Modulation of 5-lipoxygenase in proteotoxicity and Alzheimer's disease

The integrated stress response in brain diseases: A double-edged sword for proteostasis and synapses

The integrated stress response (ISR) is a highly conserved biochemical pathway that regulates protein synthesis. The ISR is activated in response to diverse stressors to restore cellular homeostasis. As such, the ISR is implicated in a wide range of diseases, including brain disorders. However, in the brain, the ISR also has potent influence on processes beyond proteostasis, namely synaptic plasticity, learning and memory. Thus, in the setting of brain diseases, ISR activity may have dual effects on proteostasis and synaptic function. In this review, we consider the ISR's contribution to brain disorders through the lens of its potential effects on synaptic plasticity. From these examples, we illustrate that at times ISR activity may be a "double-edged sword". We also highlight its potential as a therapeutic target to improve circuit function in brain diseases independent of its role in disease pathogenesis.

Novel insights into the activating transcription factor 4 in Alzheimer's disease and associated aging-related diseases: Mechanisms and therapeutic implications

Ageing is inherent to all human beings, most mechanistic explanations of ageing results from the combined effects of various physiological and pathological processes. Additionally, aging pivotally contributes to several chronic diseases. Activating transcription factor 4 (ATF4), a member of the ATF/cAMP response element-binding protein family, has recently emerged as a pivotal player owing to its indispensable role in the pathophysiological processes of Alzheimer's disease and aging-related diseases. Moreover, ATF4 is integral to numerous biological processes. Therefore, this article aims to comprehensively review relevant research on the role of ATF4 in the onset and progression of aging-related diseases, elucidating its potential mechanisms and therapeutic approaches. Our objective is to furnish scientific evidence for the early identification of risk factors in aging-related diseases and pave the way for new research directions for their treatment. By elucidating the signaling pathway network of ATF4 in aging-related diseases, we aspire to gain a profound understanding of the molecular and cellular mechanisms, offering novel strategies for addressing aging and developing related therapeutics.

Oxidative damage in neurodegeneration: roles in the pathogenesis and progression of Alzheimer disease

Alzheimer disease (AD) is associated with multiple etiologies and pathological mechanisms, among which oxidative stress (OS) appears as a major determinant. Intriguingly, OS arises in various pathways regulating brain functions, and it seems to link different hypotheses and mechanisms of AD neuropathology with high fidelity. The brain is particularly vulnerable to oxidative damage, mainly because of its unique lipid composition, resulting in an amplified cascade of redox reactions that target several cellular components/functions ultimately leading to neurodegeneration. The present review highlights the "OS hypothesis of AD," including amyloid beta-peptide-associated mechanisms, the role of lipid and protein oxidation unraveled by redox proteomics, and the antioxidant strategies that have been investigated to modulate the progression of AD. Collected studies from our groups and others have contributed to unraveling the close relationships between perturbation of redox homeostasis in the brain and AD neuropathology by elucidating redox-regulated events potentially involved in both the pathogenesis and progression of AD. However, the complexity of AD pathological mechanisms requires an in-depth understanding of several major intracellular pathways affecting redox homeostasis and relevant for brain functions. This understanding is crucial to developing pharmacological strategies targeting OS-mediated toxicity that may potentially contribute to slow AD progression as well as improve the quality of life of persons with this severe dementing disorder.

Dynamic reversibility of α-synuclein serine-129 phosphorylation is impaired in synucleinopathy models

α-Synuclein phosphorylation at serine-129 (pS129) is a widely used surrogate marker of pathology in Parkinson's disease and other synucleinopathies. However, we recently demonstrated that phosphorylation of S129 is also a physiological activator of synaptic transmission. In a feed-forward fashion, neuronal activity triggers reversible pS129. Here, we show that Parkinson's disease-linked missense mutations in SNCA impact activity-dependent pS129. Under basal conditions, cytosol-enriched A30P, H50Q, and G51D mutant forms of α-synuclein exhibit reduced pS129 levels in rat primary cortical neurons. A53T pS129 levels are similar to wild-type, and E46K pS129 levels are higher. A30P and E46K mutants show impaired reversibility of pS129 after stimulation. For the engineered profoundly membrane-associated α-synuclein mutant "3K" (E35K + E46K + E61K), de-phosphorylation was virtually absent after blocking stimulation, implying that reversible pS129 is severely compromised. Importantly, pS129 excess resulting from proteasome inhibition is also associated with reduced reversibility by neuronal inhibition, kinase inhibition, or phosphatase activation. Our findings suggest that perturbed pS129 dynamics are probably a shared characteristic of pathology-associated α-synuclein, with possible implications for synucleinopathy treatment and diagnosis.

Proteasomal Stimulation by MK886 and Its Derivatives Can Rescue Tau-Induced Neurite Pathology

Proteasomal degradation of intrinsically disordered proteins, such as tau, is a critical component of proteostasis in both aging and neurodegenerative diseases. In this study, we investigated proteasomal activation by MK886 (MK). We previously identified MK as a lead compound capable of modulating tau oligomerization in a cellular FRET assay and rescuing P301L tau-induced cytotoxicity. We first confirmed robust proteasomal activation by MK using 20S proteasomal assays and a cellular proteasomal tau-GFP cleavage assay. We then show that MK treatment can significantly rescue tau-induced neurite pathology in differentiated SHSY5Y neurospheres. Due to this compelling result, we designed a series of seven MK analogs to determine if proteasomal activity is sensitive to structural permutations. Using the proteasome as the primary MOA, we examined tau aggregation, neurite outgrowth, inflammation, and autophagy assays to identify two essential substituents of MK that are required for compound activity: (1) removal of the N-chlorobenzyl group from MK negated both proteasomal and autophagic activity and reduced neurite outgrowth; and (2) removal of the indole-5-isopropyl group significantly improved neurite outgrowth and autophagy activity but reduced its anti-inflammatory capacity. Overall, our results suggest that the combination of proteasomal/autophagic stimulation and anti-inflammatory properties of MK and its derivatives can decrease tau-tau interactions and help rebalance dysfunctional proteostasis. Further development of MK to optimize its proteasomal, autophagic, and anti-inflammatory targets may lead to a novel therapeutic that would be beneficial in aging and neurodegenerative diseases.

Diet and lifestyle impact the development and progression of Alzheimer's dementia

Dementia is a growing public health concern, with an estimated prevalence of 57 million adults worldwide. Alzheimer's disease (AD) accounts for 60-80% of the cases. Clinical trials testing potential drugs and neuroprotective agents have proven futile, and currently approved drugs only provide symptomatic benefits. Emerging epidemiological and clinical studies suggest that lifestyle changes, including diet and physical activity, offer an alternative therapeutic route for slowing and preventing cognitive decline and dementia. Age is the single most common risk factor for dementia, and it is associated with slowing cellular bioenergetics and metabolic processes. Therefore, a nutrient-rich diet is critical for optimal brain health. Furthermore, type 2 diabetes (T2D) is a risk factor for AD, and diets that reduce the risk of T2D may confer neuroprotection. Foods predominant in Mediterranean, MIND, and DASH diets, including fruits, leafy green vegetables, fish, nuts, and olive oil, may prevent or slow cognitive decline. The mechanisms by which these nutrients promote brain health, however, are not yet completely understood. Other dietary approaches and eating regimes, including ketogenic and intermittent fasting, are also emerging as beneficial for brain health. This review summarizes the pathophysiology, associated risk factors, and the potential neuroprotective pathways activated by several diets and eating regimes that have shown promising results in promoting brain health and preventing dementia.

