Amyloid β oligomer-induced ERK1/2-dependent serine 636/639 phosphorylation of insulin receptor substrate-1 impairs insulin signaling and glycogen storage in human astrocytes

A phase 2, open-label study of anti-inflammatory NE3107 in patients with dementias

BACKGROUND

Alzheimer's disease (AD) is a progressive, multifactorial, neurodegenerative disorder affecting >6 million Americans. Chronic, low-grade neuroinflammation, and insulin resistance may drive AD pathogenesis. We explored the neurophysiological and neuropsychological effects of NE3107, an oral, anti-inflammatory, insulin-sensitizing molecule, in AD.

METHODS

In this phase 2, open-label study, 23 patients with mild cognitive impairment or mild dementia received 20-mg oral NE3107 twice daily for 3 months. Primary endpoints assessed changes from baseline in neurophysiological health and oxidative stress (glutathione level) using advanced neuroimaging analyses. Secondary endpoints evaluated changes from baseline in neuropsychological health using cognitive assessments, including the 11-item Alzheimer's Disease Assessment Scale-Cognitive Subscale (ADAS-Cog11), Mini-Mental State Examination (MMSE), Montreal Cognitive Assessment, Clinical Dementia Rating, Quick Dementia Rating Scale, Alzheimer's Disease Composite Score, and Global Rating of Change (GRC). Exploratory endpoints assessed changes from baseline in neuroinflammation biomarkers (tumor necrosis factor alpha, TNF-α) and AD (amyloid beta and phosphorylated tau [P-tau]).

RESULTS

NE3107 was associated with clinician-rated improvements in cerebral blood flow and functional connectivity within the brain. In patients with MMSE ≥ 20 (mild cognitive impairment to mild AD; n = 17), NE3107 was associated with directional, but statistically nonsignificant, changes in brain glutathione levels, along with statistically significant improvements in ADAS-Cog11 (P = .017), Clinical Dementia Rating (P = .042), Quick Dementia Rating Scale (P = .002), Alzheimer's Disease Composite Score (P = .0094), and clinician-rated GRC (P < .001), as well as in cerebrospinal fluid P-tau levels (P = .034) and P-tau:amyloid beta 42 ratio (P = .04). Biomarker analyses also demonstrated directional, but statistically non-significant, changes in plasma TNF-α, consistent with the expected mechanism of NE3107. Importantly, we observed a statistically significant correlation (r = 0.59) between improvements in TNF-α levels and ADAS-Cog11 scores (P = .026) in patients with baseline MMSE ≥ 20.

CONCLUSION

Our results indicate that in this study NE3107 was associated with what appear to be positive neurophysiological and neuropsychological findings, as well as evidence of improvement in biomarkers associated with neuroinflammation and AD in patients diagnosed with dementia. Our findings are consistent with previous preclinical and clinical observations and highlight a central role of neuroinflammation in AD pathogenesis.

Treatment of Alzheimer's Disease: Beyond Symptomatic Therapies

In an ever-increasing aged world, Alzheimer's disease (AD) represents the first cause of dementia and one of the first chronic diseases in elderly people. With 55 million people affected, the WHO considers AD to be a disease with public priority. Unfortunately, there are no final cures for this pathology. Treatment strategies are aimed to mitigate symptoms, i.e., acetylcholinesterase inhibitors (AChEI) and the N-Methyl-D-aspartate (NMDA) antagonist Memantine. At present, the best approaches for managing the disease seem to combine pharmacological and non-pharmacological therapies to stimulate cognitive reserve. Over the last twenty years, a number of drugs have been discovered acting on the well-established biological hallmarks of AD, deposition of β-amyloid aggregates and accumulation of hyperphosphorylated tau protein in cells. Although previous efforts disappointed expectations, a new era in treating AD has been working its way recently. The Food and Drug Administration (FDA) gave conditional approval of the first disease-modifying therapy (DMT) for the treatment of AD, aducanumab, a monoclonal antibody (mAb) designed against Aβ plaques and oligomers in 2021, and in January 2023, the FDA granted accelerated approval for a second monoclonal antibody, Lecanemab. This review describes ongoing clinical trials with DMTs and non-pharmacological therapies. We will also present a future scenario based on new biomarkers that can detect AD in preclinical or prodromal stages, identify people at risk of developing AD, and allow an early and curative treatment.

