Current knowledge of intestinal absorption of bioactive peptides

Evaluating intestinal absorption of peptide Met-Lys-Pro in casein hydrolysate using Caco-2 and human iPS cell-derived small intestinal epithelial cells

High blood pressure is a major risk factor for cardiovascular disease. Our previous study confirmed that daily intake of casein hydrolysate that contained Met-Lys-Pro (MKP) can safely lower mildly elevated blood pressure. The present study aimed to evaluate the intestinal absorption differences between peptide MKP as a casein hydrolysate and synthetic MKP alone using Caco-2 cells and human iPS cell-derived small intestinal epithelial cells (hiSIECs). MKP was transported intact through Caco-2 cells and hiSIECs with permeability coefficient (Papp) values of 0.57 ± 0.14 × 10-7 and 1.03 ± 0.44 × 10-7 cm/s, respectively. This difference in Papp suggests differences in the tight junction strength and peptidase activity of each cell. Moreover, the transepithelial transport and residual ratio of intact MKP after adding casein hydrolysate containing MKP was significantly higher than that after adding synthetic MKP alone, suggesting that other peptides in casein hydrolysate suppressed MKP degradation and increased its　transport. These findings suggest that hiSIECs could be useful for predicting the human intestinal absorption of bioactive peptides; ingesting MKP as a casein hydrolysate may also improve MKP bioavailability.

The Comparative Analysis of Peptides in Enteral Nutrition Products and Foods for Special Medical Purposes

Enteral nutrition (EN) and foods for special medical purposes (FSMPs) can be used to meet the specific nutritional needs of patients. There are multiple types of EN products and nutritionally complete FSMPs on the market. The peptides in these products are important nutritional components, while their presence in different products remains unclear. To provide better clinical guidelines, we analyzed and compared the molecular weight (MW) distribution, types, and quantities of peptides and bioactive peptides of two EN products (liquid products) and two FSMPs with nutritionally complete formulas (powder products). Our results showed that each product had a unique peptide profile. The two liquid products and one powder product (Samples 1-3) had a higher content of peptides. Sample 1 contained 75.60% peptides with an MW less than 375 Da and contained 95.21% peptides with an MW less than 1000 Da, being rich in short peptides. Sample 2 and 3 had high levels of peptides with MW values between 180 Da and 2000 Da. Additionally, Sample 4 contained high levels of proteins, containing 69.18% peptides with MW values larger than 10,000 Da. Further, Sample 1 had more bioactive dipeptides and Sample 2 had more long bioactive peptides. Our results suggest that peptides in different EN and FSMP products are very different and should be evaluated in more detail. This will provide valuable information for clinical medical professionals, help them to guide patients with different physiological conditions better, and ultimately benefit patients.

Effect of Bioactive Peptides on Gut Microbiota and Their Relations to Human Health

Bioactive peptides derived from both exogenous and endogenous origins have been studied extensively to use their beneficial effects in humans and animals. Bioactive peptides exhibit beneficial bodily functions and contribute to a healthy gastrointestinal system by influencing barrier functions, immune responses, and gut microbiota. Gut microbiota is a diverse microbial community that significantly influences the overall well-being and homeostasis of the body. Factors such as diet, age, lifestyle, medication, and environmental circumstances can affect the composition and diversity of the gut microbiota. The disturbances or imbalances in the gut microbiota have been associated with various health problems. The interplays between bioactive peptides and gut microbiota are not fully understood, but bioactive peptides hold promise as modulators of the gut microbiota to promote gut health. Almost all the bioactive research on human health, including the development of therapeutics and nutritional interventions, uses cell culture, even though their direct biofunctional activities can only occur when absorbed in the intestine and into the blood system. This review focuses on the current understanding of bioactive peptides in gut microbiota and their impact and mechanisms on gut and human health. The novelty of this review lies in its comprehensive analysis of the multifaceted interactions between bioactive peptides and gut microbiota, integrating knowledge from diverse disciplines between microbiology and nutrition. By elucidating the underlying mechanisms and identifying current research gaps, this review offers an outlook on the potential of bioactive peptides in promoting gut health and shaping future therapeutic and nutritional interventions.

