Antioxidants for Alzheimer disease: a randomized clinical trial with cerebrospinal fluid biomarker measures

Recent advances in the natural product analogues for the treatment of neurodegenerative diseases

Neurodegenerative diseases (NDs) represent a hallmark of numerous incapacitating and untreatable conditions, the incidence of which is escalating swiftly, exemplified by Alzheimer's disease and Parkinson's disease. There is an urgent necessity to create pharmaceuticals that exhibit high efficacy and minimal toxicity in order to address these debilitating diseases. The structural complexity and diversity of natural products confer upon them a broad spectrum of biological activities, thereby significantly contributing to the history of drug discovery. Nevertheless, natural products present challenges in drug discovery, including time-consuming separation processes, low content, low bioavailability, and other related issues. To address these challenges, numerous analogs of natural products have been synthesized. This methodology enables the rapid synthesis of analogs of natural products with the potential to serve as lead compounds for drug development, thereby paving the way for the discovery of novel pharmaceuticals. This paper provides a summary of 127 synthetic analogues featuring various natural product structures, including flavonoids, alkaloids, coumarins, phenylpropanoids, terpenoids, polyphenols, and amides. The compounds are categorized based on their efficacy in treating various diseases. Furthermore, this article delves into the structure-activity relationship (SAR) of certain analogues, offering a thorough point of reference for the systematic development of pharmaceuticals aimed at addressing neurodegenerative conditions.

Breaking Barriers in Alzheimer's Disease: the Role of Advanced Drug Delivery Systems

Alzheimer's disease (AD), characterized by cognitive impairment, brain plaques, and tangles, is a global health concern affecting millions. It involves the build-up of amyloid-β (Aβ) and tau proteins, the formation of neuritic plaques and neurofibrillary tangles, cholinergic system dysfunction, genetic variations, and mitochondrial dysfunction. Various signaling pathways and metabolic processes are implicated in AD, along with numerous biomarkers used for diagnosis, risk assessment, and research. Despite these, there is no cure or effective treatment for AD. It is critically important to address this immediately to develop novel drug delivery systems (NDDS) capable of targeting the brain and delivering therapeutic agents to modulate the pathological processes of AD. This review summarizes AD, its pathogenesis, related signaling pathways, biomarkers, conventional treatments, the need for NDDS, and their application in AD treatment. It also covers preclinical, clinical, and ongoing trials, patents, and marketed AD formulations.

Recent Insights into the Neurobiology of Alzheimer's Disease and Advanced Treatment Strategies

In recent years, significant advancements have been made in understanding Alzheimer's disease from both neurobiological and clinical perspectives. Exploring the complex systems underlying AD has unveiled insights that could potentially revolutionize therapeutic approaches. Recent investigations have highlighted intricate interactions among genetic, molecular, and environmental factors in AD. Optimism arises from neurobiological advancements and diverse treatment options, potentially slowing or halting disease progression. Amyloid-beta plaques and tau protein tangles crucially influence AD onset and progression. Emerging treatments involve diverse strategies, such as approaches targeting multiple pathways involved in AD pathogenesis, such as inflammation, oxidative stress, and synaptic dysfunction pathways. Clinical trials using humanized monoclonal antibodies, focusing on immunotherapies eliminating amyloid-beta, have shown promise. Nonpharmacological interventions such as light therapy, electrical stimulation, cognitive training, physical activity, and dietary changes have drawn attention for their potential to slow cognitive aging and enhance brain health. Precision medicine, which involves tailoring therapies to individual genetic and molecular profiles, has gained traction. Ongoing research and interdisciplinary collaboration are expected to yield more effective treatments.

The Relation of Serum Vitamin C Concentrations with Alzheimer's Disease Mortality in a National Cohort of Community-Dwelling Elderly Adults

The relation of vitamin C with Alzheimer's disease (AD) is equivocal. The aim of this study was to assess the relation of serum vitamin C levels with AD-related mortality, and to evaluate the threshold beyond which the potential benefits of higher serum concentrations of vitamin C for AD mortality ceases. The cohort consisted of 4504 adults aged ≥60 years enrolled in the National Health and Nutrition Examination Survey who had serum measures of vitamin C and no cognitive impairment at baseline (1988-1994) and were followed-up for mortality until 2019. Vitamin C was assayed from fasting blood samples using isocratic high-performance liquid chromatography. At baseline, the mean age of participants was 70 years, with 42.7% being men. At the end of follow-up (median: 15 years), the AD mortality rate was 2.4 per 1000 person-years. In the Cox regression models, compared to participants in the lowest tertile of serum vitamin C (<0.56 mg/dL), those in the highest tertile (>0.98 mg/dL) had a lower risk of AD mortality (hazard ratio: 0.44, 95% confidence intervals: 0.25-0.77) after adjusting for sociodemographic factors, behavior/lifestyle factors, prevalent health conditions, and dietary vitamin C intake. In dose-response analysis using restricted cubic splines, vitamin C concentrations beyond 2.3 mg/dL were associated with the elevated risk of AD-related mortality. The findings from this national sample of community-dwelling elderly adults suggest that higher levels of serum vitamin C are associated with slower AD disease progression, although levels beyond the normal reference values were associated with a higher risk of AD mortality.

Does Nutritional Supplementation Have a Disease-Modifying Effect on the Alzheimer's Disease Neurodegenerative Process?

Because nutrition is one of the main factors related to Alzheimer's disease (AD), questions arise about how taking nutrients as supplements can affect its pathophysiological process. In the present study, an overview of the potential effects of nutritional supplementation on the main biomarkers related to the AD pathophysiology (i.e., amyloid-β and tau) is explored. Trials testing the supplementation of single or combined nutrients versus placebo identified effects on some AD biomarkers, but changes were not always accompanied by positive effects on cognitive function. Differences in characteristics of studied populations (cognitive status, age, educational level), choice of nutrient combinations and doses, duration of intervention, and adjustments for potential confounders are some factors that may explain discrepancies in findings.

Riboflavin (vitamin B2) sensitized photooxidation of ascorbic acid (vitamin C): A kinetic study

Ascorbic acid (AH2) photoxidation sensitized by riboflavin (RF) has been studied between pH 2.0 and 12.0 in ambient air and anaerobic environment using UV and visible irradiation sources. The kinetics of AH2 degradation in aqueous medium along with RF is found to be first-order for its photodegradation. AH2 photolysis rate constants in aerobic and anaerobic conditions with RF (1.0-5.0 × 10-5 M) are 0.14-3.89 × 10-2 and 0.026-0.740 × 10-2 min-1, respectively. The rate constants (k2) of second-order kinetics for AH2 and RF photochemical interaction in aerobic and anaerobic conditions are in the range of 0.24-3.70 to 0.05-0.70 × 10-3 M-1 min-1, respectively, which manifests that increasing the RF concentration also increases the rate of photodegradation (photooxidation) of AH2. The k2 versus pH graph is bell-shaped which indicates that increasing the pH increases photolytic degradation rate of AH2 with RF. Increasing the pH results in the increased ionization of AH2 (ascorbyl anion, AH-) and redox potential which leads to the higher rates of photodegradation of AH2. Two-component spectrophotometric (243 and 266 nm, AH2 and RF, respectively) and high-performance liquid chromatography (HPLC) methods have been used to determine the concentration of AH2 and RF in pure and degraded solutions. The results obtained from these two methods are compared using a student t-test which showed no noteworthy difference between them.