NM101 Phase III study of NE3107 in Alzheimer's disease: rationale, design and therapeutic modulation of neuroinflammation and insulin resistance

Recently, the roles of inflammation and insulin resistance in neurodegeneration have become better appreciated. NE3107, an oral small molecule, blood-brain permeable anti-inflammatory insulin sensitizer that binds extracellular signal-regulated kinase, has been shown to selectively inhibit inflammation-driven ERK- and NF-κB-stimulated inflammatory mediators, including TNF-α, without inhibiting their homeostatic functions. We describe the rationale and design of NM101, the first randomized, multicenter Phase III clinical study to examine the safety and efficacy of 30 week treatment with NE3107 versus placebo in elderly adults with mild-to-moderate Alzheimer's disease. Patients (316) will be randomized in a 1:1 ratio. The co-primary end points measure cognitive function (ADAS Cog12), and functional and behavioral characteristics (ADCS CGIC). Trial registration number: NCT04669028 (Clinicaltrials.gov).

Hyperinsulinemia Induced Altered Insulin Signaling Pathway in Muscle of High Fat- and Carbohydrate-Fed Rats: Effect of Exercise

Insulin resistance is a state of impaired responsiveness to insulin action. This condition not only results in deficient glucose uptake but increases the risk for cardiovascular diseases (CVD), stroke, and obesity. The present work investigates the molecular mechanisms of high carbohydrate and fat diet in inducing prediabetic hyperinsulinemia and effect of exercise on InsR signaling events, muscular AChE, and lactate dehydrogenase activity. Adult male Wistar rats were divided into the control (C) diet group, high-carbohydrate diet (HCD) group, high-fat diet (HFD) group, and HCD and HFD groups with exercise (HCD Ex and HFD Ex, respectively). Acetyl choline esterase activity, lactate dehydrogenase activity, total lactate levels, IRS1 phosphorylations, and Glut4 expression patterns were studied in the muscle tissue among these groups. High carbohydrate and fat feeding led to hyperinsulinemic status with reduced acetylcholine esterase (AChE) activity and impaired phosphorylation of IRS1 along with increased lactate concentrations in the muscle. Exercise significantly upregulated phosphoinositide 3 kinase (PI3K) docking site phosphorylation and downregulated the negative IRS1 phosphorylations thereby increasing the glucose transporter (GLUT) expressions and reducing the lactate accumulation. Also, the levels of second messengers like IP3 and cAMP were increased with exercise. Increased second messenger levels induce calcium release thereby activating the downstream pathway promoting the translocation of GLUT4 to the plasma membrane. Our results showed that the metabolic and signaling pathway dysregulations seen during diet-induced hyperinsulinemia, a metabolic condition seen during the early stages in the development of prediabetes, were improved with vigorous physical exercise. Thus, exercise can be considered as an excellent management approach over drug therapy for diabetes and its complications.

Common Pathological Mechanisms and Risk Factors for Alzheimer's Disease and Type-2 Diabetes: Focus on Inflammation

BACKGROUND

Diabetes is considered as a risk factor for Alzheimer's Disease, but it is yet unclear whether this pathological link is reciprocal. Although Alzheimer's disease and diabetes appear as entirely different pathological entities affecting the Central Nervous System and a peripheral organ (pancreas), respectively, they share a common pathological core. Recent evidence suggests that in the pancreas in the case of diabetes, as in the brain for Alzheimer's Disease, the initial pathological event may be the accumulation of toxic proteins yielding amyloidosis. Moreover, in both pathologies, amyloidosis is likely responsible for local inflammation, which acts as a driving force for cell death and tissue degeneration. These pathological events are all inter-connected and establish a vicious cycle resulting in the progressive character of both pathologies.