The potential roles of ATF family in the treatment of Alzheimer's disease

Activating transcription factors, ATFs, is a family of transcription factors that activate gene expression and transcription by recognizing and combining the cAMP response element binding proteins (CREB). It is present in various viruses as a cellular gene promoter. ATFs is involved in regulating the mammalian gene expression that is associated with various cell physiological processes. Therefore, ATFs play an important role in maintaining the intracellular homeostasis. ATF2 and ATF3 is mostly involved in mediating stress responses. ATF4 regulates the oxidative metabolism, which is associated with the survival of cells. ATF5 is presumed to regulate apoptosis, and ATF6 is involved in the regulation of endoplasmic reticulum stress (ERS). ATFs is actively studied in oncology. At present, there has been an increasing amount of research on ATFs for the treatment of neurological diseases. Here, we have focused on the different types of ATFs and their association with Alzheimer's disease (AD). The level of expression of different ATFs have a significant difference in AD patients when compared to healthy control. Recent studies have suggested that ATFs are implicated in the pathogenesis of AD, such as neuronal repair, maintenance of synaptic activity, maintenance of cell survival, inhibition of apoptosis, and regulation of stress responses. In this review, the potential role of ATFs for the treatment of AD has been highlighted. In addition, we have systematically reviewed the progress of research on ATFs in AD. This review will provide a basic and innovative understanding on the pathogenesis and treatment of AD.

Oxidative Stress and Antioxidants in Neurodegenerative Disorders

Neurodegenerative disorders constitute a substantial proportion of neurological diseases with significant public health importance. The pathophysiology of neurodegenerative diseases is characterized by a complex interplay of various general and disease-specific factors that lead to the end point of neuronal degeneration and loss, and the eventual clinical manifestations. Oxidative stress is the result of an imbalance between pro-oxidant species and antioxidant systems, characterized by an elevation in the levels of reactive oxygen and reactive nitrogen species, and a reduction in the levels of endogenous antioxidants. Recent studies have increasingly highlighted oxidative stress and associated mitochondrial dysfunction to be important players in the pathophysiologic processes involved in neurodegenerative conditions. In this article, we review the current knowledge of the general effects of oxidative stress on the central nervous system, the different specific routes by which oxidative stress influences the pathophysiologic processes involved in Alzheimer's disease, Parkinson's disease, Amyotrophic Lateral Sclerosis and Huntington's disease, and how oxidative stress may be therapeutically reversed/mitigated in order to stall the pathological progression of these neurodegenerative disorders to bring about clinical benefits.

Unveiling the Potential of Polyphenols as Anti-Amyloid Molecules in Alzheimer's Disease

Alzheimer's disease (AD) is a devastating neurodegenerative disease that mostly affects the elderly population. Mechanisms underlying AD pathogenesis are yet to be fully revealed, but there are several hypotheses regarding AD. Even though free radicals and inflammation are likely to be linked with AD pathogenesis, still amyloid-beta (Aβ) cascade is the dominant hypothesis. According to the Aβ hypothesis, a progressive buildup of extracellular and intracellular Aβ aggregates has a significant contribution to the AD-linked neurodegeneration process. Since Aβ plays an important role in the etiology of AD, therefore Aβ-linked pathways are mainly targeted in order to develop potential AD therapies. Accumulation of Aβ plaques in the brains of AD individuals is an important hallmark of AD. These plaques are mainly composed of Aβ (a peptide of 39-42 amino acids) aggregates produced via the proteolytic cleavage of the amyloid precursor protein. Numerous studies have demonstrated that various polyphenols (PPHs), including cyanidins, anthocyanins, curcumin, catechins and their gallate esters were found to markedly suppress Aβ aggregation and prevent the formation of Aβ oligomers and toxicity, which is further suggesting that these PPHs might be regarded as effective therapeutic agents for the AD treatment. This review summarizes the roles of Aβ in AD pathogenesis, the Aβ aggregation pathway, types of PPHs, and distribution of PPHs in dietary sources. Furthermore, we have predominantly focused on the potential of food-derived PPHs as putative anti-amyloid drugs.

Age-linked suppression of lipoxin A4 associates with cognitive deficits in mice and humans

Age increases the risk for cognitive impairment and is the single major risk factor for Alzheimer's disease (AD), the most prevalent form of dementia in the elderly. The pathophysiological processes triggered by aging that render the brain vulnerable to dementia involve, at least in part, changes in inflammatory mediators. Here we show that lipoxin A4 (LXA4), a lipid mediator of inflammation resolution known to stimulate endocannabinoid signaling in the brain, is reduced in the aging central nervous system. We demonstrate that genetic suppression of 5-lipoxygenase (5-LOX), the enzyme mediating LXA4 synthesis, promotes learning impairment in mice. Conversely, administration of exogenous LXA4 attenuated cytokine production and memory loss induced by inflammation in mice. We further show that cerebrospinal fluid LXA4 is reduced in patients with dementia and positively associated with cognitive performance, brain-derived neurotrophic factor (BDNF), and AD-linked amyloid-β. Our findings suggest that reduced LXA4 levels may lead to vulnerability to age-related cognitive disorders and that promoting LXA4 signaling may comprise an effective strategy to prevent early cognitive decline in AD.

The Interplay of the Unfolded Protein Response in Neurodegenerative Diseases: A Therapeutic Role of Curcumin

Abnormal accumulation of misfolded proteins in the endoplasmic reticulum and their aggregation causes inflammation and endoplasmic reticulum stress. This promotes accumulation of toxic proteins in the body tissues especially brain leading to manifestation of neurodegenerative diseases. The studies suggest that deregulation of proteostasis, particularly aberrant unfolded protein response (UPR) signaling, may be a common morbific process in the development of neurodegeneration. Curcumin, the mixture of low molecular weight polyphenolic compounds from turmeric, Curcuma longa has shown promising response to prevents many diseases including current global severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection and neurodegenerative disorders. The UPR which correlates positively with neurodegenerative disorders were found affected by curcumin. In this review, we examine the evidence from many model systems illustrating how curcumin interacts with UPR and slows down the development of various neurodegenerative disorders (ND), e.g., Alzheimer's and Parkinson's diseases. The recent global increase in ND patients indicates that researchers and practitioners will need to develop a new pharmacological drug or treatment to manage and cure these neurodegenerative diseases.

Untangling the web of 5-lipoxygenase-derived products from a molecular and structural perspective: The battle between pro- and anti-inflammatory lipid mediators

Arachidonic acid (AA) is the precursor to leukotrienes (LT), potent mediators of the inflammatory response. In the 35 + years since cysteinyl-LTs were reported to mediate antigen-induced constriction of bronchi in tissue from asthma patients, numerous cellular responses evoked by the LTs, such as chemoattraction and G protein-coupled receptor (GPCR) activation, have been elucidated and revealed a potential for 5-lipoxygenase (5-LOX) as a promising drug target that goes beyond asthma. We describe herein early work identifying 5-LOX as the key enzyme that initiates LT biosynthesis and the discovery of its membrane-embedded helper protein required to execute the two-step reaction that transforms AA to the progenitor leukotriene A4 (LTA4). 5-LOX must traffic to the nuclear membrane to interact with its partner and undergo a conformational change so that AA can enter the active site. Additionally, the enzyme must retain the hydroperoxy-reaction intermediate for its final transformation to LTA4. Each of these steps provide a unique target for inhibition. Next, we describe the recent structures of GPCRs that recognize metabolites of the 5-LOX pathway and thus provide target alternatives. We also highlight the role of 5-LOX in the biosynthesis of anti-inflammatory lipid mediators (LM), the so-called specialized pro-resolving mediators (SPM). The involvement of 5-LOX in the biosynthesis of LM with opposing functions undoubtedly complicates the continuing search for 5-LOX inhibitors as therapeutic leads. Finally, we address the recent discovery of how some allosteric 5-LOX inhibitors promote oxygenation at the 12/15 carbon on AA to generate mediators that resolve, rather than promote, inflammation.

