Iso-α-acids, the bitter components of beer, improve hippocampus-dependent memory through vagus nerve activation

Impaired learning, memory, and extinction in posttraumatic stress disorder: translational meta-analysis of clinical and preclinical studies

Current evidence-based treatments for post-traumatic stress disorder (PTSD) are efficacious in only part of PTSD patients. Therefore, novel neurobiologically informed approaches are urgently needed. Clinical and translational neuroscience point to altered learning and memory processes as key in (models of) PTSD psychopathology. We extended this notion by clarifying at a meta-level (i) the role of information valence, i.e. neutral versus emotional/fearful, and (ii) comparability, as far as applicable, between clinical and preclinical phenotypes. We hypothesized that cross-species, neutral versus emotional/fearful information processing is, respectively, impaired and enhanced in PTSD. This preregistered meta-analysis involved a literature search on PTSD+Learning/Memory+Behavior, performed in PubMed. First, the effect of information valence was estimated with a random-effects meta-regression. The sources of variation were explored with a random forest-based analysis. The analyses included 92 clinical (N = 6732 humans) and 182 preclinical (N = 6834 animals) studies. A general impairment of learning, memory and extinction processes was observed in PTSD patients, regardless of information valence. Impaired neutral learning/memory and fear extinction were also present in animal models of PTSD. Yet, PTSD models enhanced fear/trauma memory in preclinical studies and PTSD impaired emotional memory in patients. Clinical data on fear/trauma memory was limited. Mnemonic phase and valence explained most variation in rodents but not humans. Impaired neutral learning/memory and fear extinction show stable cross-species PTSD phenotypes. These could be targeted for novel PTSD treatments, using information gained from neurobiological animal studies. We argue that apparent cross-species discrepancies in emotional/fearful memory deserve further in-depth study; until then, animal models targeting this phenotype should be applied with utmost care.

An Updated Review of the Genus Humulus: A Valuable Source of Bioactive Compounds for Health and Disease Prevention

The medicinal potential of hop (Humulus lupulus L.) is widely cited in ancient literature and is also allowed in several official pharmacopoeias for the treatment of a variety of ailments, mainly related to anxiety states. This is due to the plethora of phytoconstituents (e.g., bitter acids, polyphenols, prenyl flavonoids) present in the female inflorescences, commonly known as cones or strobili, endowed with anti-inflammatory, antioxidant, antimicrobial, and phytoestrogen activities. Hop has recently attracted the interest of the scientific community due to the presence of xanthohumol, whose strong anti-cancer activity against various types of cancer cells has been well documented, and for the presence of 8-prenyl naringenin, the most potent known phytoestrogen. Studies in the literature have also shown that hop compounds can hinder numerous signalling pathways, including ERK1/2 phosphorylation, regulation of AP-1 activity, PI3K-Akt, and nuclear factor NF-κB, which are the main targets of the antiproliferative action of bitter acids and prenylflavonoids. In light of these considerations, the aim of this review was to provide an up-to-date overview of the main biologically active compounds found in hops, as well as their in vitro and in vivo applications for human health and disease prevention. To this end, a quantitative literature analysis approach was used, using VOSviewer software to extract and process Scopus bibliometric data. In addition, data on the pharmacokinetics of bioactive hop compounds and clinical studies in the literature were analysed. To make the information more complete, studies on the beneficial properties of the other two species belonging to the genus Humulus, H. japonicus and H. yunnanensis, were also reviewed for the first time.

Targeting gut microbiota to alleviate neuroinflammation in Alzheimer's disease

The gut microbiota came into focus within the last years regarding being associated with or even underlying neuropsychiatric diseases. The existence of the gut-brain-axis makes it highly plausible that bacterial metabolites or toxins that escape the intestinal environment or approach the vagal connections towards the brain, exert devastating effects on the central nervous system. In Alzheimer's disease (AD), growing evidence for dysbiotic changes in the gut microbiota is obtained, even though the question for cause or consequence remains open. Nevertheless, using modulation of microbiota to address inflammatory processes seems an attractive therapeutic approach as certain microbial products such as short chain fatty acids have been proven to exert beneficial cognitive effects. In this review, we summarize, contemporary knowledge on neuroinflammation and inflammatory processes within the brain and even more detailed in the gut in AD, try to conclude whom to target regarding human microbial commensals and report on current interventional trials.