Endogenous chemicals guard health through inhibiting ferroptotic cell death

Ferroptosis is a new form of regulated cell death caused by iron-dependent accumulation of lethal polyunsaturated phospholipids peroxidation. It has received considerable attention owing to its putative involvement in a wide range of pathophysiological processes such as organ injury, cardiac ischemia/reperfusion, degenerative disease and its prevalence in plants, invertebrates, yeasts, bacteria, and archaea. To counter ferroptosis, living organisms have evolved a myriad of intrinsic efficient defense systems, such as cyst(e)ine-glutathione-glutathione peroxidase 4 system (cyst(e)ine-GPX4 system), guanosine triphosphate cyclohydrolase 1/tetrahydrobiopterin (BH4) system (GCH1/BH4 system), ferroptosis suppressor protein 1/coenzyme Q10 system (FSP1/CoQ10 system), and so forth. Among these, GPX4 serves as the only enzymatic protection system through the reduction of lipid hydroperoxides, while other defense systems ultimately rely on small compounds to scavenge lipid radicals and prevent ferroptotic cell death. In this article, we systematically summarize the chemical biology of lipid radical trapping process by endogenous chemicals, such as coenzyme Q10 (CoQ10), BH4, hydropersulfides, vitamin K, vitamin E, 7-dehydrocholesterol, with the aim of guiding the discovery of novel ferroptosis inhibitors.

CoQ10 and Mitochondrial Dysfunction in Alzheimer's Disease

The progress in understanding the pathogenesis and treatment of Alzheimer's disease (AD) is based on the recognition of the primary causes of the disease, which can be deduced from the knowledge of risk factors and biomarkers measurable in the early stages of the disease. Insights into the risk factors and the time course of biomarker abnormalities point to a role for the connection of amyloid beta (Aβ) pathology, tau pathology, mitochondrial dysfunction, and oxidative stress in the onset and development of AD. Coenzyme Q10 (CoQ10) is a lipid antioxidant and electron transporter in the mitochondrial electron transport system. The availability and activity of CoQ10 is crucial for proper mitochondrial function and cellular bioenergetics. Based on the mitochondrial hypothesis of AD and the hypothesis of oxidative stress, the regulation of the efficiency of the oxidative phosphorylation system by means of CoQ10 can be considered promising in restoring the mitochondrial function impaired in AD, or in preventing the onset of mitochondrial dysfunction and the development of amyloid and tau pathology in AD. This review summarizes the knowledge on the pathophysiology of AD, in which CoQ10 may play a significant role, with the aim of evaluating the perspective of the pharmacotherapy of AD with CoQ10 and its analogues.

Real-time imaging of mitochondrial redox reveals increased mitochondrial oxidative stress associated with amyloid β aggregates in vivo in a mouse model of Alzheimer's disease

BACKGROUND

Reactive oxidative stress is a critical player in the amyloid beta (Aβ) toxicity that contributes to neurodegeneration in Alzheimer's disease (AD). Damaged mitochondria are one of the main sources of reactive oxygen species and accumulate in Aβ plaque-associated dystrophic neurites in the AD brain. Although Aβ causes neuronal mitochondria reactive oxidative stress in vitro, this has never been directly observed in vivo in the living mouse brain. Here, we tested for the first time whether Aβ plaques and soluble Aβ oligomers induce mitochondrial oxidative stress in surrounding neurons in vivo, and whether this neurotoxic effect can be abrogated using mitochondrial-targeted antioxidants.

METHODS

We expressed a genetically encoded fluorescent ratiometric mitochondria-targeted reporter of oxidative stress in mouse models of the disease and performed intravital multiphoton microscopy of neuronal mitochondria and Aβ plaques.

RESULTS

For the first time, we demonstrated by direct observation in the living mouse brain exacerbated mitochondrial oxidative stress in neurons after both Aβ plaque deposition and direct application of soluble oligomeric Aβ onto the brain, and determined the most likely pathological sequence of events leading to oxidative stress in vivo. Oxidative stress could be inhibited by both blocking calcium influx into mitochondria and treating with the mitochondria-targeted antioxidant SS31. Remarkably, the latter ameliorated plaque-associated dystrophic neurites without impacting Aβ plaque burden.

CONCLUSIONS

Considering these results, combination of mitochondria-targeted compounds with other anti-amyloid beta or anti-tau therapies hold promise as neuroprotective drugs for the prevention and/or treatment of AD.

The entrancing role of dietary polyphenols against the most frequent aging-associated diseases

Aging, a fundamental physiological process influenced by innumerable biological and genetic pathways, is an important driving factor for several aging-associated disorders like diabetes mellitus, osteoporosis, cancer, and neurodegenerative diseases including Alzheimer's and Parkinson's diseases. In the modern era, the several mechanisms associated with aging have been deeply studied. Treatment and therapeutics for age-related diseases have also made considerable advances; however, for the effective and long-lasting treatment, nutritional therapy particularly including dietary polyphenols from the natural origin are endorsed. These dietary polyphenols (e.g., apigenin, baicalin, curcumin, epigallocatechin gallate, kaempferol, quercetin, resveratrol, and theaflavin), and many other phytochemicals target certain molecular, genetic mechanisms. The most common pathways of age-associated diseases are mitogen-activated protein kinase, reactive oxygen species production, nuclear factor kappa light chain enhancer of activated B cells signaling pathways, metal chelation, c-Jun N-terminal kinase, and inflammation. Polyphenols slow down the course of aging and help in combatting age-linked disorders. This exemplified in the form of clinical trials on specific dietary polyphenols in various aging-associated diseases. With this context in mind, this review reveals the new insights to slow down the aging process, and consequently reduce some classic diseases associated with age such as aforementioned, and targeting age-associated diseases by the activities of dietary polyphenols of natural origin.

Improving Clinical Trials of Antioxidants in Alzheimer's Disease

Maintaining diversity in drug development in research into Alzheimer's disease (AD) is necessary to avoid over-reliance on targeting AD neuropathology. Treatments that reduce or prevent the generation of oxidative stress, frequently cited for its causal role in the aging process and AD, could be useful in at-risk populations or diagnosed AD patients. However, in this review, it is argued that clinical research into antioxidants in AD could provide more useful feedback as to the therapeutic value of the oxidative stress theory of AD. Improving comparability between randomized controlled trials (RCTs) is vital from a waste-reduction and priority-setting point of view for AD clinical research. For as well as attempting to improve meaningful outcomes for patients, RCTs of antioxidants in AD should strive to maximize the extraction of clinically useful information and actionable feedback from trial outcomes. Solutions to maximize information flow from RCTs of antioxidants in AD are offered here in the form of checklist questions to improve ongoing and future trials centered around the following dimensions: adhesion to reporting guidelines like CONSORT, biomarker enrichment, simple tests of treatment, and innovative trial design.

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.

Mitochondrial Targeting against Alzheimer's Disease: Lessons from Hibernation

Alzheimer's disease (AD) is the most common cause of dementia worldwide and yet remains without effective therapy. Amongst the many proposed causes of AD, the mitochondrial cascade hypothesis is gaining attention. Accumulating evidence shows that mitochondrial dysfunction is a driving force behind synaptic dysfunction and cognitive decline in AD patients. However, therapies targeting the mitochondria in AD have proven unsuccessful so far, and out-of-the-box options, such as hibernation-derived mitochondrial mechanisms, may provide valuable new insights. Hibernators uniquely and rapidly alternate between suppression and re-activation of the mitochondria while maintaining a sufficient energy supply and without acquiring ROS damage. Here, we briefly give an overview of mitochondrial dysfunction in AD, how it affects synaptic function, and why mitochondrial targeting in AD has remained unsuccessful so far. We then discuss mitochondria in hibernation and daily torpor in mice, covering current advancements in hibernation-derived mitochondrial targeting strategies. We conclude with new ideas on how hibernation-derived dual mitochondrial targeting of both the ATP and ROS pathways may boost mitochondrial health and induce local synaptic protein translation to increase synaptic function and plasticity. Further exploration of these mechanisms may provide more effective treatment options for AD in the future.

Multi-nutrient interventions and cognitive ageing: are we barking up the right tree?

