Tryptophan-related dipeptides in fermented dairy products suppress microglial activation and prevent cognitive decline

Molecular Mechanisms of Dietary Bioactive Peptides in Treating Alzheimer's Disease and Mild Cognitive Impairment by Network Pharmacology and Molecular Docking Analysis

Emerging evidence suggests that bioactive peptides from various foods have therapeutic potentials in improving cognitive function in Alzheimer's disease (AD) and mild cognitive impairment (MCI). We aimed to explore the characteristics of these peptides and their mechanisms on AD/MCI using a network pharmacology approach. We compiled a dataset of cognition-enhancing peptides from literatures and identified shared targets between these peptides and AD/MCI using Swiss Target Predication, PharmMapper, OMIM, GeneCards, TTD, and Drugbank databases. We then performed functional enrichment analysis and constructed a gene-gene interaction network to identify key hub targets. Additionally, we investigated the transcription factors (TFs) and microRNAs (miRNAs) regulating these hub genes. Molecular docking and dynamic simulations were performed using AutoDock Vina and GROMACS. We identified 59 cognition-enhancing oligopeptides, typically short and rich in arginine. These peptides were predicted to interact with 222 potential targets relevant to AD/MCI, with functional pathways mainly involving neuroactive ligand-receptor interactions and inflammation. We identified 15 hub targets, regulated by 144 TFs and 95 miRNAs. Notably, peptides containing the "Trp-Tyr" sequence demonstrated strong binding affinities to many hub targets, especially matrix metalloproteinase-9. The findings provided valuable insights into the molecular mechanisms through which bioactive peptides may act against AD/MCI and highlight the potential of network pharmacology for future exploration of bioactive peptides from natural foods.

Bioactive peptides as multipotent molecules bespoke and designed for Alzheimer's disease

In an increasingly aging world where neurodegenerative diseases (NDs) are exponentially rising, research into more effective and innovative treatments seems paramount. Bioactive peptides (BPs) emerge as promising compounds with revolutionary potential in the treatment of NDs, particularly in well-known conditions like Alzheimer's disease (AD). The biological potential of these compounds is primarily attributed to their drug development advantages such as enhanced penetration, low toxicity, and rapid clearance, as well as, their antioxidant, and anti-inflammatory properties bio-linked to the neuroprotective effect, able to attenuate the multifactorial pathologies of AD. BPs can be sourced from common dietary origins, like animals, plants, marine, and from emerging sources like edible insects. However, to isolate an active BP with beneficial biological effects it must first be released from its parent protein, followed by a synthesis-flow. While in silico approaches can predict a BP's potential bioactivity and structural characteristics, in vitro, cell-based, and in vivo assays should be conducted to ensure these properties. The blood-brain-barrier (BBB) microenvironment and permeability in health or disease state are key factors to consider since they can limit the ability of circulating therapeutical agents, including BPs, to reach the brain. This review focuses on the bioactivity properties of BPs from different dietary protein sources and explores their beneficial effect and neuroprotective activity in AD, unraveling new paths of treatment.

Gut microbiota in Alzheimer's disease: Understanding molecular pathways and potential therapeutic perspectives

Accumulating evidence suggests that gut microbiota (GM) plays a crucial role in Alzheimer's disease (AD) pathogenesis and progression. This narrative review explores the complex interplay between GM, the immune system, and the central nervous system in AD. We discuss mechanisms through which GM dysbiosis can compromise intestinal barrier integrity, enabling pro-inflammatory molecules and metabolites to enter systemic circulation and the brain, potentially contributing to AD hallmarks. Additionally, we examine other pathophysiological mechanisms by which GM may influence AD risk, including the production of short-chain fatty acids, secondary bile acids, and tryptophan metabolites. The role of the vagus nerve in gut-brain communication is also addressed. We highlight potential therapeutic implications of targeting GM in AD, focusing on antibiotics, probiotics, prebiotics, postbiotics, phytochemicals, and fecal microbiota transplantation. While preclinical studies showed promise, clinical evidence remains limited and inconsistent. We critically assess clinical trials, emphasizing challenges in translating GM-based therapies to AD patients. The reviewed evidence underscores the need for further research to elucidate precise molecular mechanisms linking GM to AD and determine whether GM dysbiosis is a contributing factor or consequence of AD pathology. Future studies should focus on large-scale clinical trials to validate GM-based interventions' efficacy and safety in AD.

Nutrition: A non-negligible factor in the pathogenesis and treatment of Alzheimer's disease

Alzheimer's disease (AD) is a degenerative disease characterized by progressive cognitive dysfunction. The strong link between nutrition and the occurrence and progression of AD pathology has been well documented. Poor nutritional status accelerates AD progress by potentially aggravating amyloid beta (Aβ) and tau deposition, exacerbating oxidative stress response, modulating the microbiota-gut-brain axis, and disrupting blood-brain barrier function. The advanced stage of AD tends to lead to malnutrition due to cognitive impairments, sensory dysfunctions, brain atrophy, and behavioral and psychological symptoms of dementia (BPSD). This, in turn, produces a vicious cycle between malnutrition and AD. This review discusses how nutritional factors and AD deteriorate each other from the early stage of AD to the terminal stages of AD, focusing on the potential of different levels of nutritional factors, ranging from micronutrients to diet patterns. This review provides novel insights into reducing the risk of AD, delaying its progression, and improving prognosis. HIGHLIGHTS: Two-fifths of Alzheimer's disease (AD) cases worldwide have been attributed to potentially modifiable risk factors. Up to ≈26% of community-dwelling patients with AD are malnourished, compared to 7%∼76% of institutionalized patients. Undernutrition effects the onset, progression, and prognosis of AD through multiple mechanisms. Various levels of nutritional supports were confirmed to be protective factors for AD via specific mechanisms.

Impact of Peptide Transport and Memory Function in the Brain

Recent studies have reported the benefits of food-derived peptides for memory dysfunction. Beyond the physiological effects of peptides, their bioavailability to the brain still remains unclear since the blood-brain barrier (BBB) strictly controls the transportation of compounds to the brain. Here, updated transportation studies on BBB transportable peptides are introduced and evaluated using in vitro BBB models, in situ perfusion, and in vivo mouse experiments. Additionally, the mechanisms of action of brain health peptides in relation to the pathogenesis of neurodegenerative diseases, particularly Alzheimer's disease, are discussed. This discussion follows a summary of bioactive peptides with neuroprotective effects that can improve cognitive decline through various mechanisms, including anti-inflammatory, antioxidative, anti-amyloid β aggregation, and neurotransmitter regulation.