Inhibition of the cysteinyl leukotriene pathways increases survival of RGCs and reduces microglial activation in ocular hypertension

Glaucoma is the second leading cause of blindness worldwide. This multifactorial, neurodegenerative group of diseases is characterized by the progressive loss of retinal ganglion cells (RGCs) and their axons, leading to irreversible visual impairment and blindness. There is a huge unmet and urging need for the development of new and translatable strategies and treatment options to prevent this progressive loss of RGC. Accumulating evidence points towards a critical role of neuroinflammation, in particular microglial cells, in the pathogenesis of glaucoma. Leukotrienes are mediators of neuroinflammation and are involved in many neurodegenerative diseases. Therefore, we tested the leukotriene receptors CysLT1R/GPR17-selective antagonist Montelukast (MTK) for its efficacy to modulate the reactive state of microglia in order to ameliorate RGCs loss in experimental glaucoma. Ocular hypertension (OHT) was induced unilaterally by injection of 8 μm magnetic microbead (MB) into the anterior chamber of female Brown Norway rats. The contralateral, untreated eye served as control. Successful induction of OHT was verified by daily IOP measurement using a TonoLab rebound tonometer. Simultaneously to OHT induction, one group received daily MTK treatment and the control group vehicle solution by oral gavage. Animals were sacrificed 13-15 days after MB injection. Retina and optic nerves (ON) of OHT and contralateral eyes were analyzed by immunofluorescence with specific markers for RGCs (Brn3a), microglial cells/macrophages (Iba1 and CD68), and cysteinyl leukotriene pathway receptors (CysLT1R and GPR17). Protein labeling was documented by confocal microscopy and analyzed with ImageJ plugins. Further, mRNA expression of genes of the inflammatory and leukotriene pathway was analyzed in retinal tissue. MTK treatment resulted in a short-term IOP reduction at day 2, which dissipated by day 5 of OHT induction in MTK treated animals. Furthermore, MTK treatment resulted in a decreased activation of Iba1⁺ microglial cells in the retina and ON, and in a significantly increased RGC survival in OHT eyes. Within the retina, GPR17 and CysLT1R expression was demonstrated in single RCGs and in microglial cells respectively. Further, increased mRNA expression of pro-inflammatory genes was detected in OHT induced retinas. In the ON, OHT induction increased the number of GPR17⁺ cells, showing a trend of reduction following MTK treatment. This study shows for the first time a significantly increased RGC survival in an acute OHT model following treatment with the leukotriene receptor antagonist MTK. These results strongly suggest a neuroprotective effect of MTK and a potential new therapeutic strategy for glaucoma treatment.

Mechanism for antiParkinsonian effect of resveratrol: Involvement of transporters, synaptic proteins, dendrite arborization, biochemical alterations, ER stress and apoptosis

The present study was undertaken to evaluate the mechanism for antiParkinsonian effect of resveratrol employing 6-hydroxydopamine (6-OHDA) induced experimental model of Parkinson's disease (PD). Resveratrol treatment significantly protects the PD related pathological markers like level of tyrosine hydroxylase, dopamine and apoptotic proteins (Bax and cleaved caspase-3). Disease pathology involves significantly decreased level of dopamine transporter, synaptophysin and postsynaptic density protein 95 (PSD-95) along with augmented level of vesicular monoamine transporter and considerably affected the dendrite arborization. Such affected neuronal communication was significantly restored with resveratrol treatment. Biochemical alterations include the depleted level of glutathione (GSH), mitochondrial complex-I activity with concomitant increased level of lipid peroxidation, nitrite level and calcium levels, which were also significantly inhibited with resveratrol treatment. Altered calcium level induces the endoplasmic reticulum (ER) stress related signalling and phosphorylated Nuclear factor erythroid 2-related factor 2 (Nrf2), and with resveratrol treatment the level of phosphorylated Nrf2 was further increased. The concurrent depleted level of proteasome activity was observed which was attenuated with resveratrol treatment. Proinflammatory cytokines and activated astrocytes were observed which was inhibited with resveratrol treatment. In conclusion, findings suggested that resveratrol exhibits the interference in neuronal communication, oxidative stress, mitochondrial pathophysiology, ER stress, protein degradation mechanism and inflammatory responses and could be utilize in clinics to treat the PD patients.

Interrelationship between the 5-lipoxygenase pathway and microbial dysbiosis in the progression of Alzheimer's disease

Alzheimer's disease (AD) is an age-related neurodegenerative disorder involving neurofibrillary tangles and amyloid plaques. The tau phosphorylation responsible for neurofibrillary tangles and amyloid deposition which causes plaques are both accelerated through the activity of 5-lipoxygenase (5-LO). In addition to these pathological pathways, 5-LO has also been linked to the neuro-inflammation associated with disease progression as well as to dysbiosis in the gut. Interestingly, gut dysbiosis itself has been correlated to AD development. Not only do gut metabolites have direct effects on the brain, but pro-inflammatory mediators such as LPS, BMAA and bacterial amyloids produced in the gut due to dysbiosis reach the brain causing increased neuro-inflammation. While microbial dysbiosis and 5-LO exert detrimental effects in the brain, the cause/effect relationship between these factors remain unknown. These issues may be addressed using mouse models of AD in the context of different knockout mice in the 5-LO pathway in specific pathogen-free, germ-free as well as gnotobiotic conditions.

Defining a pharmacological inhibitor fingerprint for oxytosis/ferroptosis

Ferroptosis was first described in 2012 as an iron- and lipid peroxidation-dependent form of regulated cell death. Since its initial description, these two characteristics have informed numerous cell culture studies where inhibitors of lipid peroxidation and/or iron chelators have been shown to prevent cell death induced by a wide range of insults. However, it is not clear whether these two characteristics are sufficient to distinguish ferroptosis from other forms of regulated cell death. Thus, the primary goal of this study was to determine whether a unique combination of features could be identified that would provide an approach to more clearly separate ferroptosis from other forms of regulated cell death. To this end, multiple pharmacological inhibitors based on a variety of studies were tested. Many of these inhibitors were previously shown to protect cells from oxytosis, a regulated cell death pathway that mechanistically overlaps with ferroptosis and is induced by some of the same chemicals as ferroptosis. These inhibitors were not only tested against both known ferroptosis and oxytosis inducers but also a number of other insults that have been suggested to induce ferroptosis. The results show that a pharmacological fingerprint for ferroptosis can be established and used to categorize toxic insults into those that overlap with oxytosis/ferroptosis and those that do not.

Identification of amyloid beta in small extracellular vesicles via Raman spectroscopy

One of the hallmarks of Alzheimer's disease (AD) pathogenesis is believed to be the production and deposition of amyloid-beta (Aβ) peptide into extracellular plaques. Existing research indicates that extracellular vesicles (EVs) can carry Aβ associated with AD. However, characterization of the EVs-associated Aβ and its conformational variants has yet to be realized. Raman spectroscopy is a label-free and non-destructive method that is able to assess the biochemical composition of EVs. This study reports for the first time the Raman spectroscopic fingerprint of the Aβ present in the molecular cargo of small extracellular vesicles (sEVs). Raman spectra were measured from sEVs isolated from Alzheimer's disease cell culture model, where secretion of Aβ is regulated by tetracycline promoter, and from midbrain organoids. The averaged spectra of each sEV group showed considerable variation as a reflection of the biochemical content of sEVs. Spectral analysis identified more intense Raman peaks at 1650 cm^-1 and 2930 cm^-1 attributable to the Aβ peptide incorporated in sEVs produced by the Alzheimer's cell culture model. Subsequent analysis of the spectra by principal component analysis differentiated the sEVs of the Alzheimer's disease cell culture model from the control groups of sEVs. Moreover, the results indicate that Aβ associated with secreted sEVs has a α-helical secondary structure and the size of a monomer or small oligomer. Furthermore, by analyzing the lipid content of sEVs we identified altered fatty acid chain lengths in sEVs that carry Aβ that may affect the fluidity of the EV membrane. Overall, our findings provide evidence supporting the use of Raman spectroscopy for the identification and characterization of sEVs associated with potential biomarkers of neurological disorders such as toxic proteins.

