Identification of novel β-lactoglobulin-derived peptides, wheylin-1 and -2, having anxiolytic-like activity in mice

Anxiolytic-like effects of milk proteins

Milk varieties and specific proteins exhibit anxiolytic-like actions in mice and rats exposed to several tests, the most prominent being the elevated plus-maze. Administrations of αs1-casein, its 91-100 (α-casozepine), 91-97, 91-93, and 91-92 fragments, the 60-69 fragment of β-casein, lactoferrin, β-lactotensin, wheylin-1, wheylin-2, and α-lactalbumin have been reported to increase open arm exploration relative to enclosed arm exploration. Anxiolytic-like actions have also been described for 91-93 and 91-92 fragments of αs1-casein, wheylin-1, α-lactalbumin, and lactoferrin in the open-field. Some effects appear to be mediated by the GABAA receptor complex, since antagonists mitigated the anxiolytic-like actions of αs1-casein, the 91-92 fragment of αs1-casein, and wheylin-1. Other neurotransmitters purported to affect such behaviors include 5HT, dopamine, and neurotensin. Further research is needed to identify their neuropharmacological actions.

Soy-fortelin: A ghrelin sensitivity-enhancing peptide that stimulates food intake in aged mice

Ghrelin sensitivity is known to decrease with aging in mice and humans, and the decrease contributes to anorexia with aging. In this study, we discovered novel ghrelin sensitivity-enhancing peptides. Ghrelin sensitivity was evaluated by examining whether dipeptide samples enhanced the calcium response to ghrelin in the growth hormone secretagogue receptor-transfected cell line. First, dipeptides were screened using a 336-dipeptide library and we revealed that Ser-Tyr (SY) potentiated ghrelin sensitivity in particular. Based on the structure-activity relationship determined using the dipeptide library and comprehensive analysis of peptides in the chymotrypsin digest of soy β-conglycinin (β-CG), which enhanced ghrelin sensitivity, candidate peptides were narrowed down. Among the chemosynthesized peptides, we discovered that an undecapeptide, SLVNNDDRDSY, corresponding to β-CGα(267-277), stimulated ghrelin sensitivity in vitro. This peptide enhanced the orexigenic activity of ghrelin in C57BL/6 mice and stimulated food intake. Thus, we demonstrated that SLVNNDDRDSY stimulated ghrelin sensitivity in vitro and in vivo and named it "soy-fortelin". Moreover, orally administered soy-fortelin had a similar but smaller effect in the young C57BL/6 mice, whereas it strongly stimulated food intake in 2-year-old aged mice that exhibited high blood ghrelin levels and low ghrelin sensitivity. In conclusion, we discovered soy-fortelin as a novel peptide that enhances ghrelin sensitivity in vivo and in vitro and increases food intake in young and aged ghrelin-resistant mice. Soy-fortelin is the first food-derived peptide reported to enhance ghrelin sensitivity.

Involvement of GABAergic and Serotonergic Systems in the Antinociceptive Effect of Jegosaponin A Isolated from Styrax japonicus

The antinociceptive activity of the flower extracts of Styrax japonicus was confirmed in our previous study. However, the key compound for analgesia has not been distinguished, and the corresponding mechanism is obscure. In this study, the active compound was isolated from the flower by multiple chromatographic techniques and structurally illustrated using spectroscopic methods and referring to the related literature. The antinociceptive activity of the compound and the underlying mechanisms were investigated using animal tests. The active compound was determined to be jegosaponin A (JA), which showed significant antinociceptive responses. JA was also shown to possess sedative and anxiolytic activities but no anti-inflammatory effect, implying the association of the antinociceptive effects with the sedative and anxiolytic activities. Further antagonists and calcium ionophore tests showed that the antinociceptive effect of JA was blocked by flumazenil (FM, antagonist for GABA-A receptor) and reversed by WAY100635 (WAY, antagonist for 5-HT_1A receptor). Contents of 5-HT and its metabolite (5-HIAA) increased significantly in the hippocampus and striatum tissues after JA administration. The results indicated that the antinociceptive effect of JA was regulated by the neurotransmitter system, especially GABAergic and serotonergic systems.