A Comparative Study of the Stability, Transport, and Structure-Activity Relationship of Round Scad Derived Peptides with Antineuroinflammatory Ability

Our previous study identified round scad neuroprotective peptides with different characteristics. However, the intrinsic relationship between their structure and bioactivity, as well as their bioavailability, remains unclear. The aim of this study is to elucidate the bioavailability of these peptides and their structure-activity relationship against neuroinflammation. Results showed that the SR and WCP peptides were resistant to gastrointestinal digestion. Additionally, peptides SR, WCP, and WCPF could transport Caco-2 monolayers as intact peptides. The permeability coefficients (Papp) of SR, WCP, and WCPF in Caco-2 monolayer were (1.53 ± 0.01) × 10-5, (2.12 ± 0.01) × 10-5, and (8.86 ± 0.03) × 10-7 cm/s, respectively. Peptides SR, WCP, and WCPF, as promising inhibitors of JAK2 and STAT3, could attenuate the levels of pro-inflammatory cytokines and regulate the NFκB and JAK2/STAT3 signaling pathway in LPS-treated BV-2 cells. WCPF exerted the highest anti-inflammatory activity. Moreover, bioinformatics, molecular docking, and quantum chemistry studies indicated that the bioactivity of SR was attributed to Arg, whereas those of WCP and WCPF were attributed to Trp. This study supports the application of round-scad peptides and deepens the understanding of the structure-activity relationship of neuroprotective peptides.

Comparison of the Protective Effects of Casein Hydrolysate Containing Tyr-Pro-Val-Glu-Pro-Phe and Casein on the Behaviors and Peripheral and Brain Functions in Mice with Chronic-Stress-Induced Anxiety and Insomnia

Chronic stress is a major inducer of anxiety and insomnia. Milk casein has been studied for its stress-relieving effects. We previously prepared a casein hydrolysate (CP) rich in the sleep-enhancing peptide YPVEPF, and this study aims to systemically investigate the different protective effects of CP and casein on dysfunction and anxiety/insomnia behavior and its underlying mechanisms in chronically stressed mice. Behavioral results showed that CP ameliorated stress-induced insomnia and anxiety more effectively than milk casein, and this difference in amelioration was highly correlated with an increase in GABA, 5-HT, GABAA, 5-HT1A receptors, and BDNF and a decrease in IL-6 and NMDA receptors in stressed mice. Furthermore, CP restored these dysfunctions in the brain and colon by activating the HPA response, modulating the ERK/CREB-BDNF-TrκB signaling pathway, and alleviating inflammation. The abundant YPVEPF (1.20 ± 0.04%) and Tyr-based/Trp-containing peptides of CP may be the key reasons for its different effects compared to casein. Thus, this work revealed the main active structures of CP and provided a novel dietary intervention strategy for the prevention and treatment of chronic-stress-induced dysfunction and anxiety/insomnia behaviors.

Adiponectin-Receptor Agonistic Dipeptide Tyr-Pro Stimulates the Acetylcholine Nervous System in NE-4C Cells

The dipeptide Tyr-Pro has physiological potential for intact transportability into the brain parenchyma, prevention of cognitive impairment, and an adiponectin receptor 1 (AdipoR1) agonistic effect. The present study aimed to understand the effect of Tyr-Pro on the acetylcholine (ACh) nervous system and its underlying mechanism in NE-4C nerve cells. Concentration-dependent ACh production was induced by stimulation with Tyr-Pro and AdipoRon (an AdipoR1 agonist), along with the expression of AdipoR1 and choline acetyltransferase (ChAT) in NE-4C cells. By knocking down AdipoR1 in the cells, Tyr-Pro promoted ChAT expression, along with the activations of AMPK and ERK 1/2. Tyr-Pro did not alter acetylcholinesterase or ACh receptors, indicating that the dipeptide might operate as an ACh accelerator in nerve cells. This study provides the first evidence that the AdipoR1 agonistic Tyr-Pro is a promising dipeptide responsible for the stimulation of the ACh nervous system by AdipoR1-induced ChAT activation.

Sports Diet and Oral Health in Athletes: A Comprehensive Review

Food and fluid supply is fundamental for optimal athletic performance but can also be a risk factor for caries, dental erosion, and periodontal diseases, which in turn can impair athletic performance. Many studies have reported a high prevalence of oral diseases in elite athletes, notably dental caries 20-84%, dental erosion 42-59%, gingivitis 58-77%, and periodontal disease 15-41%, caused by frequent consumption of sugars/carbohydrates, polyunsaturated fats, or deficient protein intake. There are three possible major reasons for poor oral health in athletes which are addressed in this review: oxidative stress, sports diet, and oral hygiene. This update particularly summarizes potential sports nutritional effects on athletes' dental health. Overall, sports diet appropriately applied to deliver benefits for performance associated with oral hygiene requirements is necessary to ensure athletes' health. The overall aim is to help athletes, dentists, and nutritionists understand the tangled connections between sports diet, oral health, and oral healthcare to develop mitigation strategies to reduce the risk of dental diseases due to nutrition.

Effect of dairy consumption on cognition in older adults: A population-based cohort study

OBJECTIVE

We aimed to assess the effect on cognitive function of adding dairy (total, fermented, non-fermented, full fat, low fat, and sugary) to the diet and of substituting some food groups for dairy.

DESIGN

Secondary analysis of a prospective population-based cohort study.

PARTICIPANTS

We analyzed data from 1334 cognitively healthy participants (median age 67 years at baseline) with a mean follow-up of 5.6 years from the CoLaus|PsyColaus cohort in Lausanne, Switzerland.

MEASUREMENTS

The participants completed a food frequency questionnaire at baseline and cognitive tests at baseline and at follow-up. Clinical dementia rating was the primary outcome. Subjective cognitive decline, memory, verbal fluency, executive and motor functions were secondary outcomes.

