

The online version of this article (10.1186/s12864-018-4480-9) contains supplementary material, which is available to authorized users.

Copper, differently from zinc, affects the conformation, oligomerization state and activity of bradykinin

The sole role of bradykinin (BK) as an inflammatory mediator is controversial, as recent data also support an anti-inflammatory role for BK in Alzheimer's disease (AD). The involvement of two different receptors (B1R and B2R) could be a key to understand this issue. However, although copper and zinc dyshomeostasis has been demonstrated to be largely involved in the development of AD, a detailed study of the interaction of BK with these two metal ions has never been addressed. In this work, we have applied mass spectrometry, circular dichroism as well as computational methods in order to assess if copper and zinc have the ability to modulate the conformation and oligomerization of BK. In addition, we have correlated the chemical data with the effect of metals on the activity of BK analyzed in cell cultures by biochemical procedures. The biochemical analyses on monocyte/macrophage cell culture (THP-1 Cell Line human) in line with the effect of metals on the conformation of BK showed that the presence of copper can affect the signaling cascade mediated by the BK receptors. The results obtained show a further role of metal ions, particularly copper, in the development and outcome of neuroinflammatory diseases. The possible implications in AD are discussed.

Inhibitory effect of donepezil on bradykinin-induced increase in the intracellular calcium concentration in cultured cortical astrocytes

Donepezil is a potent and selective acetylcholinesterase inhibitor developed for the treatment of Alzheimer's disease. In the present study, we investigated the responses of astrocytes to bradykinin, an inflammatory mediator, and the effect of donepezil on these responses using cultured cortical astrocytes. Bradykinin induced a transient increase of intracellular calcium concentration ([Ca²⁺]_i) in cultured astrocytes. Bradykinin-induced [Ca²⁺]_i increase was inhibited by the exposure to thapsigargin, which depletes Ca²⁺ stores on endoplasmic reticulum, but not by the exclusion of extracellular Ca²⁺. Twenty four hours pretreatment of donepezil reduced the bradykinin-induced [Ca²⁺]_i increase. This reduction was inhibited not only by mecamylamine, a nAChR antagonist, but also by PI3K and Akt inhibitors. In addition, donepezil inhibited bradykinin-induced increase of the intracellular reactive oxygen species level in astrocytes. These results suggest that donepezil inhibits the inflammatory response induced by bradykinin via nAChR and PI3K-Akt pathway in astrocytes.

Involvement of the Bradykinin B1 Receptor in Microglial Activation: In Vitro and In Vivo Studies

The importance of brain inflammation to Alzheimer's disease (AD) pathogenesis has been accepted of late, with it currently being held that brain inflammation aggravates AD pathology. One important aspect of brain inflammation is the recruitment and activation of microglia, a process termed microgliosis. Kinins and bradykinin (BK), in particular, are major pro-inflammatory mediators in the periphery, although all of the factors comprising the kinin system have also been described in the brain. Moreover, it was shown that the amyloid β (Aβ) peptide (a component of AD plaques) enhances kinin secretion and activates BK receptors that can, in turn, stimulate Aβ production. Still, the role of bradykinin in modulating brain inflammation and AD is not completely understood. In this study, we aimed to investigate the roles of the bradykinin B₁ receptor (B₁R) and bradykinin B₂ receptor (B₂R) in regulating microglial secretion of pro-inflammatory factors in vitro. Furthermore, the effects of intranasal administration of specific B₁R and B₂R antagonists on Aβ burden and microglial accumulation in the brains of transgenic AD mice were studied. The data obtained show that neither R-715 (a B₁R antagonist) nor HOE 140 (a B₂R antagonist) altered microglial cell viability. However, R-715, but not HOE 140, markedly increased lipopolysaccharide-induced nitric oxide (NO) and tumor necrosis factor-alpha (TNF-α) release, as well as inducible nitric oxide synthase expression in BV2 microglial cells. Neither antagonist altered NO nor TNF-α production in non-stimulated cells. We also showed that intranasal administration of R-715 but not HOE 140 to 8-week-old 5X familial AD mice enhanced amyloid burden and microglia/macrophage accumulation in the cortex. To conclude, we provide evidence supporting a role of B₁R in brain inflammation and in the regulation of amyloid deposition in AD mice, possibly with microglial/macrophage involvement. Further studies are required to test whether modulation of this receptor can serve as a novel therapeutic strategy for AD.

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.

Kinin B2 receptor can play a neuroprotective role in Alzheimer's disease

Alzheimer's disease (AD) is characterized by cognitive decline, presence of amyloid-beta peptide (Aβ) aggregates and neurofibrillary tangles. Kinins act through B1 and B2 G-protein coupled receptors (B1R and B2R). Chronic infusion of Aβ peptide leads to memory impairment and increases in densities of both kinin receptors in memory processing areas. Similar memory impairment was observed in C57BL/6 mice (WTAβ) but occurred earlier in mice lacking B2R (KOB2Aβ) and was absent in mice lacking B1R (KOB1Aβ). Thus, the aim of this study was to evaluate the participation of B1R and B2R in Aβ peptide induced cognitive deficits through the evaluation of densitiesof kinin receptors, synapses, cell bodies and number of Aβ deposits in brain ofWTAβ, KOB1Aβ and KOB2Aβ mice. An increase in B2R density was observed in both WTAβ and KOB1Aβ in memory processing related areas. KOB1Aβ showed a decrease in neuronal density and an increase in synaptic density and, in addition, an increase in Aβ deposits in KOB2Aβ was observed. In conclusion, memory preservation in KOB1Aβ, could be due to the increase in densities of B2R, suggesting a neuroprotective role for B2R, reinforced by the increased number of Aβ plaques in KOB2Aβ. Our data point to B2R as a potential therapeutic target in AD.