Rivastigmine attenuates the Alzheimer's disease related protein degradation and apoptotic neuronal death signalling

Rivastigmine is a clinical drug for patients of Alzheimer's disease (AD) exerting its inhibitory effect on acetylcholinesterase activity however, its effect on other disease-related pathological mechanisms are not yet known. This study was conducted to evaluate the effect of rivastigmine on protein aggregation and degradation related mechanisms employing streptozotocin (STZ) induced experimental rat model. The known inhibitory effect of rivastigmine on cognition and acetylcholinesterase activity was observed in both cortex and hippocampus and further its effect on tau level, amyloid aggregation, biochemical alterations, endoplasmic reticulum (ER) stress, calcium homeostasis, proteasome activity and apoptosis was estimated. STZ administration in rat brain caused significant cognitive impairment, augmented acetylcholinesterase activity, tau phosphorylation and amyloid aggregation which were significantly inhibited with rivastigmine treatment. STZ also caused significant biochemical alterations which were attenuated with rivastigmine treatment. Since AD pathology is related to protein aggregation and we have found disease-related amyloid aggregation, further the investigation was done to decipher the ER functionality and apoptotic signalling. STZ caused significantly altered level of ER stress related markers (GRP78, GADD153 and caspase-12) which were significantly inhibited with rivastigmine treatment. Furthermore, the effect of rivastigmine was estimated on proteasome activity in both regions. Rivastigmine treatment significantly enhances the proteasome activity and may contributes in removal of amyloid aggregation. In conclusion, findings suggested that along with inhibitory effect of rivastigmine on acetylcholinesterase activity and up to some extent on cognition, it has significant effect on disease-related biochemical alterations, ER functionality, protein degradation machinery and neuronal apoptosis.

Pyrazole Scaffold Synthesis, Functionalization, and Applications in Alzheimer's Disease and Parkinson's Disease Treatment (2011-2020)

The remarkable prevalence of pyrazole scaffolds in a versatile array of bioactive molecules ranging from apixaban, an anticoagulant used to treat and prevent blood clots and stroke, to bixafen, a pyrazole-carboxamide fungicide used to control diseases of rapeseed and cereal plants, has encouraged both medicinal and organic chemists to explore new methods in developing pyrazole-containing compounds for different applications. Although numerous synthetic strategies have been developed in the last 10 years, there has not been a comprehensive overview of synthesis and the implication of recent advances for treating neurodegenerative disease. This review first presents the advances in pyrazole scaffold synthesis and their functionalization that have been published during the last decade (2011-2020). We then narrow the focus to the application of these strategies in the development of therapeutics for neurodegenerative diseases, particularly for Alzheimer's disease (AD) and Parkinson's disease (PD).

Inflammation Drives Alzheimer's Disease: Emphasis on 5-lipoxygenase Pathways

It is a known fact that inflammation affects several physiological processes, including the functioning of the central nervous system. Additionally, impairment of lipid mechanisms/pathways have been associated with a number of neurodegenerative disorders and Alzheimer's Disease (AD) is one of them. However, much attention has been given to the link between tau and beta- amyloid hypothesis in AD pathogenesis/prognosis. Increasing evidences suggest that biologically active lipid molecules could influence the pathophysiology of AD via a different mechanism of inflammation. This review intends to highlight the role of inflammatory responses in the context of AD with the emphasis on biochemical pathways of lipid metabolism enzyme, 5-lipoxygenase (5- LO).

Phytocannabinoids: General Aspects and Pharmacological Potential in Neurodegenerative Diseases

In the last few years research into Cannabis and its constituent phytocannabinoids has burgeoned, particularly in the potential application of novel cannabis phytochemicals for the treatment of diverse illnesses related to neurodegeneration and dementia, including Alzheimer's (AD), Parkinson's (PD) and Huntington's disease (HD). To date, these neurological diseases have mostly relied on symptomatological management. However, with an aging population globally, the search for more efficient and disease-modifying treatments that could delay or mitigate disease progression is imperative. In this context, this review aims to present state of the art in the research with cannabinoids and novel cannabinoid-based drug candidates that have been emerged as novel promising alternatives for drug development and innovation in the therapeutics of a number of diseases, especially those related to CNS-disturbance and impairment.

Using the Oxytosis/Ferroptosis Pathway to Understand and Treat Age-Associated Neurodegenerative Diseases

Oxytosis was first described over 30 years ago in nerve cells as a non-excitotoxic pathway for glutamate-induced cell death. The key steps of oxytosis, including glutathione depletion, lipoxygenase activation, reactive oxygen species accumulation, and calcium influx, were identified using a combination of chemical and genetic tools. A pathway with the same characteristics as oxytosis was identified in transformed fibroblasts in 2012 and named ferroptosis. Importantly, the pathophysiological changes seen in oxytosis and ferroptosis are also observed in multiple neurodegenerative diseases as well as in the aging brain. This led to the hypothesis that this pathway could be used as a screening tool to identify novel drug candidates for the treatment of multiple age-associated neurological disorders, including Alzheimer's disease (AD). Using this approach, we have identified several AD drug candidates, one of which is now in clinical trials, as well as new target pathways for AD.

Intracellular amyloid toxicity induces oxytosis/ferroptosis regulated cell death

Amyloid beta (Aβ) accumulates within neurons in the brains of early stage Alzheimer’s disease (AD) patients. However, the mechanism underlying its toxicity remains unclear. Here, a triple omics approach was used to integrate transcriptomic, proteomic, and metabolomic data collected from a nerve cell model of the toxic intracellular aggregation of Aβ. It was found that intracellular Aβ induces profound changes in the omics landscape of nerve cells that are associated with a pro-inflammatory, metabolic reprogramming that predisposes cells to die via the oxytosis/ferroptosis regulated cell death pathway. Notably, the degenerative process included substantial alterations in glucose metabolism and mitochondrial bioenergetics. Our findings have implications for the understanding of the basic biology of proteotoxicity, aging, and AD as well as for the development of future therapeutic interventions designed to target the oxytosis/ferroptosis regulated cell death pathway in the AD brain.

5-lipoxygenase pathway and its downstream cysteinyl leukotrienes as potential therapeutic targets for Alzheimer's disease

5-lipoxygenase (ALOX5) is an enzyme involved in arachidonic acid (AA) metabolism, a metabolic pathway in which cysteinyl leukotrienes (CysLTs) are the resultant metabolites. Both ALOX5 and CysLTs are clinically significant in a number of inflammatory diseases, such as in asthma and allergic rhinitis, and drugs antagonizing the effect of these molecules have long been successfully used to counter these diseases. Interestingly, recent advances in 'neuroinflammation' research has led to the discovery of several novel inflammatory pathways regulating many cerebral pathologies, including the ALOX5 pathway. By means of pharmacological and genetic studies, both ALOX5 and CysLTs receptors have been shown to be involved in the pathogenesis of Alzheimer's disease (AD) and other neurodegenerative/neurological diseases, such as in Parkinson's disease, multiple sclerosis, and epilepsy. In both transgenic and sporadic models of AD, it has been shown that the levels of ALOX5/CysLTs are elevated, and that genetic/pharmacological interventions of these molecules can alleviate AD-related behavioral and pathological conditions. Clinical relevance of these molecules has also been found in AD brain samples. In this review, we aim to summarize such important findings on the role of ALOX5/CysLTs in AD pathophysiology, from both the cellular and the molecular aspects, and also discuss the potential of their blockers as possible therapeutic choices to curb AD-related conditions.

Diverse proteins aggregate in mild cognitive impairment and Alzheimer's disease brain

BACKGROUND

All cells accumulate insoluble protein aggregates throughout their lifespan. While many studies have characterized the canonical disease-associated protein aggregates, such as those associated with amyloid plaques, additional, undefined proteins aggregate in the brain and may be directly associated with disease and lifespan.

METHODS

A proteomics approach was used to identify a large subset of insoluble proteins in the mild cognitively impaired (MCI) and Alzheimer's disease (AD) human brain. Cortical samples from control, MCI, and AD patients were separated into detergent-soluble and detergent-insoluble fractions, and high-resolution LC/MS/MS technology was used to determine which proteins became more insoluble in the disease state. Bioinformatics analyses were used to determine if the alteration of protein aggregation between AD and control patients was associated with any specific biological process. Western blots were used to validate the proteomics data and to assess the levels of secondary protein modifications in MCI and AD.

RESULTS

There was a stage-dependent increase in detergent-insoluble proteins, with more extreme changes occurring in the AD cohort. Glycolysis was the most significantly overrepresented gene ontology biological process associated with the alteration of protein aggregation between AD and control patients. It was further shown that many low molecular weight proteins that were enriched in the AD brain were also highly aggregated, migrating on SDS-PAGE far above their predicted molecular masses. Glucose-6-phosphate isomerase, ubiquitin carboxyl-terminal hydrolase isoenzyme L1 (UCHL1/PARK5), and the DNA damage repair enzyme KU70 were among the top insoluble proteins identified by proteomics and validated by Western blot to be increased in the insoluble fractions of both MCI and AD brain samples.