METHODS

Our exposure was the consumption of total and 5 sub-types of dairy products (g/d). We used marginal structural models to compute average causal effects of 1) increasing dairy consumption by 100 g/d and 2) substituting 100 g/d of meat, fish, eggs, fruits and vegetables with dairy on the outcomes. We used inverse probability of the treatment and lost to follow-up weighting to account for measured confounding and non-random loss to follow-up.

RESULTS

Overall, the effects of adding dairy products to the diet on cognition were negligible and imprecise. No substitution had a substantial and consistent effect on clinical dementia rating. The substitution of fish [11.7% (-3% to 26.5%)] and eggs [18% (2.3%-33.7%)] for dairy products could negatively impact verbal memory and neurolinguistic processes.

CONCLUSION

We found no effect of adding dairy to the diet or substituting meat, vegetables or fruit for dairy on cognitive function in this cohort of older adults. The substitution of fish and eggs for dairy could have a negative effect on some secondary outcomes, but more studies modeling food substitutions are needed to confirm these results.

Food-derived Peptides as Promising Neuroprotective Agents: Mechanism and Therapeutic Potential

Many food-derived peptides have the potential to improve brain health and slow down neurodegeneration. Peptides are produced by the enzymatic hydrolysis of proteins from different food sources. These peptides have been shown to be involved in antioxidant and anti-inflammatory activity, neuro-transmission modulation, and gene expression regulation. Although few peptides directly affect chromatin remodeling and histone alterations, others indirectly affect the neuroprotection process by interfering with epigenetic changes. Fish-derived peptides have shown neuroprotective properties that reduce oxidative stress and improve motor dysfunction in Parkinson's disease models. Peptides from milk and eggs have been found to have anti-inflammatory properties that reduce inflammation and improve cognitive function in Alzheimer's disease models. These peptides are potential therapeutics for neurodegenerative diseases, but more study is required to assess their efficacy and the underlying neuroprotective benefits. Consequently, this review concentrated on each mechanism of action used by food-derived peptides that have neuroprotective advantages and applications in treating neurodegenerative diseases. This article highlights various pathways, such as inflammatory pathways, major oxidant pathways, apoptotic pathways, neurotransmitter modulation, and gene regulation through which food-derived peptides interact at the cellular level.

Dairy Intake and Risk of Cognitive Decline and Dementia: A Systematic Review and Dose-Response Meta-Analysis of Prospective Studies

Dairy intake may influence cognition through several molecular pathways. However, epidemiologic studies yield inconsistent results, and no dose-response meta-analysis has been conducted yet. Therefore, we performed a systematic review with a dose-response meta-analysis about the association between dairy intake and cognitive decline or incidence of dementia. We investigated prospective studies with a follow-up ≥6 mo on cognitive decline or dementia incidence in adults without known chronic conditions through a systematic search of Embase, Medline, Cochrane Library, Web of Science, and Google Scholar from inception to 11 July 2023. We evaluated the dose-response association using a random-effects model. We identified 15 eligible cohort studies with >300,000 participants and a median follow-up of 11.4 y. We observed a negative nonlinear association between cognitive decline/dementia incidence and dairy intake as assessed through the quantity of consumption, with the nadir at ∼150 g/d (risk ratio: 0.88; 95% confidence interval: 0.78, 0.99). Conversely, we found an almost linear negative association when we considered the frequency of consumption (risk ratio for linear trend: 0.84; 95% confidence interval: 0.77, 0.92 for 1 time/d increase of dairy products). Stratified analysis by dairy products showed different shapes of the association with linear inverse relationship for milk intake, whereas possibly nonlinear for cheese. The inverse association was limited to Asian populations characterized by generally lower intake of dairy products, compared with the null association reported by European studies. In conclusion, our study suggests a nonlinear inverse association between dairy intake and cognitive decline or dementia, also depending on dairy types and population characteristics, although the heterogeneity was still high in overall and several subgroup analyses. Additional studies should be performed on this topic, including a wider range of intake and types of dairy products, to confirm a potential preventing role of dairy intake on cognitive decline and identify ideal intake doses. This review was registered at PROSPERO as CRD42020192395.

A memory-improving dipeptide, Tyr-Pro, can reach the mouse brain after oral administration

The transport and accumulation of orally administered functional food-derived peptides in the brain was not fully explored. Thus, in the present study, we aimed to provide critical evidence regarding brain accumulation of a memory-improving soy dipeptide, Tyr-Pro, following oral administration. Stable isotope-labeled Tyr-Pro (Tyr-[13C5,15N]Pro) was orally administered to male ICR mice at 10 or 100 mg/kg. Surprisingly, the intact labeled Tyr-Pro exhibited maximal plasma and brain levels 15 min after administration (plasma: area under the curve [AUC0-120 min], 1331 ± 267 pmol·min/mL-plasma; brain: AUC0-120 min of 0.34 ± 0.11 pmol·min/mg-dry brain, at 10 mg/kg). In addition, we detected labeled Tyr-Pro in the brain parenchyma, indicating a validated blood-brain-barrier (BBB) transportability. Moreover, we confirmed the preferable accumulation of Tyr-Pro in the hypothalamus, hippocampus, and cortex with > 0.02 pmol/mg-tissue. In conclusion, we provided the first evidence that orally administered Tyr-Pro at 10 mg/kg directly entered the blood circulation with an absorption ratio of 0.15%, of which 2.5% of Tyr-Pro was transported from the plasma to the mouse brain parenchyma.

Dietary Protection against Cognitive Impairment, Neuroinflammation and Oxidative Stress in Alzheimer's Disease Animal Models of Lipopolysaccharide-Induced Inflammation

Alzheimer's disease (AD) is a rapidly growing epidemic with a heavy social and economic burden. Evidence suggests that systemic inflammation, dysregulation of the immune response and the resulting neuroinflammation and neurodegeneration play a significant role in AD pathogenesis. Currently, given that there is no fully convincing cure for AD, the interest in lifestyle factors (such as diet), which potentially delay onset and reduce the severity of symptoms, is increasing. This review is aimed at summarizing the effects of dietary supplementation on cognitive decline, neuroinflammation and oxidative stress in AD-like animal models with a focus on neuroinflammation induced by lipopolysaccharide (LPS) injection, which mimics systemic inflammation in animals. The compounds reviewed include curcumin, krill oil, chicoric acid, plasmalogens, lycopene, tryptophan-related dipeptides, hesperetin and selenium peptides. Despite the heterogeneity of these compounds, there is a strong consensus on their counteracting action on LPS-induced cognitive deficits and neuroinflammatory responses in rodents by modulating cell-signaling processes, such as the NF-κB pathway. Overall, dietary interventions could represent an important resource to oppose AD due to their influence in neuroprotection and immune regulation.