As we continue to elucidate the mechanisms underlying age-related brain diseases, the reductionist strategy in nutrition–brain function research has focused on establishing the impact of individual foods. However, the biological processes connecting diet and cognition are complex. Therefore, consideration of a combination of nutritional compounds may be most efficacious. One barrier to establishing the efficacy of multi-nutrient interventions is that the area lacks an established set of evidence-based guidelines for studying their effect on brain health. This review is an output of the International Life Sciences Institute (ILSI) Europe. A multi-disciplinary expert group was assembled with the aim of developing a set of considerations to guide research into the effects of multi-nutrient combinations on brain functions. Consensus recommendations converged on six key issues that should be considered to advance research in this area: (1) establish working mechanisms of the combination and contributions of each individual compound; (2) validate the relevance of the mechanisms for the targeted human condition; (3) include current nutrient status, intake or dietary pattern as inclusion/exclusion criteria in the study design; (4) select a participant population that is clinically and biologically appropriate for all nutritional components of the combination; (5) consider a range of cognitive outcomes; (6) consider the limits of reductionism and the ‘gold standard’ randomised controlled trial. These guiding principles will enhance our understanding of the interactive/complementary activities of dietary components, thereby strengthening the evidence base for recommendations aimed at delaying cognitive decline.

Effect of nutritional supports on malnutrition, cognition, function and biomarkers of Alzheimer's disease: a systematic review

AIM

To summarize the nutritional supplementation on biochemical parameters, cognition, function, Alzheimer's Disease (AD) biomarkers and nutritional status.

MATERIALS AND METHODS

PubMed, Web of Science, Korean Journal Database, Russian Science Citation Index, SciELO Citation Index, Cochrane Library and Scopus databases were searched until 16 April 2021. 22.193 records in total were reached according to inclusion and exclusion criteria. Included Studies were evaluated through the Modified Jadad Scale and gathered under four subheadings.

RESULTS

Forty-eight studies with a total of 7009 AD patients were included. Souvenaid, ONS (368 ± 69 kcal), Vegenat-med, 500 mg Resveratrol, ONS (200 mL) were effective nutritional supplements on promoting weight gain and protecting malnutrition status but showed conflicting results in Body mass index, Mid-Upper-Arm Circumference and Triceps Skin Fold Thickness. ONS and a lyophilized whole supplementation Vegenat-med intake made an increase in MNA scores. While all nutritional supplements showed controversial results in biochemical parameters but caused a decrease in Hcy levels which caused reductions in brain Aβ plaque (increase serum Aβ), p-Tau and cognitive improvement. Folic acid and vitamin D decreased serum APP, BACE1, BACE1mRNA. Resveratrol, Hericium erinaceus mycelia, vitamin D and Betaine supplements improved cognitive, functional prognosis and quality of life unlike other nutritional supplements had no effect on cognitive scales.

CONCLUSIONS

Better designed trials with holistic measures are needed to investigate the effect of nutritional support on the AD biomarkers, cognitive status, biochemical parameters and functional states. Also, more beneficial results can be obtained by examining the simultaneous effects of nutritional supplements with larger sample groups.

Amyloid β Proteoforms Elucidated by Quantitative LC/MS in the 5xFAD Mouse Model of Alzheimer's Disease

Numerous Aβ proteoforms, identified in the human brain, possess differential neurotoxic and aggregation propensities. These proteoforms contribute in unknown ways to the conformations and resultant pathogenicity of oligomers, protofibrils, and fibrils in Alzheimer's disease (AD) manifestation owing to the lack of molecular-level specificity to the exact chemical composition of underlying protein products with widespread interrogating techniques, like immunoassays. We evaluated Aβ proteoform flux using quantitative top-down mass spectrometry (TDMS) in a well-studied 5xFAD mouse model of age-dependent Aβ-amyloidosis. Though the brain-derived Aβ proteoform landscape is largely occupied by Aβ1-42, 25 different forms of Aβ with differential solubility were identified. These proteoforms fall into three natural groups defined by hierarchical clustering of expression levels in the context of mouse age and proteoform solubility, with each group sharing physiochemical properties associated with either N/C-terminal truncations or both. Overall, the TDMS workflow outlined may hold tremendous potential for investigating proteoform-level relationships between insoluble fibrils and soluble Aβ, including low-molecular-weight oligomers hypothesized to serve as the key drivers of neurotoxicity. Similarly, the workflow may also help to validate the utility of AD-relevant animal models to recapitulate amyloidosis mechanisms or possibly explain disconnects observed in therapeutic efficacy in animal models vs humans.

Modeling Gasotransmitter Availability to Brain Capillary Endothelial Cells with Ultrasound-sensitive Microbubbles

BACKGROUND

Vascular cognitive impairment and dementia results from blood components passing through disrupted blood brain barriers (BBBs). Current treatments can reduce further progress of neuronal damage but do not treat the primary cause. Instead, these treatments typically aim to temporarily disrupt the BBB. Alternatively, this study computationally assessed the feasibility of delivering carbon monoxide (CO) from ultrasound-sensitive microbubbles (MBs) as a strategy to promote BBB repair and integrity. CO can interact with heme-containing compounds within cells and promote cell growth. However, careful dose control is critical for safety and efficacy because CO also binds at high affinity to hemoglobin (Hb).

METHODS

Ultrasound activation was simulated at the internal carotid artery, and CO released from the resulting MB rupture was tracked along the shortest path to the BBB for several activation times and doses. The CO dose available to brain capillary endothelial cells (BCECs) was predicted by considering hemodynamics, mass transport, and binding kinetics.

RESULTS

The half-life of CO binding to Hb indicated that CO is available to interact with BCECs for several cardiac cycles. Further, MB and COHb concentrations would not be near toxic levels and free Hb would be available. The axisymmetric model indicated that biologically-relevant CO concentrations will be available to BCECs, and these levels can be sustained with controlled ultrasound activation. A patient-specific geometry shows that while vessel tortuosity provides a heterogeneous response, a relevant CO concentration could still be achieved.

CONCLUSIONS

This computational study demonstrates feasibility of the CO / MB strategy, and that controlled delivery is important for viability of this strategy.

Effects of Redox Homeostasis and Mitochondrial Damage on Alzheimer's Disease

Bioenergetic mitochondrial dysfunction is a common feature of several diseases, including Alzheimer's disease (AD), where redox imbalance also plays an important role in terms of disease development. AD is an age-related disease and begins many years before the appearance of neurodegenerative symptoms. Intracellular tau aggregation, extracellular β-amyloid (Aβ) deposition in the brain, and even the APOE4 genotype contribute to the process of AD by impairing redox homeostasis and mitochondrial dysfunction. This review summarizes the evidence for the redox imbalance and mitochondrial dysfunction in AD and demonstrates the current therapeutic strategies related to mitochondrial maintenance.

Advancements in the Application of Nanomedicine in Alzheimer's Disease: A Therapeutic Perspective

Alzheimer's disease (AD) is a progressive neurodegenerative disease that affects most people worldwide. AD is a complex central nervous system disorder. Several drugs have been designed to cure AD, but with low success rates. Because the blood-brain and blood-cerebrospinal fluid barriers are two barriers that protect the central nervous system, their presence has severely restricted the efficacy of many treatments that have been studied for AD diagnosis and/or therapy. The use of nanoparticles for the diagnosis and treatment of AD is the focus of an established and rapidly developing field of nanomedicine. Recent developments in nanomedicine have made it possible to effectively transport drugs to the brain. However, numerous obstacles remain to the successful use of nanomedicines in clinical settings for AD treatment. Furthermore, given the rapid advancement in nanomedicine therapeutics, better outcomes for patients with AD can be anticipated. This article provides an overview of recent developments in nanomedicine using different types of nanoparticles for the management and treatment of AD.

Oxidative Stress Occurs Prior to Amyloid Aβ Plaque Formation and Tau Phosphorylation in Alzheimer's Disease: Role of Glutathione and Metal Ions

Alzheimer's disease (AD) is an insidious and progressive neurodegenerative disorder that affects millions of people worldwide. Although the pathogenesis remains obscure, there are two dominant causal hypotheses. Since last three decades, amyloid beta (Aβ) deposition was the most prominent hypothesis, and the other is the tau hyperphosphorylation hypothesis. The confirmed diagnostic criterion for AD is the presence of neurofibrillary tangles (NFTs) composed of hyperphosphorylated tau and the deposition of toxic oligomeric Aβ in the autopsied brain. Consistent with these hypotheses, oxidative stress (OS) is garnering major attention in AD research. OS results from an imbalance of pro-oxidants and antioxidants. There is a considerable debate in the scientific community on which process occurs first, OS or plaque deposition/tau hyperphosphorylation. Based on recent scientific observations of various laboratories including ours along with critical analysis of those information, we believe that OS is the early event that leads to oligomeric Aβ deposition as well as dimerization of tau protein and its subsequent hyperphosphorylation. This OS hypothesis immediately suggests the consideration of novel therapeutic approaches to include antioxidants involving glutathione enrichment in the brain by supplementation with or without an iron chelator.