CONCLUSIONS

Diverse proteins became more detergent-insoluble in the brains of both MCI and AD patients compared to age-matched controls, suggesting that multiple proteins aggregate in these diseases, likely posing a direct toxic insult to neurons. Furthermore, detergent-insoluble proteins included those with important biological activities for critical cellular processes such as energetics, proteolysis, and DNA damage repair. Thus, reduced protein solubility likely promotes aggregation and limits functionality, reducing the efficiency of multiple aspects of cell physiology. Pharmaceutical interventions that increase autophagy may provide a useful therapeutic treatment to combat protein aggregation.

Curcumin Derivative GT863 Inhibits Amyloid-Beta Production via Inhibition of Protein N-Glycosylation

Amyloid-β (Aβ) peptides play a crucial role in the pathogenesis of Alzheimer's disease (AD). Aβ production, aggregation, and clearance are thought to be important therapeutic targets for AD. Curcumin has been known to have an anti-amyloidogenic effect on AD. In the present study, we performed screening analysis using a curcumin derivative library with the aim of finding derivatives effective in suppressing Aβ production with improved bioavailability of curcumin using CHO cells that stably express human amyloid-β precursor protein and using human neuroblastoma SH-SY5Y cells. We found that the curcumin derivative GT863/PE859, which has been shown to have an inhibitory effect on Aβ and tau aggregation in vivo, was more effective than curcumin itself in reducing Aβ secretion. We further found that GT863 inhibited neither β- nor γ-secretase activity, but did suppress γ-secretase-mediated cleavage in a substrate-dependent manner. We further found that GT863 suppressed N-linked glycosylation, including that of the γ-secretase subunit nicastrin. We also found that mannosidase inhibitors that block the mannose trimming step of N-glycosylation suppressed Aβ production in a similar fashion, as was observed as a result of treatment with GT863. Collectively, these results suggest that GT863 downregulates N-glycosylation, resulting in suppression of Aβ production without affecting secretase activity.

Efficacy of Cannabinoids in a Pre-Clinical Drug-Screening Platform for Alzheimer's Disease

Finding a therapy for Alzheimer's disease (AD) is perhaps the greatest challenge for modern medicine. The chemical scaffolds of many drugs in the clinic today are based upon natural products from plants, yet Cannabis has not been extensively examined as a source of potential AD drug candidates. Here, we determine if a number of non-psychoactive cannabinoids are neuroprotective in a novel pre-clinical AD and neurodegeneration drug-screening platform that is based upon toxicities associated with the aging brain. This drug discovery paradigm has yielded several compounds in or approaching clinical trials for AD. Eleven cannabinoids were assayed for neuroprotection in assays that recapitulate proteotoxicity, loss of trophic support, oxidative stress, energy loss, and inflammation. These compounds were also assayed for their ability to remove intraneuronal amyloid and subjected to a structure-activity relationship analysis. Pairwise combinations were assayed for their ability to synergize to produce neuroprotective effects that were greater than additive. Nine of the 11 cannabinoids have the ability to protect cells in four distinct phenotypic neurodegeneration screening assays, including those using neurons that lack CB1 and CB2 receptors. They are able to remove intraneuronal Aβ, reduce oxidative damage, and protect from the loss of energy or trophic support. Structure-activity relationship (SAR) data show that functional antioxidant groups such as aromatic hydroxyls are necessary but not sufficient for neuroprotection. Therefore, there is a need to focus upon CB1 agonists that have these functionalities if neuroprotection is the goal. Pairwise combinations of THC and CBN lead to a synergistic neuroprotective interaction. Together, these results significantly extend the published data by showing that non-psychoactive cannabinoids are potential lead drug candidates for AD and other neurodegenerative diseases.

Targeting the ensemble of heterogeneous tau oligomers in cells: A novel small molecule screening platform for tauopathies

OBJECTIVE

Understanding the heterogeneous pathology in Alzheimer's disease and related tauopathies is one of the most urgent and fundamental challenges facing the discovery of novel disease-modifying therapies. Through monitoring ensembles of toxic and nontoxic tau oligomers spontaneously formed in cells, our biosensor technology can identify tool compounds that modulate tau oligomer structure and toxicity, providing much needed insight into the nature and properties of toxic tau oligomers.

BACKGROUND

Tauopathies are a group of neurodegenerative disorders characterized by pathologic aggregation of the microtubule binding protein tau. Recent studies suggest that tau oligomers are the primary toxic species in tauopathies.

NEW/UPDATED HYPOTHESIS

We hypothesize that tau biosensors capable of monitoring tau oligomer conformation are able to identify tool compounds that modulate the structure and conformation of these tau assemblies, providing key insight into the unique structural fingerprints of toxic tau oligomers. These fingerprints will provide gravely needed biomarker profiles to improve staging of early tauopathy pathology and generate lead compounds for potential new therapeutics. Our time-resolved fluorescence resonance energy transfer biosensors provide us an exquisitely sensitive technique to monitor minute structural changes in monomer and oligomer conformation. In this proof-of-concept study, we identified a novel tool compound, MK-886, which directly binds tau, perturbs the conformation of toxic tau oligomers, and rescues tau-induced cytotoxicity. Furthermore, we show that MK-886 alters the conformation of tau monomer at the proline-rich and microtubule binding regions, stabilizing an on-pathway oligomer.

MAJOR CHALLENGES FOR THE HYPOTHESIS

Our approach monitors changes in the ensemble of assemblies that are spontaneously formed in cells but does not specifically isolate or enrich unique toxic tau species. However, time-resolved fluorescence resonance energy transfer does not provide high-resolution, atomic scale information, requiring additional experimental techniques to resolve the structural features stabilized by different tool compounds.

LINKAGE TO OTHER MAJOR THEORIES

Our biosensor technology is broadly applicable to other areas of tauopathy therapeutic development. These biosensors can be readily modified for different isoforms of tau, specific post-translational modifications, and familial Alzheimer's disease-associated mutations. We are eager to explore tau interactions with chaperone proteins, monitor cross-reactivity with other intrinsically disordered proteins, and target seeded oligomer pathology.

Enhanced autophagic-lysosomal activity and increased BAG3-mediated selective macroautophagy as adaptive response of neuronal cells to chronic oxidative stress

Oxidative stress and a disturbed cellular protein homeostasis (proteostasis) belong to the most important hallmarks of aging and of neurodegenerative disorders. The proteasomal and autophagic-lysosomal degradation pathways are key measures to maintain proteostasis. Here, we report that hippocampal cells selected for full adaptation and resistance to oxidative stress induced by hydrogen peroxide (oxidative stress-resistant cells, OxSR cells) showed a massive increase in the expression of components of the cellular autophagic-lysosomal network and a significantly higher overall autophagic activity. A comparative expression analysis revealed that distinct key regulators of autophagy are upregulated in OxSR cells. The observed adaptive autophagic response was found to be independent of the upstream autophagy regulator mTOR but is accompanied by a significant upregulation of further downstream components of the canonical autophagy network such as Beclin1, WIPI1 and the transmembrane ATG9 proteins. Interestingly, the expression of the HSP70 co-chaperone BAG3, mediator of BAG3-mediated selective macroautophagy and highly relevant for the clearance of aggregated proteins in cells, was found to be increased in OxSR cells that were consequently able to effectively overcome proteotoxic stress. Overexpression of BAG3 in oxidative stress-sensitive HT22 wildtype cells partly established the vesicular phenotype and the enhanced autophagic flux seen in OxSR cells suggesting that BAG3 takes over an important part in the adaptation process. A full proteome analysis demonstrated additional changes in the expression of mitochondrial proteins, metabolic enzymes and different pathway regulators in OxSR cells as consequence of the adaptation to oxidative stress in addition to autophagy-related proteins. Taken together, this analysis revealed a wide variety of pathways and players that act as adaptive response to chronic redox stress in neuronal cells.