Rice-memolin, a novel peptide derived from rice bran, improves cognitive function after oral administration in mice

Many people eat polished rice, while rice bran, a by-product known to be rich in protein and expected to have potential functions for health benefits, has not been effectively utilized. In this study, we determined that orally administered Val-Tyr-Thr-Pro-Gly (VYTPG) derived from rice bran protein improved cognitive decline in mice fed a high-fat diet (HFD). It was demonstrated that VYTPG was released from model peptides corresponding to fragment sequences of original rice proteins (Os01g0941500, Os01g0872700, and allergenic protein) after treatment with thermolysin, a microorganism-derived enzyme often used in industrial scale processes. The thermolysin digest also improved cognitive decline after oral administration in mice. Because VYTPG (1.0 mg/kg) potently improved cognitive decline and is enzymatically produced from the rice bran, we named it rice-memolin. Next, we investigated the mechanisms underlying the cognitive decline improvement associated with rice-memolin. Methyllycaconitine, an antagonist for α7 nicotinic acetylcholine receptor, suppressed the rice-memolin-induced effect, suggesting that rice-memolin improved cognitive decline coupled to the acetylcholine system. Rice-memolin increased the number of 5-bromo-2'-deoxyuridine (BrdU)-positive cells and promoted the mRNA expression of EGF and FGF-2 in the hippocampus, implying that these neurotropic factors play a role in hippocampal neurogenesis after rice-memolin administration. Epidemiologic studies demonstrated that diabetes is a risk factor for dementia; therefore, we also examined the effect of rice-memolin on glucose metabolism. Rice-memolin improved glucose intolerance. In conclusion, we identified a novel rice-derived peptide that can improve cognitive decline. The mechanisms are associated with acetylcholine and hippocampal neurogenesis. Rice-memolin is the first rice-brain-derived peptide able to improve cognitive decline.

Derivatization to increase the detectability of small peptides in blood serum in the analysis by ESI and MALDI high resolution mass spectrometric methods

This work highlights the efficient approach to highly sensitive determination of dipeptides that can present in biological liquids at very low and trace quantities. The approach involves preliminary derivatization of peptides with tris(2,4,6-trimethoxyphenyl)-methyl carbenium hexafluoroborate followed by ESI and MALDI high-resolution mass spectrometry. Using model dipeptides with various amino acid compositions and sequences, it was shown that the derivatization reaction proceeded smoothly in mild conditions and gave rise to pink-red colored salt derivatives. Ready cations of interest for the analysis are easily desorbed from the salt-derivatives providing strong signals in ESI and MALDI mass spectra and this ensures high sensitivity of the analysis. Another positive aspect is the removal of the target signal from the region of a matrix noise, since the introduced fragment possesses a large mass increment (359 Da). High resolution mass spectrometry, which provides the determination of accurate weights and elemental compositions of ions, was used to reliably detect model dipeptides added to artificial urine and blood serum. A number of these dipeptides was shown to be present in real blood serum collected from volunteers. Collision induced dissociation of precursor cations composed of derivatizing reagent and dipeptide moieties gives rise to characteristic and simple fragmentation mass spectra. A comparison of limits of detection (LOD) measured for non-modified and derivatized dipeptides showed that the latter derivatives provide the highest sensitivity when LOD is determined by using multiple reaction monitoring (MRM) transitions. The suggested derivatization approach was shown to be useful for unambiguous identification of special dipeptides in artificial media and dietary supplements.

Tryptophan-tyrosine dipeptide improves tau-related symptoms in tauopathy mice

Neurodegenerative diseases involving pathological tau protein aggregation are collectively known as tauopathies and include Alzheimer's disease and Pick's disease. Recent studies show that the intake of tryptophan-tyrosine (Trp-Tyr)-related β-lactopeptides, including β-lactolin, attenuates cognitive decline in the elderly and prevents the amyloid pathology in mouse models of Alzheimer's disease. However, the effects of Trp-Tyr-related β-lactopeptides on tau-related pathology have not been investigated. In the present study, we examined the effects of Trp-Tyr dipeptide intake on tauopathy in PS19 transgenic mice, a well-established tauopathy model. Intake of Trp-Tyr dipeptide improved the behavioral deficits observed in the open field test, prevented tau phosphorylation, and increased the dopamine turnover and synaptophysin expression in the frontal cortex. Levels of short-chain fatty acids in the cecum were lower in PS19 mice than those in wild-type mice and were increased by treatment with Trp-Tyr dipeptide. In addition, intake of Trp-Tyr dipeptide extended the lifespan of PS19 mice. These findings suggest that the intake of Trp-Tyr-related peptides improves tauopathy symptoms, resulting in improvements in behavioral deficits and longevity. Hence, the intake of Trp-Tyr-related peptides, including β-lactolin, may be beneficial for preventing dementia.

Clinical and Preclinical Studies of Fermented Foods and Their Effects on Alzheimer’s Disease

The focus on managing Alzheimer’s disease (AD) is shifting towards prevention through lifestyle modification instead of treatments since the currently available treatment options are only capable of providing symptomatic relief marginally and result in various side effects. Numerous studies have reported that the intake of fermented foods resulted in the successful management of AD. Food fermentation is a biochemical process where the microorganisms metabolize the constituents of raw food materials, giving vastly different organoleptic properties and additional nutritional value, and improved biosafety effects in the final products. The consumption of fermented foods is associated with a wide array of nutraceutical benefits, including anti-oxidative, anti-inflammatory, neuroprotective, anti-apoptotic, anti-cancer, anti-fungal, anti-bacterial, immunomodulatory, and hypocholesterolemic properties. Due to their promising health benefits, fermented food products have a great prospect for commercialization in the food industry. This paper reviews the memory and cognitive enhancement and neuroprotective potential of fermented food products on AD, the recently commercialized fermented food products in the health and food industries, and their limitations. The literature reviewed here demonstrates a growing demand for fermented food products as alternative therapeutic options for the prevention and management of AD.