Understanding the Transepithelial Transport and Transbilayer Diffusion of the Antihypertensive Peptide Asn-Cys-Trp: Insights from Caco-2 Cell Monolayers and the DPPC Model Membrane

Understanding the transport mechanism of the peptide Asn-Cys-Trp (NCW) is crucial to improving its intestinal absorption and bioavailability. This study investigated the absorption of NCW through Caco-2 cell monolayers and its interaction with the DPPC bilayers. Results revealed that after a 3 h incubation, the Papp (AP-BL) and Papp (BL-AP) values of NCW at a concentration of 5 mmol/L were (22.24 ± 4.52) × 10-7 and (6.63 ± 2.31) × 10-7 cm/s, respectively, with the transport rates of 1.59 ± 0.32 and 0.62 ± 0.20%, indicating its moderate absorption. NCW was found to be transported via PepT1 and paracellular transport pathways, as evidenced by the significant impact of Gly-Pro and cytochalasin D on the Papp values. Moreover, NCW upregulated ZO-1 mRNA expression. Further investigation of the ZO-1-mediated interaction between NCW and tight junction proteins will contribute to a better understanding of the paracellular transport mechanism of NCW. The interaction between NCW and the DPPC bilayers was predominantly driven by entropy. NCW permeated the bilayers through electrostatic, hydrogen bonding, and hydrophobic interactions, resulting in increased fluidity, flexibility, and disorder as well as phase transition and phase separation of the bilayers.

Anionic polysaccharides benefit the bioavailability of pork myofibrillar protein gels: Evidence from a perspective of protein absorption and metabolism

This study aimed to probe the bioavailability of myofibrillar protein (MP) gels in mice as affected by incorporating anionic xanthan (XMP) and sodium alginate (SMP)/cationic chitosan (CSMP)/neutral curdlan (CMP) and konjac (KMP), respectively. The results showed that the numbers of peptides absorbed were obviously higher in anionic XMP and SMP groups (88 and 126, respectively) than in the cationic CSMP (51) group. The contents of free amino acids absorbed in SMP and XMP were significantly greater than that in CSMP and CMP groups (P < 0.05). Furthermore, the antioxidant capacity of bioactive compounds absorbed in the SMP group was higher than those in the other groups (P < 0.05), and the expression of tight junction protein (Occludin and ZO-1) was up-regulated in SMP group. The low contents of free ammonia, indole and p-cresol were observed in the anionic XMP, SMP and neutral KMP groups, compared to CSMP group. This work highlights the benefits of anionic polysaccharides (sodium alginate and xanthan) in developing low-fat meat products with high MP bioavailability.

Whole genome sequencing analysis of Limosilactobacillus reuteri from the intestinal tract of mice recovering from ulcerative colitis and preliminary study on anti-inflammatory effects of its derived peptides

Limosilactobacillus reuteri is an indigenous inhabitant of the animal gut known for its probiotic effects on the host. In our previous study, a large number of L. reuteri strains were isolated from the gastrointestinal tract of mice recovering from ulcerative colitis, from which we randomly selected L. reuteri RE225 for whole genome sequencing to explore its probiotic properties. The results of next-generation sequencing and third-generation single molecule sequencing showed that L. reuteri RE225 contained many genes encoding functional proteins associated with adhesion, anti-inflammatory and pathogen inhibition. And compared to other L. reuteri strains in NCBI, L. reuteri RE225 has unique gene families with probiotic functions. In order to further explore the probiotic effect of the L. reuteri RE225, the derived peptides were identified by LC-MS/MS, and the peptides with tumor necrosis factor-α binding ability were screened by reverse molecular docking and microscale thermophoresis. Finally, cell experiments demonstrated the anti-inflammatory ability of the peptides. Western blotting and qPCR analyses confirmed that the selected peptides might alleviate LPS-induced inflammation in NCM460 cells by inhibiting JAK2/STAT3 pathway activation.