The impact of curcumin and its modified formulations on Alzheimer's disease

Alzheimer's disease (AD) is a major health problem worldwide, with no effective treatment approach. Curcumin is the main ingredient of turmeric traditionally used in Asian medicine. Several experimental studies have indicated the protective effect of curcumin and its novel formulations in AD. Curcumin has antioxidant, anti-inflammatory and neurotrophic activities, proposing a strong potential to prevent neurodegenerative diseases. However, there are no sufficient clinical trials to confirm curcumin use in AD patients. Low bioavailability following oral administration of curcumin limits its usage in human. The present study was designed to gather the effects of curcumin and its modified formulations in human and experimental models of AD.

CNB-001 reduces paraplegia in rabbits following spinal cord ischemia

Spinal cord ischemia associated with trauma and surgical procedures including thoraco-abdominal aortic aneurysm repair and thoracic endovascular aortic repair results in devastating clinical deficits in patients. Because spinal cord ischemia is inadequately treated, we studied the effects of [4-((1E)-2-(5-(4-hydroxy-3-methoxystyryl-)-1-phenyl-1H-pyrazoyl-3-yl) vinyl)-2-methoxy-phenol)] (CNB-001), a novel curcumin-based compound, in a rabbit SCI model. CNB-001 is known to inhibit human 5-lipoxygenase and 15-lipoxygenase and reduce the ischemia-induced inflammatory response. Moreover, CNB-001 can reduce the level of oxidative stress markers and potentiate brain-derived neurotrophic factor and brain-derived neurotrophic factor receptor signaling. The Tarlov scale and quantal analysis technique results revealed that CNB-001 administered as an intravenous dose (bolus) 30 minutes prior to spinal cord ischemia improved the behaviors of female New Zealand White rabbits. The improvements were similar to those produced by the uncompetitive N-methyl-D-aspartate receptor antagonist memantine. At 48 hours after aortic occlusion, there was a 42.7% increase (P < 0.05) in tolerated ischemia duration (n = 14) for rabbits treated with CNB-001 (n = 16), and a 72.3% increase for rabbits treated with the positive control memantine (P < 0.05) (n = 23) compared to vehicle-treated ischemic rabbits (n = 22). CNB-001 is a potential important novel treatment for spinal cord ischemia induced by aortic occlusion. All experiments were approved by the CSMC Institutional Animal Care and Use Committee (IACUC #4311) on November 1, 2012.

CNB-001, a pleiotropic drug is efficacious in embolized agyrencephalic New Zealand white rabbits and ischemic gyrencephalic cynomolgus monkeys

Ischemic stroke is an acute neurodegenerative disease that is extremely devastating to patients, their families and society. Stroke is inadequately treated even with endovascular procedures and reperfusion therapy. Using an extensive translational screening process, we have developed a pleiotropic cytoprotective agent with the potential to positively impact a large population of brain ischemia patients and revolutionize the process used for the development of new drugs to treat complex brain disorders. In this unique translational study article, we document that the novel curcumin-based compound, CNB-001, when administered as a single intravenous dose, has significant efficacy to attenuate clinically relevant behavioral deficits following ischemic events in agyrencephalic rabbits when administered 1 h post-embolization and reduces infarct growth in gyrencephalic non-human primates, when administered 5 min after initiation of middle cerebral artery occlusion. CNB-001 is safe and does not increase morbidity or mortality in either research species. Mechanistically, CNB-001 inhibits human 5- and 15-lipoxygenase in vitro, and can attenuate ischemia-induced inflammatory markers, and oxidative stress markers, while potentially promoting synaptic plasticity mediated by enhanced brain-derived neurotrophic factor (BDNF).

Quantitative peptidomics of endogenous peptides involved in TGF-β1-induced epithelial mesenchymal transition of renal epithelial cells

TGF-β1 is a key fibrotic factor mediating epithelial mesenchymal transition (EMT) of epithelial cells through various signaling pathways. However, roles of proteolytic cleavage and endogenous peptide dynamics in TGF-β1-induced EMT remain unknown. We therefore performed quantitative peptidomics of TGF-β1-induced EMT in renal tubular epithelial cells. The acquired mesenchymal characteristics were confirmed, including morphological change (from cobblestone-like to fibroblast-like), decreased epithelial marker (ZO-1), and increased mesenchymal marker (vimentin). Quantitative peptidomics using stable isotope labeling revealed significantly altered levels of 70 unique endogenous peptides (derived from internal and C-terminal parts of 39 unique precursor proteins) after EMT induction. Interestingly, the majority of these peptides were derived from non-short-lived proteins, and analysis of P1 position revealed predominance of hydrophobic residues, suggesting that these endogenous peptides were generated mainly from proteasome cleavage. This hypothesis was confirmed by treating the cells with MG132 (a proteasome inhibitor), which provided almost identical endogenous peptide pattern as of the TGF-β1-treated cells. Moreover, validation assay showed marked reduction of proteasome peptidase activity in both TGF-β1-treated and MG132-treated cells. This is the first peptidome dataset that provides several novel aspects of mechanisms for TGF-β1-induced EMT. Our data also suggest that TGF-β1 exerts inhibitory effect against proteasome activity during EMT induction.

Use of curcumin in diagnosis, prevention, and treatment of Alzheimer's disease

This review summarizes and describes the use of curcumin in diagnosis, prevention, and treatment of Alzheimer's disease. For diagnosis of Alzheimer's disease, amyloid-β and highly phosphorylated tau protein are the major biomarkers. Curcumin was developed as an early diagnostic probe based on its natural fluorescence and high binding affinity to amyloid-β. Because of its multi-target effects, curcumin has protective and preventive effects on many chronic diseases such as cerebrovascular disease, hypertension, and hyperlipidemia. For prevention and treatment of Alzheimer's disease, curcumin has been shown to effectively maintain the normal structure and function of cerebral vessels, mitochondria, and synapses, reduce risk factors for a variety of chronic diseases, and decrease the risk of Alzheimer's disease. The effect of curcumin on Alzheimer's disease involves multiple signaling pathways: anti-amyloid and metal iron chelating properties, antioxidation and anti-inflammatory activities. Indeed, there is a scientific basis for the rational application of curcumin in prevention and treatment of Alzheimer's disease.

CNB-001, a synthetic pyrazole derivative of curcumin, suppresses lipopolysaccharide-induced nitric oxide production through the inhibition of NF-κB and p38 MAPK pathways in microglia

CNB-001, a pyrazole derivative of curcumin, has been found to exert neuroprotective and memory-enhancing effects that may be effective for the treatment of Alzheimer's disease. Since aberrant activation of microglia is involved in the pathogenesis of Alzheimer's disease, the present study was undertaken to investigate the effect of CNB-001 on microglia-mediated inflammatory responses. In primary cultured rat microglia, CNB-001 (1-10µM) suppressed the lipopolysaccharide (LPS)-induced nitric oxide (NO) production and expression of inducible NO synthase (iNOS), and the potency of CNB-001 was stronger than curcumin. CNB-001 also suppressed the LPS-induced nuclear translocation of nuclear factor κB (NF-κB), which is essential for the expression of iNOS. LPS treatment promoted phosphorylation of extracellular signal-regulated kinase (ERK), c-Jun N-terminal kinase (JNK), and p38 mitogen-activated protein kinase (MAPK). CNB-001 significantly suppressed the LPS-induced phosphorylation of p38 MAPK, but not ERK and JNK. The suppressive effect of CNB-001 on NO production was mimicked by blockade of the p38 MAPK signaling pathway with SB203580. These results suggest that CNB-001 exerts anti-inflammatory effects through inhibition of NF-κB and p38 MAPK pathways in microglia.

Intraneuronal protein aggregation as a trigger for inflammation and neurodegeneration in the aging brain

Age is, by far, the greatest risk factor for Alzheimer's disease (AD), yet few AD drug candidates have been generated that target pathways specifically associated with the aging process itself. Two ubiquitous features of the aging brain are the intracellular accumulation of aggregated proteins and inflammation. As intraneuronal amyloid protein is detected before markers of inflammation, we argue that old, age-associated, aggregated proteins in neurons can induce inflammation, resulting in multiple forms of brain toxicities. The consequence is the increased risk of old, age-associated, neurodegenerative diseases. As most of these diseases are associated with the accumulation of aggregated proteins, it is possible that any therapeutic that reduces intracellular protein aggregation will benefit all.-Currais, A., Fischer, W., Maher, P., Schubert, D. Intraneuronal protein aggregation as a trigger for inflammation and neurodegeneration in the aging brain.

