A Long Journey into Aging, Brain Aging, and Alzheimer's Disease Following the Oxidative Stress Tracks

The Impact of New Biomarkers and Drug Targets on Age-Related Disorders

The increase in the human lifespan has not been paralleled by an increase in healthy life. With the increase in the proportion of the aged population, there has been a natural increase in the prevalence of age-related disorders, such as Alzheimer's disease, type 2 diabetes mellitus, frailty, and various other disorders. A continuous rise in these conditions could lead to a widespread medical and social burden. There are now considerable efforts underway to address these deficits in preclinical and clinical studies, which include the use of better study cohorts, longitudinal designs, improved translation of data from preclinical models, multi-omics profiling, identification of new biomarker candidates and refinement of computational tools and databases containing relevant information. Such efforts will support future interdisciplinary studies and help to identify potential new targets that are amenable to therapeutic approaches such as pharmacological interventions to increase the human healthspan in parallel with the lifespan.

Diabetes drugs in the fight against Alzheimer's disease

Alzheimer's disease (AD) is the most prevalent form of dementia, particularly in old age subjects. Hyperinsulinemia and insulin resistance, which are known as pathophysiological features of Type 2 Diabetes Mellitus (T2DM), have also been demonstrated to have a significant impact on cognitive impairment. Studies have shown that an altered insulin pathway may interact with amyloid-β protein deposition and tau protein phosphorylation, both leading factors for AD development. Drugs used for T2DM treatment from insulin and metformin through dipeptidyl peptidase-4 inhibitors and glucagon-like peptide-1 receptor agonists may represent a promising approach to fight AD. With this review from animal to human studies, we aim at responding to the reasons why drugs for diabetes may represent potential treatments for AD.

Bacopa monnieri, a Neuroprotective Lead in Alzheimer Disease: A Review on Its Properties, Mechanisms of Action, and Preclinical and Clinical Studies

Alzheimer disease is a neurodegenerative disease that is signified by cognitive decline, memory loss, and erratic behavior. Till date, no cure for Alzheimer exists and the current Alzheimer medications have limited effectiveness. However, herbal medicines may slow down the disease’s progression, which may hopefully reduce the number of cases in the years to come. Numerous studies have been done on characterizing the neuroprotective properties from plants belonging to Scrophulariaceae family, particularly Bacopa monnieri and its polyphenolic compounds known as bacosides. This review presents the findings on bacosides in therapeutic plants and their impact on Alzheimer disease pathology. These reports present data on the clinical, cellular activities, phytochemistry, and biological applications that may be used in new drug treatment for Alzheimer disease.

Hesperetin inhibits neuroinflammation on microglia by suppressing inflammatory cytokines and MAPK pathways

Neuroinflammation is a specific or nonspecific immunological reaction in the central nervous system that is induced by microglia activation. Appropriate regulation of activated microglial cells is therefore important for inhibiting neuroinflammation. Hesperetin is a natural flavanone and an aglycone of hesperidin that is found in citrus fruits. Hesperetin reportedly possesses anti-inflammatory, anti-cancer, and antioxidant effects. However, the anti-neuroinflammatory effects of hesperetin on microglia are still unknown. Here, we investigated the anti-neuroinflammatory effects of hesperetin on lipopolysaccharide (LPS)-stimulated BV-2 microglial cells. We found that hesperetin strongly inhibited nitric oxide production and expression of inducible nitric oxide synthase in LPS-stimulated BV-2 microglial cells. Hesperetin also significantly reduced secretion of inflammatory cytokines including interleukin (IL)-1β and IL-6. Furthermore, hesperetin down-regulated the phosphorylation of extracellular signal-regulated kinase (ERK)1/2 and p38 mitogen-activated protein kinase, exerting anti-inflammatory effects. Hesperetin suppressed astrocyte and microglia activation in the LPS-challenged mouse brain. Collectively, our findings indicate that hesperetin inhibits microglia-mediated neuroinflammation and could be a prophylactic treatment for neurodegenerative diseases.