OBJECTIVE

To address the literature supporting the hypothesis of a common pathological core for both diseases.

DISCUSSION

We will focus on the analogies and differences between the disease-related inflammatory changes in a peripheral organ, such as the pancreas, versus those observed in the brain. Recent evidence suggesting an impact of peripheral inflammation on neuroinflammation in Alzheimer's disease will be presented.

CONCLUSION

We propose that it is now necessary to consider whether neuroinflammation in Alzheimer's disease affects inflammation in the pancreas related to diabetes.

The Precursor to Glutathione (GSH), γ-Glutamylcysteine (GGC), Can Ameliorate Oxidative Damage and Neuroinflammation Induced by Aβ40 Oligomers in Human Astrocytes

Glutathione (GSH) is one of the most abundant thiol antioxidants in cells. Many chronic and age-related diseases are associated with a decline in cellular GSH levels or impairment in the catalytic activity of the GSH biosynthetic enzyme glutamate cysteine ligase (GCL). γ-glutamylcysteine (GGC), a precursor to glutathione (GSH), can replenish depleted GSH levels under oxidative stress conditions, by circumventing the regulation of GSH biosynthesis and providing the limiting substrate. Soluble amyloid-β (Aβ) oligomers have been shown to induce oxidative stress, synaptic dysfunction and memory deficits which have been reported in Alzheimer’s disease (AD). Calcium ions, which are increased with age and in AD, have been previously reported to enhance the formation of Aβ₄₀ oligomers, which have been casually associated with the pathogenesis of the underlying neurodegenerative condition. In this study, we examined the potential beneficial effects of GGC against exogenous Aβ₄₀ oligomers on biomarkers of apoptosis and cell death, oxidative stress, and neuroinflammation, in human astrocytes. Treatment with Aβ₄₀ oligomers significantly reduced the cell viability and apoptosis of astrocyte brain cultures and increased oxidative modifications of DNA, lipids, and protein, enhanced pro-inflammatory cytokine release and increased the activity of the proteolytic matrix metalloproteinase enzyme, matric metalloproteinase (MMP)-2 and reduced the activity of MMP-9 after 24 h. Co-treatment of Aβ₄₀ oligomers with GGC at 200 μM increased the activity of the antioxidant enzymes superoxide dismutase (SOD) and glutathione peroxidase (GPx) and led to significant increases in the levels of the total antioxidant capacity (TAC) and GSH and reduced the GSSG/GSH ratio. GGC also upregulated the level of the anti-inflammatory cytokine IL-10 and reduced the levels of the pro-inflammatory cytokines (TNF-α, IL-6, and IL-1β) and attenuated the changes in metalloproteinase activity in oligomeric Aβ₄₀-treated astrocytes. Our data provides renewed insight on the beneficial effects of increased GSH levels by GGC in human astrocytes, and identifies yet another potential therapeutic strategy to attenuate the cytotoxic effects of Aβ oligomers in AD.

Structure and Regulation of Glycogen Synthase in the Brain

Brain glycogen synthesis is a regulated, multi-step process that begins with glucose transport across the blood brain barrier and culminates with the actions of glycogen synthase and the glycogen branching enzyme to elongate glucose chains and introduce branch points in a growing glycogen molecule. This review focuses on the synthesis of glycogen in the brain, with an emphasis on glycogen synthase, but draws on salient studies in mammalian muscle and liver as well as baker's yeast, with the goal of providing a more comprehensive view of glycogen synthesis and highlighting potential areas for further study in the brain. In addition, deficiencies in the glycogen biosynthetic enzymes which lead to glycogen storage diseases in humans are discussed, highlighting effects on the brain and discussing findings in genetically modified animal models that recapitulate these diseases. Finally, implications of glycogen synthesis in neurodegenerative and other diseases that impact the brain are presented.