The role of microglia in Alzheimer's disease and progress of treatment

Microglia are permanent immune cells of the central nervous system. Microglia play an important role in the pathological process of Alzheimer's disease (AD). They are mainly involved in the uptake and clearance of amyloid-β (Aβ), as well as the formation of neuroinflammation. We found that overactivated microglia increase Aβ and Tau, and Aβ and Tau in turn act as activators of microglia. Additionally, various cytokines and proteins, high cholesterol, and telomere shortening are all associated with microglia activation. More activated microglia induce the release of inflammatory and anti-inflammatory factors to regulate inflammation, while microglia express multiple homologous receptors that bind to neuroimmunomodulators to prevent microglia overactivation. Moreover, aging of the body promotes neuroinflammation by increasing the response to IFN-γ (interferon-γ), and aging of the microglia themselves promotes AD by inducing the accumulation of large amounts of iron and reducing autophagy by regulating protein levels. Cognitive dysfunction occurs when activated microglia induce an increase in beta oligomers, promoting the production of pro-inflammatory factors that alter the shape, composition, and density of synapses. Based on their correlation, microglia-mediated AD therapy as well as the corresponding targets and drugs are discussed. In contrast to similar reviews, this article also summarizes some novel microglia-mediated AD treatment methods over the recent years.

Exogenous Bioactive Peptides Have a Potential Therapeutic Role in Delaying Aging in Rodent Models

In recent years, some exogenous bioactive peptides have been shown to have promising anti-aging effects. These exogenous peptides may have a mechanism similar to endogenous peptides, and some can even regulate the release of endogenous active peptides and play a synergistic role with endogenous active peptides. Most aging studies use rodents that are easy to maintain in the laboratory and have relatively homogenous genotypes. Moreover, many of the anti-aging studies using bioactive peptides in rodent models only focus on the activity of single endogenous or exogenous active peptides, while the regulatory effects of exogenous active peptides on endogenous active peptides remain largely under-investigated. Furthermore, the anti-aging activity studies only focus on the effects of these bioactive peptides in individual organs or systems. However, the pathological changes of one organ can usually lead to multi-organ complications. Some anti-aging bioactive peptides could be used for rescuing the multi-organ damage associated with aging. In this paper, we review recent reports on the anti-aging effects of bioactive peptides in rodents and summarize the mechanism of action for these peptides, as well as discuss the regulation of exogenous active peptides on endogenous active peptides.

Bioactive Components in Traditional Foods Aimed at Health Promotion: A Route to Novel Mechanistic Insights and Lead Molecules?

Traditional foods and diets can provide health benefits beyond their nutrient composition because of the presence of bioactive compounds. In various traditional healthcare systems, diet-based approaches have always played an important role, which has often survived until today. Therefore, investigating traditional foods aimed at health promotion could render not only novel bioactive substances but also mechanistic insights. However, compared to pharmacologically focused research on natural products, investigating such nutrition-based interventions is even more complicated owing to interacting compounds, less potent and relatively subtle effects, the food matrix, and variations in composition and intake. At the same time, technical advances in 'omics' technologies, cheminformatics, and big data analysis create new opportunities, further strengthened by increasing insights into the biology of health and homeostatic resilience. These are to be combined with state-of-the-art ethnobotanical research, which is key to obtaining reliable and reproducible data. Unfortunately, socioeconomic developments and climate change threaten traditional use and knowledge as well as biodiversity. Expected final online publication date for the Annual Review of Food Science and Technology, Volume 13 is March 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Differential Expression of miR-381-3p in Alzheimer's Disease Patients and Its Role in Beta-Amyloid-Induced Neurotoxicity and Inflammation

INTRODUCTION

This study aimed to explore the diagnostic value and effect of miR-381-3p on Alzheimer's disease (AD).

METHODS

RT-qPCR was used for the measurement of miR-381-3p levels. Pearson correlation coefficient was used for the correlation analysis. Receiver operating characteristic (ROC) curve was constructed to assess the distinct ability of miR-381-3p for AD. SH-SY5Y cells were treated with Aβ25-35 to establish an AD cell model. The role of miR-381-3p on cell proliferation and apoptosis was detected. ELISA was applied to detect the protein levels of inflammatory cytokine expression. The target relationship of miR-381-3p with PTGS2 was verified by luciferase reporter gene assay.

RESULTS

Low expression of miR-381-3p was detected in the serum of AD patients and cell models. There was a negative association of serum miR-381-3p with the serum inflammatory cytokines. The ROC curve demonstrated the distinct ability of serum miR-381-3p for AD, with the AUC value of 0.898, with a sensitivity of 87.5%, and a specificity of 77.7%. Overexpression of miR-381-3p reversed the influence of Aβ25-35 on cell proliferation and apoptosis, but miR-381-3p downregulation exacerbated the influence. miR-381-3p overexpression inhibited the release of IL-6, IL-1β, and TNF-α induced by Aβ25-35 treatment, whereas miR-381-3p downregulation further promoted the release of inflammatory cytokines. PTGS2 was the target gene of miR-381-3p and was upregulated in AD cell models.

CONCLUSION

miR-381-3p is less expressed in the serum of AD patients and has potential diagnostic values for AD. Overexpression of miR-381-3p may attenuate Aβ25-35-induced neurotoxicity and inflammatory responses via targeting PTGS2 in SH-SY5Y cells.