Identification of Human Brain Proteins for Bitter-Sweet Taste Perception: A Joint Proteome-Wide and Transcriptome-Wide Association Study

Objective: Bitter or sweet beverage perception is associated with alterations in brain structure and function. Our aim is to analyze the genetic association between bitter or sweet beverage perception and human brain proteins. Materials and methods: In our study, 8356 and 11,518 proteins were first collected from two reference datasets of human brain proteomes, the ROS/MAP and Banner. The bitter or sweet beverage perception-related proteome-wide association studies (PWAS) were then conducted by integrating recent genome-wide association study (GWAS) data (n = 422,300) of taste perception with human brain proteomes. The human brain gene expression profiles were collected from two reference datasets, including the brain RNA-seq (CBR) and brain RNA-seq splicing (CBRS). The taste perception-related transcriptome-wide association studies (TWAS) were finally performed by integrating the same GWAS data with human brain gene expression profiles to validate the PWAS findings. Results: In PWAS, four statistically significant proteins were identified using the ROS/MAP and then replicated using the Banner reference dataset (all permutated p < 0.05), including ABCG2 for total bitter beverages and tea, CPNE1 for total bitter beverage, ACTR1B for artificially sweetened beverages, FLOT2 for alcoholic bitter beverages and total sweet beverages. In TWAS analysis, six statistically significant genes were detected by CBR and confirmed by the CBRS reference dataset (all permutated p < 0.05), including PIGG for total bitter beverages and non-alcoholic bitter beverages, C3orf18 for total bitter beverages, ZSWIM7 for non-alcoholic bitter beverages, PEX7 for coffee, PKP4 for tea and RPLP2 for grape juice. Further comparison of the PWAS and TWAS found three common statistically significant proteins/genes identified from the Banner and CBR reference datasets, including THBS4 for total bitter beverages, CA4 for non-alcoholic bitter beverages, LIAS for non-grape juices. Conclusions: Our results support the potential effect of bitter or sweet beverage perception on brain function and identify several candidate brain proteins for bitter or sweet beverage perception.

Iso-α-acids in Nonalcoholic and Alcoholic Beer Stimulate Growth of Neuron-like SH-SY5Y Cells and Neuroepithelial Stem Cells

With the increasing popularity of nonalcoholic beer, the association between beer drinking and alcohol intake is lost. In the present study, we show that nonalcoholic beer can stimulate the expansion of neuron-like cell lines and neuroepithelial stem cells in culture, yielding an effect comparable to that of alcoholic beer. One ingredient in beer is hops, which is derived from the flower of hop plants. The female flower contains humulones, which are transformed into iso-α-acids during wort boiling and give beer its bitter taste. In this study, we tested the effects of these iso-α-acids and/or alcohol on the proliferation of neuron-like cells and neuroepithelial stem cells in culture. Iso-α-acids enhanced cell expansion, showing a bimodal dose-response curve with peaks around 2-30 nM and 2-5 μM, of which nanomolar concentrations are relevant in beer drinking. The more lipophilic trans-iso-α-acids, found to a greater extent in beer foam, are even more potent. Our results indicate that iso-α-acids, acting via peroxisome proliferator-activated receptors could be responsible for the observed effects. Altogether, our results indicate that nonalcoholic beer with ingredients such as iso-α-acids stimulate the proliferation of neuroepithelial stem cells.

Redox and Anti-Inflammatory Properties from Hop Components in Beer-Related to Neuroprotection

Beer is a fermented beverage widely consumed worldwide with high nutritional and biological value due to its bioactive components. It has been described that both alcoholic and non-alcoholic beer have several nutrients derived from their ingredients including vitamins, minerals, proteins, carbohydrates, and antioxidants that make beer a potential functional supplement. Some of these compounds possess redox, anti-inflammatory and anticarcinogenic properties making the benefits of moderate beer consumption an attractive way to improve human health. Specifically, the hop cones used for beer brewing provide essential oils, bitter acids and flavonoids that are potent antioxidants and immune response modulators. This review focuses on the redox and anti-inflammatory properties of hop derivatives and summarizes the current knowledge of their neuroprotective effects.

Hop Bitter Acids Increase Hippocampal Dopaminergic Activity in a Mouse Model of Social Defeat Stress

As daily lifestyle is closely associated with mental illnesses, diet-based preventive approaches are receiving attention. Supplementation with hop bitter acids such as iso-α-acids (IAA) and mature hop bitter acids (MHBA) improves mood states in healthy older adults. However, the underlying mechanism remains unknown. Since acute oral consumption with IAA increases dopamine levels in hippocampus and improves memory impairment via vagal nerve activation, here we investigated the effects of chronic administration of hop bitter acids on the dopaminergic activity associated with emotional disturbance in a mouse model of repeated social defeat stress (R-SDS). Chronic administration of IAA and MHBA significantly increased dopaminergic activity based on the dopamine metabolite to dopamine ratio in the hippocampus and medial prefrontal cortex following R-SDS. Hippocampal dopaminergic activity was inversely correlated with the level of R-SDS-induced social avoidance with or without IAA administration. Therefore, chronic treatment with hop bitter acids enhances stress resilience-related hippocampal dopaminergic activity.

