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

Enhancement of memory and emotional functions by long-term ingestion of protease-treated porcine liver extract in mice

The relationship between diet and brain functions has garnered attention. Previous studies have shown that ingesting a protease-treated porcine liver decomposition product (PLDP) improves cognitive function in humans. In this study, we investigated the effects of PLDP ingestion on cognitive and emotional functions in mice. Mice were fed a PLDP-enhanced diet for 16 weeks and subjected to various behavioral assessments. PLDP ingestion enhanced long-term memory in Barnes maze test. Moreover, mice fed the PLDP diet exhibited reduced anxiety- and depression-like behaviors as evidenced by their performance in open-field, elevated plus maze, marble-burying, and forced swim tests. They also increased locomotor activity. RNA sequencing analysis of the brain tissue revealed substantial changes in gene expression, particularly in pathways associated with learning, memory, and anxiety regulation. Collectively, these results suggest that PLDP induces changes in gene expression associated with brain function, potentially contributing to the enhancement of cognitive function and psychological health. Furthermore, our findings not only enhance our understanding of the relationship between nutrition and brain function but also indicate the potential of interventions utilizing dietary components, such as PLDP, to support cognitive function and psychological health.

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.

Exploring the potential anti-senescence effects of soybean-derived peptide Soymetide in mice hippocampal neurons via the Wnt/β-catenin pathway

Soybean-based foods enhance cognitive functions by influencing hippocampal mechanisms. These salutary effects have so far been attributed to isoflavones present in soybeans. Considering cellular senescence contributes to cognitive decline and that no specific soy-derived peptides are known for their potential to mitigate senescence, we examined the efficacy of a thirteen amino acid soy-derived peptide, Soymetide, on a doxorubicin-induced senescence mice model. Soymetide pretreatment lowered the senescence markers p53, p21 and p16, pro-inflammatory cytokines, and Senescence β-Galactosidase staining while enhancing the mature neuronal marker NeuN in the hippocampus. This anti-senescent effect was comparable with that of a well-known senolytic combination (dasatinib and quercetin). Research indicates that Wnt signaling influences cellular senescence, and our findings here demonstrate that doxorubicin decreased hippocampal Wnt3a, p-LRP6, Frizzled, Dishevelled, Axin1, and β-catenin levels and increased GSK-3β, while Soymetide mitigated these effects. Additionally, upon inhibition of the Wnt/β-catenin pathway, Soymetide's ability to reduce senescence markers and restore NeuN expression was reduced. We validated the anti-senescence impact on hippocampal neurons by co-immunostaining Wnt/β-catenin and senescence indicators alongside NeuN in mice and assessed it in primary hippocampal neurons. Further examining the neuronal survival and functions revealed that Soymetide blocked the doxorubicin-induced loss in Nissl-stained surviving neurons and learning-memory performances, measured by Y-Maze and Passive Avoidance tests, which Wnt/β-catenin inhibitors could counteract. In conclusion, our study identifies a novel Wnt/β-catenin-linked mechanism of doxorubicin-induced senescence in the hippocampal neurons and demonstrates Soymetide's effectiveness in reversing this process. Hence, this suggests Soymetide's potential therapeutic application in addressing cognitive decline associated with cellular aging.

Ergothioneine Stimulates Ca2+-Mediated Brain-Derived Neurotrophic Factor Expression in NE-4C Nerve Cells

Ergothioneine (EGT), a naturally occurring histidine derivative, has been reported to modulate neurodegenerative diseases; however, the underlying mechanism remains unclear. This study aimed to investigate the brain-beneficial role of the natural amino acid EGT in NE-4C nerve cells. In the nerve cells, EGT treatment of >10 μM for 48 h significantly increased the expression of brain-derived neurotrophic factor (BDNF), as well as the phosphorylation of cAMP response element-binding protein (CREB), whereas no change was observed in acetylcholine receptor expression. Additionally, EGT induced an increase in intracellular Ca2+ levels via stimulation of the inositol 1,4,5-triphosphate receptor (IP3R) in the endoplasmic reticulum; this increase was abrogated by the inhibition of organic cation transporter 1 (OCTN1). Structure-activity relationship analysis revealed the importance of the trimethylammonium group in EGT for intracellular events. In conclusion, EGT incorporated into cells via the OCTN1 route may act as a nerve transmission stimulator via IP3R-mediated Ca2+-CREB/BDNF activation.