Regional Brain Analysis of Modified Amino Acids and Dipeptides during the Sleep/Wake Cycle

Sleep is a state in which important restorative and anabolic processes occur. Understanding changes of these metabolic processes during the circadian rhythm in the brain is crucial to elucidate neurophysiological mechanisms important for sleep function. Investigation of amino acid modifications and dipeptides has recently emerged as a valuable approach in the metabolic profiling of the central nervous system. Nonetheless, very little is known about the effects of sleep on the brain levels of amino acid analogues. In the present study, we examined brain regional sleep-induced alterations selective for modified amino acids and dipeptides using Ultra-high performance liquid chromatography-MS/MS (UHPLC-MS/MS) based metabolomics. Our approach enabled the detection and identification of numerous amino acid-containing metabolites in the cortex, the hippocampus, the midbrain, and the cerebellum. In particular, analogues of the aromatic amino acids phenylalanine, tyrosine and tryptophan were significantly altered during sleep in the investigated brain regions. Cortical levels of medium and long chain N-acyl glycines were higher during sleep. Regional specific changes were also detected, especially related to tyrosine analogues in the hippocampus and the cerebellum. Our findings demonstrate a strong correlation between circadian rhythms and amino acid metabolism specific for different brain regions that provide previously unknown insights in brain metabolism.

Characterizing the spatial distribution of dipeptides in rodent tissue using MALDI MS imaging with on-tissue derivatization

A highly efficient on-tissue derivatization method for the matrix-assisted laser desorption/ionization mass spectrometry imaging (MALDI MSI) of dipeptides in tissues has been developed via a combination of a home-built laser-assisted chemical transfer (LACT) technique and hexafluoroisopropanol (HFIP).

Dietary Regulation of Gut-Brain Axis in Alzheimer's Disease: Importance of Microbiota Metabolites

Alzheimer's disease (AD) is a neurodegenerative disease that impacts 45 million people worldwide and is ranked as the 6th top cause of death among all adults by the Centers for Disease Control and Prevention. While genetics is an important risk factor for the development of AD, environment and lifestyle are also contributing risk factors. One such environmental factor is diet, which has emerged as a key influencer of AD development/progression as well as cognition. Diets containing large quantities of saturated/trans-fats, refined carbohydrates, limited intake of fiber, and alcohol are associated with cognitive dysfunction while conversely diets low in saturated/trans-fats (i.e., bad fats), high mono/polyunsaturated fats (i.e., good fats), high in fiber and polyphenols are associated with better cognitive function and memory in both humans and animal models. Mechanistically, this could be the direct consequence of dietary components (lipids, vitamins, polyphenols) on the brain, but other mechanisms are also likely to be important. Diet is considered to be the single greatest factor influencing the intestinal microbiome. Diet robustly influences the types and function of micro-organisms (called microbiota) that reside in the gastrointestinal tract. Availability of different types of nutrients (from the diet) will favor or disfavor the abundance and function of certain groups of microbiota. Microbiota are highly metabolically active and produce many metabolites and other factors that can affect the brain including cognition and the development and clinical progression of AD. This review summarizes data to support a model in which microbiota metabolites influence brain function and AD.

Copper-Binding Peptides Attenuate Microglia Inflammation through Suppression of NF-kB Pathway

SCOPE

Activation of microglia, the resident immune cells of the central nervous system, has been related to the etiology and progression of neurodegenerative diseases; thus, finding novel approaches to suppress the neuroinflammatory process is of utmost relevance.

METHODS AND RESULTS

The anti-inflammatory activity of whey Cu-, Fe-, and Zn-binding peptides and their possible underlying mechanism of action were evaluated in microglia. Whey metal-binding peptides decreased nitric oxide production and tumor necrosis factor α (TNF-α) at mRNA and protein levels by stimulated BV-2 microglia in comparison to the control with no peptide treatment. The hydrophobicity, specific sequences, and possible synergistic effects seem to play a role. Cu-binding peptides (Cu-bp) presented anti-inflammatory activity both in BV-2 and primary microglia cultures. These peptides exert their action by suppressing nuclear factor kappa B (NF-kB) pathway since nuclear translocation of NF-kB p65 is decreased by roughly 30% upon Cu-bp treatment. Specific sequences identified in Cu-bp showed high affinity to bind NF-kB p65 by molecular docking (up to -8.8 kcal mol-1 ), corroborating the immunofluorescence studies.

CONCLUSION

Cu-bp represent food-derived peptides that may be useful for neuroprotective purposes. Chelation of copper excess in the CNS and the bioavailability of such peptides, as well as their behavior in in vivo models, deserve further research for future applications.

Round Scad-Derived Octapeptide WCPFSRSF Confers Neuroprotection by Regulating Akt/Nrf2/NFκB Signaling

We previously identified peptides derived from round scad as potential Nrf2 activators. However, the neuroprotection of these peptides is still unclear. In this study, we aimed to investigate the neuroprotective effect of WCPFSRSF against glutamate-induced neurotoxicity, and the memory-improving effects of WCPFSRSF in mice were also explored. Results showed that WCPFSRSF ameliorated oxidative stress by improving the activities of antioxidant enzymes and promoting the Nrf2-mediated endogenous defense system. Moreover, there is an interaction between the up-regulation of Nrf2 and the down-regulation of NFκB induced by the peptide, which was related to the generation of reactive oxygen species (ROS) and could be abolished by the Akt inhibitor LY294002. Further analysis demonstrated that WCPFSRSF may act as a radical scavenger and Nrf2 activator. The antioxidant and anti-inflammatory effects might be related to the Cys and Trp in WCPFSRSF. Moreover, WCPFSRSF could improve spatial memory impairment in sleep-deprived mice. Thus, this work provided evidence for WCPFSRSF as a potential candidate against neurotoxicity and memory deficits.

β-Lactolin Reduces Age-Related Inflammation and Cognitive Decline

With the rapid increase in aging populations worldwide, there has been an increase in demand for preventive and therapeutic measures for age-related cognitive decline and dementia. Epidemiological studies show that consumption of dairy products reduces the risk for cognitive decline and dementia in the elderly. We have previously demonstrated in randomized trials that the consumption of β-lactolin, a whey-derived Gly-Thr-Trp-Tyr lactotetrapeptide, improves cognitive function in older adults. Orally administered β-lactolin is delivered to the brain and inhibits monoamine oxidase, resulting in alleviation of memory impairment. However, there is currently no evidence of the effects of long-term β-lactolin intake on aging. Here, we found that the discrimination index in the novel object recognition test for object recognition memory was reduced in mice aged 20 months compared with that in young mice, indicating that age-related cognitive decline was induced in the aged mice; in aged mice fed β-lactolin for 3 months, memory impairment was subsequently alleviated. In aged mice, impairment of light/dark activity cycles was found to be induced, which was subsequently alleviated by β-lactolin consumption. Additionally, the number of activated microglia in the hippocampus and cortex and the production of cytokines (tumor necrosis factor-α, macrophage inflammatory protein-1α, and macrophage chemoattractant protein-1) were increased in aged mice compared with those in young mice but were reduced in aged mice fed β-lactolin. The age-related hippocampal atrophy was improved in aged mice fed β-lactolin. Cytochrome c levels in the hippocampus and cortex were increased in aged mice compared with those in young mice but were also reduced by β-lactolin consumption. These results suggest that β-lactolin consumption prevents neural inflammation and alleviates aging-related cognitive decline.