Vitamin E and Alzheimer's disease: what do we know so far?

Vitamin E has been proposed as a potential clinical intervention for Alzheimer's disease (AD) given the plausibility of its various biological functions in influencing the neurodegenerative processes associated with the condition. The tocopherol and tocotrienol isoforms of vitamin E have multiple properties including potent antioxidant and anti-inflammatory characteristics, in addition to influences on immune function, cellular signalling and lowering cholesterol. Several of these roles offer a theoretical rationale for providing benefit for the treatment of AD-associated pathology. Diminished circulating concentrations of vitamin E have been demonstrated in individuals with AD. Reduced plasma levels have furthermore been associated with an increased risk of AD development while intake, particularly from dietary sources, may limit or reduce the rate of disease progression. This benefit may be linked to synergistic actions between vitamin E isoforms and other micronutrients. Nevertheless, randomised trials have found limited and inconsistent evidence of vitamin E supplementation as an effective clinical intervention. Thus, despite a strong rationale in support of a beneficial role for vitamin E for the treatment of AD, the evidence remains inconclusive. Several factors may partly explain this discrepancy and represent the difficulties of translating complex laboratory evidence and dietary interactions into clinical interventions. Methodological design limitations of existing randomised trials and restrictions to supplementation with a single vitamin E isoform may also limit the influence of effect. Moreover, several factors influence individual responsiveness to vitamin E intake and recent findings suggest variation in the underlying genetic architecture attenuates vitamin E biological availability and activity which likely contributes to the variation in clinical responsiveness and the failure of randomised trials to date. Importantly, the clinical safety of vitamin E remains controversial and warrants further investigation.

Mitochondria- and Oxidative Stress-Targeting Substances in Cognitive Decline-Related Disorders: From Molecular Mechanisms to Clinical Evidence

Alzheimer's disease (AD) is the most common form of dementia affecting people mainly in their sixth decade of life and at a higher age. It is an extensively studied neurodegenerative disorder yet incurable to date. While its main postmortem brain hallmarks are the presence of amyloid-β plaques and hyperphosphorylated tau tangles, the onset of the disease seems to be largely correlated to mitochondrial dysfunction, an early event in the disease pathogenesis. AD is characterized by flawed energy metabolism in the brain and excessive oxidative stress, processes that involve less adenosine triphosphate (ATP) and more reactive oxygen species (ROS) production respectively. Mitochondria are at the center of both these processes as they are responsible for energy and ROS generation through mainly oxidative phosphorylation. Standardized Ginkgo biloba extract (GBE), resveratrol, and phytoestrogens as well as the neurosteroid allopregnanolone have shown not only some mitochondria-modulating properties but also significant antioxidant potential in in vitro and in vivo studies. According to our review of the literature, GBE, resveratrol, allopregnanolone, and phytoestrogens showed promising effects on mitochondria in a descending evidence order and, notably, this order pattern is in line with the existing clinical evidence level for each entity. In this review, the effects of these four entities are discussed with special focus on their mitochondria-modulating effects and their mitochondria-improving and antioxidant properties across the spectrum of cognitive decline-related disorders. Evidence from preclinical and clinical studies on their mechanisms of action are summarized and highlighted.

Associations of Lipophilic Micronutrients with Physical and Cognitive Fitness in Persons with Mild Cognitive Impairment

Age-associated cognitive impairment in general and dementia in particular are a global concern. Preventive lifestyle strategies are highly used but there is a lack of information on the reciprocal relationships between nutrition biomarkers and measures of both cognitive and physical performance. To fill this gap of knowledge, the relationship between plasma levels of the robust nutrition- and antioxidant defense-related biomarkers carotenoid and tocopherols and both indicators of cognitive and physical performance was investigated in a group of persons with mild cognitive impairment participating in the NeuroExercise Study at the German Sport University in Cologne, Germany. In 56 participants with full dataset, significant correlations independently of fruit and vegetable intake were found between plasma levels of β-cryptoxanthin and Timed Up&Go test (p < 0.05), γ-tocopherol and number of daily steps (p < 0.01), as well as between four out of six measured carotenoids—lutein; zeaxanthin; β-cryptoxanthin and β-carotene—and the computerized CogState International Shopping List subtest (p < 0.01). In light of the increasing attention towards the nutritional cognitive neuroscience of carotenoids, computerized measures of cognitive performance might be further implemented in future studies investigating the effects of lifestyle interventions against cognitive and physical impairment.