Preventive effect of Tyr-Pro, a blood-brain barrier transportable dipeptide, on memory impairment in SAMP8 mice

In a series of studies on blood-brain barrier transportable peptides, a soybean dipeptide, Tyr-Pro, penetrated the mouse brain parenchyma after oral intake and improved short and long memory impairment in acute Alzheimer's model mice. Here, we aimed to clarify the anti-dementia effects of this peptide administered to SAMP8 mice prior to dementia onset. At the end of the 25-week protocol in 16-week-old SAMP8 mice, Tyr-Pro (10 mg/kg/day) significantly improved the reduced spatial learning ability compared with that in the control and amino acid (Tyr + Pro) groups as indicated by the results of Morris water maze tests conducted for five consecutive days. The hippocampus and cortex regions of SAMP8 harvested after the test showed lower amyloid ß (Aß) accumulation in the Tyr-Pro group than those in the control and amino acid groups. Consistent with the lower level of Aß, decreased expression of ß-secretase (BACE1) and markedly increased expression (4-times higher) of insulin degrading enzyme (IDE) were obtained compared to those in the control group. Collectively, we demonstrated that long-term daily intake of the dipeptide Tyr-Pro in SAMP8 mice may be sufficient for maintaining cognitive ability by preventing excess Aß accumulation through downregulated BACE1 and particularly upregulated IDE.

Research Progress on Food-Derived Bioactive Peptides: An Overview of the 3rd International Symposium on Bioactive Peptides

Interest in food-derived bioactive peptides is on the rise. In 2023, the 3rd International Symposium on Bioactive Peptides (ISBP) was held in Niagara Falls, Canada, to provide a platform for knowledge exchange, networking, and collaboration among researchers in this field. This article aims to provide a high-level overview of the key progress and emerging trends in bioactive peptides based on the 3rd ISBP. This review highlights the production of bioactive peptides from sustainable sources through the integration of artificial intelligence and wet-lab research, the emerging roles of bioactive peptides in cognitive function, and the ability of peptides to act as taste modifiers. The emerging research trend in bioactive peptides focuses on utilizing novel processing technologies, understanding peptide-receptor interactions, applying omics in mechanistic studies, conducting clinical trials, and facilitating product development and commercialization.

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.

Dandouchi Polypeptide Alleviates Depressive-like Behavior and Promotes Hippocampal Neurogenesis by Activating the TRIM67/NF-κB Pathway in CUMS-Induced Mice

Background: Dandouchi polypeptide (DDCP) is derived from Semen Sojae Praeparatum (Dandouchi in Chinese), a fermented product of Glycine max (L.) Merr. Semen Sojae Praeparatum is widely used in the food industry for its unique flavor and nutritional value, and DDCP, as its derivative, also shows potential health benefits in food applications. However, the specific active substances responsible for Semen Sojae Praeparatum and the underlying mechanisms involved have not been fully elucidated. Methods: DDCP was extracted from Semen Sojae Praeparatum using enzymes, and its antidepressant effects were tested in chronic unpredictable mild stress (CUMS)-induced mice. Immunohistochemistry, immunofluorescence, and western blotting were used to analyze neurogenesis and the nuclear factor κB (NF-κB) pathway. Moreover, an adeno-associated virus (AAV) shRNA was used to induce tripartite motif-containing 67 (TRIM67) deficiency to examine the function of TRIM67 in the neuroprotective effects of DDCP in depressive disorders. Results: DDCP reduced depressive behaviors in CUMS mice and the expression of proinflammatory markers in the hippocampus. DDCP promoted neurogenesis and modulated the TRIM67/NF-κB pathway, with TRIM67 deficiency impairing its antidepressant effect. Conclusions: This research revealed that DDCP has a protective effect on countering depression triggered by CUMS. Notably, TRIM67 plays a crucial role in mitigating depression through DDCP, positioning DDCP as a potential therapeutic option for treating depressive disorders.