Effects of β-Lactolin on Regional Cerebral Blood Flow within the Dorsolateral Prefrontal Cortex during Working Memory Task in Healthy Adults: A Randomized Controlled Trial

Epidemiological studies have reported that consumption of dairy products rich in β-lactolin is beneficial for cognitive decline among elderly individuals. Although previous studies have shown that β-lactolin supplementation improves memory function and attention in healthy adults, the mechanism through which β-lactolin affects human brain function has yet to be elucidated. This placebo-controlled randomized double-blind study therefore examined the effects of β-lactolin on human regional cerebral blood flow (rCBF) using near-infrared spectroscopy (NIRS) according to the Consolidated Standards of Reporting Trials guidelines. A total of 114 healthy participants aged between 50 and 75 years with relatively low cognition were randomly allocated into the β-lactolin or placebo groups (n = 57 for both groups) and received supplementation for 6 weeks. After the 6 weeks of supplementation, total hemoglobin during cognitive tasks (Kraepelin and 2-back tasks) was measured using two-channel NIRS to determine rCBF. Accordingly, the β-lactolin group had significantly higher changes in total hemoglobin at the left dorsolateral prefrontal cortex (DLPFC) area measured using the left-side channel during the 2-back tasks (p = 0.027) compared to the placebo group. The present study suggests that β-lactolin supplementation increases rCBF and DLPFC activity during working memory tasks.

A trip of peptides to the brain

Abstract

Dietary di/tripeptides elicit preventive effects against lifestyle-related diseases such as hypertension, and hypercholesterolemia, etc. Although there have been evidential reports that the intake of protein hydrolysate improved impaired memory in human, limited studies on bioavailability, in particular, beyond the blood-brain barrier (BBB) of candidates in hydrolysate may prevent their extensive physiological studies. Thus, this review discusses the updated studies on BBB transport of peptides showing improved cognitive decline. Furthermore, their accumulation in the brain cerebral parenchyma is also introduced.

Graphical abstract

Isolation and Sequencing of Cu-, Fe-, and Zn-Binding Whey Peptides for Potential Neuroprotective Applications as Multitargeted Compounds

This study aims to isolate metal-binding peptides and synthesize promising amino acid sequences to potentially act as neuroprotective compounds in the future, targeting different mechanisms. Fractions of whey metal-binding peptides (Cu, Fe, and Zn) isolated by immobilized metal affinity chromatography showed different amino acid profiles according to the metal. The Cu-binding peptides presented roughly twofold increase in the in vitro antioxidant, as assessed by oxygen radical absorbance capacity and anticholinesterase activities over the hydrolysate. This is probably because of the higher concentration of aromatic and basic residues, the latter being crucial for binding to the anionic sites of acetylcholinesterase. Six peptide sequences were synthesized based on the metal-binding sites, molecular mass, hydrophobicity, and bioactivity probability. Among the synthetic peptides, the VF dipeptide stood out both for its in vitro antioxidant and anticholinesterase activities. This peptide, as well as the fraction of Cu-binding peptides, should be further studied because it may act through different mechanisms related to neurodegenerative diseases, in addition to the chelation of the excess of metals in the central nervous system.

Design, synthesis and biological evaluation of anticholinesterase peptides: Fragment-based vs. template-based peptide design

The prevalence of Alzheimer's disease (AD) has become a substantial global concern. Approved AChE inhibitors have been used for symptomatic treatment of AD. Binding of amyloid β (Aβ) to the peripheral anionic site of AChE facilitates the formation of Aβ plaques. Blocking this proposed protein-protein interaction by inhibition of the peripheral anionic site of AChE, in addition to increasing the level of ACh, reduces the Aβ aggregation and might qualify to slow down the progression of disease besides the palliative treatment. Targeting protein-protein interactions consider as one of the most challenging issues in the realm of drug design in which peptides have potentials to excel in. In the present study, we applied two virtual fragment-based and template-based approaches to design peptidic inhibitors of the PAS of AChE. Based on the in silico studies, high scored peptides p2 (WTWYGYWVW) and p10 (NHRMLTRRY) obtained from fragment-based and template-based design respectively. Regarding in vitro results, p2 (IC₅₀ = 16 ± 3.2 μM) and p10 (IC₅₀ = 23.6 ± 4.9 μM) showed significant AChE inhibitory effects. The molecular mechanism of inhibition studied by Lineweaver-Burk plots was mixed inhibition for both peptides. The in vitro results conformed to the in silico results and showed that both peptides occupied the CAS and PAS of AChE. The comparison of two peptide-design approaches revealed that the fragment-based design had more chemical diversity and showed priority to the template-based design. According to the obtained results, peptidic inhibitors of AChE designed by the proposed fragment-based approach might be more efficient in comparison to traditional approaches.