Roles of Oxidative Stress in Synaptic Dysfunction and Neuronal Cell Death in Alzheimer's Disease

Alzheimer's disease (AD) is a brain disorder that progressively undermines memory and thinking skills by affecting the hippocampus and entorhinal cortex. The main histopathological hallmarks of AD are the presence of abnormal protein aggregates (Aβ and tau), synaptic dysfunction, aberrant proteostasis, cytoskeletal abnormalities, altered energy homeostasis, DNA and RNA defects, inflammation, and neuronal cell death. However, oxidative stress or oxidative damage is also evident and commonly overlooked or considered a consequence of the advancement of dementia symptoms. The control or onset of oxidative stress is linked to the activity of the amyloid-β peptide, which may serve as both antioxidant and pro-oxidant molecules. Furthermore, oxidative stress is correlated with oxidative damage to proteins, nucleic acids, and lipids in vulnerable cell populations, which ultimately lead to neuronal death through different molecular mechanisms. By recognizing oxidative stress as an integral feature of AD, alternative therapeutic or preventive interventions are developed and tested as potential or complementary therapies for this devastating neurodegenerative disease.

Antibody-Mediated Clearance of Brain Amyloid-β: Mechanisms of Action, Effects of Natural and Monoclonal Anti-Aβ Antibodies, and Downstream Effects

Immunotherapeutic efforts to slow the clinical progression of Alzheimer's disease (AD) by lowering brain amyloid-β (Aβ) have included Aβ vaccination, intravenous immunoglobulin (IVIG) products, and anti-Aβ monoclonal antibodies. Neither Aβ vaccination nor IVIG slowed disease progression. Despite conflicting phase III results, the monoclonal antibody Aducanumab received Food and Drug Administration (FDA) approval for treatment of AD in June 2021. The only treatments unequivocally demonstrated to slow AD progression to date are the monoclonal antibodies Lecanemab and Donanemab. Lecanemab received FDA approval in January 2023 based on phase II results showing lowering of PET-detectable Aβ; phase III results released at that time indicated slowing of disease progression. Topline results released in May 2023 for Donanemab's phase III trial revealed that primary and secondary end points had been met. Antibody binding to Aβ facilitates its clearance from the brain via multiple mechanisms including promoting its microglial phagocytosis, activating complement, dissolving fibrillar Aβ, and binding of antibody-Aβ complexes to blood-brain barrier receptors. Antibody binding to Aβ in peripheral blood may also promote cerebral efflux of Aβ by a peripheral sink mechanism. According to the amyloid hypothesis, for Aβ targeting to slow AD progression, it must decrease downstream neuropathological processes including tau aggregation and phosphorylation and (possibly) inflammation and oxidative stress. This review discusses antibody-mediated mechanisms of Aβ clearance, findings in AD trials involving Aβ vaccination, IVIG, and anti-Aβ monoclonal antibodies, downstream effects reported in those trials, and approaches which might improve the Aβ-clearing ability of monoclonal antibodies.

Hypometabolism, Alzheimer's Disease, and Possible Therapeutic Targets: An Overview

The brain is a highly dynamic organ that requires a constant energy source to function normally. This energy is mostly supplied by glucose, a simple sugar that serves as the brain's principal fuel source. Glucose transport across the blood-brain barrier (BBB) is primarily controlled via sodium-independent facilitated glucose transport, such as by glucose transporter 1 (GLUT1) and 3 (GLUT3). However, other glucose transporters, including GLUT4 and the sodium-dependent transporters SGLT1 and SGLT6, have been reported in vitro and in vivo. When the BBB endothelial layer is crossed, neurons and astrocytes can absorb the glucose using their GLUT1 and GLUT3 transporters. Glucose then enters the glycolytic pathway and is metabolized into adenosine triphosphate (ATP), which supplies the energy to support cellular functions. The transport and metabolism of glucose in the brain are impacted by several medical conditions, which can cause neurological and neuropsychiatric symptoms. Alzheimer's disease (AD), Parkinson's disease (PD), epilepsy, traumatic brain injury (TBI), schizophrenia, etc., are a few of the most prevalent disorders, characterized by a decline in brain metabolism or hypometabolism early in the course of the disease. Indeed, AD is considered a metabolic disorder related to decreased brain glucose metabolism, involving brain insulin resistance and age-dependent mitochondrial dysfunction. Although the conventional view is that reduced cerebral metabolism is an effect of neuronal loss and consequent brain atrophy, a growing body of evidence points to the opposite, where hypometabolism is prodromal or at least precedes the onset of brain atrophy and the manifestation of clinical symptoms. The underlying processes responsible for these glucose transport and metabolic abnormalities are complicated and remain poorly understood. This review article provides a comprehensive overview of the current understanding of hypometabolism in AD and potential therapeutic targets.

Protective effects of alpha lipoic acid (ALA) are mediated by hormetic mechanisms

The endogenous and dietary agent, alpha lipoic acid (ALA) is evaluated for its capacity to induce a broad spectrum of adaptive responses via hormetic dose responses and their underlying mechanisms. ALA was shown to induce hormetic effects in a wide range of experimental models within in vitro and in vivo experimental settings which included direct exposure and pre- and post-conditioning experimental protocols. The hormetic effects occur in a broad range of organ systems, including the brain, heart, kidney and other tissues, with possible public health and clinical/therapeutic applications linked to reducing the onset and progression of neurogenerative diseases and also in the preservation of sperm health and functionality during cryopreservation. This paper provides the first integrated assessment of ALA-induced hormetic dose responses. Underlying mechanisms that mediated the occurrence of ALA-induced hormetic effects involved the induction of low levels of ROS that activate key cell signaling antioxidant (e.g. Nrf2) pathways.

Nutrition and cognitive health: A life course approach

Multiple factors affect cognitive health, such as age-related changes in the brain, injuries, mood disorders, substance abuse, and diseases. While some cannot be changed, evidence exists of many potentially possibly modifiable lifestyle factors: diet, physical activity, cognitive and social engagement, smoking and alcohol consumption which may stabilize or improve declining cognitive function. In nutrition, the focus has been mainly on its role in brain development in the early years. There is a strong emerging need to identify the role of diet and nutrition factors on age-related cognitive decline, which will open up the use of new approaches for prevention, treatment or management of age-related disorders and maintaining a good quality of life among older adults. While data on effect of high protein diets is not consistent, low-fat diets are protective against cognitive decline. Several micronutrients like B group vitamins and iron, as well as many polyphenols play a crucial role in cognitive health. Mediterranean, Nordic, DASH, and MIND diets are linked to a lower risk of cognitive decline and dementia. The relationship between the gut microbiome and brain function through the gut-brain axis has led to the emergence of data on the beneficial effects of dietary fibers and probiotics through the management of gut microbes. A “whole diet” approach as well as macro- and micro-nutrient intake levels that have protective effects against cardiovascular diseases are most likely to be effective against neurodegenerative disorders too. Young adulthood and middle age are crucial periods for determining cognitive health in old age. The importance of cardio metabolic risk factors such as obesity and hypertension, smoking and physical inactivity that develop in middle age suggest that preventive approaches are required for target populations in their 40s and 50s, much before they develop dementia. The commonality of dementia risk with cardiovascular and diabetes risk suggests that dementia could be added to present non-communicable disease management programs in primary healthcare and broader public health programs.

