Overexpression of amyloid-β protein precursor induces mitochondrial oxidative stress and activates the intrinsic apoptotic cascade

Lost in translation: Inconvenient truths on the utility of mouse models in Alzheimer's disease research

The recent, controversial approval of antibody-based treatments for Alzheimer's disease (AD) is fueling a heated debate on the molecular determinants of this condition. The discussion should also incorporate a critical revision of the limitations of preclinical mouse models in advancing our understanding of AD. We critically discuss the limitations of animal models, stressing the need for careful consideration of how experiments are designed and results interpreted. We identify the shortcomings of AD models to recapitulate the complexity of the human disease. We dissect these issues at the quantitative, qualitative, temporal, and context-dependent levels. We argue that these models are based on the oversimplistic assumptions proposed by the amyloid cascade hypothesis (ACH) of AD and fail to account for the multifactorial nature of the condition. By shedding light on the constraints of current experimental tools, this review aims to foster the development and implementation of more clinically relevant tools. While we do not rule out a role for preclinical models, we call for alternative approaches to be explored and, most importantly, for a re-evaluation of the ACH.

Alzheimer's Disease: Cellular and Pharmacological Aspects

Alzheimer's disease was described more than 100 years ago and despite the fact that several molecules are being tested for its treatment, which are in phase III trials, the disease continues to progress. The main problem is that these molecules function properly in healthy neurons, while neuronal pathology includes plasma membrane disruption, malfunction of various organelles, and hyperphosphorylation of Tau and amyloid plaques. The main objective of this article is the discussion of a neuronal restoration therapy, where molecules designed for the treatment of Alzheimer's disease would probably be more effective, and the quality of life of people would be better.

Lipid nanoparticle mediated small interfering RNA delivery as a potential therapy for Alzheimer's disease

Alzheimer's disease (AD) is a neurodegenerative condition that exhibits a gradual decline in cognitive function and is prevalent among a significant number of individuals globally. The use of small interfering RNA (siRNA) molecules in RNA interference (RNAi) presents a promising therapeutic strategy for AD. Lipid nanoparticles (LNPs) have been developed as a delivery vehicle for siRNA, which can selectively suppress target genes, by enhancing cellular uptake and safeguarding siRNA from degradation. Numerous research studies have exhibited the effectiveness of LNP-mediated siRNA delivery in reducing amyloid beta (Aβ) levels and enhancing cognitive function in animal models of AD. The feasibility of employing LNP-mediated siRNA delivery as a therapeutic approach for AD is emphasized by the encouraging outcomes reported in clinical studies for other medical conditions. The use of LNP-mediated siRNA delivery has emerged as a promising strategy to slow down or even reverse the progression of AD by targeting the synthesis of tau phosphorylation and other genes linked to the condition. Improvement of the delivery mechanism and determination of the most suitable siRNA targets are crucial for the efficacious management of AD. This review focuses on the delivery of siRNA through LNPs as a promising therapeutic strategy for AD, based on the available literature.

The Role of Tau Pathology in Alzheimer's Disease and Down Syndrome

Background: Individuals with Down syndrome (DS) exhibit an almost complete penetrance of Alzheimer's disease (AD) pathology but are underrepresented in clinical trials for AD. The Tau protein is associated with microtubule function in the neuron and is crucial for normal axonal transport. In several different neurodegenerative disorders, Tau misfolding leads to hyper-phosphorylation of Tau (p-Tau), which may seed pathology to bystander cells and spread. This review is focused on current findings regarding p-Tau and its potential to seed pathology as a "prion-like" spreader. It also considers the consequences of p-Tau pathology leading to AD, particularly in individuals with Down syndrome. Methods: Scopus (SC) and PubMed (PM) were searched in English using keywords "tau AND seeding AND brain AND down syndrome". A total of 558 SC or 529 PM potentially relevant articles were identified, of which only six SC or three PM articles mentioned Down syndrome. This review was built upon the literature and the recent findings of our group and others. Results: Misfolded p-Tau isoforms are seeding competent and may be responsible for spreading AD pathology. Conclusions: This review demonstrates recent work focused on understanding the role of neurofibrillary tangles and monomeric/oligomeric Tau in the prion-like spreading of Tau pathology in the human brain.

A Near-Infrared Fluorogenic Probe for Rapid, Specific, and Ultrasensitive Detection of Sphingosine in Living Cells and In Vivo

Sphingosine (Sph) plays important roles in various complex biological processes. Abnormalities in Sph metabolism can result in various diseases, including neurodegenerative disorders. However, due to the lack of rapid and accurate detection methods, understanding sph metabolic in related diseases is limited. Herein, a series of near-infrared fluorogenic probes DMS-X (X = 2F, F, Cl, Br, and I) are designed and synthesized. The fast oxazolidinone ring formation enables the DMS-2F to detect Sph selectively and ultrasensitively, and the detection limit reaches 9.33 ± 0.41 nm. Moreover, it is demonstrated that DMS-2F exhibited a dose- and time-dependent response to Sph and can detect sph in living cells. Importantly, for the first time, the changes in Sph levels induced by Aβ42 oligomers and H2 O2 are assessed through a fluorescent imaging approach, and further validated the physiological processes by which Aβ42 oligomers and reactive oxygen species (ROS)-induce changes in intracellular Sph levels. Additionally, the distribution of Sph in living zebrafish is successfully mapped by in vivo imaging of a zebrafish model. This work provides a simple and efficient method for probing Sph in living cells and in vivo, which will facilitate investigation into the metabolic process of Sph and the connection between Sph and disease pathologies.

A multi-layered network model identifies Akt1 as a common modulator of neurodegeneration

The accumulation of misfolded and aggregated proteins is a hallmark of neurodegenerative proteinopathies. Although multiple genetic loci have been associated with specific neurodegenerative diseases (NDs), molecular mechanisms that may have a broader relevance for most or all proteinopathies remain poorly resolved. In this study, we developed a multi-layered network expansion (MLnet) model to predict protein modifiers that are common to a group of diseases and, therefore, may have broader pathophysiological relevance for that group. When applied to the four NDs Alzheimer's disease (AD), Huntington's disease, and spinocerebellar ataxia types 1 and 3, we predicted multiple members of the insulin pathway, including PDK1, Akt1, InR, and sgg (GSK-3β), as common modifiers. We validated these modifiers with the help of four Drosophila ND models. Further evaluation of Akt1 in human cell-based ND models revealed that activation of Akt1 signaling by the small molecule SC79 increased cell viability in all models. Moreover, treatment of AD model mice with SC79 enhanced their long-term memory and ameliorated dysregulated anxiety levels, which are commonly affected in AD patients. These findings validate MLnet as a valuable tool to uncover molecular pathways and proteins involved in the pathophysiology of entire disease groups and identify potential therapeutic targets that have relevance across disease boundaries. MLnet can be used for any group of diseases and is available as a web tool at http://ssbio.cau.ac.kr/software/mlnet.