Chronic ingestion of soy peptide supplementation reduces aggressive behavior and abnormal fear memory caused by juvenile social isolation

Juvenile loneliness is a risk factor for psychopathology in later life. Deprivation of early social experience due to peer rejection has a detrimental impact on emotional and cognitive brain function in adulthood. Accumulating evidence indicates that soy peptides have many positive effects on higher brain function in rodents and humans. However, the effects of soy peptide use on juvenile social isolation are unknown. Here, we demonstrated that soy peptides reduced the deterioration of behavioral and cellular functions resulting from juvenile socially-isolated rearing. We found that prolonged social isolation post-weaning in male C57BL/6J mice resulted in higher aggression and impulsivity and fear memory deficits at 7 weeks of age, and that these behavioral abnormalities, except impulsivity, were mitigated by ingestion of soy peptides. Furthermore, we found that daily intake of soy peptides caused upregulation of postsynaptic density 95 in the medial prefrontal cortex and phosphorylation of the cyclic adenosine monophosphate response element binding protein in the hippocampus of socially isolated mice, increased phosphorylation of the adenosine monophosphate-activated protein kinase in the hippocampus, and altered the microbiota composition. These results suggest that soy peptides have protective effects against juvenile social isolation-induced behavioral deficits via synaptic maturation and cellular functionalization.

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.

Natural Plant Materials as a Source of Neuroprotective Peptides

In many circumstances, some crucial elements of the neuronal defense system fail, slowly leading to neurodegenerative diseases. Activating this natural process by administering exogenous agents to counteract unfavourable changes seems promising. Therefore, looking for neuroprotective therapeutics, we have to focus on compounds that inhibit the primary mechanisms leading to neuronal injuries, e.g., apoptosis, excitotoxicity, oxidative stress, and inflammation. Among many compounds considered neuroprotective agents, protein hydrolysates and peptides derived from natural materials or their synthetic analogues are good candidates. They have several advantages, such as high selectivity and biological activity, a broad range of targets, and high safety profile. This review aims to provide biological activities, the mechanism of action and the functional properties of plant-derived protein hydrolysates and peptides. We focused on their significant role in human health by affecting the nervous system and having neuroprotective and brain-boosting properties, leading to memory and cognitive improving activities. We hope our observation may guide the evaluation of novel peptides with potential neuroprotective effects. Research into neuroprotective peptides may find application in different sectors as ingredients in functional foods or pharmaceuticals to improve human health and prevent diseases.

Food-Derived Peptides: Beneficial CNS Effects and Cross-BBB Transmission Strategies

Food-derived peptides, as dietary supplements, have significant effects on promoting brain health and relieving central nervous system (CNS) diseases. However, the blood-brain barrier (BBB) greatly limits their in-brain bioavailability. Thus, overcoming the BBB to target the CNS is a major challenge for bioactive peptides in the prevention and treatment of CNS diseases. This review discusses improvement in the neuroprotective function of food-derived active peptides in CNS diseases, as well as the source of BBB penetrating peptides (BBB-shuttles) and the mechanism of transmembrane transport. Notably, this review also discusses various peptide modification methods to overcome the low permeability and stability of the BBB. Lipification, glycosylation, introduction of disulfide bonds, and cyclization are effective strategies for improving the penetration efficiency of peptides through the BBB. This review provides a new prospective for improving their neuroprotective function and developing treatments to delay or even prevent CNS diseases.

Fermented soybean foods (natto) ameliorate age-related cognitive decline by hippocampal TAAR1-mediated activation of the CaMKII/CREB/BDNF signaling pathway in senescence-accelerated mouse prone 8 (SAMP8)

Natto is a traditional fermented soybean-based food that has been an integral part of Japanese cuisine for several centuries. Although there have been extensive studies on the cognitive benefits of soybeans, only limited studies have examined the effects of natto on cognitive function. This study investigated the potential cognitive benefits of natto in senescence-accelerated mouse-prone 8 (SAMP8) mice. After 12 weeks of oral administering natto fermented for 18 h, the spatial learning and memory performance were improved compared with those in SAMP8 control mice. Furthermore, activation of the brain-derived neurotrophic factor (BDNF)/tropomyosin receptor kinase B (TrkB)/cAMP response element-binding protein (CREB) signaling and N-methyl-D-aspartate receptor (NMDAR)-calcium/calmodulin-dependent protein kinase II (CaMKII) cascade was observed in the hippocampus of SAMP8 mice that were fed natto. Additionally, natto administration upregulated trace amine-associated receptor 1 (TAAR1) as a modulator of NMDAR. These findings suggest that natto ameliorates cognitive decline by activating the TAAR1-mediated CaMKII/CREB/BDNF signaling pathway in the hippocampus of SAMP8 mice.

