Does the imbalance in the apolipoprotein E isoforms underlie the pathophysiological process of sporadic Alzheimer's disease?

Human apolipoprotein E (apoE) is a 299-amino acid secreted glycoprotein binding cholesterol and phospholipids, and with three common isoforms (APOE ε2, APOE ε3, and APOE ε4). The exact mechanism by which APOE gene variants increase/decrease Alzheimer's disease (AD) risk is not fully understood, but APOE isoforms differently affect brain homeostasis and neuroinflammation, blood-brain barrier (BBB) permeability, glial function, synaptogenesis, oral/gut microbiota, neural networks, amyloid beta (Aß) deposition, and tau-mediated neurodegeneration. In this perspective, we propose a comprehensive interpretation of APOE-mediated effects within AD pathophysiology, describing some specific cellular, biochemical, and epigenetic mechanisms and updating the different APOE-targeting approaches being developed as potential AD therapies. Intracisternal adeno-associated viral-mediated delivery of APOE ε2 is being tested in AD APOE ε4/ε4 carriers, while APOE mimetics are being used in subjects with perioperative neurocognitive disorders. Other approaches including APOE ε4 antisense oligonucleotides, anti-APOE ε4 monoclonal antibodies, APOE ε4 structure correctors, and APOE-Aß interaction inhibitors produced positive results in transgenic AD mouse models.

Molecular mechanisms of skin wound healing in non-diabetic and diabetic mice in excision and pressure experimental wounds.

Experimental models for chronic skin lesions are excision and pressure ulcer, defined as "open" and "closed" lesions, respectively, only the latter characterized by tissue hypoxia. Moreover, systemic diseases, such as diabetes mellitus, affect wound repair. Thus, models for testing new therapies should be carefully selected according to the expected targets. In this study, we present an extensive and comparative histological, immunohistochemical, and molecular characterization of these two lesions in diabetic (db/db) and non-diabetic (C57BL/6 J) mice. In db/db mice, we found significant reduction in PGP9.5-IR innervation, reduction of capillary network, and reduced expression of NGF receptors. We found an increase in VEGF receptor Kdr expression, and the PI3K-Akt signaling pathway at the core of the altered molecular network. Db/db mice with pressure ulcers showed an impairment in the molecular regulation of hypoxia-related genes (Hif1a, Flt1, and Kdr), while extracellular matrix encoding genes (Itgb3, Timp1, Fn1, Col4a1) were upregulated by hyperglycemia and lesions. Overall, the molecular analysis suggests that db/db mice have a longer inflammatory phase of the wound repair process, delaying the progression toward the proliferation and remodeling phases.

Are apolipoprotein E fragments a promising new therapeutic target for Alzheimer's disease?

Human apolipoprotein E (ApoE) is a 299-amino acid secreted glycoprotein that binds cholesterol and phospholipids. ApoE exists as three common isoforms (ApoE2, ApoE3, and ApoE4) and heterozygous carriers of the ε4 allele of the gene encoding ApoE (APOE) have a fourfold greater risk of developing Alzheimer's disease (AD). The enzymes thrombin, cathepsin D, α-chymotrypsin-like serine protease, and high-temperature requirement serine protease A1 are responsible for ApoE proteolytic processing resulting in bioactive C-terminal-truncated fragments that vary depending on ApoE isoforms, brain region, aging, and neural injury. The objectives of the present narrative review were to describe ApoE processing, discussing current hypotheses about the potential role of various ApoE fragments in AD pathophysiology, and reviewing the current development status of different anti-ApoE drugs. The exact mechanism by which APOE gene variants increase/decrease AD risk and the role of ApoE fragments in the deposition are not fully understood, but APOE is known to directly affect tau-mediated neurodegeneration. ApoE fragments co-localize with neurofibrillary tangles and amyloid ß (Aß) plaques, and may cause neurodegeneration. Among anti-ApoE approaches, a fascinating strategy may be to therapeutically overexpress ApoE2 in APOE ε4/ε4 carriers through vector administration or liposomal delivery systems. Another approach involves reducing ApoE4 expression by intracerebroventricular antisense oligonucleotides that significantly decreased Aß pathology in transgenic mice. Differences in the proteolytic processing of distinct ApoE isoforms and the use of ApoE fragments as mimetic peptides in AD treatment are also under investigation. Treatment with peptides that mimic the structural and biological properties of native ApoE may reduce Aß deposition, tau hyperphosphorylation, and glial activation in mouse models of Aß pathology. Alternative strategies involve the use of ApoE4 structure correctors, passive immunization to target a certain form of ApoE, conversion of the ApoE4 aminoacid sequence into that of ApoE3 or ApoE2, and inhibition of the ApoE-Aß interaction.