β-lactolin increases cerebral blood flow in dorsolateral prefrontal cortex in healthy adults: a randomized controlled trial

The number of elderly individuals with age-related cognitive decline or dementia is rapidly increasing. Dairy product consumption, including β-lactolin, is beneficial for their cognitive function. The underlying mechanism of β-lactolin's effects on human brain activity is yet to be investigated. We examined the β-lactolin effects on human cerebral blood flow (CBF) using near-infrared spectroscopy (NIRS) in a placebo-controlled randomized double-blind study, which reported according to the CONSORT guidelines. Fifty healthy participants (aged 45-60 years) were randomly allocated into the β-lactolin or the placebo group (n = 25 each) and supplemented for 6 weeks. During the 6^th week, oxy-hemoglobin during the working memory tasks was measured using 34-channels (CHs) NIRS. The changes of oxy-hemoglobin, which represents the CBF, in CH 23 located at the left dorsolateral prefrontal cortex (DLPFC) during the spatial working memory task showed higher statistical significance (false discovery rate (q) = 0.045) in the β-lactolin than in the placebo group. The oxy-Hb changes in CH23 have a co-relationship with the working memory task reaction time. This clinical trial showed an increase in the CBF in the left DLPFC area during the 6-week β-lactolin supplementation. This study contributes to elucidating the underlying mechanisms of β-lactolin on cognitive performance.

Intake of Fermented Dairy Products Induces a Less Pro-Inflammatory Postprandial Peripheral Blood Mononuclear Cell Gene Expression Response than Non-Fermented Dairy Products: A Randomized Controlled Cross-Over Trial

SCOPE

It is aimed to investigate how intake of high-fat meals composed of different dairy products with a similar fat content affects postprandial peripheral blood mononuclear cell (PBMC) expression of inflammation-related genes, as well as circulating inflammatory markers and metabolites.

METHODS AND RESULTS

Healthy subjects (n = 47) consume four different high-fat meals composed of either butter, cheese, whipped cream, or sour cream in a randomized controlled cross-over study. Fasting and postprandial PBMC gene expression, plasma metabolites, and circulating inflammatory markers are measured. Using a linear mixed model, it is found that expression of genes related to lymphocyte activation, cytokine signaling, chemokine signaling, and cell adhesion is differentially altered between the four meals. In general, intake of the fermented products cheese and sour cream reduces, while intake of the non-fermented products butter and whipped cream increases, expression of these genes. Plasma amino acid concentrations increase after intake of cheese compared to the other meals, and the amino acid changes correlate with several of the differentially altered genes.

CONCLUSION

Intake of fermented dairy products, especially cheese, induces a less inflammatory postprandial PBMC gene expression response than non-fermented dairy products. These findings may partly explain inconsistent findings in studies on health effects of dairy products.

Brain-transportable soy dipeptide, Tyr-Pro, attenuates amyloid β peptide25-35-induced memory impairment in mice

In this study, experiments on amyloid β peptide_25-35-induced mice were performed to provide in vivo evidence on the potential of the blood–brain barrier transportable soy dipeptide, Tyr-Pro, in combating memory impairment. We demonstrated for the first time that oral administration of Tyr-Pro (100 mg/kg, twice a day) in mice for 16 days significantly improved impaired memory by spontaneous alternation and shortened step-through latency in amyloid β-induced mice.

Gut microbiota and pro/prebiotics in Alzheimer's disease

Alzheimer’s disease is characterized by the accumulation of amyloid and dysfunctional tau protein in the brain along with the final development of dementia. Accumulation of amyloid in the brain was observed 10-20 years before the onset of clinical symptoms by diagnostic methods based on image analysis. This is a serious public health problem, incidence and prevalence being expected to reach epidemic proportions over the next few decades if the disease cannot be prevented or slowed down. Recently, in addition to the strongly developing ischemic etiology of Alzheimer’s disease, it is suggested that the gut microbiota may also participate in the development of this disease. The brain and gut are thought to form a network called the “gut-brain-microbiota axis”, and it is strongly supported idea that the intestinal microflora can be involved in Alzheimer’s disease. Lately, many new studies have been conducted that draw attention to the relationship between Alzheimer’s disease and gut microbiota. This review presents a possible relationship between Alzheimer’s disease and a microbiome. It is a promising idea for prevention or therapeutic intervention. Modulation of the gut microbiota through a personalized diet or beneficial microflora intervention like pro/prebiotics, changing microbiological partners and their products, including amyloid protein, can become a new treatment for Alzheimer’s disease.

β-lactolin, a whey-derived glycine-threonine-tryptophan-tyrosine lactotetrapeptide, improves prefrontal cortex-associated reversal learning in mice

Dementia and cognitive decline have become worldwide public health problems. We have previously reported that a whey-derived glycine-threonine-tryptophan-tyrosine peptide, β-lactolin, improves hippocampus-dependent memory functions in mice. The supplementation with a whey digest rich in β-lactolin improves memory retrieval and executive function in a clinical trial, but the effect of β-lactolin on prefrontal cortex (PFC)-associated cognitive function was unclear. Here we examined the effect of β-lactolin and the whey digest on PFC-associated visual discrimination (VD) and reversal discrimination (RD) learning, using a rodent touch panel-based operant system. β-Lactolin and the whey digest significantly improved the RD learning, and the whey digest enhanced the response latency during the VD task, indicating that β-lactolin and the whey digest improve PFC-associated cognitive functions. Given the translational advantages of the touch panel operant system, consumption of β-lactolin in daily life could be beneficial for improving human PFC-associated cognitive function, helping to prevent dementia.

Preventive Effects of Tryptophan-Methionine Dipeptide on Neural Inflammation and Alzheimer's Pathology

Preventive approaches for age-related memory decline and dementia have become a high priority in the aging society because of the lack of therapeutic approaches. Recent epidemiological studies have reported that fermented dairy products can help prevent dementia. Previously, we identified tryptophan-tyrosine (WY) and tryptophan-methionine (WM) peptides as the suppressants of activation of the primary microglia and showed that WY peptide consumption suppresses inflammation in the brains of Alzheimer's disease model mice. However, the effects of the WM peptide on inflammation in the brain and Alzheimer's pathology have not been investigated. Here, we evaluated the effect of WM peptide consumption on Alzheimer's disease model (5×FAD) mice. In 5×FAD mice, intake of WM peptide suppressed the production of inflammatory cytokines, activation of microglia, and infiltration of activated microglia around β amyloid (Aβ) depositions. WM peptide intake reduced Aβ deposition in the cortex and hippocampus and then improved the object recognition memory. Taken together with previous reports, the current findings indicate that ingestion of tryptophan-related peptides or food material rich in tryptophan-related peptides, thereby regulating microglial activity, represents a potential preventive approach for cognitive decline and dementia related to inflammation.