The Role of Dietary Antioxidants and Their Potential Mechanisms in Alzheimer’s Disease Treatment

Alzheimer’s disease (AD) is a progressive neurodegenerative disorder associated with cognitive decline and characterized by amyloid-β plaques and neurofibrillary tau tangles. Although AD’s exact pathophysiology remains unclear, oxidative stress is known to play a role in the neurodegenerative process. Since no curative treatment exists, antioxidants represent a potential treatment for AD due to their ability to modulate oxidative stress. Therefore, this review aims to examine the impact of antioxidant supplementation and its potential mechanisms on cognitive function. The review primarily discusses research articles published between 2012 and 2022 reporting the results of clinical trials involving antioxidant supplementation on cognitive function in individuals with AD. Antioxidant supplementation included probiotics, selenium, melatonin, resveratrol, rosmarinic acid, carotenoids, curcumin, vitamin E, and coenzyme Q. While the studies included in this review did not provide much evidence for the beneficial role of antioxidant supplements on cognitive function in AD, the results varied from antioxidant to antioxidant and among trials examining the same antioxidant. Furthermore, many of the studies’ findings face several limitations, including short trial durations, small sample sizes, and a lack of diversity among study participants. As a result, more research is required to examine the impact of antioxidant supplementation on cognitive function in AD.

Antiamnesic Effects of Novel Phthalimide Derivatives in Scopolamine-Induced Memory Impairment in Mice: A Useful Therapy for Alzheimer's Disease

Phthalimides have diverse bioactivities and are attractive molecules for drug discovery and development. Here, we explored new synthesized phthalimide derivatives (compounds 1-3) in improving memory impairment associated with Alzheimer's disease (AD), using in vitro and ex vivo acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE) inhibition and in vivo models, including Y-maze test and novel object recognition test (NORT). Compounds 1-3 exhibited significant AChE activity with IC₅₀ values of 10, 140, and 18 μM and BuChE with IC₅₀ values of 80, 50, and 11 μM, respectively. All compounds 1-3 showed excellent antioxidant potential in DPPH and ABTS assays with IC₅₀ values in the range of 105-340 and 205-350 μM, respectively. In ex vivo studies, compounds 1-3 also significantly inhibited both enzymes in a concentration-dependent manner along with significant antioxidant activities. In in vivo studies, compounds 1-3 reversed scopolamine-induced amnesia as indicated by a significant increase in the spontaneous alternation in the Y-maze test and an increase in the discrimination index in the NORT. Molecular docking was also conducted for compounds 1-3 against AChE and BuChE, which showed that compounds 1 and 3 have excellent binding with AChE and BuChE as compared to 2. These findings suggest that compounds 1-3 possess significant antiamnesic potential and may serve as useful leads to develop novel therapeutics for the symptomatic management and treatment of AD.

Coenzyme Q10 and Dementia: A Systematic Review

It is well known that coenzyme Q₁₀ (CoQ₁₀) has important antioxidant properties. Because one of the main mechanisms involved in the pathogenesis of Alzheimer's disease (AD) and other neurodegenerative diseases is oxidative stress, analysis of the concentrations of CoQ₁₀ in different tissues of AD patients and with other dementia syndromes and the possible therapeutic role of CoQ₁₀ in AD have been addressed in several studies. We performed a systematic review and a meta-analysis of these studies measuring tissue CoQ₁₀ levels in patients with dementia and controls which showed that, compared with controls, AD patients had similar serum/plasma CoQ₁₀ levels. We also revised the possible therapeutic effects of CoQ₁₀ in experimental models of AD and other dementias (which showed important neuroprotective effects of coenzyme Q₁₀) and in humans with AD, other dementias, and mild cognitive impairment (with inconclusive results). The potential role of CoQ₁₀ treatment in AD and in improving memory in aged rodents shown in experimental models deserves future studies in patients with AD, other causes of dementia, and mild cognitive impairment.

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.

Cognitive and Mood Effect of Alpha-Lipoic Acid Supplementation in a Nonclinical Elder Sample: An Open-Label Pilot Study

BACKGROUND

Memory disorders are common among elder people, and nonclinical cognitive decline is commonly experienced with age. Preclinical investigations have explored the possible role of alpha-lipoic acid (ALA), a known antioxidant compound abundant in vegetables and animal tissues, in reducing oxidative stress in the aging brain and preventing cognitive decline. However, clinical evidence is limited, and the few existing results are contrasting. In addition, while most of the existing trials have been focused on the effects of ALA administration in Alzheimer's disease (AD) or other types of dementia, studies evaluating its effects on nonclinical elder population are still missing.

METHODS

In the present open-label, pilot study, fifteen elder patients (mean age: 84.5 ± 5.77) received ALA at a daily dose of 600 mg/day for 12 weeks. General cognitive function, executive function, and mood symptom assessment were carried out at baseline and at the endpoint.

RESULTS

Overall, ALA administration was generally well-tolerated (only one dropout due to gastrointestinal side effects). However, no statistically significant effects either on cognitive function, executive function, or mood were found.

CONCLUSIONS

Despite several limitations, our study found no evidence of positive effects on cognition and mood after ALA administration in elder people without the diagnosis of AD or cognitive impairment. Further clinical trials are needed to better investigate ALA effectiveness on cognition and mood in elder subjects.

Non-Enzymatic Antioxidants against Alzheimer's Disease: Prevention, Diagnosis and Therapy

Alzheimer's disease (AD) is a neurodegenerative disorder characterized by progressive memory loss and cognitive decline. Although substantial research has been conducted to elucidate the complex pathophysiology of AD, the therapeutic approach still has limited efficacy in clinical practice. Oxidative stress (OS) has been established as an early driver of several age-related diseases, including neurodegeneration. In AD, increased levels of reactive oxygen species mediate neuronal lipid, protein, and nucleic acid peroxidation, mitochondrial dysfunction, synaptic damage, and inflammation. Thus, the identification of novel antioxidant molecules capable of detecting, preventing, and counteracting AD onset and progression is of the utmost importance. However, although several studies have been published, comprehensive and up-to-date overviews of the principal anti-AD agents harboring antioxidant properties remain scarce. In this narrative review, we summarize the role of vitamins, minerals, flavonoids, non-flavonoids, mitochondria-targeting molecules, organosulfur compounds, and carotenoids as non-enzymatic antioxidants with AD diagnostic, preventative, and therapeutic potential, thereby offering insights into the relationship between OS and neurodegeneration.

Therapeutic Potential of Natural Compounds in Neurodegenerative Diseases: Insights from Clinical Trials

Neurodegenerative diseases are caused by the gradual loss of neurons' function. These neurological illnesses remain incurable, and current medicines only alleviate the symptoms. Given the social and economic burden caused by the rising frequency of neurodegenerative diseases, there is an urgent need for the development of appropriate therapeutics. Natural compounds are gaining popularity as alternatives to synthetic drugs due to their neuroprotective properties and higher biocompatibility. While natural compounds' therapeutic effects for neurodegenerative disease treatment have been investigated in numerous in vitro and in vivo studies, only few have moved to clinical trials. This article provides the first systematic review of the clinical trials evaluating natural compounds' safety and efficacy for the treatment of the five most prevalent neurodegenerative disorders: Alzheimer's disease, Parkinson's disease, multiple sclerosis, amyotrophic lateral sclerosis, and Huntington's disease.

The role of mitochondrial dysfunction in Alzheimer's disease pathogenesis

To promote new thinking of the pathogenesis of Alzheimer's disease (AD), we examine the central role of mitochondrial dysfunction in AD. Pathologically, AD is characterized by progressive neuronal loss and biochemical abnormalities including mitochondrial dysfunction. Conventional thinking has dictated that AD is driven by amyloid beta pathology, per the Amyloid Cascade Hypothesis. However, the underlying mechanism of how amyloid beta leads to cognitive decline remains unclear. A model correctly identifying the pathogenesis of AD is critical and needed for the development of effective therapeutics. Mitochondrial dysfunction is closely linked to the core pathological feature of AD: neuronal dysfunction. Targeting mitochondria and associated proteins may hold promise for new strategies for the development of disease-modifying therapies. According to the Mitochondrial Cascade Hypothesis, mitochondrial dysfunction drives the pathogenesis of AD, as baseline mitochondrial function and mitochondrial change rates influence the progression of cognitive decline. HIGHLIGHTS: The Amyloid Cascade Model does not readily account for various parameters associated with Alzheimer's disease (AD). A unified model correctly identifying the pathogenesis of AD is greatly needed to inform the development of successful therapeutics. Mitochondria play a key and central role in the maintenance of optimal neuronal and synaptic function, the core pathological feature of AD. Mitochondrial dysfunction may be the primary cause of AD, and is a promising target for new therapeutic strategies.