Rat Glioma Cell-Based Functional Characterization of Anti-Stress and Protein Deaggregation Activities in the Marine Carotenoids, Astaxanthin and Fucoxanthin

Stress, protein aggregation, and loss of functional properties of cells have been shown to contribute to several deleterious pathologies including cancer and neurodegeneration. The incidence of these pathologies has also been shown to increase with age and are often presented as evidence to the cumulative effect of stress and protein aggregation. Prevention or delay of onset of these diseases may prove to be unprecedentedly beneficial. In this study, we explored the anti-stress and differentiation-inducing potential of two marine bioactive carotenoids (astaxanthin and fucoxanthin) using rat glioma cells as a model. We found that the low (nontoxic) doses of both protected cells against UV-induced DNA damage, heavy metal, and heat-induced protein misfolding and aggregation of proteins. Their long-term treatment in glioma cells caused the induction of physiological differentiation into astrocytes. These phenotypes were supported by upregulation of proteins that regulate cell proliferation, DNA damage repair mechanism, and glial differentiation, suggesting their potential for prevention and treatment of stress, protein aggregation, and age-related pathologies.

Icariin Delays Brain Aging in Senescence-Accelerated Mouse Prone 8 (SAMP8) Model via Inhibiting Autophagy

Icariin (ICA), a major flavonoid extracted from the Chinese tonic herb Epimedium, exerts beneficial effects in a variety of age-dependent diseases, such as Alzheimer's disease (AD). However, the antiaging mechanisms remain unclear. The senescence-accelerated mouse-prone 8 (SAMP8) model has been used to study age-related neurodegenerative changes associated with aging and the pathogenesis of AD. Hence, the current study was designed to examine the effect of ICA on age-related cognitive decline in SAMP8 mice and explore the role of autophagy in the ICA-mediated neuroprotection. SAMP8 mice were administered with ICA starting at 5 months of age, and the treatment lasted for 3 consecutive months. Morris water maze was used to evaluate cognitive function. The senescence-associated β-galactosidase staining was used to determine the number of senescence cells. The neuronal morphologic changes were examined via Nissl staining. The hippocampal neuronal ultrastructure was examined by transmission electron microscopy. The expression of autophagy protein was examined by Western blot. ICA-treated SAMP8 mice exhibited a robust improvement in spatial learning and memory function. Meanwhile, ICA reduced the number of senescence cells in the brains of SAMP8 mice, inhibited neuronal loss, and reversed neuronal structural changes in the hippocampi of SAMP8 mice. Moreover, ICA treatment also decreased the formation of autophagosomes in the hippocampus of SAMP8 mice, and reduced the expression of autophagy-related proteins LC3-II and p62. These results demonstrate that ICA possesses the ability to delay brain aging in SAMP8 mice, and the mechanisms are possibly mediated through the regulation of autophagy.

The potent therapeutic effect of novel cyanobacterial isolates against oxidative stress damage in redox rats

AIMS

Cyanobacteria are immense sources of several pharmacological active compounds such as flavonoids and carotenoids with anti-inflammatory and antioxidant activity. The potential therapeutic effect of two novel cyanobacterial isolates, Cronbergia siamensis (KY296358.1) and Sphaerospermopsis aphanizomenoides (KU212886.1), against hydrogen peroxide (H₂ O₂ )-induced oxidative stress damage in the rat model was determined in this study.