Amyloid Beta monomers regulate cyclic adenosine monophosphate response element binding protein functions by activating type-1 insulin-like growth factor receptors in neuronal cells

Alzheimer's disease (AD) is a progressive neurodegenerative disorder associated with synaptic dysfunction, pathological accumulation of β-amyloid (Aβ), and neuronal loss. The self-association of Aβ monomers into soluble oligomers seems to be crucial for the development of neurotoxicity (J. Neurochem., 00, 2007 and 1172). Aβ oligomers have been suggested to compromise neuronal functions in AD by reducing the expression levels of the CREB target gene and brain-derived neurotrophic factor (BDNF) (J. Neurosci., 27, 2007 and 2628; Neurobiol. Aging, 36, 2015 and 20406 Mol. Neurodegener., 6, 2011 and 60). We previously reported a broad neuroprotective activity of physiological Aβ monomers, involving the activation of type-1 insulin-like growth factor receptors (IGF-IRs) (J. Neurosci., 29, 2009 and 10582, Front Cell Neurosci., 9, 2015 and 297). We now provide evidence that Aβ monomers, by activating the IGF-IR-stimulated PI3-K/AKT pathway, induce the activation of CREB in neurons and sustain BDNF transcription and release.

Hydroxytyrosol restores proper insulin signaling in an astrocytic model of Alzheimer's disease

Recent epidemiological evidence demonstrated that diabetes is a risk factor for AD onset and development. Indeed, meta-analyses of longitudinal epidemiologic studies show that diabetes increases AD risk by 50-100%, being insulin resistance (IR) the main binding link between diabetes and AD. Astrocytes are the foremost cerebral macroglial cells and are responsible for converting glucose into lactate and transfer it to neurons that use it as fuel, but Aβ(1-42) impairs insulin signaling and glycogen storage. Recent prospective studies showed that the Mediterranean diet is associated with lower incidence of AD. We hypothesized that hydroxytyrosol (HT, the preeminent polyphenol of olives and olive oil) could exert beneficial effects on IR associated with AD and investigated it mechanisms of action in an astrocytic model of AD. The astrocytic cell line C6 was exposed to Aβ(25-35) and co-incubated with HT for different periods. After treatment with Aβ(25-35), astrocytes' viability was significantly decreased as compared with controls; however, both pre- and post-treatment with HT prevented this effect. Mechanistically, we found that the preventive role of HT on Aβ(25-35)- induced cytotoxicity in astrocytes is moderated by an increased HT-induced activation of Akt, which is mediated by the insulin signaling pathway. In addition, we report that HT prevented the pronounced activation of mTOR, thereby restoring proper insulin signaling. In conclusion, we demonstrate that HT protects Aβ(25-35)-treated astrocytes by improving insulin sensitivity and restoring proper insulin-signaling. These data provide some mechanistic insight on the observed inverse association between olive oil consumption and prevalence of cognitive impairment. © 2017 BioFactors, 43(4):540-548, 2017.

Endoplasmic reticulum stress mediates JNK-dependent IRS-1 serine phosphorylation and results in Tau hyperphosphorylation in amyloid β oligomer-treated PC12 cells and primary neurons

AIMS

Endoplasmic reticulum stress (ERS) and insulin signaling impairment are commonly observed in Alzheimer's disease (AD), but the association between these two factors in AD has not been carefully studied. In peripheral insulin signaling impairment, ERS interferes with insulin signaling through c-Jun. N-terminal kinase (JNK)-dependent insulin receptor substance-1 (IRS-1) serine phosphorylation. We conducted this study to determine whether a similar mechanism contributes to insulin signaling impairment in AD pathogenesis.