Hop bitter acids containing a β-carbonyl moiety prevent inflammation-induced cognitive decline via the vagus nerve and noradrenergic system

The prevention of age-related cognitive decline and dementia is becoming a high priority because of the rapid growth of aging populations. We have previously shown that hop bitter acids such as iso-α-acids (IAAs) and matured hop bitter acids (MHBAs) activate the vagus nerve and improve memory impairment. Moreover, supplements with MHBAs were shown to improve memory retrieval in older adults. However, the underlying mechanisms have not been entirely elucidated. We aimed to investigate the effects of MHBAs and the common β-tricarbonyl moiety on memory impairment induced by the activation of microglia and the loss of the noradrenergic system. MHBAs and a model compound with β-tricarbonyl moiety were administered to LPS-inoculated mice and 5 × FAD Alzheimer’s disease (AD) model mice, following the evaluation in behavioral tests and microglial activation. To evaluate the association of noradrenaline with MHBAs effects, mice treated with N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine (DSP-4), a noradrenergic neurotoxin that selectively damages noradrenergic projections from the locus coeruleus, were subjected to the behavioral evaluation. MHBAs reduced brain inflammation and improved LPS-induced memory impairment. A model compound possessing the β-tricarbonyl moiety improved the LPS-induced memory impairment and neuronal loss via the vagus nerve. Additionally, the protective effects of MHBAs on memory impairment were attenuated by noradrenaline depletion using DSP-4. MHBAs suppressed the activation of microglia and improved the memory impairment in 5 × FAD mice, which was also attenuated by noradrenaline depletion. Treatment with MHBAs increased cholecystokinin production from the intestinal cells. Generally, cholecystokinin activates the vagal nerve, which stimulate the noradrenergic neuron in the locus ceruleus. Taken together, our results reveal that food ingredients such as hop bitter acids with a β-tricarbonyl moiety suppress microglial activation and improve memory impairment induced by inflammation or AD pathology via the activation of the gut-brain axis and noradrenergic system. Supplements with hop bitter acids, including MHBAs, might be a novel approach for the prevention of cognitive decline and dementia.

Distillation remnants of shochu, a traditional Japanese liquor, improve pork meat quality by reducing stress

Distillation remnants of Shochu, a traditional Japanese liquorare fed to livestock, but their effects on livestock health have not been investigated. Here, we investigated the effects of these remnants on pig stress and pork quality (N = 6/group). The remnants reduced plasma cortisol (17.94 ± 0.92 [control] and 10.59 ± 1.28 [sample]) and increased salivary IgA (6.06 ± 2.21 [control] and 21.60 ± 5.37 [sample]). Blind sensory assessments showed that, in remnant-fed pork, sirloin tenderness (3.18 ± 0.19 [control] and 4.27 ± 0.38 [sample]) and the juiciness, umami, and fat tastiness of fillets were improved. Oleic acid percentages were higher (35.23 ± 0.65 [control] and 37.87 ± 0.60 [sample]) in remnant-fed pork, contributing to a favorable sensory evaluation. Two-group comparisons were analyzed by student's t test. p < 0.05. This study promotes the reutilization of remnants to reduce livestock stress and improve meat quality.

Improving Effects of Hop-Derived Bitter Acids in Beer on Cognitive Functions: A New Strategy for Vagus Nerve Stimulation

Dementia and cognitive decline are global public health problems. Moderate consumption of alcoholic beverages reduces the risk of dementia and cognitive decline. For instance, resveratrol, a polyphenolic compound found in red wine, has been well studied and reported to prevent dementia and cognitive decline. However, the effects of specific beer constituents on cognitive function have not been investigated in as much detail. In the present review, we discuss the latest reports on the effects and underlying mechanisms of hop-derived bitter acids found in beer. Iso-α-acids (IAAs), the main bitter components of beer, enhance hippocampus-dependent memory and prefrontal cortex-associated cognitive function via dopamine neurotransmission activation. Matured hop bitter acids (MHBAs), oxidized components with β-carbonyl moieties derived from aged hops, also enhance memory functions via norepinephrine neurotransmission-mediated mechanisms. Furthermore, the effects of both IAAs and MHBAs are attenuated by vagotomy, suggesting that these bitter acids enhance cognitive function via vagus nerve stimulation. Moreover, supplementation with IAAs attenuates neuroinflammation and cognitive impairments in various rodent models of neurodegeneration including Alzheimer's disease. Daily supplementation with hop-derived bitter acids (e.g., 35 mg/day of MHBAs) may be a safe and effective strategy to stimulate the vagus nerve and thus enhance cognitive function.