METHODS AND RESULTS

In vitro antioxidant activity of the two studied isolates was evaluated by radical scavenging assay and ferric reducing power. The possible prophylactic activity of S. aphanizomenoides (KU212886.1) against H₂ O₂ -induced oxidative stress in the rat model was assessed in vivo. Serum alanine transaminase and aspartate transaminase were measured for the liver functions in redox rats. Liver malondialdehyde (MDA), glutathione, oxidized glutathione, nitric oxide, superoxide dismutase (SOD) and catalase (CAT) were assessed as oxidative stress markers. The effect of S. aphanizomenoides on the transcripts level of superoxide dismutase (Mn-SOD) and catalase (CAT) genes in the rat's liver tissues was measured using qRT-PCR. Oral administration of S. aphanizomenoides extract in low and high doses (100, 200 mg kg^-1 b.w) resulted in significant improvement in biochemical parameters of liver functions and oxidative stress markers. Also, the endogenous antioxidant defence enzymes and the expression of their related genes (Mn/SOD, CAT) were upregulated. Immunohistochemistry of Caspase-3, an apoptotic marker, showed potent amelioration in the liver tissues.

CONCLUSIONS

The novel isolate S. aphanizomenoides proved in vitro and in vivo antioxidant activity against redox rat model.

SIGNIFICANCE AND IMPACT OF THE STUDY

This isolate provides a new source of pharmacological compounds with great importance in pharmacological and medical fields.

Nrf2/ARE Pathway Modulation by Dietary Energy Regulation in Neurological Disorders

Nuclear factor erythroid 2-related factor 2 (Nrf2) regulates the expression of an array of enzymes with important detoxifying and antioxidant functions. Current findings support the role of high levels of oxidative stress in the pathogenesis of neurological disorders. Given the central role played by Nrf2 in counteracting oxidative damage, a number of studies have targeted the modulation of this transcription factor in order to confer neuroprotection. Nrf2 activity is tightly regulated by oxidative stress and energy-based stimuli. Thus, many dietary interventions based on energy intake regulation, such as dietary energy restriction (DER) or high-fat diet (HFD), modulate Nrf2 with consequences for a variety of cellular processes that affect brain health. DER, by either restricting calorie intake or meal frequency, activates Nrf2 thereby triggering its protective effects, whilst HFD inhibit this pathway, thereby exacerbating oxidative stress. Consequently, DER protocols can be valuable strategies in the management of central nervous system (CNS) disorders. Herein, we review current knowledge of the role of Nrf2 signaling in neurological diseases, namely Alzheimer’s disease, Parkinson’s disease, multiple sclerosis and cerebral ischemia, as well as the potential of energy intake regulation in the management of Nrf2 signaling.

Gene expression patterns indicate that a high-fat–high-carbohydrate diet causes mitochondrial dysfunction in fish

Expensive and unsustainable fishmeal is increasingly being replaced with cheaper lipids and carbohydrates as sources of energy in aquaculture. Although it is known that the excess of lipids and carbohydrates has negative effects on nutrient utilization, growth, metabolic homeostasis, and health of fish, our current understanding of mechanisms behind these effects is limited. To improve the understanding of diet-induced metabolic disorders (both in fish and other vertebrates), we conducted an eight-week high-fat–high-carbohydrate diet feeding trial on blunt snout bream (Megalobrama amblycephala), and studied gene expression changes (transcriptome and qPCR) in the liver. Disproportionately large numbers of differentially expressed genes were associated with mitochondrial metabolism, neurodegenerative diseases (Alzheimer’s, Huntington’s, and Parkinson’s), and functional categories indicative of liver dysfunction. A high-fat–high-carbohydrate diet may have caused mitochondrial dysfunction, and possibly downregulated the mitochondrial biogenesis in the liver. While the relationship between diet and neurodegenerative disorders is well-established in mammals, this is the first report of this connection in fish. We propose that fishes should be further explored as a potentially promising model to study the mechanisms of diet-associated neurodegenerative disorders in humans.