The Impressive Anti-Inflammatory Activity of Cerium Oxide Nanoparticles: More than Redox?

Cerium oxide nanoparticles (CNPs) are biocompatible nanozymes exerting multifunctional biomimetic activities, including superoxide dismutase (SOD), catalase, glutathione peroxidase, photolyase, and phosphatase. SOD- and catalase-mimesis depend on Ce3+/Ce4+ redox switch on nanoparticle surface, which allows scavenging the most noxious reactive oxygen species in a self-regenerating, energy-free manner. As oxidative stress plays pivotal roles in the pathogenesis of inflammatory disorders, CNPs have recently attracted attention as potential anti-inflammatory agents. A careful survey of the literature reveals that CNPs, alone or as constituents of implants and scaffolds, strongly contrast chronic inflammation (including neurodegenerative and autoimmune diseases, liver steatosis, gastrointestinal disorders), infections, and trauma, thereby ameliorating/restoring organ function. By general consensus, CNPs inhibit inflammation cues while boosting the pro-resolving anti-inflammatory signaling pathways. The mechanism of CNPs' anti-inflammatory effects has hardly been investigated, being rather deductively attributed to CNP-induced ROS scavenging. However, CNPs are multi-functional nanozymes that exert additional bioactivities independent from the Ce3+/Ce4+ redox switch, such as phosphatase activity, which could conceivably mediate some of the anti-inflammatory effects reported, suggesting that CNPs fight inflammation via pleiotropic actions. Since CNP anti-inflammatory activity is potentially a pharmacological breakthrough, it is important to precisely attribute the described effects to one or another of their nanozyme functions, thus achieving therapeutic credibility.

Antioxidant Nanozymes: Mechanisms, Activity Manipulation, and Applications

Antioxidant enzymes such as catalase, superoxide dismutase, and glutathione peroxidase play important roles in the inhibition of oxidative-damage-related pathological diseases. However, natural antioxidant enzymes face some limitations, including low stability, high cost, and less flexibility. Recently, antioxidant nanozymes have emerged as promising materials to replace natural antioxidant enzymes for their stability, cost savings, and flexible design. The present review firstly discusses the mechanisms of antioxidant nanozymes, focusing on catalase-, superoxide dismutase-, and glutathione peroxidase-like activities. Then, we summarize the main strategies for the manipulation of antioxidant nanozymes based on their size, morphology, composition, surface modification, and modification with a metal-organic framework. Furthermore, the applications of antioxidant nanozymes in medicine and healthcare are also discussed as potential biological applications. In brief, this review provides useful information for the further development of antioxidant nanozymes, offering opportunities to improve current limitations and expand the application of antioxidant nanozymes.

Untangle the mystery behind DS-associated AD - Is APP the main protagonist?

Amyloid precursor protein profusion in Trisomy 21, also called Down Syndrome (DS), is rooted in the genetic determination of Alzheimer's disease (AD). With the recent development in patient care, the life expectancy of DS patients has gradually increased, leading to the high prospect of AD development, consequently leading to the development of plaques of amyloid proteins and neurofibrillary tangles made of tau by the fourth decade of the patient leading to dementia. The altered gene expression resulted in cellular dysfunction due to impairment of autophagy, mitochondrial and lysosomal dysfunction, and copy number variation controlled by the additional genes in Trisomy 21. The cognitive impairment and mechanistic insights underlying DS-AD conditions have been reviewed in this article. Some recent findings regarding biomarkers and therapeutics of DS-AD conditions were highlighted in this review.

Structure-Activity Relationship of Carbon Nitride Dots in Inhibiting Tau Aggregation

Due to the numerous failed clinical trials of anti-amyloid drugs, microtubule associated protein tau (MAPT) now stands out as one of the most promising targets for AD therapy. In this study, we report for the first time the structure-dependent MAPT aggregation inhibition of carbon nitride dots (CNDs). CNDs have exhibited great promise as a potential treatment of Alzheimer's disease (AD) by inhibiting the aggregation of MAPT. In order to elucidate its structure-activity relationship, CNDs were separated via column chromatography and five fractions with different structures were obtained that were characterized by multiple spectroscopy methods. The increase of surface hydrophilic functional groups is consistent with the increase of polarity from fraction 1 to 5. Particle sizes (1-2 nm) and zeta potentials (~-20 mV) are similar among five fractions. With the increase of polarity from fraction 1 to 5, their MAPT aggregation inhibition capacity was weakened. This suggests hydrophobic interactions between CNDs and MAPT, validated via molecular dynamics simulations. With a zebrafish blood-brain barrier (BBB) model, CNDs were observed to cross the BBB through passive diffusion. CNDs were also found to inhibit the generation of multiple reactive oxygen species, which is an important contributor to AD pathogenesis.

Triplication of HSA21 on alterations in structure and function of mitochondria

Triplication of genes encoded in human chromosome 21 (HSA21) is responsible for the phenotypes of Down syndrome (DS). The dosage-imbalance of the nuclear genes and the extra-nuclear mitochondrial DNA (mtDNA) jointly contributes to patho-mechanisms in DS. The mitochondrial organelles are the power house of cells for generation of ATP and maintaining cellular calcium and redox homeostasis, and cellular energy-metabolism processes. Each cell contains hundreds to thousands of mitochondria depending on their energy consumption. The dynamic structure of mitochondria is maintained with continuous fission and fusion events, and thus, content of mtDNA and its genetic composition are widely variable among cells. Cells of brain and heart tissues of DS patients and DS-mouse models have demonstrated elevated number but reduced amount of mtDNA due to higher fission process. This mechanism perturbs the oxidative phosphorylation (OXPHOS) and generates more free radicals such as reactive oxygen species (ROS), suggesting contribution of mtDNA in proliferation and protection of cells from endogenous toxic environment and external stressors. Gene-dosage in DS population collectively contributes to mitochondrial dysfunction by lowering energy production and respiratory capacity via the impaired OXPHOS, and damaged redox homeostasis and mitochondrial dynamics in all types of cells in DS. The context is highly complex and affects the functioning of all organs. The effect in brain and heart tissues promotes myriads of neurodegenerative diseases and cardiac complexities in individuals with DS. Crosstalk between trisomic nuclear and mitochondrial genome has been crucial for identification of potential therapeutic targets.