METHODS

Changes in the levels of ERS markers, JNK activation, the insulin signaling status and Tau hyperphosphorylation were examined in amyloid β1-42 (Aβ1-42) oligomer-treated PC12 cells and primary neurons by western blotting and real-time fluorescence quantitative PCR. Inhibitors of ERS and JNK were utilized to confirm their association.

RESULTS

Our results demonstrated that Aβ1-42 oligomers significantly induced ERS and JNK activation. In addition, in response to Aβ1-42 oligomers, IRS-1 phosphorylation at serines 307, 318 and 612 was increased. Further, an increase in Tau hyperphosphorylation at threonine 181 was observed following Aβ1-42 oligomer treatment. Moreover, inhibition of ERS or JNK could partially reverse the changes induced by the Aβ1-42 oligomers.

CONCLUSIONS

These findings suggest that ERS may contribute to insulin signaling impairment in AD through JNK-dependent IRS-1 serine phosphorylation. The ERS/JNK/IRS-1 pathway may be involved in Aβ1-42 oligomer-induced Tau hyperphosphorylation in AD.

Insulin Attenuates Beta-Amyloid-Associated Insulin/Akt/EAAT Signaling Perturbations in Human Astrocytes

The excitatory amino acid transporters 1 and 2 (EAAT1 and EAAT2), mostly located on astrocytes, are the main mediators for glutamate clearance in humans. Malfunctions of these transporters may lead to excessive glutamate accumulation and subsequent excitotoxicity to neurons, which has been implicated in many kinds of neurodegenerative disorders including Alzheimer's disease (AD). Yet, the specific mechanism of the glutamate system dysregulation remains vague. To explore whether the insulin/protein kinase B (Akt)/EAAT signaling in human astrocytes could be disturbed by beta-amyloid protein (Aβ) and be protected by insulin, we incubated HA-1800 cells with varying concentrations of Aβ1-42 oligomers and insulin. Then the alterations of several key substrates in this signal transduction pathway were determined. Our results showed that expressions of insulin receptor, phospho-insulin receptor, phospho-protein kinase B, phospho-mammalian target of rapamycin, and EAAT1 and EAAT2 were decreased by the Aβ1-42 oligomers in a dose-dependent manner (p < 0.05) and this trend could be recovered by insulin treatment (p < 0.05). However, the expressions of total Akt and mTOR were invariant (p > 0.05), and the mRNA levels of EAAT1 and EAAT2 were also unchanged (p > 0.05). Taken together, this study indicates that Aβ1-42 oligomers could cause disturbances in insulin/Akt/EAAT signaling in astrocytes, which might be responsible for AD onset and progression. Additionally, insulin can exert protective functions to the brain by modulating protein modifications or expressions.

Soluble amyloid-β oligomers as synaptotoxins leading to cognitive impairment in Alzheimer's disease

Alzheimer’s disease (AD) is the most common form of dementia in the elderly, and affects millions of people worldwide. As the number of AD cases continues to increase in both developed and developing countries, finding therapies that effectively halt or reverse disease progression constitutes a major research and public health challenge. Since the identification of the amyloid-β peptide (Aβ) as the major component of the amyloid plaques that are characteristically found in AD brains, a major effort has aimed to determine whether and how Aβ leads to memory loss and cognitive impairment. A large body of evidence accumulated in the past 15 years supports a pivotal role of soluble Aβ oligomers (AβOs) in synapse failure and neuronal dysfunction in AD. Nonetheless, a number of basic questions, including the exact molecular composition of the synaptotoxic oligomers, the identity of the receptor(s) to which they bind, and the signaling pathways that ultimately lead to synapse failure, remain to be definitively answered. Here, we discuss recent advances that have illuminated our understanding of the chemical nature of the toxic species and the deleterious impact they have on synapses, and have culminated in the proposal of an Aβ oligomer hypothesis for Alzheimer’s pathogenesis. We also highlight outstanding questions and challenges in AD research that should be addressed to allow translation of research findings into effective AD therapies.