Nutrition and prevention of cognitive impairment

Nutrition is an important lifestyle factor that can modify the risk of future cognitive impairment and dementia. Some, but not conclusive, evidence (mostly from observational studies and infrequently from clinical trials) exists of a protective association between certain nutrients (eg, folate, flavonoids, vitamin D, and certain lipids) or food groups (eg, seafood, vegetables, and fruits, and potentially moderate alcohol and caffeine consumption) and cognitive outcomes in older people. For some nutrients and food groups, protection might be greater in individuals with either deficiencies in certain nutrients or a genetic predisposition to cognitive impairment. Identification of potentially different associations between such subgroups should be a priority for future research. At present, evidence of an association between nutrition and cognitive outcomes is somehow stronger for healthy dietary patterns, such as the Mediterranean-type diet, than for individual nutrients and food groups, possibly because of the cumulative beneficial effects of the many ingredients in these diets. Multidomain interventions (including a nutrition component) might also hold some promise for the prevention of cognitive impairment and dementia, but their effectiveness is still uncertain. Use of advanced technologies for nutrition assessment (eg, metabolomics and innovative methods of dietary intake assessment) and recently identified biomarkers of nutrition and neurobiological outcomes will be important to achieve this goal.

Enhanced activity of superoxide dismutase is a common response to dietary and genetically induced increased cholesterol levels

Objectives: Hypercholesterolaemia has been implicated in the pathogenesis of neurodegenerative diseases. In this work, we tested whether cholesterol-mediated neurodegeneration induced either by cholesterol-rich diet or genetic mutation may share a common mechanism involving increased oxidative stress and mitochondria oxidant status. Additionally, we analysed whether upon cholesterol-rich diet, different brain regions (prefrontal cortex, cortex, hippocampus, and cerebellum) show distinct vulnerability to an oxidative stress response.Methods: Oxidative stress parameters were measured both in vivo (in the liver and in different brain regions) in cholesterol-fed mice and in vitro in genetically induced cholesterol accumulation in NPC1-null cells.Results: Increased superoxide dismutase (SOD) activity was a common feature of cholesterol-mediated antioxidant response in both models. Moreover, upon high-cholesterol diet, all four brain regions analysed responded via somewhat different capacity of antioxidant defence, hippocampus showing the highest basal activity of SOD. Increased activity of SOD upon cholesterol accumulation in vitro involves mitochondrial SOD2. We found that SOD/SOD2 activities are modulated by cholesterol levels.Discussion: Hypercholesterolaemia could potentiate brain dysfunction and neurodegenerative processes via oxidative stress, and activity of mitochondrial SOD2 may play a key role in this process. Our findings suggest that preventing/reducing mitochondrial oxidative stress may represent a common approach against neurodegenerative diseases.

Aerobic exercise-stimulated Klotho upregulation extends life span by attenuating the excess production of reactive oxygen species in the brain and kidney

Aerobic exercise induces many adaptive changes in the whole body and improves metabolic characteristics. Klotho, an anti-aging gene, is mainly expressed in the brain and kidney. The roles of Klotho in the brain and kidney during aerobic exercise remain largely unknown. The present study aimed to determine whether aerobic exercise could influence the expression of Klotho, decrease reactive oxygen species (ROS) and prolong life span. Sprague Dawley rats were exercised on a motor treadmill. Klotho mRNA and protein expression levels in rat brain and kidney tissues were examined using reverse transcription-quantitative polymerase chain reaction and western blotting, respectively. ROS production was detected following intermittent aerobic exercise (IAE) or continuous aerobic exercise (CAE). Kaplan-Meier curve analysis demonstrated that aerobic exercise significantly improved rat survival (P<0.001). The ROS levels in rat brain and kidney tissues were decreased in the aerobic exercise groups compared with the control group (P<0.05). In addition, Klotho mRNA and protein expression levels were increased significantly following aerobic exercise compared with controls (P<0.05). There was no significant difference between the IAE and CAE groups in any experiments (P>0.05). These results suggest that aerobic exercise-stimulated Klotho upregulation extends the life span by attenuating the excess production of ROS in the brain and kidney. As Klotho exhibits a potential anti-aging effect, promoting Klotho expression through aerobic exercise may be a novel approach for the prevention and treatment of aging and aging-related diseases.