The amyloid precursor protein: a converging point in Alzheimer's disease

The decades of evidence that showcase the role of amyloid precursor protein (APP), and its fragment amyloidβ (Aβ), in Alzheimer's disease (AD) pathogenesis are irrefutable. However, the absolute focus on the single APP metabolite Aβ as the cause for AD has resulted in APP and its other fragments that possess toxic propensity, to be overlooked as targets for treatment. The complexity of its processing and its association with systematic metabolism suggests that, if misregulated, APP has the potential to provoke an array of metabolic dysfunctions. This review discusses APP and several of its cleaved products with a particular focus on their toxicity and ability to disrupt healthy cellular function, in relation to AD development. We subsequently argue that the reduction of APP, which would result in a concurrent decrease in Aβ as well as all other toxic APP metabolites, would alleviate the toxic environment associated with AD and slow disease progression. A discussion of those drug-like compounds already identified to possess this capacity is also included.

Integrated Quantitative Neuro-Transcriptome Analysis of Several Brain Areas in Human Trisomy 21

Background: Although Down syndrome (DS) is the most frequent human chromosomal disorder and it causes mainly intellectual disability, its clinical presentation is complex and variable. Objective: We aimed to analyze and compare the transcriptome disruption in several brain areas from individuals with DS and euploid controls as a new approach to consider a global systemic differential disruption of gene expression beyond chromosome 21. Methods: We used data from a DNA microarray experiment with ID GSE59630 previously deposited in the GEO DataSet of NCBI database. The array contained log2 values of 17,537 human genes expressed in several aeras of the human brain. We calculated the differential gene expression (Z-ratio) of all genes. Results: We found several differences in gene expression along the DS brain transcriptome, not only in the genes located at chromosome 21 but in other chromosomes. Moreover, we registered the lowest Z-ratio correlation between the age ranks of 16–22 weeks of gestation and 39–42 years (R2 = 0.06) and the highest Z-ratio correlation between the age ranks of 30–39 years and 40–42 years (R2 = 0.89). The analysis per brain areas showed that the hippocampus and the cerebellar cortex had the most different gene expression pattern when compared to the brain as a whole. Conclusions: Our results support the hypothesis of a systemic imbalance of brain protein homeostasis, or proteostasis network of cognitive and neuroplasticity process, as new model to explain the important effect on the neurophenotype of trisomy that occur not only in the loci of chromosome 21 but also in genes located in other chromosomes.

Defective mitophagy and induction of apoptosis by the depleted levels of PINK1 and parkin in Pb and β-amyloid peptide induced toxicity

Exposure to lead (Pb), an environmental pollutant, is closely associated with the development of neurodegenerative disorders through oxidative stress induction and alterations in mitochondrial function. Damaged mitochondria could be one of the reasons for the progression of Alzheimer's Disease (AD). Mitophagy is vital in keeping the cell healthy. To know its role in Pb-induced AD, we investigated the PINK1/parkin dependent pathway by studying specific mitophagy marker proteins such as PINK1 and parkin in differentiated SH-SY5Y cells. Our data have indicated a significant reduction in the levels of PINK1 and parkin in cells exposed to Pb and β-amyloid peptides, both Aβ (25-35) and Aβ (1-40) individually and in different combinations, resulting in defective mitophagy. Also, the study unravels the status of mitochondrial permeability transition pore (MPTP), mitochondrial mass, mitochondrial membrane potential (MMP) and mitochondrial ROS production in cells treated with individual and different combination of Pb and Aβ peptides. An increase in mitochondrial ROS production, enhanced MPTP opening, depolarization of membrane potential and reduced mitochondrial mass in the exposed groups were observed. Also, in the present study, we found that Pb and β-amyloid peptides could trigger apoptosis by activating the Bak protein, which releases the cytochrome c from mitochondria through MPTP that further activates the AIF (apoptosis inducing factor) and caspase-3 proteins in the cytosol. The above findings reveal the potential role of mechanisms like PINK1/parkin mediated mitophagy and dysfunctional mitochondria mediated apoptosis in Pb induced neurotoxicity.

Mechanisms associated with the dysregulation of mitochondrial function due to lead exposure and possible implications on the development of Alzheimer's disease

Lead (Pb) is a multimedia contaminant with various pathophysiological consequences, including cognitive decline and neural abnormalities. Recent findings have reported an association of Pb toxicity with Alzheimer's disease (AD). Studies have revealed that mitochondrial dysfunction is a pathological characteristic of AD. According to toxicology reports, Pb promotes mitochondrial oxidative stress by lowering complex III activity in the electron transport chain, boosting reactive oxygen species formation, and reducing the cell's antioxidant defence system. Here, we review recent advances in the role of mitochondria in Pb-induced AD pathology, as well as the mechanisms associated with the mitochondrial dysfunction, such as the depolarisation of the mitochondrial membrane potential, mitochondrial permeability transition pore opening; mitochondrial biogenesis, bioenergetics and mitochondrial dynamics alterations; and mitophagy and apoptosis. We also discuss possible therapeutic options for mitochondrial-targeted neurodegenerative disease (AD).

Mitochondrial Targeting of Amyloid-β Protein Precursor Intracellular Domain Induces Hippocampal Cell Death via a Mechanism Distinct from Amyloid-β

BACKGROUND

Amyloid-β (Aβ) is a principal cleavage product of amyloid-β protein precursor (AβPP) and is widely recognized as a key pathogenic player in Alzheimer's disease (AD). Yet, there is increasing evidence of a neurotoxic role for the AβPP intracellular domain (AICD) which has been proposed to occur through its nuclear function. Intriguingly, there is a γ-secretase resident at the mitochondria which could produce AICD locally.

OBJECTIVE

We examined the potential of AICD to induce neuronal apoptosis when targeted specifically to the mitochondria and compared its mechanism of neurotoxicity to that of Aβ.