Rice Endoplasmic Protein-Derived Peptides, Rice-Ghretropins A and B, Stimulate Ghrelin Release in MGN3-1 Cells and Increase Plasma Acylated Ghrelin and Food Intake in Mice

In this study, we demonstrated that novel rice-derived bioactive peptides promote the secretion of ghrelin, an endogenous orexigenic hormone secreted from the stomach. The enzymatic digest of rice endosperm protein with subtilisin, a microorganism-derived enzyme, stimulated acylated ghrelin secretion in the ghrelin-releasing cell line MGN3-1 and increased food intake after oral administration in mice. By performing a comprehensive analysis based on structure-activity relationships, we selected candidate peptides from over 30,000 peptides in the rice digest. Among them, we found that QAFEPIRSV and TNPWHSPRQGSF, corresponding to the amino acid sequence of the rice endoplasmic proteins glutelin A1 or A2(52-60) and B1 or B2(31-42), respectively, stimulated acylated ghrelin release in MGN3-1 cells. We named them rice-ghretropins A and B. Pyroglutamate formation of rice-ghretropin A, [pyr¹]-rice-ghretropin A, also promoted ghrelin secretion. Furthermore, oral administration of rice-ghretropins increased food intake, plasma ghrelin concentration, and small intestinal transit in mice. In addition, the subtilisin digest of the rice protein significantly increased food intake for 4 h in 9 month-old (control: 0.61 ± 0.049 g; digest: 0.83 ± 0.059 g) and 24 month-old mice (control: 0.52 ± 0.067 g; digest: 1.01 ± 0.064 g). In summary, we found that novel bioactive peptides, namely, rice-ghretropins, from the enzymatic digest of rice endosperm stimulated acylated ghrelin secretion and increased food intake. This is the first report of rice-derived exogenous bioactive peptides that increase acylated ghrelin secretion.

A Lupin (Lupinusangustifolius) Protein Hydrolysate Exerts Anxiolytic-Like Effects in Western Diet-Fed ApoE−/− Mice

Anxiety is the most prevalent psychiatric disorder worldwide, causing a substantial economic burden due to the associated healthcare costs. Given that commercial anxiolytic treatments may cause important side effects and have medical restrictions for prescription and high costs, the search for new natural and safer treatments is gaining attention. Since lupin protein hydrolysate (LPH) has been shown to be safe and exert anti-inflammatory and antioxidant effects, key risk factors for the anxiety process and memory impairment, we evaluated in this study the potential effects of LPH on anxiety and spatial memory in a Western diet (WD)-induced anxiety model in ApoE^−/− mice. We showed that 20.86% of the 278 identified LPH peptides have biological activity related to anxiolytic/analgesic effects; the principal motifs found were the following: VPL, PGP, YL, and GQ. Moreover, 14 weeks of intragastrical LPH treatment (100 mg/kg) restored the WD-induced anxiety effects, reestablishing the anxiety levels observed in the standard diet (SD)-fed mice since they spent less time in the anxiety zones of the elevated plus maze (EPM). Furthermore, a significant increase in the number of head dips was recorded in LPH-treated mice, which indicates a greater exploration capacity and less fear due to lower levels of anxiety. Interestingly, the LPH group showed similar thigmotaxis, a well-established indicator of animal anxiety and fear, to the SD group, counteracting the WD effect. This is the first study to show that LPH treatment has anxiolytic effects, pointing to LPH as a potential component of future nutritional therapies in patients with anxiety.

Bioactive peptides of whey: obtaining, activity, mechanism of action, and further applications

Bioactive peptides derived from diverse food proteins have been part of diverse investigations. Whey is a rich source of proteins and components related to biological activity. It is known that proteins have effects that promote health benefits. Peptides derived from whey proteins are currently widely studied. These bioactive peptides are amino acid sequences that are encrypted within the first structure of proteins, which required hydrolysis for their release. The hydrolysis could be through in vitro or in vivo enzymatic digestion and using microorganisms in fermented systems. The biological activities associated with bio-peptides include immunomodulatory properties, antibacterial, antihypertensive, antioxidant and opioid, etc. These functions are related to general conditions of health or reduced risk of certain chronic illnesses. To determine the suitability of these peptides/ingredients for applications in food technology, clinical studies are required to evaluate their bioavailability, health claims, and safety of them. This review aimed to describe the biological importance of whey proteins according to the incidence in human health, their role as bioactive peptides source, describing methods, and obtaining technics. In addition, the paper exposes biochemical mechanisms during the activity exerted by biopeptides of whey, and their application trends.