Different Sides of Depression in the Elderly: An In-depth View on the Role of Aß Peptides.

BACKGROUND: Late-onset depression (LOD) is the most common neuropsychiatric disorder associated with Alzheimer's disease (AD), often associated with structural and functional brain changes, neuropsychological impairments and negative family history for affective disorders. LOD could be a risk factor or a prodromal phase of AD; this has led to the investigation of the link between depression and amyloid-ß (Aß) peptides by measuring Aß levels in plasma, cerebrospinal fluid (CSF) and brains of elderly depressed subjects. OBJECTIVE: This study aims to clarify the complex relationship between depression, Aß peptides and AD. METHODS: We evaluated all articles published up to 2019 in PubMed in which Aß was measured in serum (or plasma), CSF or brain in elderly with Major Depressive Disorder or depressive symptoms evaluated with standard scales. RESULTS: Low plasma Aß42 levels are strongly associated with depression severity. Plasma Aß40 levels are higher in younger depressed, drug-resistant and those with more severe symptoms. CSF Aß42 levels are lower in depressed than controls. PET-detected global and region-specific increases in Aß deposition are sometimes associated with LOD, cognitive impairment, anxiety but not with Cardiovascular Diseases (CVDs)/CVD risk factors. Elderly depressed with CVDs/CVD risk factors have more frequently high plasma Aß40 levels and drug-resistance; those without Conclusion: Two specific Aß profiles emerge in the depressed elderly. One is associated with Aß42 reductions in plasma and CSF, possibly reflecting increased brain amyloid deposition and prodromal AD. The other one is characterized by high plasma Aß40 levels, cerebrovascular disease and is clinically associated with increased AD risk.

Type 2 Diabetes Mellitus, Platelet Activation and Alzheimer's Disease: A Possible Connection.

Type 2 diabetes mellitus DM (T2DM) is associated with a 70% increased risk for dementia, including Alzheimer's disease (AD). Insulin resistance has been proposed to play a pivotal role in both T2DM and AD and the concept of "brain insulin resistance" has been suggested as an interpretation to the growing literature regarding cognitive impairment and T2DM. Subjects with T2DM present an abnormal platelet reactivity that together with insulin resistance, hyperglycaemia and dyslipidaemia effect the vascular wall by a series of events including endothelial dysfunction, oxidative stress and low-grade inflammation. Activated platelets directly contribute to cerebral amyloid angiopathy (CAA) by promoting the formation of ß-amyloid (Aß) aggregates and that Aß, in turn, activates platelets, creating a feed-forward loop suggesting the involvement of platelets in the AD pathogenesis. Moreover, islet amyloid polypeptide deposition, co-localized with Aß deposits, is a common finding in the brain of patients with T2DM. These observations raise the intriguing prospect that traditional or novel antiplatelet therapeutic strategies may alleviate fibril formation and could be used in the prevention or treatment of AD subjects with diabetes.

Can platelet activation result in increased plasma Aß levels and contribute to the pathogenesis of Alzheimer's disease?

One of the central lesions in the brain of subjects with Alzheimer's disease (AD) is represented by aggregates of ß-amyloid (Aß), a peptide of 40-42 amino acids derived from the amyloid precursor protein (APP). The reasons why Aß accumulates in the brain of individuals with sporadic forms of AD are unknown. Platelets are the primary source of circulating APP and, upon activation, can secrete significant amounts of Aß into the blood which can be actively transported to the brain across the blood-brain barrier and promote amyloid deposition. Increased platelet activity can stimulate platelet adhesion to endothelial cells, trigger the recruitment of leukocytes into the vascular wall and cause perivascular inflammation, which can spread inflammation in the brain. Neuroinflammation is fueled by activated microglial cells and reactive astrocytes that release neurotoxic cytokines and chemokines. Platelet activation is also associated with the progression of carotid artery disease resulting in an increased risk of cerebral hypoperfusion which may also contribute to the AD neurodegenerative process. Platelet activation may thus be a pathophysiological mechanism of AD and for the strong link between AD and cerebrovascular diseases. Interfering with platelet activation may represent a promising potential adjunct therapeutic approach for AD.