A novel Alzheimer's disease drug candidate targeting inflammation and fatty acid metabolism

Background

CAD-31 is an Alzheimer’s disease (AD) drug candidate that was selected on the basis of its ability to stimulate the replication of human embryonic stem cell-derived neural precursor cells as well as in APPswe/PS1ΔE9 AD mice. To move CAD-31 toward the clinic, experiments were undertaken to determine its neuroprotective and pharmacological properties, as well as to assay its therapeutic efficacy in a rigorous mouse model of AD.

Results

CAD-31 has potent neuroprotective properties in six distinct nerve cell assays that mimic toxicities observed in the old brain. Pharmacological and preliminary toxicological studies show that CAD-31 is brain-penetrant and likely safe. When fed to old, symptomatic APPswe/PS1ΔE9 AD mice starting at 10 months of age for 3 additional months in a therapeutic model of the disease, there was a reduction in the memory deficit and brain inflammation, as well as an increase in the expression of synaptic proteins. Small-molecule metabolic data from the brain and plasma showed that the major effect of CAD-31 is centered on fatty acid metabolism and inflammation. Pathway analysis of gene expression data showed that CAD-31 had major effects on synapse formation and AD energy metabolic pathways.

Conclusions

All of the multiple physiological effects of CAD-31 were favorable in the context of preventing some of the toxic events in old age-associated neurodegenerative diseases.

Electronic supplementary material

The online version of this article (doi:10.1186/s13195-017-0277-3) contains supplementary material, which is available to authorized users.

Amyloid proteotoxicity initiates an inflammatory response blocked by cannabinoids

The beta amyloid (Aβ) and other aggregating proteins in the brain increase with age and are frequently found within neurons. The mechanistic relationship between intracellular amyloid, aging and neurodegeneration is not, however, well understood. We use a proteotoxicity model based upon the inducible expression of Aβ in a human central nervous system nerve cell line to characterize a distinct form of nerve cell death caused by intracellular Aβ. It is shown that intracellular Aβ initiates a toxic inflammatory response leading to the cell's demise. Aβ induces the expression of multiple proinflammatory genes and an increase in both arachidonic acid and eicosanoids, including prostaglandins that are neuroprotective and leukotrienes that potentiate death. Cannabinoids such as tetrahydrocannabinol stimulate the removal of intraneuronal Aβ, block the inflammatory response, and are protective. Altogether these data show that there is a complex and likely autocatalytic inflammatory response within nerve cells caused by the accumulation of intracellular Aβ, and that this early form of proteotoxicity can be blocked by the activation of cannabinoid receptors.

Arachidonate 5-lipoxygenase (ALOX5) gene polymorphism is associated with Alzheimer's disease and body mass index

Dementias of old age, in particular Alzheimer's disease (AD), pose a growing threat to the longevity and quality of life of individuals as well as whole societies world-wide. The risk factors are both genetic and environmental (life-style) and there is an overlap with similar factors predisposing to cardiovascular diseases (CVD). Using a case-control genetic approach, we have identified a SNP (rs10507391) in ALOX5 gene, previously associated with an increased risk of stroke, as a novel genetic risk factor for AD. ALOX5 gene encodes a 5'-lipoxygenase (5'-LO) activating protein (FLAP), a crucial component of the arachidonic acid/leukotriene inflammatory cascade. A-allele of rs4769874 polymorphism increases the risk of AD 1.41-fold (p<0.0001), while AA genotype does so 1.79-fold (p<0.0001). In addition, GG genotype of rs4769874 polymorphism is associated with a modest increase in body mass index (BMI). We discuss potential biochemical mechanisms linking the SNP to AD and suggest possible preventive pharmacotherapies some of which are based on commonly available natural products. Finally, we set the newly identified AD risk factors into a broader context of similar CVD risk factors to generate a more comprehensive picture of interacting genetics and life-style habits potentially leading to the deteriorating mental health in the old age.

UPS Activation in the Battle Against Aging and Aggregation-Related Diseases: An Extended Review

Aging is a biological process accompanied by gradual increase of damage in all cellular macromolecules, i.e., nucleic acids, lipids, and proteins. When the proteostasis network (chaperones and proteolytic systems) cannot reverse the damage load due to its excess as compared to cellular repair/regeneration capacity, failure of homeostasis is established. This failure is a major hallmark of aging and/or aggregation-related diseases. Dysfunction of the major cellular proteolytic machineries, namely the proteasome and the lysosome, has been reported during the progression of aging and aggregation-prone diseases. Therefore, activation of these pathways is considered as a possible preventive or therapeutic approach against the progression of these processes. This chapter focuses on UPS activation studies in cellular and organismal models and the effects of such activation on aging, longevity and disease prevention or reversal.

Alzheimer's as a Systems-Level Disease Involving the Interplay of Multiple Cellular Networks

Alzheimer's disease (AD), and many neurodegenerative disorders, are multifactorial in nature. They involve a combination of genomic, epigenomic, interactomic and environmental factors. Progress is being made, and these complex diseases are beginning to be understood as having their origin in altered states of biological networks at the cellular level. In the case of AD, genomic susceptibility and mechanisms leading to (or accompanying) the impairment of the central Amyloid Precursor Protein (APP) processing and tau networks are widely accepted as major contributors to the diseased state. The derangement of these networks may result in both the gain and loss of functions, increased generation of toxic species (e.g., toxic soluble oligomers and aggregates) and imbalances, whose effects can propagate to supra-cellular levels. Although well sustained by empirical data and widely accepted, this global perspective often overlooks the essential roles played by the main counteracting homeostatic networks (e.g., protein quality control/proteostasis, unfolded protein response, protein folding chaperone networks, disaggregases, ER-associated degradation/ubiquitin proteasome system, endolysosomal network, autophagy, and other stress-protective and clearance networks), whose relevance to AD is just beginning to be fully realized. In this chapter, an integrative perspective is presented. Alzheimer's disease is characterized to be a result of: (a) intrinsic genomic/epigenomic susceptibility and, (b) a continued dynamic interplay between the deranged networks and the central homeostatic networks of nerve cells. This interplay of networks will underlie both the onset and rate of progression of the disease in each individual. Integrative Systems Biology approaches are required to effect its elucidation. Comprehensive Systems Biology experiments at different 'omics levels in simple model organisms, engineered to recapitulate the basic features of AD may illuminate the onset and sequence of events underlying AD. Indeed, studies of models of AD in simple organisms, differentiated cells in culture and rodents are beginning to offer hope that the onset and progression of AD, if detected at an early stage, may be stopped, delayed, or even reversed, by activating or modulating networks involved in proteostasis and the clearance of toxic species. In practice, the incorporation of next-generation neuroimaging, high-throughput and computational approaches are opening the way towards early diagnosis well before irreversible cell death. Thus, the presence or co-occurrence of: (a) accumulation of toxic Aβ oligomers and tau species; (b) altered splicing and transcriptome patterns; (c) impaired redox, proteostatic, and metabolic networks together with, (d) compromised homeostatic capacities may constitute relevant 'AD hallmarks at the cellular level' towards reliable and early diagnosis. From here, preventive lifestyle changes and tailored therapies may be investigated, such as combined strategies aimed at both lowering the production of toxic species and potentiating homeostatic responses, in order to prevent or delay the onset, and arrest, alleviate, or even reverse the progression of the disease.