Neuromodulatory peptides: Orally active anxiolytic-like and antidepressant-like peptides derived from dietary plant proteins

Mental disorders are a severe health problem, and the number of patients is growing worldwide. Increased anxiety and decreased motivation due to excessive mental stress further accelerated the severity of the problem. Enzymatic digestion of food proteins produces bioactive peptides with various physiological functions, some of which exhibit neuromodulatory effects with oral administration. Recently, studies reported that some peptides produced from plant proteins such as soybeans, leaves, and grains exhibit emotional regulatory functions such as strong anxiolytic-like and antidepressant-like effects comparable to pharmaceuticals. Conventionally, researchers investigated bioactive peptides by fractionation of protein hydrolysates and structure-activity relationship. As a novel methodology for analyzing bioactive peptides, the information obtained by peptidomics simultaneous analysis of the digested fractions of proteins using mass spectrometry has been effectively utilized. Some small-sized peptides such as dipeptides and tripeptides released food-derived proteins show emotional regulating effects. Moreover, some middle-sized peptides produced after intestinal digestion may exhibit the emotional regulating effect via the vagus nerve, and the importance of the gut-brain axis is also focused. As the central mechanism of emotional regulation, it has been found that these plant-derived peptides regulated monoamine neurotransmitter signaling and hippocampal neurogenesis.

Food protein-derived anxiolytic peptides: their potential role in anxiety management

Could bioactive peptides from food proteins be used as prophylactic in the management of anxiety disorders?

Dipeptide tyrosyl-leucine exhibits antidepressant-like activity in mice

Depression is a worldwide health problem. In the present study, we found that a dipeptide, tyrosyl leucine (Tyr-Leu, YL), administered orally, intracerebroventricularly, or intraperitoneally exhibited a potent antidepressant-like activity in the forced swim and tail suspension tests in naïve mice. YL increased the amount of cells expressing c-Fos, a marker for neuronal activity, in the dentate gyrus of the hippocampus. YL increased bromo-2′-deoxyuridine-positive cells and doublecortin expression in the dentate gyrus of the hippocampus, suggesting that YL enhanced the proliferation of hippocampal progenitor cells in vivo and in vitro. YL did not affect hippocampal mRNA and protein expression of BDNF, which is a regulatory factor of both neurogenesis and depression-like behavior. Intriguingly, YL suppressed activation of the hypothalamo-pituitary-adrenal axis by forced swim stress. Moreover, other aromatic amino acid-leucines, Phe-Leu and Trp-Leu, also exhibited antidepressant-like activities, suggesting that the structure of aromatic amino acid-leucine may be important for antidepressant activity. In addition, bovine milk casein-derived peptide, Tyr-Leu-Gly (YLG), an anxiolytic peptide, exhibited an antidepressant-like activity. Our findings demonstrate that YL exhibits an antidepressant-like effect, moderates the stress response, and induces hippocampal neuronal proliferation through a signal pathway independent of BDNF.

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.

Comprehensive analysis of a dipeptide library to identify ghrelin release-modulating peptides

We performed a comprehensive analysis of ghrelin release-modulating activity of a dipeptide library using MGN3-1, a ghrelin-producing cell line. We found that most dipeptides suppress ghrelin secretion, whereas the N-terminal Ser-containing dipeptides and a few others stimulate it. N-terminal amino acid residues, but not C-terminal residues, play a dominant role in the effects of dipeptides. Among dipeptides, Leu-Ile (LI) and Ser-Val (SV) most strongly suppress and stimulate ghrelin secretion, respectively. LI activates G_i signaling and SV acts via the MAPK pathway. Orally administered LI and SV reduce and increase plasma ghrelin levels and food intake in mice, respectively. In conclusion, LI and SV, found based on the comprehensive screening of a dipeptide library, modulate ghrelin secretion in vitro and in vivo.