The ß-Secretase BACE1 in Alzheimer's Disease.

BACE1 (beta-site amyloid precursor protein cleaving enzyme 1) was initially cloned and characterized in 1999. It is required for the generation of all monomeric forms of amyloid-ß (Aß), including Aß42, which aggregates into bioactive conformational species and likely initiates toxicity in Alzheimer's disease (AD). BACE1 concentrations and rates of activity are increased in AD brains and body fluids, thereby supporting the hypothesis that BACE1 plays a critical role in AD pathophysiology. Therefore, BACE1 is a prime drug target for slowing down Aß production in early AD. Besides the amyloidogenic pathway, BACE1 has other substrates that may be important for synaptic plasticity and synaptic homeostasis. Indeed, germline and adult conditional BACE1 knockout mice display complex neurological phenotypes. Despite BACE1 inhibitor clinical trials conducted so far being discontinued for futility or safety reasons, BACE1 remains a well-validated therapeutic target for AD. A safe and efficacious compound with high substrate selectivity as well as a more accurate dose regimen, patient population, and disease stage may yet be found. Further research should focus on the role of Aß and BACE1 in physiological processes and key pathophysiological mechanisms of AD. The functions of BACE1 and the homologue BACE2, as well as the biology of Aß in neurons and glia, deserve further investigation. Cellular and molecular studies of BACE1 and BACE2 knockout mice coupled with biomarker-based human research will help elucidate the biological functions of these important enzymes and identify their substrates and downstream effects. Such studies will have critical implications for BACE1 inhibition as a therapeutic approach for AD.

Liver fibrosis score, physical frailty, and the risk of dementia in older adults: The Italian Longitudinal Study on Aging.

INTRODUCTION: Liver fibrosis increases progressively with aging and has been associated with poorer cognitive performance in middle-aged and older adults. We investigated the relationships between a non-invasive score for advanced liver fibrosis (non-alcoholic fatty liver disease [NAFLD] fibrosis score [NFS]) and dementia risk. We also assessed physical frailty, a common geriatric condition which is associated to dementia. We tested the joint effects of physical frailty and fibrosis on dementia incidence. METHODS: A total of 1061 older adults (65 to 84 years), from the Italian Longitudinal Study on Aging, were prospectively evaluated for the risk of dementia in a period between 1992 and 2001. Liver fibrosis was defined according to the NFS. Physical frailty was assessed according to the Fried's criteria. Cox proportional hazards models were used to estimate the short- and long-term risk of overall dementia, associated to the NFS, testing the effect modifier of physical frailty status. RESULTS: Older adults with only high NFS (F3-F4) did not exhibit a significant increased risk of overall dementia. Over 8 years of follow-up, frail older adults with high NFS had an increased risk of overall dementia (hazard ratio [HR]: 4.23; 95% confidence interval [CI]: 1.22 to 14.70, P = .023). Finally, physically frail older adults with low albumin serum levels (albumin < 4.3 g/dL) and with advanced liver fibrosis (F3-F4 NFS) compared to those with lower liver fibrosis score (F0-F2 NFS) were more likely to have a higher risk of overall dementia in a long term-period (HR: 16.42; 95% CI: 1.44 to 187.67, P = .024). DISCUSSION: Advanced liver fibrosis (F3-F4 NFS) could be a long-term predictor for overall dementia in people with physical frailty. These findings should encourage a typical geriatric, multidisciplinary assessment which accounts also for the possible co-presence of frail condition in older adults with chronic liver disease and liver fibrosis.

Should drug discovery scientists still embrace the amyloid hypothesis for Alzheimer's disease or should they be looking elsewhere?