METHODS

We utilized transient transfection of HT22 neuronal cells with bicistronic plasmids coding for DsRed and either empty vector (Ires), Aβ, AICD59, or mitochondrial-targeted AICD (mitoAICD) in combination with various inhibitors of pathways involved in apoptosis.

RESULTS

AICD induced significant neuronal apoptosis only when targeted to the mitochondria. Apoptosis required functional mitochondria as neither Aβ nor mitoAICD induced significant toxicity in cells devoid of mitochondrial DNA. Both glutathione and a Bax inhibitor protected HT22 cells from either peptide. However, inhibition of the mitochondrial permeability transition pore only protected from Aβ, while pan-caspase inhibitors uniquely rescued cells from mitoAICD.

CONCLUSION

Our results show that AICD displays a novel neurotoxic function when targeted to mitochondria. Moreover, mitoAICD induces apoptosis via a mechanism that is distinct from that of Aβ. These findings suggest that AICD produced locally at mitochondria via organelle-specific γ-secretase could act in a synergistic manner with Aβ to cause mitochondrial dysfunction and neuronal death in AD.

Interaction of Amyloid-β-(1-42) Peptide and Its Aggregates with Lipid/Water Interfaces Probed by Vibrational Sum-Frequency Generation Spectroscopy

In this study, we use surface-sensitive vibrational sum-frequency generation (VSFG) spectroscopy to investigate the interaction between model lipid monolayers and Aβ(1-42) in its monomeric and aggregated states. Combining VSFG with atomic force microscopy (AFM) and thioflavin T (ThT) fluorescence measurements, we found that only small aggregates with probably a β-hairpin-like structure adsorbed to the zwitterionic lipid monolayer (DOPC). In contrast, larger aggregates with an extended β-sheet structure adsorbed to a negatively charged lipid monolayer (DOPG). The adsorption of small, initially formed aggregates strongly destabilized both monolayers, but only the DOPC monolayer was completely disrupted. We showed that the intensity of the amide-II' band in achiral (SSP) and chiral (SPP) polarization combinations increased in time when Aβ(1-42) aggregates accumulated at the DOPG monolayer. Nevertheless, almost no adsorption of preformed mature fibrils to DOPG monolayers was detected. By performing spectral VSFG calculations, we revealed a clear correlation between the amide-II' signal and the degree of amyloid aggregates (e.g., oligomers or (proto)fibrils) of various Aβ(1-42) structures. The calculations showed that only structures with a significant amyloid β-sheet content have a strong amide-II' intensity, in line with previous Raman studies. The combination of the presented results substantiates the amide-II(') band as a legitimate amyloid marker.

Multifunctional peptide-assembled micelles for simultaneously reducing amyloid-β and reactive oxygen species

The excessive production and deposition of amyloid-β (Aβ) is one of the most important etiologies of Alzheimer's disease (AD). The interaction between Aβ and metal ions produces aberrant reactive oxygen species (ROS), which induce oxidative stress and accelerate the progression of AD. To reduce Aβ plaques and ROS to maintain their homeostasis is an emerging and ingenious strategy for effective treatment of AD. Herein, we report the rational design of multifunctional micelles (MPGLT) based on a polymer-grafted peptide to simultaneously clear Aβ and ROS for AD therapy. The MPGLT integrating three functional peptides as a ROS scavenger (tk-GSH), β-sheet breaker (LP) and an autophagy activator (TK) respectively, could capture and degrade Aβ. Meanwhile, the tk-GSH on the surface of MPGLT effectively scavenges the intracellular ROS. Consequently, MPGLT reduced the cytotoxicity of Aβ and ROS. In vivo animal studies using an AD mouse model further showed that MPGLT could transport across the blood-brain barrier for decreasing the Aβ plaque and eliminating ROS in vivo. This peptide micelle-based synergistic strategy may provide novel insight for AD therapy.

Effect of Treadmill Exercise and Trans-Cinnamaldehyde against d-Galactose- and Aluminum Chloride-Induced Cognitive Dysfunction in Mice

Mild cognitive impairment (MCI) generally refers to impairment in cognition above that which accompanies the normal age-related cognitive decline and has attracted attention in recent years. Trans-cinnamaldehyde (TCA), which is isolated from cinnamon, has anti-inflammatory and antioxidant properties. Treadmill exercise also has diverse positive effects. The purpose of this study was to investigate the combination effects of TCA and treadmill exercise on learning and memory in a cognitive impairment mouse induced by a combination of d-galactose (d-gal) and aluminum chloride (AlCl₃). We found that exercise and TCA attenuated cognitive impairment in mice with induced MCI. This effect was further increased by costimulation of exercise and TCA. To clarify the mechanisms of the positive effects of TCA and exercise, we analyzed the nuclear factor erythroid 2-related factor (Nrf2) and related signaling pathways. We found that TCA and exercise upregulated Nrf2, NAD(P)H dehydrogenase quinone 1 (NQO-1), heme oxygenase 1 (HO-1), and superoxide dismutase 1 (SOD-1); this suggests that TCA and exercise attenuate cognitive dysfunction by reducing oxidative stress. We also found that Nrf2-related signaling pathways, i.e., the AMP-activated protein kinase (AMPK)/Nrf2 and SIRT1/PGC-1a/Nrf2-ARE pathways, exerted antioxidant effects. Together, these results suggest that costimulation with TCA and exercise may be a therapeutic candidate for mild cognitive impairment.