Effects of Hop Bitter Acids, Bitter Components in Beer, on Cognition in Healthy Adults: A Randomized Controlled Trial

The present study aimed to investigate the effects of matured hop bitter acids (MHBAs) on human cognition, mental fatigue, and mood state. In this randomized double-blind placebo-controlled study, 60 healthy adults (age 45-64 years) with self-awareness of cognitive decline were randomly divided into 2 groups and received either orally administered MHBAs (35 mg/day) or placebo for 12 weeks. Cognitive functions and mental states were assessed using neuropsychological tests or questionnaires at baseline and weeks 6 and 12 of the intervention. The change in verbal fluency score at week 6 compared with that at baseline was significantly higher in the MHBAs-treated group compared with that in the placebo group (P = 0.034), and Stroop test score at week 12 was significantly lower in the MHBAs-treated group compared with the placebo group (P = 0.019). Furthermore, subjective fatigue and anxiety at week 12 were significantly improved in the MHBAs-treated group (P = 0.008 and 0.043, respectively) compared with the placebo group. This is the first study to evaluate the effects of bitter ingredients in beer on cognition, subjective mood, and mental fatigue in a clinical trial. Our findings suggest that hop-derived bitter acids might be beneficial for cognition and mood state.

Effects of iso-α-acids, the hop-derived bitter components in beer, on the MRI-based Brain Healthcare Quotient in healthy middle-aged to older adults

Aim

Neurological disorders are a major public health issue worldwide and are often associated with structural changes in the brain. We have previously demonstrated that iso‐α‐acids (IAAs), the hop‐derived bitter components in beer, improve memory impairment in aged and Alzheimer's disease mouse models. In this study, we evaluated the effects of IAA intake on the brain structure in healthy middle‐aged to older adults. This study was conducted under the Impulsing Paradigm Change through Disruptive Technologies Program (ImPACT) study launched by the Cabinet office of Japan.

Method

This study employed an open‐labeled, single‐arm, before and after design. Healthy middle‐aged to older adults consumed a beverage containing IAAs (3 mg/190 mL) for 4 weeks.Recently developed magnetic resonance imaging‐based brain health indicators were used to evaluate the following brain conditions: the Brain Healthcare Quotient (BHQ) based on gray matter volume (GM‐BHQ) and white matter fractional anisotropy (FA‐BHQ).

Results

In total, 25 subjects were recruited, and GM‐BHQ and FA‐BHQ were measured before and after intervention. In all subjects, no significant differences in GM‐BHQ and FA‐BHQ were observed. In subjects aged ≥ 60 years (mean 54.5; standard deviation 3.9) (n = 8), GM‐BHQ was significantly increased 4 weeks after intervention compared with that before intervention.

Conclusion

Intake of beverages containing IAAs might affect brain aging, particularly in healthy older adults, which may prevent the development of neurological disorders. Future studies employing more robust designs can elucidate the effects of IAAs on GM‐BHQ and cognitive functions.

This is the first clinical trial evaluating the effects of intake of bitter component of beer, iso‐alpha‐acid, on brain structure. The brain structure before and after intervention was measured by recently developed magnetic resonance imaging‐based method. The gray matter volume of older adults was improved by the intake of iso‐alpha‐acid.

Iso-α-acids and matured hop bitter acids in beer improve obesity-induced cognitive impairment

Dementia and cognitive decline have become public health issues worldwide and life-style-related diseases and obesity have recently been reported as key risk factors. We have recently demonstrated that short-term administration of iso-α-acids (IAAs), hop-derived bitter components of beer, improves spatial and object recognition memory. However, the short-term effects of IAAs on obesity-induced cognitive impairment remain to be investigated. Furthermore, although matured hop bitter acids (MHBAs) are also derived from hops, their effect on obesity-induced cognitive decline remains unknown. In the present study, the short-term administration of IAAs improved memory deficits in high-fat diet (HFD)-fed mice, as assessed in the novel object recognition test (NORT). Dietary MHBAs supplementation administered to HFD-fed mice prevented obesity and improved memory deficits in the NORT. Moreover, the short-term administration of MHBAs improved episodic and spatial reference memory in obese mice. These hop-derived bitter acids may contribute toward improving obesity-induced cognitive impairments.