INTRODUCTION: Alzheimer's Disease (AD) represents a large and growing challenge to patients, carers and healthcare systems, yet extensive efforts to develop therapeutics to modify its course have been met with repeated failure in recent decades. Although the evident presence of accumulated ß-amyloid (Aß) in AD brains has singled it out as an obvious therapeutic target, the effective reduction of plaque load or soluble Aß by numerous drug candidates has not produced commensurate clinical benefits - calling into question the Aß cascade hypothesis of AD. A similar path is now unfolding in the pursuit of therapeutics targeting hyperphosphorylated tau-comprised neurofibrillary tangles. AREAS COVERED: This perspective reviews the basis of the Aß cascade hypothesis of AD and how clinical trials of anti-Aß drugs have failed to support it, and reflects upon the early findings suggesting that a similar path is being followed with therapeutics targeting tau. Other potential approaches to identifying therapeutics for AD are explored herein. EXPERT OPINION: The relevance of the Aß cascade hypothesis to the development of therapeutics for AD appears disproven. Drugs targeting tau appear to be suffering the same fate but may yet produce better results. Alternative approaches are being pursued, some of them with initial small-scale, but promising, results.

Do anti-amyloid-ß drugs affect neuropsychiatric status in Alzheimer's disease patients?

In the Alzheimer's disease (AD) brain, accumulation of the amyloid-ß (Aß) peptide starts 15-20 years before clinical symptoms become apparent and is believed to be the initial event of the pathological process. Unfortunately, candidate drugs targeting production, clearance and deposition of Aß have failed to show clinical benefit in patients with established or prodromal disease, or in cognitively normal subjects with high risk of developing AD. Surprisingly, several potent anti-Aß drugs accelerated cognitive decline of AD and, in some cases, worsened neuropsychiatric symptoms (NPS) and triggered suicidal ideation. Clarifying the relationships between the AD-related pathology and NPS of AD patients may be useful for elucidating the underlying pathophysiological process. We believe that steady overproduction of Aß in AD may represent an attempt of the brain to mitigate or repair neuronal damage/insult. Sudden reductions of brain Aß levels with potent anti-Aß drugs may worsen cognition and exacerbate NPS.

Neuroprotective and Anti-Apoptotic Effects of CSP-1103 in Primary Cortical Neurons Exposed to Oxygen and Glucose Deprivation.

CSP-1103 (formerly CHF5074) has been shown to reverse memory impairment and reduce amyloid plaque as well as inflammatory microglia activation in preclinical models of Alzheimer's disease. Moreover, it was found to improve cognition and reduce brain inflammation in patients with mild cognitive impairment. Recent evidence suggests that CSP-1103 acts through a single molecular target, the amyloid precursor protein intracellular domain (AICD), a transcriptional regulator implicated in inflammation and apoptosis. We here tested the possible anti-apoptotic and neuroprotective activity of CSP-1103 in a cell-based model of post-ischemic injury, wherein the primary mouse cortical neurons were exposed to oxygen-glucose deprivation (OGD). When added after OGD, CSP-1103 prevented the apoptosis cascade by reducing cytochrome c release and caspase-3 activation and the secondary necrosis. Additionally, CSP-1103 limited earlier activation of p38 and nuclear factor κB (NF-κB) pathways. These results demonstrate that CSP-1103 is neuroprotective in a model of post-ischemic brain injury and provide further mechanistic insights as regards its ability to reduce apoptosis and potential production of pro-inflammatory cytokines. In conclusion, these findings suggest a potential use of CSP-1103 for the treatment of brain ischemia.

Examination of level of knowledge in Italian general practitioners attending an education session on diagnosis and management of the early stage of Alzheimer's disease: pass or fail?

BACKGROUND: We detected the general level of knowledge about the early diagnosis of Alzheimer's disease (AD) and subsequent care in general practitioners (GPs) from Southern Italy. We explored also the GP perception about their knowledge and training on diagnosis and management of AD. METHODS: On a sample of 131 GPs, we administered two questionnaires: the GP-Knowledge, evaluating GPs' expertise about AD epidemiology, differential diagnosis, and available treatments, and the GP-QUestionnaire on Awareness of Dementia (GP-QUAD), assessing the GPs' attitudes, awareness, and practice regarding early diagnosis of dementia. RESULTS: Specific screening tests or protocols to diagnose and manage dementia were not used by 53% of our GPs. The training on the recognition of early AD signs and symptoms was considered inadequate by 55% of the participants. Females were more likely to consider their training insufficient (58%) compared to males (53%). Female GPs were less likely to prescribe antipsychotic drugs to control neuropsychiatric symptoms (NPS) and suggest specialist advice in late stage of cognitive impairment. Multiple Correspondence Analysis (MCA) performed only on GP-QUAD suggested two dimensions explaining 26.1% ("GP attitude") and 20.1% ("GP knowledge") of the inertia for a total of 46.2%, CONCLUSION: In our survey on GP clinical practice, several problems in properly recognizing early AD symptoms and subsequently screening patients to be referred to secondary/tertiary care centers for diagnosis confirmation have emerged. In the future, specific training programs and educational projects for GPs should be implemented also in Italy to improve detection rates and management of dementia in primary care.