An overview on recent in vivo biological application of cerium oxide nanoparticles

Cerium oxide nanoparticles (CNPs) possess a great potential as therapeutic agents due to their ability to self-regenerate by reversibly switching between two valences +3 and +4. This article reviews recent articles dealing with in vivo studies of CNPs towards Alzheimer's disease, obesity, liver inflammation, cancer, sepsis, amyotrophic lateral sclerosis, acute kidney injury, radiation-induced tissue damage, hepatic ischemia reperfusion injury, retinal diseases and constipation. In vivo anti-cancer studies revealed the effectiveness of CNPs to reduce tumor growth and angiogenesis in melanoma, ovarian, breast and retinoblastoma cancer cell-induced mice, with their conjugation with folic acid, doxorubicin, CPM, or CXC receptor-4 antagonist ligand eliciting higher efficiency. After conjugation with triphenylphosphonium or magnetite nanoparticles, CNPs were shown to combat Alzheimer's disease by reducing amyloid-β, glial fibrillary acidic protein, inflammatory and oxidative stress markers in mice. By improving muscle function and longevity, the citrate/EDTA-stabilized CNPs could ameliorate amyotrophic lateral sclerosis. Also, they could effectively reduce obesity in mice by scavenging ROS and reducing adipogenesis, triglyceride synthesis, GAPDH enzyme activity, leptin and insulin levels. In CCl4-induced rats, stress signaling pathways due to inflammatory cytokines, liver enzymes, oxidative and endoplasmic reticulum messengers could be attenuated by CNPs. Commercial CNPs showed protective effects on rats with hepatic ischemia reperfusion and peritonitis-induced hepatic/cardiac injuries by decreasing oxidative stress and hepatic/cardiac inflammation. The same CNPs could improve kidney function by diminishing renal superoxide, hyperglycemia and tubular damage in peritonitis-induced acute kidney injury in rats. Radiation-induced lung and testicular tissue damage could be alleviated in mice, with the former showing improvement in pulmonary distress and bronchoconstriction and the latter exhibiting restoration in spermatogenesis rate and spermatid/spermatocyte number. Through enhancement of gastrointestinal motility, the CNPs could alleviate constipation in both young and old rats. They could also protect rat from light-induced retinal damage by slowing down neurodegenerative process and microglial activation.

The amyloid precursor protein affects glyceraldehyde 3-phosphate dehydrogenase levels, organelle localisation and thermal stability

Glyceraldehyde 3-phosphate dehydrogenase's (GAPDH) proapoptotic response to cellular oxidative stress has suspected implication for Alzheimer's disease (AD). Interestingly, the overexpression of the amyloid precursor protein (APP) can initiate oxidative stress responses within mammalian cell lines. Here, APP695 and APP770 overexpression significantly increased the level of GAPDH, while no effect was observed when the APP homologues APLP1 or APLP2 were used. Heterologous expression of APP695 was shown to increase the level of GAPDH within the cytoplasm by over 100% and within the mitochondria by approximately 50%. Moreover, a shift in organelle distribution from cytoplasm > nucleus > mitochondria in control cell lines to cytoplasm > mitochondria > nucleus in the APP695 overexpressing cell line was also observed. Further, the overexpression of APP695 increased GAPDH aggregation temperature by 3.09 ± 0.46 °C, indicative of greater thermal stability. These results demonstrate a clear correlation between APP overexpression and GAPDH levels, organelle distribution and thermal stability.

Nanoparticle-mediated approaches for Alzheimer's disease pathogenesis, diagnosis, and therapeutics

Alzheimer's disease (AD) is an irreversible and progressive neurodegenerative disorder manifested by memory loss and cognitive impairment. Deposition of the amyloid β plaques has been identified as the most common AD pathology; however, the excessive accumulation of phosphorylated or total tau proteins, reactive oxygen species, and higher acetylcholinesterase activity are also strongly associated with Alzheimer's dementia. Several therapeutic approaches targeting these pathogenic mechanisms have failed in clinical or preclinical trials, partly due to the limited bioavailability, poor cell, and blood-brain barrier penetration, and low drug half-life of current regimens. The nanoparticles (NPs)-mediated drug delivery systems improve drug solubility and bioavailability, thus renders as superior alternatives. Moreover, NPs-mediated approaches facilitate multiple drug loading and targeted drug delivery, thereby increasing drug efficacy. However, certain NPs can cause acute toxicity damaging cellular and tissue architecture, therefore, NP material should be carefully selected. In this review, we summarize the recent NPs-mediated studies that exploit various pathologic mechanisms of AD by labeling, identifying, and treating the affected brain pathologies. The disadvantages of the select NP-based deliveries and the future aspects will also be discussed.

The Role of the Antioxidant Response in Mitochondrial Dysfunction in Degenerative Diseases: Cross-Talk between Antioxidant Defense, Autophagy, and Apoptosis

The mitochondrion is an essential organelle important for the generation of ATP for cellular function. This is especially critical for cells with high energy demands, such as neurons for signal transmission and cardiomyocytes for the continuous mechanical work of the heart. However, deleterious reactive oxygen species are generated as a result of mitochondrial electron transport, requiring a rigorous activation of antioxidative defense in order to maintain homeostatic mitochondrial function. Indeed, recent studies have demonstrated that the dysregulation of antioxidant response leads to mitochondrial dysfunction in human degenerative diseases affecting the nervous system and the heart. In this review, we outline and discuss the mitochondrial and oxidative stress factors causing degenerative diseases, such as Alzheimer's disease, Parkinson's disease, amyotrophic lateral sclerosis, Huntington's disease, and Friedreich's ataxia. In particular, the pathological involvement of mitochondrial dysfunction in relation to oxidative stress, energy metabolism, mitochondrial dynamics, and cell death will be explored. Understanding the pathology and the development of these diseases has highlighted novel regulators in the homeostatic maintenance of mitochondria. Importantly, this offers potential therapeutic targets in the development of future treatments for these degenerative diseases.

Alzheimer's Disease: Recent Concepts on the Relation of Mitochondrial Disturbances, Excitotoxicity, Neuroinflammation, and Kynurenines

The pathomechanism of Alzheimer's disease (AD) certainly involves mitochondrial disturbances, glutamate excitotoxicity, and neuroinflammation. The three main aspects of mitochondrial dysfunction in AD, i.e., the defects in dynamics, altered bioenergetics, and the deficient transport, act synergistically. In addition, glutamatergic neurotransmission is affected in several ways. The balance between synaptic and extrasynaptic glutamatergic transmission is shifted toward the extrasynaptic site contributing to glutamate excitotoxicity, a phenomenon augmented by increased glutamate release and decreased glutamate uptake. Neuroinflammation in AD is predominantly linked to central players of the innate immune system, with central nervous system (CNS)-resident microglia, astroglia, and perivascular macrophages having been implicated at the cellular level. Several abnormalities have been described regarding the activation of certain steps of the kynurenine (KYN) pathway of tryptophan metabolism in AD. First of all, the activation of indolamine 2,3-dioxygenase, the first and rate-limiting step of the pathway, is well-demonstrated. 3-Hydroxy-L-KYN and its metabolite, 3-hydroxy-anthranilic acid have pro-oxidant, antioxidant, and potent immunomodulatory features, giving relevance to their alterations in AD. Another metabolite, quinolinic acid, has been demonstrated to be neurotoxic, promoting glutamate excitotoxicity, reactive oxygen species production, lipid peroxidation, and microglial neuroinflammation, and its abundant presence in AD pathologies has been demonstrated. Finally, the neuroprotective metabolite, kynurenic acid, has been associated with antagonistic effects at glutamate receptors, free radical scavenging, and immunomodulation, giving rise to potential therapeutic implications. This review presents the multiple connections of KYN pathway-related alterations to three main domains of AD pathomechanism, such as mitochondrial dysfunction, excitotoxicity, and neuroinflammation, implicating possible therapeutic options.