Abbreviations: IAAs: iso-α-acids; MHBAs: matured hop bitter acids; HFD: high fat diet; NORT: novel object recognition test; NOLT: novel object location test

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.

Hop-Derived Iso-α-Acids in Beer Improve Visual Discrimination and Reversal Learning in Mice as Assessed by a Touch Panel Operant System

Dementia and cognitive decline have become worldwide health problems due to rapid growth of the aged population in many countries. We previously demonstrated that single or short-term administration of iso-α-acids, hop-derived bitter acids in beer, improves the spatial memory of scopolamine-induced amnesia model mice in the Y-maze and enhances novel object recognition in normal mice via activation of the vagus nerve and hippocampal dopaminergic system. However, these behavioral tests do not replicate the stimulus conditions or response requirements of human memory tests, and so may have poor translational validity. In this report, we investigated the effects of iso-α-acids on visual discrimination (VD) and reversal discrimination (RD) using a touch panel-based operant system similar to that used for human working memory tests. In the VD task, scopolamine treatment reduced correct response rate and prolonged response latency in mice, deficits reversed by prior oral administration of iso-α-acids. In the RD task, administration of iso-α-acids significantly increased correct response rate compared to vehicle administration. Previous studies have reported that dopamine signaling is involved in both VD and RD learning, suggesting that enhancement of dopamine release contributes to improved memory performance in mice treated with iso-α-acids. Taken together, iso-α-acids improve VD and RD learning, which are considered high-order cognitive functions. Given the translational advantages of the touch panel-based operant system, the present study suggests that iso-α-acids could be effective for improvement of working memory in human dementia patients.

Tryptophan-Tyrosine Dipeptide, the Core Sequence of β-Lactolin, Improves Memory by Modulating the Dopamine System

Tryptophan-tyrosine (WY)-related peptides including the β-lactopeptide of the glycine-threonine-tryptophan-tyrosine peptide, β-lactolin, improve spatial memory. However, whether and how the WY dipeptide as the core sequence in WY-related peptides improves memory functions has not been investigated. This study assessed the pharmacological effects of the WY dipeptide on memory impairment to elucidate the mechanisms. Here, we showed that oral administration of dipeptides of WY, tryptophan-methionine (WM), tryptophan-valine, tryptophan-leucine, and tryptophan-phenylalanine improved spontaneous alternation of the Y-maze test in scopolamine-induced amnesic mice. In contrast, tyrosine-tryptophan, methionine-tryptophan, tryptophan, tyrosine, and methionine had no effect. These results indicated that the conformation of dipeptides with N-terminal tryptophan is required for their memory improving effects. WY dipeptide inhibited the monoamine oxidase B activity in vitro and increased dopamine levels in the hippocampus and frontal cortex, whereas tryptophan did not cause these effects. In addition, the treatment with SCH-23390, a dopamine D1-like receptor antagonist, and the knockdown of the hippocampal dopamine D1 receptor partially attenuated the memory improvement induced by the WY dipeptide. Importantly, WY dipeptide improved the spontaneous alternations of the Y-maze test in aged mice. These results suggest that the WY dipeptide restores memory impairments by augmenting dopaminergic activity. The development of supplements rich in these peptides might help to prevent age-related cognitive decline.

Theaflavins Improve Memory Impairment and Depression-Like Behavior by Regulating Microglial Activation

Inflammation in the brain is associated with various disorders including Alzheimer's disease and depression. Thus, inflammation has received increasing attention regarding preventive approaches to such disorders. Epidemiological investigations have reported that drinking tea reduces the risk of dementia and depression. Theaflavins, a polyphenol found in black tea, are known to have anti-oxidative and anti-inflammation effects, but the effects of theaflavins on cognitive decline and depression induced by inflammation have not been investigated. To address this research gap, the present study assessed whether theaflavins could protect synapses and dendrites damaged by inflammation and prevent concomitant memory impairment and depression-like behavior in mice. Intracerebroventricular injection with lipopolysaccharide (LPS) induces neural inflammation associated with reduced spontaneous alternations in the Y-maze test and increased immobility in the tail suspension test, indicating impaired spatial memory and depression-like behavior, respectively. Oral administration with theaflavins prevented these behavioral changes induced by LPS. Theaflavins also suppressed productions of inflammatory cytokines and prevented dendritic atrophy and spine loss in the brain. Notably, theaflavins have a stronger anti-inflammatory effect than other polyphenols such as catechin, chlorogenic acid, and caffeic acid. These results suggest that theaflavins can suppress neural inflammation and prevent the symptoms of inflammation-related brain disorders.