Alterations in the sequence and bioactivity of food-derived oligopeptides during simulated gastrointestinal digestion and absorption: a review

Food-derived oligopeptides (FOPs) exhibit various bioactivities. However, little was known about their sequence changes in the gastrointestinal tract and the effect of changes on bioactivities. FOPs' sequence features, changes and effects on bioactivities have been summarised. The sequence length of FOPs decreases with increased exposure of hydrophobic and basic amino acids at the terminal during simulated gastrointestinal digestion. A decrease in bioactivities after simulated intestinal absorption has correlated with a decrease of Leu, Ile, Arg, Tyr, Gln and Pro. The sequence of FOPs that pass readily through the intestinal epithelium corresponds to transport modes, and FOPs whose sequences remain unchanged after transport are the most bioactive. These include mainly dipeptides to tetrapeptides, consisting of numerous hydrophobic and basic amino acids, found mostly at the end of the peptide chain, especially at the C-terminal. This review aims to provide a foundation for applications of FOPs in nutritional supplements and functional foods.

Digestive properties and peptide profiles exhibited significant differences between skim camel milk and bovine milk powder after static in vitro simulated infant gastrointestinal digestion

This study aims to analyze the differences in digestion properties and peptide profiles between the skim camel and bovine milk powder after static in vitro simulated infant gastrointestinal digestion. The hydrolysis degree of camel milk proteins exceeded by 13.18% that of bovine milk. The concentration and release rate of free amino groups in the camel milk digesta was higher than that of bovine milk powder, which was likely due to the higher β-/αs-casein ratio and larger casein micelle size in camel milk. Camel milk powder presented higher β-CN coverage and comparatively shorter bioactive peptides compared to bovine milk powder. The anti-inflammatory peptide KVLPVPQ displayed the highest abundance in camel milk powder. Outcomes of this study showed that camel milk proteins possessed superior digestibility and unique peptides, which outlined the potential nutritional implications of camel milk for infants.

Dietary fish intake increased the concentration of soluble ACE2 in rats: can fish consumption reduce the risk of COVID-19 infection through interception of SARS-CoV-2 by soluble ACE2?

The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) enters the cells after binding to the membrane-bound receptor angiotensin-converting enzyme 2 (ACE2), but this may be prevented through interception by soluble ACE2 (sACE2) or by inhibition of the ACE2 receptor, thus obstructing cell entry and replication. The main objective of this study was to investigate if fish intake affected the concentration of sACE2 in rats. The secondary aim was to evaluate the in vitro ACE2-inhibiting activity of fish proteins. Rats were fed cod muscle as 25 % of dietary protein, and blood was collected after 4 weeks of intervention. Muscle, backbone, skin, head, stomach, stomach content, intestine and swim bladder from haddock, saithe, cod and redfish were hydrolysed with trypsin before ACE2-inhibiting activity was measured in vitro. In vivo data were compared using unpaired Student's t test, and in vitro data were compared using one-way ANOVA followed by the Tukey HSD post hoc test. The mean sACE2 concentration was 47 % higher in rats fed cod when compared with control rats (P 0·034), whereas serum concentrations of angiotensin II and TNF-α were similar between the two experimental groups. Muscle, backbone, skin and head from all four fish species inhibited ACE2 activity in vitro, whereas the remaining fractions had no effect. To conclude, our novel data demonstrate that fish intake increased the sACE2 concentration in rats and that the hydrolysed fish proteins inhibited ACE2 activity in vitro.