Nutrients and amyloid β status in the brain: A narrative review

Amyloid beta (Aβ) is a peptide and a hallmark of Alzheimer's disease (AD). Emerging evidence suggests that Aβ levels could be influenced by diet. However, the evidence is sparse and for some nutrients, controversial. The aim of this narrative review is to gather the findings of observational and clinical trials involving human participants on the relationships between nutrients and brain Aβ status. Some dietary patterns are associated to reduced levels of Aβ in the brain, such as the Mediterranean diet, ketogenic diet as well as low intake of saturated fat, high-glycemic-index food, sodium, and junk/fast food. Low Aβ status in the brain was also associated with higher density lipoproteins (HDL) cholesterol and polyunsaturated fatty acids consumption. Data on alcohol intake is not conclusive. On the contrary, high Aβ levels in the brain were related to a higher intake of total cholesterol, triglycerides, low-density lipoproteins (LDL) cholesterol, saturated fat, sucrose, and fructose. Folic acid, cobalamin, vitamin E, and vitamin D were not associated to Aβ status, while high blood concentrations of Calcium, Aluminum, Zinc, Copper, and Manganese were associated with decreased Aβ blood levels but were not associated with Aβ cerebral spinal fluid (CSF) concentrations. In conclusion, certain dietary patterns and nutrients are associated to brain Aβ status. Further research on the association between nutrients and brain Aβ status is needed in order to pave the way to use nutritional interventions as efficacious strategies to prevent Aβ disturbance and potentially AD.

Mitochondrial Dysfunction and Neurodegenerative Disorders: Role of Nutritional Supplementation

Mitochondrial dysfunction has been implicated in the pathogenesis of a number of neurodegenerative disorders, including Parkinson's disease, Alzheimer's disease, amyotrophic lateral sclerosis, multisystem atrophy, and progressive supranuclear palsy. This article is concerned specifically with mitochondrial dysfunction as defined by reduced capacity for ATP production, the role of depleted levels of key nutritionally related metabolites, and the potential benefit of supplementation with specific nutrients of relevance to normal mitochondrial function in the above neurodegenerative disorders. The article provides a rationale for a combination of CoQ10, B-vitamins/NADH, L-carnitine, vitamin D, and alpha-lipoic acid for the treatment of the above neurodegenerative disorders.

Combined Supplementation of Coenzyme Q10 and Other Nutrients in Specific Medical Conditions

Coenzyme Q10 (CoQ10) is a compound with a crucial role in mitochondrial bioenergetics and membrane antioxidant protection. Despite the ubiquitous endogenous biosynthesis, specific medical conditions are associated with low circulating CoQ10 levels. However, previous studies of oral CoQ10 supplementation yielded inconsistent outcomes. In this article, we reviewed previous CoQ10 trials, either single or in combination with other nutrients, and stratified the study participants according to their metabolic statuses and medical conditions. The CoQ10 supplementation trials in elders reported many favorable outcomes. However, the single intervention was less promising when the host metabolic statuses were worsening with the likelihood of multiple nutrient insufficiencies, as in patients with an established diagnosis of metabolic or immune-related disorders. On the contrary, the mixed CoQ10 supplementation with other interacting nutrients created more promising impacts in hosts with compromised nutrient reserves. Furthermore, the results of either single or combined intervention will be less promising in far-advanced conditions with established damage, such as neurodegenerative disorders or cancers. With the limited high-level evidence studies on each host metabolic category, we could only conclude that the considerations of whether to take supplementation varied by the individuals' metabolic status and their nutrient reserves. Further studies are warranted.

Diet, nutrition, and cognitive function: A narrative review of Japanese longitudinal studies

In aging societies, the number of older people with cognitive decline and dementia is increasing. Proper nutrition is a key factor that can help in the prevention of these age-related impairments. This narrative review of longitudinal studies in Japan outlines the relationship between nutrition and the brain and focuses on Japanese nutritional epidemiologic studies. The results of Japanese cohort studies suggest that rather than a single food or nutrient, a nutritionally balanced diet that integrates a variety of foods and nutrients can contribute to the maintenance of brain function and be effective in preventing dementia. In addition, this review considers a nutritional approach to reducing the severity of cognitive decline in individuals with mild cognitive impairment and dementia, and suggests lifelong strategies for the prevention of cognitive decline. It is important that we consider the practice of eating not only as a way to obtain nutrients, but also as an important lifestyle habit to maintain our physical and mental health. Geriatr Gerontol Int 2022; 22: 825-831.

A quantitative meta-analysis of vitamin C in the pathophysiology of Alzheimer’s disease

Purpose

Alzheimer’s disease (AD) is a multifaceted neurodegenerative disorder with many complex pathways feeding into its pathogenesis and progression. Vitamin C, an essential dietary antioxidant, is vital for proper neurological development and maintenance. This meta-analysis and systematic review attempted to define the relationship between vitamin C plasma levels and AD while highlighting the importance and involvement of vitamin C in the pathogenesis of AD.

Materials and methods

PRISMA guidelines were used to obtain studies quantifying the plasma levels of vitamin C in AD and control subjects. The literature was searched in the online databases PubMed, Google Scholar, and Web of Science. A total of 12 studies were included (n = 1,100) and analyzed using Comprehensive Meta-Analysis 3.0.

Results

The results show that there is a significant decrease in the plasma vitamin C levels of AD patients as compared to healthy controls (pooled SMD with random-effect model: −1.164, with 95%CI: −1.720 to −0.608, Z = −4.102, p = 0.00) with significant heterogeneity (I² = 93.218). The sensitivity analysis showed directionally similar results. Egger’s regression test (p = 0.11) and visual inspection of the funnel plot showed no publication bias.

Conclusion

Based on these studies, it can be deduced that the deficiency of vitamin C is involved in disease progression and supplementation is a plausible preventive and treatment strategy. However, clinical studies are warranted to elucidate its exact mechanistic role in AD pathophysiology and prevention.

Targeting Oxidative Stress Mechanisms to Treat Alzheimer’s and Parkinson’s Disease: A Critical Review

Neurodegenerative disorders such as Alzheimer's disease (AD) and Parkinson's disease (PD) are becoming more frequent as the age increases. Contemporary therapies provide symptom resolution instead of targeting underlying pathological pathways. Consequently, there is considerable heterogeneity in response to treatment. Research has elucidated multiple potential of pathophysiological mechanisms contributing to neurodegenerative conditions, among which oxidative stress pathways appear to be suitable drug targets. The oxidative stress pathway has given rise to numerous novel pharmacological therapies that may provide a new avenue for neurodegenerative diseases. For example, SKQ (plastoquinone), MitoVitE, vitamin E, SOD mimic, MitoTEMPO (SOD mimetic), and bioactive molecules like curcumin and vitamin C have indeed been examined. To better understand how oxidative stress contributes to neurodegenerative diseases (such as Alzheimer's and Parkinson's), we analyzed the medicinal qualities of medicines that target markers in the cellular oxidative pathways. The specific pathway by which mitochondrial dysfunction causes neurodegeneration will require more investigation. An animal study should be carried out on medications that tackle cellular redox mechanisms but are not currently licensed for use in the management of neurodegenerative conditions.