Soybean-Derived Glycine-Arginine Dipeptide Administration Promotes Neurotrophic Factor Expression in the Mouse Brain

Brain-derived neurotrophic factor (BDNF), a member of the neurotrophin family, plays an important role in cognitive abilities, including memory and learning. We demonstrated that soybean protein hydrolysate (SPH) diet suppresses age-related cognitive decline via the upregulation of BDNF in a mouse model of senescence. Our purpose was to identify novel bioactive peptides in SPH, which enhance BDNF expression. We treated mouse primary astrocytes with SPH as well as with its positively charged chromatographic fraction. Significant increases in the expression of BDNF were observed in the treatment with positively charged fraction of SPH. Among the synthesized peptides, the dipeptide glycine-arginine (GR) increased BDNF expression in vitro, and LC-TOF-MS analysis showed the presence of GR in the SPH. Furthermore, its administration in vivo increased the expression of BDNF in the cerebral cortex and the number of neurons in hippocampus and cerebral cortex. These data indicate that GR might promote neurogenesis by upregulating BDNF levels.

Enzymatic digest of whey protein and wheylin-1, a dipeptide released in the digest, increase insulin sensitivity in an Akt phosphorylation-dependent manner

Wheylin-1 is the first whey-derived peptide that increases insulin sensitivity in an Akt phosphorylation-dependent manner and lowers blood glucose levels.

Rational identification of a novel soy-derived anxiolytic-like undecapeptide acting via gut-brain axis after oral administration

Here we found that the chymotryptic digest of soy β-conglycinin, a major storage protein, exhibited anxiolytic-like effects in mice. We then searched for anxiolytic-like peptides in the digest. Based on a comprehensive peptide analysis of the chymotryptic digest by high performance liquid chromatograph connected to an LTQ Orbitrap mass spectrometer and the structure-activity relationship of known peptides, we explored anxiolytic-like peptides present in the digest. FLSSTEAQQSY, which corresponds to 323-333 of the β-conglycinin α subunit [βCGα(323-333)] emerged as a candidate. Oral administration of synthetic βCGα(323-333) exhibited anxiolytic-like effects in the elevated plus-maze and open-field test in male mice. Orally administered βCGα(323-333) exhibited anxiolytic-like effects in sham-operated control mice but not in vagotomized mice. In addition, oral administration of βCGα(323-333) increased the expression of c-Fos, a marker of neuronal activity, in the nucleus of the solitary tract, which receives inputs from the vagus nerve. These results suggest that the anxiolytic-like effects were mediated by the vagus nerve. The anxiolytic-like effects of βCGα(323-333) were also blocked by antagonists of the serotonin 5-HT1A, dopamine D1 and GABAA receptors. However βCGα(323-333) had no affinity for these receptors, suggesting it stimulates the release of endogenous neurotransmitters to activate the receptors. Taken together, a soy-derived undecapeptide, βCGα(323-333), may exhibit anxiolytic-like effects after oral administration via the vagus nerve and 5-HT1A, D1 and GABAA systems.

Bioactive peptides derived from natural proteins with respect to diversity of their receptors and physiological effects

We have found various bioactive peptides derived from animal and plant proteins, which interact with receptors for endogenous bioactive peptides such as opioids, neurotensin, complements C3a and C5a, oxytocin, and formyl peptides etc. Among them, rubiscolin, a δ opioid peptide derived from plant RuBisCO, showed memory-consolidating, anxiolytic-like, and food intake-modulating effects. Soymorphin, a μ opioid peptide derived from β-conglycinin showed anxiolytic-like, anorexigenic, hypoglycemic, and hypotriglyceridemic effects. β-Lactotensin derived from β-lactoglobulin, the first natural ligand for the NTS2 receptor, showed memory-consolidating, anxiolytic-like, and hypocholesterolemic effects. Weak agonist peptides for the complements C3a and C5a receptors were released from many proteins and exerted various central effects. Peptides showing anxiolytic-like antihypertensive and anti-alopecia effects via different types of receptors such as OT, FPR and AT2 were also obtained. Based on these study, new functions and post-receptor mechanisms of receptor commom to endogenous and exogenous bioactive peptides have been clarified.

A novel Alaska pollack-derived peptide, which increases glucose uptake in skeletal muscle cells, lowers the blood glucose level in diabetic mice

We found that the tryptic digest of Alaska pollack protein (APP) and novel APP-derived peptide exhibited a glucose-lowering effect in KK-Ay mice, a type II diabetic mice.