Mitochondrial therapeutic interventions in Alzheimer's disease

Alzheimer's Disease (AD) is one of the most common age-related neurodegenerative diseases in the developed world. Treatment of AD is particularly challenging as the drug must overcome the blood brain barrier (BBB) before it can reach its target. Mitochondria are recognized as one of the most important targets for neurological drugs as the organelle is known to play a critical role in diverse cellular processes such as energy production and apoptosis regulation. Mitochondrial targeting was originally developed to study mitochondrial dysfunction and the organelles interaction with other sub-cellular organelles. The purpose of this review is to provide an overview of mitochondrial dysfunction and its role in late onset AD pathology. We then highlight recent antioxidant and enzymatic treatments used to alleviate mitochondrial dysfunction. Finally, we describe current applications of targeted mitochondrial delivery in the treatment of AD.

Mitochondrial dysfunction in down syndrome: molecular mechanisms and therapeutic targets

Trisomy of chromosome 21 (TS21) is the most common autosomal aneuploidy compatible with postnatal survival with a prevalence of 1 in 700 newborns. Its phenotype is highly complex with constant features, such as mental retardation, dysmorphic traits and hypotonia, and variable features including heart defects, susceptibility to Alzheimer’s disease (AD), type 2 diabetes, obesity and immune disorders. Overexpression of genes on chromosome-21 (Hsa21) is responsible for the pathogenesis of Down syndrome (DS) phenotypic features either in a direct or in an indirect manner since many Hsa21 genes can affect the expression of other genes mapping to different chromosomes. Many of these genes are involved in mitochondrial function and energy conversion, and play a central role in the mitochondrial dysfunction and chronic oxidative stress, consistently observed in DS subjects.

Recent studies highlight the deep interconnections between mitochondrial dysfunction and DS phenotype. In this short review we first provide a basic overview of mitochondrial phenotype in DS cells and tissues. We then discuss how specific Hsa21 genes may be involved in determining the disruption of mitochondrial DS phenotype and biogenesis. Finally we briefly focus on drugs that affect mitochondrial function and mitochondrial network suggesting possible therapeutic approaches to improve and/or prevent some aspects of the DS phenotype.

Redox-active nanomaterials for nanomedicine applications

Nanomedicine utilizes the remarkable properties of nanomaterials for the diagnosis, treatment, and prevention of disease. Many of these nanomaterials have been shown to have robust antioxidative properties, potentially functioning as strong scavengers of reactive oxygen species. Conversely, several nanomaterials have also been shown to promote the generation of reactive oxygen species, which may precipitate the onset of oxidative stress, a state that is thought to contribute to the development of a variety of adverse conditions. As such, the impacts of nanomaterials on biological entities are often associated with and influenced by their specific redox properties. In this review, we overview several classes of nanomaterials that have been or projected to be used across a wide range of biomedical applications, with discussion focusing on their unique redox properties. Nanomaterials examined include iron, cerium, and titanium metal oxide nanoparticles, gold, silver, and selenium nanoparticles, and various nanoscale carbon allotropes such as graphene, carbon nanotubes, fullerenes, and their derivatives/variations. Principal topics of discussion include the chemical mechanisms by which the nanomaterials directly interact with biological entities and the biological cascades that are thus indirectly impacted. Selected case studies highlighting the redox properties of nanomaterials and how they affect biological responses are used to exemplify the biologically-relevant redox mechanisms for each of the described nanomaterials.

Inhibitory Effect of Lychee Seed Saponins on Apoptosis Induced by Aβ25-35 through Regulation of the Apoptotic and NF-κB Pathways in PC12 Cells

Neuronal apoptosis plays a critical role in the pathogenesis of Alzheimer's disease (AD). Previous studies have shown that lychee seed saponins (LSS), isolated and extracted from traditional Chinese medicine lychee seeds, possess many beneficial activities including anti-oxidation, anti-diabetes, anti-AD, etc. In the present study, we established an in vitro neuronal apoptotic model of PC12 cells induced by Aβ25-35 and studied the effect of LSS on apoptosis by the methods of Hoechst 33342/propidium iodide (PI) fluorescence double staining, Annexin V/PI double staining, and terminal deoxynucleotidyl transferase (TdT)-mediated dUTP nick-end labeling (TUNEL). We also investigated the effects of LSS on mitochondria membrane potential, the expressions of Bcl-2 and Bax proteins, and the mRNA expression and the nuclear translocation of NF-κBp65 in PC12 cells. The results showed that LSS markedly inhibited apoptosis, improved the mitochondria membrane potentials, upregulated the expression of Bcl-2 protein, downregulated the expression of Bax protein, and decreased the mRNA expression and nuclear translocation of NF-κBp65 in PC12 cells. The study demonstrated that LSS significantly inhibited apoptosis induced by Aβ25-35 via regulation of the apoptotic and NF-κB pathways in PC12 cells. Therefore, LSS has the potential to be developed as a novel agent or nutrient supplement for the prevention and/or treatment of AD.

Mitochondria-Targeting Ceria Nanoparticles as Antioxidants for Alzheimer's Disease

Mitochondrial oxidative stress is a key pathologic factor in neurodegenerative diseases, including Alzheimer's disease. Abnormal generation of reactive oxygen species (ROS), resulting from mitochondrial dysfunction, can lead to neuronal cell death. Ceria (CeO2) nanoparticles are known to function as strong and recyclable ROS scavengers by shuttling between Ce(3+) and Ce(4+) oxidation states. Consequently, targeting ceria nanoparticles selectively to mitochondria might be a promising therapeutic approach for neurodegenerative diseases. Here, we report the design and synthesis of triphenylphosphonium-conjugated ceria nanoparticles that localize to mitochondria and suppress neuronal death in a 5XFAD transgenic Alzheimer's disease mouse model. The triphenylphosphonium-conjugated ceria nanoparticles mitigate reactive gliosis and morphological mitochondria damage observed in these mice. Altogether, our data indicate that the triphenylphosphonium-conjugated ceria nanoparticles are a potential therapeutic candidate for mitochondrial oxidative stress in Alzheimer's disease.