Plants, Plants, and More Plants: Plant-Derived Nutrients and Their Protective Roles in Cognitive Function, Alzheimer’s Disease, and Other Dementias

Background and Objectives: Alzheimer’s disease (AD) is the most common form of dementia, with the risk of developing it attributed to non-modifiable and modifiable factors. Currently, there is no cure for AD. A plant-based diet may protect against cognitive decline, due to the effects of plant-based nutrients such as vitamins, antioxidants, and fiber. The aim of the review is to summarize current literature on plant-based nutrients and their impact on cognition. Materials and Methods: A search was conducted on PubMed for clinical and murine studies, using combinations of the following words: “Alzheimer’s disease”, “dementia”, “cognition”, “plant-based diet”, “mild cognitive impairment”, “vitamin B”, “vitamin C”, “vitamin E, “beta carotene”, “antioxidants”, “fiber”, “vitamin K”, “Mediterranean diet”, “vitamin D”, and “mushrooms”. Results and Conclusions: A diet rich in vitamin B and antioxidants can benefit the cognitive functions of individuals as shown in randomized clinical trials. Vitamin K is associated with improved cognition, although large randomized controlled trials need to be done. Fiber has been shown to prevent cognitive decline in animal studies. Vitamin D may contribute to cognitive health via anti-inflammatory processes. Several medical organizations have recommended a plant-based diet for optimizing cognitive health and potentially helping to prevent dementia.

Oxidative Stress in Tauopathies: From Cause to Therapy

Oxidative stress (OS) is the result of an imbalance between the production of reactive oxygen species (ROS) and the antioxidant capacity of cells. Due to its high oxygen demand, the human brain is highly susceptible to OS and, thus, it is not a surprise that OS has emerged as an essential component of the pathophysiology of several neurodegenerative diseases, including tauopathies. Tauopathies are a heterogeneous group of age-related neurodegenerative disorders characterized by the deposition of abnormal tau protein in the affected neurons. With the worldwide population aging, the prevalence of tauopathies is increasing, but effective therapies have not yet been developed. Since OS seems to play a key role in tauopathies, it has been proposed that the use of antioxidants might be beneficial for tau-related neurodegenerative diseases. Although antioxidant therapies looked promising in preclinical studies performed in cellular and animal models, the antioxidant clinical trials performed in tauopathy patients have been disappointing. To develop effective antioxidant therapies, the molecular mechanisms underlying OS in tauopathies should be completely understood. Here, we review the link between OS and tauopathies, emphasizing the causes of OS in these diseases and the role of OS in tau pathogenesis. We also summarize the antioxidant therapies proposed as a potential treatment for tauopathies and discuss why they have not been completely translated to clinical trials. This review aims to provide an integrated perspective of the role of OS and antioxidant therapies in tauopathies. In doing so, we hope to enable a more comprehensive understanding of OS in tauopathies that will positively impact future studies.

Age-Associated Glia Remodeling and Mitochondrial Dysfunction in Neurodegeneration: Antioxidant Supplementation as a Possible Intervention

Aging induces substantial remodeling of glia, including density, morphology, cytokine expression, and phagocytic capacity. Alterations of glial cells, such as hypertrophy of lysosomes, endosomes and peroxisomes, and the progressive accumulation of lipofuscin, lipid droplets, and other debris have also been reported. These abnormalities have been associated with significant declines of microglial processes and reduced ability to survey the surrounding tissue, maintain synapses, and recover from injury. Similarly, aged astrocytes show reduced capacity to support metabolite transportation to neurons. In the setting of reduced glial activity, stressors and/or injury signals can trigger a coordinated action of microglia and astrocytes that may amplify neuroinflammation and contribute to the release of neurotoxic factors. Oxidative stress and proteotoxic aggregates may burst astrocyte-mediated secretion of pro-inflammatory cytokines, thus activating microglia, favoring microgliosis, and ultimately making the brain more susceptible to injury and/or neurodegeneration. Here, we discuss the contribution of microglia and astrocyte oxidative stress to neuroinflammation and neurodegeneration, highlight the pathways that may help gain insights into their molecular mechanisms, and describe the benefits of antioxidant supplementation-based strategies.

Enhanced defense against ferroptosis ameliorates cognitive impairment and reduces neurodegeneration in 5xFAD mice

Oxidative damage including lipid peroxidation is widely reported in Alzheimer's disease (AD) with the peroxidation of phospholipids in membranes being the driver of ferroptosis, an iron-dependent oxidative form of cell death. However, the importance of ferroptosis in AD remains unclear. This study tested whether ferroptosis inhibition ameliorates AD. 5xFAD mice, a widely used AD mouse model with cognitive impairment and robust neurodegeneration, exhibit markers of ferroptosis including increased lipid peroxidation, elevated lyso-phospholipids, and reduced level of Gpx4, the master defender against ferroptosis. To determine if enhanced defense against ferroptosis retards disease development, we generated 5xFAD mice that overexpress Gpx4, i.e., 5xFAD/GPX4 mice. Consistent with enhanced defense against ferroptosis, neurons from 5xFAD/GPX4 mice showed an augmented capacity to reduce lipid reactive oxygen species. In addition, compared with control 5xFAD mice, 5xFAD/GPX4 mice showed significantly improved learning and memory abilities and had reduced neurodegeneration. Moreover, 5xFAD/GPX4 mice exhibited attenuated markers of ferroptosis. Our results indicate that enhanced defense against ferroptosis is effective in ameliorating cognitive impairment and decreasing neurodegeneration of 5xFAD mice. The findings support the notion that ferroptosis is a key contributor to AD pathogenesis.

Antioxidant Therapy in Oxidative Stress-Induced Neurodegenerative Diseases: Role of Nanoparticle-Based Drug Delivery Systems in Clinical Translation

Free radicals are formed as a part of normal metabolic activities but are neutralized by the endogenous antioxidants present in cells/tissue, thus maintaining the redox balance. This redox balance is disrupted in certain neuropathophysiological conditions, causing oxidative stress, which is implicated in several progressive neurodegenerative diseases. Following neuronal injury, secondary injury progression is also caused by excessive production of free radicals. Highly reactive free radicals, mainly the reactive oxygen species (ROS) and reactive nitrogen species (RNS), damage the cell membrane, proteins, and DNA, which triggers a self-propagating inflammatory cascade of degenerative events. Dysfunctional mitochondria under oxidative stress conditions are considered a key mediator in progressive neurodegeneration. Exogenous delivery of antioxidants holds promise to alleviate oxidative stress to regain the redox balance. In this regard, natural and synthetic antioxidants have been evaluated. Despite promising results in preclinical studies, clinical translation of antioxidants as a therapy to treat neurodegenerative diseases remains elusive. The issues could be their low bioavailability, instability, limited transport to the target tissue, and/or poor antioxidant capacity, requiring repeated and high dosing, which cannot be administered to humans because of dose-limiting toxicity. Our laboratory is investigating nanoparticle-mediated delivery of antioxidant enzymes to address some of the above issues. Apart from being endogenous, the main advantage of antioxidant enzymes is their catalytic mechanism of action; hence, they are significantly more effective at lower doses in detoxifying the deleterious effects of free radicals than nonenzymatic antioxidants. This review provides a comprehensive analysis of the potential of antioxidant therapy, challenges in their clinical translation, and the role nanoparticles/drug delivery systems could play in addressing these challenges.

Sodium-calcium exchanger isoform-3 targeted Withania somnifera (L.) Dunal therapeutic intervention ameliorates cognition in the 5xFAD mouse model of Alzheimer's disease

The third isoform of the Na+-Ca2+ exchanger (NCX3) is crucial for a physiological fine-tuning of the Ca2+ fluxes in excitable tissues. In this view, the NCX3 accounts for the aberrant Ca2+ influx seen during neuronal excitotoxicity, such as in Alzheimer's disease (AD). However, little is known about NCX3 regulation and functional properties. Withania somnifera (L.) Dunal (W. somnifera), a traditional indigenous plant widely recognized for having numerous medicinal values, was undertaken to determine its potential therapeutic benefit against aggregated Aβ1-42-induced NCX3 dysregulation and the thereof cognition impairment in 5xFAD mice. The undertaken sourced dried roots of authenticated W. somnifera physicochemical compositional tests satisfied standards of pharmacognostic quality, and further phytochemical analysis of the roots methanol extract revealed the roots constitute several antioxidants. Following an intra-gastric gavage administration of synthesized W. somnifera roots methanolic extract from postnatal day 30 (P30) to P75, in vivo cognitional studies and then neurochemical examinations of the NCX3 expression level, Aβ plaque deposition, and antioxidant activities in the AD-associated brain regions of 4-month-old 5xFAD mice suggests that the oxidative stress normalizing effects of W. somnifera constituents, operating on the NCX3, may have a therapeutic role in the improvement of cognition in AD.