Human Cytomegalovirus Inhibits the PARsylation Activity of Tankyrase--A Potential Strategy for Suppression of the Wnt Pathway

Human cytomegalovirus (HCMV) was reported to downregulate the Wnt/β-catenin pathway. Induction of Axin1, the negative regulator of the Wnt pathway, has been reported as an important mechanism for inhibition of β-catenin. Since Tankyrase (TNKS) negatively regulates Axin1, we investigated the effect of HCMV on TNKS expression and poly-ADP ribose polymerase (PARsylation) activity, during virus replication. Starting at 24 h post infection, HCMV stabilized the expression of TNKS and reduced its PARsylation activity, resulting in accumulation of Axin1 and reduction in its PARsylation as well. General PARsylation was not changed in HCMV-infected cells, suggesting specific inhibition of TNKS PARsylation. Similarly, treatment with XAV939, a chemical inhibitor of TNKS’ activity, resulted in the accumulation of TNKS in both non-infected and HCMV-infected cell lines. Reduction of TNKS activity or knockdown of TNKS was beneficial for HCMV, evidenced by its improved growth in fibroblasts. Our results suggest that HCMV modulates the activity of TNKS to induce Axin1, resulting in inhibition of the β-catenin pathway. Since HCMV replication is facilitated by TNKS knockdown or inhibition of its activity, TNKS may serve as an important virus target for control of a variety of cellular processes.

The Lipoxygenases: Their Regulation and Implication in Alzheimer's Disease

Inflammatory processes and alterations of lipid metabolism play a crucial role in Alzheimer’s disease (AD) and other neurodegenerative disorders. Polyunsaturated fatty acids (PUFA) metabolism impaired by cyclooxygenases (COX-1, COX-2), which are responsible for formation of several eicosanoids, and by lipoxygenases (LOXs) that catalyze the addition of oxygen to linolenic, arachidonic (AA), and docosahexaenoic acids (DHA) and other PUFA leading to formation of bioactive lipids, significantly affects the course of neurodegenerative diseases. Among several isoforms, 5-LOX and 12/15-LOX are especially important in neuroinflammation/neurodegeneration. These two LOXs are regulated by substrate concentration and availability, and by phosphorylation/dephosphorylation through protein kinases PKA, PKC and MAP-kinases, including ERK1/ERK2 and p38. The protein/protein interaction also is involved in the mechanism of 5-LOX regulation through FLAP protein and coactosin-like protein. Moreover, non-heme iron and calcium ions are potent regulators of LOXs. The enzyme activity significantly depends on the cell redox state and is differently regulated by various signaling pathways. 5-LOX and 12/15-LOX convert linolenic acid, AA, and DHA into several bioactive compounds e.g. hydroperoxyeicosatetraenoic acids (5-HPETE, 12S-HPETE, 15S-HPETE), which are reduced to corresponding HETE compounds. These enzymes synthesize several bioactive lipids, e.g. leucotrienes, lipoxins, hepoxilins and docosahexaenoids. 15-LOX is responsible for DHA metabolism into neuroprotectin D1 (NPD1) with significant antiapoptotic properties which is down-regulated in AD. In this review, the regulation and impact of 5-LOX and 12/15-LOX in the pathomechanism of AD is discussed. Moreover, we describe the role of several products of LOXs, which may have significant pro- or anti-inflammatory activity in AD, and the cytoprotective effects of LOX inhibitors.

Examining the potential clinical value of curcumin in the prevention and diagnosis of Alzheimer’s disease

Curcumin derived from turmeric is well documented for its anti-carcinogenic, antioxidant and anti-inflammatory properties. Recent studies show that curcumin also possesses neuroprotective and cognitive-enhancing properties that may help delay or prevent neurodegenerative diseases, including Alzheimer’s disease (AD). Currently, clinical diagnosis of AD is onerous, and it is primarily based on the exclusion of other causes of dementia. In addition, phase III clinical trials of potential treatments have mostly failed, leaving disease-modifying interventions elusive. AD can be characterised neuropathologically by the deposition of extracellular β amyloid (Aβ) plaques and intracellular accumulation of tau-containing neurofibrillary tangles. Disruptions in Aβ metabolism/clearance contribute to AD pathogenesis. In vitro studies have shown that Aβ metabolism is altered by curcumin, and animal studies report that curcumin may influence brain function and the development of dementia, because of its antioxidant and anti-inflammatory properties, as well as its ability to influence Aβ metabolism. However, clinical studies of curcumin have revealed limited effects to date, most likely because of curcumin’s relatively low solubility and bioavailability, and because of selection of cohorts with diagnosed AD, in whom there is already major neuropathology. However, the fresh approach of targeting early AD pathology (by treating healthy, pre-clinical and mild cognitive impairment-stage cohorts) combined with new curcumin formulations that increase bioavailability is renewing optimism concerning curcumin-based therapy. The aim of this paper is to review the current evidence supporting an association between curcumin and modulation of AD pathology, including in vitro and in vivo studies. We also review the use of curcumin in emerging retinal imaging technology, as a fluorochrome for AD diagnostics.

Combination therapies: The next logical Step for the treatment of synucleinopathies?

Currently there are no disease-modifying alternatives for the treatment of most neurodegenerative disorders. The available therapies for diseases such as Parkinson's disease (PD), PD dementia (PDD), dementia with Lewy bodies (DLB), and multiple system atrophy (MSA), in which the protein alpha-synuclein (α-Syn) accumulates within neurons and glial cells with toxic consequences, are focused on managing the disease symptoms. However, using strategic drug combinations and/or multi-target drugs might increase the treatment efficiency when compared with monotherapies. Synucleinopathies are complex disorders that progress through several stages, and toxic α-Syn aggregates exhibit prion-like behavior spreading from cell to cell. Therefore, it follows that these neurodegenerative disorders might require equally complex therapeutic approaches to obtain significant and long-lasting results. Hypothetically, therapies aimed at reducing α-Syn accumulation and cell-to-cell transfer, such as immunotherapy against α-Syn, could be combined with agents that reduce neuroinflammation with potential synergistic outcomes. Here we review the current evidence supporting this type of approach, suggesting that such rational therapy combinations, together with the use of multi-target drugs, may hold promise as the next logical step for the treatment of synucleinopathies.

Proteasome activation: An innovative promising approach for delaying aging and retarding age-related diseases

Aging is a natural process accompanied by a progressive accumulation of damage in all constituent macromolecules (nucleic acids, lipids and proteins). Accumulation of damage in proteins leads to failure of proteostasis (or vice versa) due to increased levels of unfolded, misfolded or aggregated proteins and, in turn, to aging and/or age-related diseases. The major cellular proteolytic machineries, namely the proteasome and the lysosome, have been shown to dysfunction during aging and age-related diseases. Regarding the proteasome, it is well established that it can be activated either through genetic manipulation or through treatment with natural or chemical compounds that eventually result to extension of lifespan or deceleration of the progression of age-related diseases. This review article focuses on proteasome activation studies in several species and cellular models and their effects on aging and longevity. Moreover, it summarizes findings regarding proteasome activation in the major age-related diseases as well as in progeroid syndromes.

Cathepsin L Mediates the Degradation of Novel APP C-Terminal Fragments

Alzheimer's disease (AD) is characterized by the deposition of amyloid β (Aβ), a peptide generated from proteolytic processing of its precursor, amyloid precursor protein (APP). Canonical APP proteolysis occurs via α-, β-, and γ-secretases. APP is also actively degraded by protein degradation systems. By pharmacologically inhibiting protein degradation with ALLN, we observed an accumulation of several novel APP C-terminal fragments (CTFs). The two major novel CTFs migrated around 15 and 25 kDa and can be observed across multiple cell types. The process was independent of cytotoxicity or protein synthesis. We further determine that the accumulation of the novel CTFs is not mediated by proteasome or calpain inhibition, but by cathepsin L inhibition. Moreover, these novel CTFs are not generated by an increased amount of BACE. Here, we name the CTF of 25 kDa as η-CTF (eta-CTF). Our data suggest that under physiological conditions, a subset of APP undergoes alternative processing and the intermediate products, the 15 kDa CTFs, and the η-CTFs aret rapidly degraded and/or processed via the protein degradation machinery, specifically, cathepsin L.

Unfolding the promise of translational targeting in neurodegenerative disease

With the rise of aging populations, new challenges for health care systems are emerging. Degenerative conditions of the central nervous system share a strikingly great deal of similarities, particularly the production and buildup of malfolded proteins. As a result, stress pathways within the endoplasmic reticulum become activated, triggering widespread neuronal apoptosis. New pharmacological compounds targeting this response are emerging as promising treatment strategies. This review examines the current evidence for protein aggregation in neurodegenerative disease states and discusses future mechanisms of therapeutically targeting the endoplasmic reticulum.