Inflammation decreases the level of alpha7 nicotinic acetylcholine receptors in the brain mitochondria and makes them more susceptible to apoptosis induction

α7 nicotinic acetylcholine receptors (α7 nAChRs) are involved in regulating inflammatory reactions, as well as the cell viability. They are expressed in both the plasma membrane and mitochondria of eukaryotic cells. Previously we found that neuroinflammation resulted in the decrease of α7 nAChR density in the brain of mice and was accompanied by accumulation of amyloid-beta (Aβ) peptides and memory impairment. In the present paper, it is shown that inflammation induced by either regular bacterial lipopolysaccharide (LPS) injections or immunizations with α7 nAChR extracellular domain (1-208) affected also the brain cell mitochondria. Using various modifications of sandwich ELISA, we observed the decrease of α7 nAChRs and accumulation of Aβ(1-40) and Aβ(1-42) in mitochondria of immunized or LPS-treated mice compared to control ones. Mitochondria of treated mice responded with cytochrome c release to lower Ca(2+) concentrations than mitochondria of control mice and were less sensitive to its attenuation with α7 nAChR agonist PNU282987. It is concluded that inflammation decreases α7 nAChR expression in both mitochondria and cell plasma membrane and makes mitochondria more susceptible to apoptosis induction.

Reduction of β-amyloid and γ-secretase by calorie restriction in female Tg2576 mice

Research indicates that female risk of developing Alzheimer's disease (AD) is greater than that of males. Moderate reduction of calorie intake, known as calorie restriction (CR), reduces pathology in AD mouse models and is a potentially translatable prevention measure for individuals at-risk for AD, as well as an important tool for understanding how the brain endogenously attenuates age-related pathology. Whether sex influences the response to CR remains unknown. In this study, we assessed the effect of CR on beta-amyloid peptide (Aβ) pathology and hippocampal CA1 neuron specific gene expression in the Tg2576 mouse model of cerebral amyloidosis. Relative to ad libitum (AL) feeding, CR feeding significantly reduced hippocampal Aβ burden in 15-month-old female, but not age-matched male, Tg2576 mice. Sustained CR also significantly reduced expression of presenilin enhancer 2 (Psenen) and presenilin 1, components of the γ-secretase complex, in Tg2576 females. These results indicate that long-term CR significantly reduces age-dependent female Tg2576 Aβ pathology, which is likely to involve CR-mediated reductions in γ-secretase-dependent amyloid precursor protein (APP) metabolism.

Protective effects of astragaloside IV against amyloid beta1-42 neurotoxicity by inhibiting the mitochondrial permeability transition pore opening

Mitochondrial dysfunction caused by amyloid β-peptide (Aβ) plays an important role in the pathogenesis of Alzheimer disease (AD). Substantial evidence has indicated that the mitochondrial permeability transition pore (mPTP) opening is involved in Aβ-induced neuronal death and reactive oxygen species (ROS) generation. Astragaloside IV (AS-IV), one of the major active constituents of Astragalus membranaceus, has been reported as an effective anti-oxidant for treating neurodegenerative diseases. However, the molecular mechanisms still need to be clarified. In this study, we investigated whether AS-IV could prevent Aβ1-42-induced neurotoxicity in SK-N-SH cells via inhibiting the mPTP opening. The results showed that pretreatment of AS-IV significantly increased the viability of neuronal cells, reduced apoptosis, decreased the generation of intracellular reactive oxygen species (ROS) and decreased mitochondrial superoxide in the presence of Aβ1-42. In addition, pretreatment of AS-IV inhibited the mPTP opening, rescued mitochondrial membrane potential (ΔΨm), enhanced ATP generation, improved the activity of cytochrome c oxidase and blocked cytochrome c release from mitochondria in Aβ1-42 rich milieu. Moreover, pretreatment of AS-IV reduced the expression of Bax and cleaved caspase-3 and increased the expression of Bcl-2 in an Aβ1-42 rich environment. These data indicate that AS-IV prevents Aβ1-42-induced SK-N-SH cell apoptosis via inhibiting the mPTP opening and ROS generation. These results provide novel insights of AS-IV for the prevention and treatment of neurodegenerative disorders such as AD.

Autophagy and apoptosis dysfunction in neurodegenerative disorders

Autophagy and apoptosis are basic physiologic processes contributing to the maintenance of cellular homeostasis. Autophagy encompasses pathways that target long-lived cytosolic proteins and damaged organelles. It involves a sequential set of events including double membrane formation, elongation, vesicle maturation and finally delivery of the targeted materials to the lysosome. Apoptotic cell death is best described through its morphology. It is characterized by cell rounding, membrane blebbing, cytoskeletal collapse, cytoplasmic condensation, and fragmentation, nuclear pyknosis, chromatin condensation/fragmentation, and formation of membrane-enveloped apoptotic bodies, that are rapidly phagocytosed by macrophages or neighboring cells. Neurodegenerative disorders are becoming increasingly prevalent, especially in the Western societies, with larger percentage of members living to an older age. They have to be seen not only as a health problem, but since they are care-intensive, they also carry a significant economic burden. Deregulation of autophagy plays a pivotal role in the etiology and/or progress of many of these diseases. Herein, we briefly review the latest findings that indicate the involvement of autophagy in neurodegenerative diseases. We provide a brief introduction to autophagy and apoptosis pathways focusing on the role of mitochondria and lysosomes. We then briefly highlight pathophysiology of common neurodegenerative disorders like Alzheimer's diseases, Parkinson's disease, Huntington's disease and Amyotrophic lateral sclerosis. Then, we describe functions of autophagy and apoptosis in brain homeostasis, especially in the context of the aforementioned disorders. Finally, we discuss different ways that autophagy and apoptosis modulation may be employed for therapeutic intervention during the maintenance of neurodegenerative disorders.