Naturally Occurring Antioxidant Therapy in Alzheimer's Disease

It is estimated that the prevalence rate of Alzheimer's disease (AD) will double by the year 2040. Although currently available treatments help with symptom management, they do not prevent, delay the progression of, or cure the disease. Interestingly, a shared characteristic of AD and other neurodegenerative diseases and disorders is oxidative stress. Despite profound evidence supporting the role of oxidative stress in the pathogenesis and progression of AD, none of the currently available treatment options address oxidative stress. Recently, attention has been placed on the use of antioxidants to mitigate the effects of oxidative stress in the central nervous system. In preclinical studies utilizing cellular and animal models, natural antioxidants showed therapeutic promise when administered alone or in combination with other compounds. More recently, the concept of combination antioxidant therapy has been explored as a novel approach to preventing and treating neurodegenerative conditions that present with oxidative stress as a contributing factor. In this review, the relationship between oxidative stress and AD pathology and the neuroprotective role of natural antioxidants from natural sources are discussed. Additionally, the therapeutic potential of natural antioxidants as preventatives and/or treatment for AD is examined, with special attention paid to natural antioxidant combinations and conjugates that are currently being investigated in human clinical trials.

Dietary Antioxidants and Risk of Parkinson's Disease: A Systematic Review and Dose-Response Meta-analysis of Observational Studies

The aim of the current review was to explore the association between various dietary antioxidants and the risk of developing Parkinson's disease (PD). PubMed, Scopus, Web of Science, and Google Scholar were searched up to March 2021. Prospective, observational cohort studies, nested case-control, and case-control designs that investigated the association between antioxidants and PD risk were included. A random-effects model was used to pool the RRs. The certainty of the evidence was rated using the GRADE (Grading of Recommendations Assessment, Development, and Evaluations) scoring system. In addition, a dose-response relation was examined between antioxidant intake and PD risk. Six prospective cohort studies and 2 nested case-control (total n = 448,737 with 4654 cases), as well as 6 case-control (1948 controls, 1273 cases) studies were eligible. The pooled RR was significantly lower for the highest compared with the lowest intake categories of vitamin E (n = 7; 0.84; 95% CI: 0.71, 0.99) and anthocyanins (n = 2; 0.76; 95% CI: 0.61, 0.96) in cohort studies. Conversely, a significantly higher risk of PD was observed for higher lutein intake (n = 3; 1.86; 95% CI: 1.20, 2.88) among case-control studies. Dose-response meta-analyses indicated a significant association between a 50-mg/d increase in vitamin C (n = 6; RR: 0.94; 95% CI: 0.88, 0.99), a 5-mg/d increment in vitamin E (n = 7; RR: 0.84; 95% CI: 0.70, 0.99), a 2-mg/d increment in β-carotene (n = 6; RR: 0.94, 95% CI: 0.89, 0.99), and a 1-mg/d increment in zinc (n = 1; OR: 0.65; 95% CI: 0.49, 0.86) and a reduced risk of PD. Overall, higher intake of antioxidant-rich foods may be associated with a lower risk of PD. Future well-designed prospective studies are needed to validate the present findings. The protocol was registered in the International Prospective Register of Systematic Reviews (PROSPERO) database (https://www.crd.york.ac.uk/PROSPERO, CRD42021242511).

Physical Activity vs. Redox Balance in the Brain: Brain Health, Aging and Diseases

It has been proven that physical exercise improves cognitive function and memory, has an analgesic and antidepressant effect, and delays the aging of the brain and the development of diseases, including neurodegenerative disorders. There are even attempts to use physical activity in the treatment of mental diseases. The course of most diseases is strictly associated with oxidative stress, which can be prevented or alleviated with regular exercise. It has been proven that physical exercise helps to maintain the oxidant–antioxidant balance. In this review, we present the current knowledge on redox balance in the organism and the consequences of its disruption, while focusing mainly on the brain. Furthermore, we discuss the impact of physical activity on aging and brain diseases, and present current recommendations and directions for further research in this area.

Coenzyme Q10 effects in neurological diseases

Coenzyme Q10 (CoQ10), a lipophilic substituted benzoquinone, is present in animal and plant cells. It is endogenously synthetized in every cell and involved in a variety of cellular processes. CoQ10 is an obligatory component of the respiratory chain in inner mitochondrial membrane. In addition, the presence of CoQ10 in all cellular membranes and in blood. It is the only endogenous lipid antioxidant. Moreover, it is an essential factor for uncoupling protein and controls the permeability transition pore in mitochondria. It also participates in extramitochondrial electron transport and controls membrane physicochemical properties. CoQ10 effects on gene expression might affect the overall metabolism. Primary changes in the energetic and antioxidant functions can explain its remedial effects. CoQ10 supplementation is safe and well-tolerated, even at high doses. CoQ10 does not cause any serious adverse effects in humans or experimental animals. New preparations of CoQ10 that are less hydrophobic and structural derivatives, like idebenone and MitoQ, are being developed to increase absorption and tissue distribution. The review aims to summarize clinical and experimental effects of CoQ10 supplementations in some neurological diseases such as migraine, Parkinson´s disease, Huntington´s disease, Alzheimer´s disease, amyotrophic lateral sclerosis, Friedreich´s ataxia or multiple sclerosis. Cardiovascular hypertension was included because of its central mechanisms controlling blood pressure in the brainstem rostral ventrolateral medulla and hypothalamic paraventricular nucleus. In conclusion, it seems reasonable to recommend CoQ10 as adjunct to conventional therapy in some cases. However, sometimes CoQ10 supplementations are more efficient in animal models of diseases than in human patients (e.g. Parkinson´s disease) or rather vague (e.g. Friedreich´s ataxia or amyotrophic lateral sclerosis).

Intracellular hydrogen peroxide produced by 6-hydroxydopamine is a trigger for nigral dopaminergic degeneration of rats via rapid influx of extracellular Zn2

To elucidate the mechanism and significance of 6-hydroxydopamine (6-OHDA)-induced Zn²⁺ toxicity, which is involved in neurodegeneration in the substantia nigra pars compacta (SNpc) of rats, we postulated that intracellular hydrogen peroxide (H₂O₂) produced by 6-OHDA is a trigger for intracellular Zn²⁺ dysregulation in the SNpc. Intracellular H₂O₂ level elevated by 6-OHDA in the SNpc was completely inhibited by co-injection of GBR 13069 dihydrochloride (GBR), a dopamine reuptake inhibitor, suggesting that 6-OHDA taken up through dopamine transporters produces H₂O₂ in the intercellular compartment of dopaminergic neurons. When the SNpc was perfused with H₂O₂, glutamate accumulated in the extracellular compartment and the accumulation was inhibited in the presence of N-(p-amylcinnamoyl)anthranilic acid (ACA), a blocker of the transient receptor potential melastatin 2 (TRPM2) channels. In addition to 6-OHDA, H₂O₂ also induced intracellular Zn²⁺ dysregulation via AMPA receptor activation followed by nigral dopaminergic degeneration. Furthermore, 6-OHDA-induced nigral dopaminergic degeneration was completely inhibited by co-injection of either HYDROP, an intracellular H₂O₂ scavenger or GBR into the SNpc. The present study indicates that H₂O₂ is produced by 6-OHDA taken up through dopamine transporters in the SNpc, is retrogradely transported to presynaptic glutamatergic terminals, activates TRPM2 channels, accumulates glutamate in the extracellular compartment, and induces intracellular Zn²⁺ dysregulation via AMPA receptor activation, resulting in nigral dopaminergic degeneration prior to movement disorder. It is likely that intracellular H₂O₂, but not extracellular H₂O₂, is a key trigger for nigral dopaminergic degeneration via intracellular Zn²⁺ dysregulation.