Dietary amino acid intake and sleep duration are additively involved in future cognitive decline in Japanese adults aged 60 years or over: a community-based longitudinal study

BACKGROUND

Sleep duration and amino acid intake are independently associated with cognitive decline. This study aimed to determine the longitudinal association between sleep duration and cognitive impairment incidence and to examine the involvement of diet, particularly amino acid intake, in these associations in community dwellers.

METHODS

In this longitudinal study in a community-based setting, we analyzed data from 623 adults aged 60-83 years without cognitive impairment at baseline. Sleep duration was assessed using a self-report questionnaire. Amino acid intake was assessed using 3-day dietary records. Cognitive impairment was defined as a Mini-Mental State Examination score ≤ 27. Participants were classified into short-, moderate-, and long-sleep groups according to baseline sleep duration (≤ 6, 7-8, and > 8 h, respectively). Using moderate sleep as a reference, odds ratios (ORs) and 95% confidence intervals (CIs) of short- and long-sleep for cognitive-impairment incidence were estimated using the generalized estimating equation. Participants were classified according to sex-stratified quartiles (Q) of 19 amino acid intake: Q1 and Q2-Q4 were low- and middle to high-intake groups, respectively. Using middle- to high-intake as a reference, ORs and 95% CIs of low intake for cognitive impairment incidence were estimated using the generalized estimating equation in each sleep-duration group. Follow-up period, sex, age, body mass index, depressive symptoms, education, smoking status, employment status, sleep aids use, physical activity, medical history, and Mini-Mental State Examination score at baseline were covariates.

RESULTS

Mean follow-up period was 6.9 ± 2.1 years. Adjusted ORs (95% CIs) for cognitive impairment in short- and long-sleep groups were 0.81 (0.49-1.35, P = 0.423) and 1.41 (1.05-1.87, P = 0.020), respectively. Particularly in long sleepers (i.e., > 8 h), cognitive impairment was significantly associated with low cystine, proline, and serine intake [adjusted ORs (95% CIs) for cognitive impairment were 2.17 (1.15-4.11, P = 0.017), 1.86 (1.07-3.23, P = 0.027), and 2.21 (1.14-4.29, P = 0.019), respectively].

CONCLUSIONS

Community-dwelling adults aged ≥ 60 years who sleep longer are more likely to have cognitive decline, and attention should be paid to the low cystine, proline, and serine intake.

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.

Improvement of memory function via a combination of exercise and soy peptide supplementation in community-dwelling older adults: A randomized controlled trial

Background

Soy peptide, when consumed as a functional food, has been reported to improve cognitive function. This study aimed to verify the combined effect of soy peptide supplementation and exercise on cognitive function among community-dwelling older adults in Japan.

Methods

In this population-based, non-blinded randomized controlled trial, 72 community-dwelling older adults who were independent in activities of daily living were randomly assigned to an "exercise plus nutrition" program (Ex + Nt group, n = 36) or an exercise program (Ex group, n = 36). For 3 months, both groups participated in an exercise and cognitive training regimen once per week, with the Ex + Nt group receiving soy supplementation once per week. Pre- and post-intervention measurements included grip strength, gait speed, skeletal muscle mass index, and scores on Addenbrooke's Cognitive Examination-Revised, trail-making test A, and the Geriatric Depression Scale. Participant enrollment for this study started in January 2019 and ended in April 2019.

Results

Exercise training increased the skeletal muscle mass index by 2.0% and 3.0% in the Ex + Nt and Ex groups, respectively. The Ex + Nt group exhibited a significant 0.3-point increase in the memory score.

Conclusion

A 3-month exercise program combined with soy peptide supplementation may be effective in improving both motor and memory function in community-dwelling older adults.