Neuroprotective effect of aqueous extract of Selaginella delicatula as evidenced by abrogation of rotenone-induced motor deficits, oxidative dysfunctions, and neurotoxicity in mice

Oxidative stress is one of the mechanisms implicated to play a significant role in the pathophysiology of Parkinson's disease. Previously, we showed that an aqueous extract of Selaginella delicatula (SDAE) offered robust neuroprotection against rotenone (ROT) in a Drosophila model. In furtherance in the present study, we validated the neuroprotective efficacy of SDAE in a chronic ROT exposure model in mice. Initially, we assessed the propensity of SDAE to modulate the levels of endogenous markers in striatal region of mice. Subsequently, the neuroprotective efficacy of SDAE (100 mg/kg bw, 21 d) to mitigate ROT-induced striatal motor deficits, oxidative stress, and neurotoxicity was examined employing a co-exposure paradigm. We found significant attenuation of ROT-induced motor deficits (stride length and landing foot spread distance) among mice given SDAE supplements. Biochemical analysis revealed that ROT-induced elevation in the levels of oxidative markers in cytosol/mitochondria of striatum were normalized with SDAE supplements. In addition, SDAE also restored the ROT-induced elevation in the levels of oxidized and nitrated proteins. Further, SDAE also restored the activities of acetylcholinesterase and butyrylcholinesterase indicating its effect on cholinergic function. While ROT exposure caused significant perturbations in the activity levels of mitochondrial electron transport chain enzymes (complex I/II), membrane potential and activity of ATPases, these functions were restored to normalcy among mice receiving SDAE suggesting its effects on mitochondrial function. Since these data corroborate our previous findings in Drosophila system, we propose that the neuroprotective property of SDAE may be largely attributed to the antioxidant properties and its ability to attenuate mitochondrial dysfunction. However, studies employing dopaminergic cell models would enable us to identify specific molecular mechanism, by which SDAE exerts neuroprotective action.

Neuroinflammation and neuronal loss precede Aβ plaque deposition in the hAPP-J20 mouse model of Alzheimer's disease

Recent human trials of treatments for Alzheimer's disease (AD) have been largely unsuccessful, raising the idea that treatment may need to be started earlier in the disease, well before cognitive symptoms appear. An early marker of AD pathology is therefore needed and it is debated as to whether amyloid-βAβ? plaque load may serve this purpose. We investigated this in the hAPP-J20 AD mouse model by studying disease pathology at 6, 12, 24 and 36 weeks. Using robust stereological methods, we found there is no neuron loss in the hippocampal CA3 region at any age. However loss of neurons from the hippocampal CA1 region begins as early as 12 weeks of age. The extent of neuron loss increases with age, correlating with the number of activated microglia. Gliosis was also present, but plateaued during aging. Increased hyperactivity and spatial memory deficits occurred at 16 and 24 weeks. Meanwhile, the appearance of plaques and oligomeric Aβ were essentially the last pathological changes, with significant changes only observed at 36 weeks of age. This is surprising given that the hAPP-J20 AD mouse model is engineered to over-expresses Aβ. Our data raises the possibility that plaque load may not be the best marker for early AD and suggests that activated microglia could be a valuable marker to track disease progression.

Significant modifications of the salivary proteome potentially associated with complications of Down syndrome revealed by top-down proteomics

People with Down syndrome, a frequent genetic disorder in humans, have increased risk of health problems associated with this condition. One clinical feature of Down syndrome is the increased prevalence and severity of periodontal disease in comparison with the general population. Because saliva plays an important role in maintaining oral health, in the present study the salivary proteome of Down syndrome subjects was investigated to explore modifications with respect to healthy subjects. Whole saliva of 36 Down syndrome subjects, divided in the age groups 10-17 yr and 18-50 yr, was analyzed by a top-down proteomic approach, based on the high performance liquid chromatography-electrospray ionization-MS analysis of the intact proteins and peptides, and the qualitative and quantitative profiles were compared with sex- and age-matched control groups. The results showed the following interesting features: 1) as opposed to controls, in Down syndrome subjects the concentration of the major salivary proteins of gland origin did not increase with age; as a consequence concentration of acidic proline rich proteins and S cystatins were found significantly reduced in older Down syndrome subjects with respect to matched controls; 2) levels of the antimicrobial α-defensins 1 and 2 and histatins 3 and 5 were significantly increased in whole saliva of older Down syndrome subjects with respect to controls; 3) S100A7, S100A8, and S100A12 levels were significantly increased in whole saliva of Down syndrome subjects in comparison with controls. The increased level of S100A7 and S100A12 may be of particular interest as a biomarker of early onset Alzheimer's disease, which is frequently associated with Down syndrome.

The triggering receptor expressed on myeloid cells 2: "TREM-ming" the inflammatory component associated with Alzheimer's disease

Alzheimer's disease (AD) is an age-related neurodegenerative disorder characterized by a progressive loss of memory and cognitive skills. Although much attention has been devoted concerning the contribution of the microscopic lesions, senile plaques, and neurofibrillary tangles to the disease process, inflammation has long been suspected to play a major role in the etiology of AD. Recently, a novel variant in the gene encoding the triggering receptor expressed on myeloid cells 2 (TREM2) has been identified that has refocused the spotlight back onto inflammation as a major contributing factor in AD. Variants in TREM2 triple one's risk of developing late-onset AD. TREM2 is expressed on microglial cells, the resident macrophages in the CNS, and functions to stimulate phagocytosis on one hand and to suppress cytokine production and inflammation on the other hand. The purpose of this paper is to discuss these recent developments including the potential role that TREM2 normally plays and how loss of function may contribute to AD pathogenesis by enhancing oxidative stress and inflammation within the CNS. In this context, an overview of the pathways linking beta-amyloid, neurofibrillary tangles (NFTs), oxidative stress, and inflammation will be discussed.

From a Cell's Viewpoint: Targeting Mitochondria in Alzheimer's disease

Mitochondria are well-known cellular organelles widely studied in relation to a variety of disease states, including Alzheimer's disease. With roles in several metabolic processes, numerous signal transduction pathways, and overall cell maintenance and survival, mitochondria are essential to understanding the inner workings of cells. As mitochondria are able to be utilized by diverse illnesses to increase the likelihood of disease progression, targeting specific processes in these organelles could provide beneficial therapeutic options.