Pharmacological targeting of the ß-amyloid precursor protein intracellular domain.

Amyloid precursor protein (APP) intracellular domain (AICD) is a product of APP processing with transcriptional modulation activity, whose overexpression causes various Alzheimer's disease (AD)-related dysfunctions. Here we report that 1-(3',4'-dichloro-2-fluoro[1,1'-biphenyl]-4-yl)-cyclopropanecarboxylic acid) (CHF5074), a compound that favorably affects neurodegeneration, neuroinflammation and memory deficit in transgenic mouse models of AD, interacts with the AICD and impairs its nuclear activity. In neuroglioma-APPswe cells, CHF5074 shifted APP cleavage from Aß42 to the less toxic Aß38 peptide without affecting APP-C-terminal fragment, nor APP levels. As revealed by photoaffinity labeling, CHF5074 does not interact with γ-secretase, but binds to the AICD and lowers its nuclear translocation. In vivo treatment with CHF5074 reduced AICD occupancy as well as histone H3 acetylation levels and transcriptional output of the AICD-target gene KAI1. The data provide new mechanistic insights on this compound, which is under clinical investigation for AD treatment/prevention, as well as on the contribution of the AICD to AD pathology.

Structural evidence for native state stabilization of a conformationally labile amyloidogenic transthyretin variant by fibrillogenesis inhibitors.

Several classes of chemicals are able to bind to the thyroxine binding sites of transthyretin (TTR), stabilizing its native state and inhibiting in vitro the amyloidogenic process. The amyloidogenic I84S TTR variant undergoes a large conformational change at moderately acidic pH. Structural evidence has been obtained by X-ray analysis for the native state stabilization of I84S TTR by two chemically distinct fibrillogenesis inhibitors. In fact, they fully prevent the acidic pH-induced protein conformational change as a result of a long-range stabilizing effect. This study provides further support to the therapeutic strategy based on the use of TTR stabilizers as anti-amyloidogenic drugs.

The γ-secretase modulator CHF5074 reduces the accumulation of native hyperphosphorylated tau in a transgenic mouse model of Alzheimer's disease.

The relationship between ß-amyloid (Aß) and tau is not fully understood, though it is proposed that in the pathogenesis of Alzheimer's disease (AD) Aß accumulation precedes and promotes tau hyperphosphorylation via activation of glycogen synthase kinase-3beta (GSK-3ß). Both events contribute to learning and memory impairments. Modulation of γ-secretase activity has proved to reduce the Aß burden and cognitive deficits in mouse models of AD, but its ability in reducing the tau pathology remains elusive. Chronic treatments with two γ-secretase modulators, ibuprofen and CHF5074, disclosed higher activity of CHF5074 in ameliorating brain plaque deposition and spatial memory deficits in transgenic mice expressing human amyloid precursor protein (hAPP) with Swedish and London mutations (APP(SL) mice). The aim of our study was to investigate in APP(SL) mice the effect of the two compounds on the accumulation of native hyperphosphorylated tau as well as on the GSK-3ß signaling. CHF5074 was more effective than ibuprofen in reducing tau pathology, though both compounds decreased the GSK-3ß level and increased the GSK-3ß inhibitory phosphorylation near to the non-Tg values. The inhibition of GSK-3ß appeared to be secondary to the reduction of Aß generation as, differently from LiCl, CHF5074 reproduced its effect in hAPP-overexpressing neuroglioma cells, but not in wild-type primary neurons. Our data show that the novel γ-secretase modulator CHF5074 can fully reverse ß-amyloid-associated tau pathology, thus representing a promising therapeutic agent for AD.