LC/MS Q-TOF Metabolomic Investigation of Amino Acids and Dipeptides in Pleurotus ostreatus Grown on Different Substrates

The well-established correlation between diet and health arouses great interest in seeking new health-promoting functional foods that may contribute to improving health and well-being. Herein, the metabolomic investigation of Pleurotus ostreatus samples grown on two different substrates (black poplar wood logs, WS, and lignocellulosic byproducts, LcS) revealed the high potential of such a mushroom as a source of bioactive species. The liquid chromatography/mass spectrometry combined with quadrupole time-of-flight (LC/MS Q-TOF) analysis allowed the identification of essential and nonessential amino acids along with the outstanding presence of dipeptides. Multivariate statistical models highlighted important differences in the expression of both classes of compounds arising from the growth of P. ostreatus strains on WS and LcS. The former, in particular, was correlated to an increased expression of carnitine-based amino acid derivatives and proline-based dipeptides. This finding may represent a potential strategy to drive the expression of bioactive compounds of interest to obtain enriched mushrooms or useful functional ingredients from them.

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.

Zinc Binding to NAP-Type Neuroprotective Peptides: Nuclear Magnetic Resonance Studies and Molecular Modeling

Aggregation of amyloid-β peptides (Aβ) is a hallmark of Alzheimer’s disease (AD), which is affecting an increasing number of people. Hence, there is an urgent need to develop new pharmaceutical treatments which could be used to prevent the AD symptomatology. Activity-dependent neuroprotective protein (ADNP) was found to be deficient in AD, whereas NAP, an 8-amino-acid peptide (¹NAPVSIPQ⁸) derived from ADNP, was shown to enhance cognitive function. The higher tendency of zinc ion to induce Aβ aggregation and formation of amorphous aggregates is also well-known in the scientific literature. Although zinc binding to Aβ peptides was extensively investigated, there is a shortage of knowledge regarding the relationship between NAP peptide and zinc ions. Therefore, here, we investigated the binding of zinc ions to the native NAP peptide and its analog obtained by replacing the serine residue in the NAP sequence with tyrosine (¹NAPVYIPQ⁸) at various molar ratios and pH values by mass spectrometry (MS) and nuclear magnetic resonancespectroscopy (NMR). Matrix-assisted laser desorption/ionization time-of-flight (MALDI ToF) mass spectrometry confirmed the binding of zinc ions to NAP peptides, while the chemical shift of Asp¹, observed in ¹H-NMR spectra, provided direct evidence for the coordinating role of zinc in the N-terminal region. In addition, molecular modeling has also contributed largely to our understanding of Zn binding to NAP peptides.

Potential of plant-derived peptides for the improvement of memory and cognitive function

Recently, there has been an increased demand for functional foods, to reduce the risk of age-related cognitive impairment, dementia, and Alzheimer's disease. Among them, plant-derived bioactive compounds, such as phytochemicals and peptides, have notable potential in improving memory and cognitive functions. Many studies have provided potential data concerning the characteristics and structure-activity relationships of memory-enhancing peptides. When considering the proof of efficacy of these plant-based peptides in humans as neurological treatment options, it is necessary to accumulate evidence concerning their bioavailability and permeability through blood-brain barrier (BBB). This review focuses on the memory-enhancing effects of peptides derived from plant proteins and presents a current perspective on their structure-activity relationships and BBB permeability.

Enhancing the binding of the β-sheet breaker peptide LPFFD to the amyloid-β fibrils by aromatic modifications: A molecular dynamics simulation study

Alzheimer's is a fatal neurodegenerative disease for which there is no cure at present. The disease is characterized by the presence of plaques in the brains of a patient, which are composed mainly of aggregates of the amyloid-β peptide in the form of β-sheet fibrils. Here, we investigated the possibility of exploiting the superior binding ability of aromatic amino acids to a particular model of the amyloid-β fibrils. which is a difficult target for drug design. The β-sheet breaker peptide LPFFD was modified with aromatic amino acids and its binding to these fibrils was studied. We found that the orientation and the electrostatic complementarity of the modified peptide with respect to the fibrils played a crucial role in determining whether its binding was improved by the aromatic amino acids. The modified LPFFD peptides were able to bind to those fibril residues. which are important in the aggregation of amyloid-β peptides and thus can potentially inhibit the further aggregation of the amyloid-beta peptides by blocking their interactions. We found that the tryptophan modified LPFFD peptides had the best binding affinities. In most cases, the aromatic amino acids in the N-terminus of the modified peptides made more contacts with the fibrils than those in the C-terminus. We also found that increasing the aromatic content did not significantly improve the binding of the LPFFD peptide to the fibrils. Our study can serve as a basis for the design of novel peptide-based drugs for Alzheimer's disease in which aromatic interactions play an important role.

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