The effect of oral supplements containing collagen peptides rich in X-Hyp or X-Hyp-Gly compared with normal collagen hydrolysates on skin elasticity and collagen holes: a randomised double-blind clinical study

Collagen peptides enriched with X-Hyp or X-Hyp-Gly have demonstrated resistance to digestive and systemic enzymes, suggesting their potential for improved absorption efficiency and enhancement of skin properties. This study aimed to evaluate the effects of oral supplementation with collagen peptides rich in X-Hyp or X-Hyp-Gly on skin properties in a clinical setting. A double-blind, randomized study was conducted on 30 healthy adult participants aged between 22 and 30. Normal collagen hydrolysates were used as the control, and each participant received a daily powdered drink containing either 5 grams of collagen peptides or hydrolysates (n = 15 in each group) for a period of 42 days. Skin elasticity was evaluated using the Cutometer, revealing a significant increase in the intervention group's skin elasticity (R2 values: 0.86 to 0.92, P < 0.001; R7 values: 0.77 to 0.84, P < 0.001). Collagen synthesis in the dermis was assessed using the SIAscope, demonstrating a substantial increase of 30.67 in the intervention group, while the control group exhibited a marginal increase of 0.49. In vitro digestion and cellular transport models were employed to evaluate the absorption and transport of Hyp-containing collagen peptides. LC-MS analysis demonstrated a significantly higher proportion of small peptide oligomers below 500 Da in the CP product compared to the control group (approximately 70% vs. 50%) after digestion. Additionally, the CP product exhibited a greater uptake of peptides (27%) compared to the control group (21%). These findings highlight the potential use of Hyp-containing collagen peptides with a low molecular weight in food supplements for improving skin health.

Absorption of egg white hydrolysate in the intestine: Clathrin-dependent endocytosis as the main transport route

This paper aimed to investigate the in vivo absorption of egg white hydrolysate (EWH) in rats and the transport route across the intestinal epithelium. Results showed that the level of plasma peptide-bound amino acid (PAA) of the EWH-supplemented rats (EWH-R) was determined to be 2012.18 ± 300.98 μmol/L, 10.72% higher than that of the control group, and was significantly positively correlated to that of EWH. Thirty-three egg white-derived peptides were successfully identified from the plasma of EWH-R, and 20 of them were found in both EWH-R plasma and EWH, indicating that these peptides tend to be absorbed through the intestinal epithelium in intact forms into the blood circulation. In addition, 637 up-regulated and 577 down-regulated genes in Caco-2 cells incubated with EWH were detected by RNA-sequencing and the clathrin-dependent endocytosis was the most enriched pathway in KEGG analysis. EWH significantly increased the mRNA levels of the key genes involved in the clathrin-dependent endocytosis but these changes would be inhibited by the clathrin-dependent endocytosis inhibitor of chlorpromazine. Moreover, the transepithelial transport of EWH across Caco-2 cell monolayers was significantly reduced by chlorpromazine. This study provided molecular-level evidence for the first time that clathrin-dependent endocytosis might be the main transport route of EWH in the intestinal epithelium.

Absorption characteristics and the effect on vascular endothelial cell permeability of an anticoagulant peptide

In the former report, the casein peptide TKLTEEEKNR (PfCN) exhibits strong thrombin inhibitory activity in vitro. Its absorption capabilities, however, are unclear. Therefore, we studied its absorption characteristics both in vivo and in vitro. PfCN was carried by cells from the apical chamber to the basolateral chamber via active translocation in Caco-2 cells. Meanwhile, it can also be transported by HUVECs. We found that PfCN can be taken up by HUVECs using confocal laser imaging. PfCN has been proven to have good absorption properties in in vivo experiments. After five minutes of oral treatment, PfCN was identified in the blood, peaking at 82.75 ± 36.52 ng/mL in 30 min. And PfCN vanished from the blood circulation after 120 min. According to in vivo experiments, excessive concentrations of PfCN will alter the permeability of HUVECs. As a result, there is a foundation for PfCN application in the food sector. Meanwhile, we also hope this article can give an idea to the researchers who studying the absorption of functional peptides.

Oxidation and side-chain modifications decrease gastrointestinal digestibility and transport of proteins from salted bighead carp fillets after frozen storage

This study examined the effects of protein oxidation on digestion behavior. The oxidation levels and in vitro digestibility of myofibrillar proteins from fresh-brined and frozen bighead carp fillets were investigated, and the intestinal transport property was characterized by comparing the peptides on both sides of the intestinal membrane. Frozen fillets showed high oxidation levels, low amino acid content and in vitro protein digestibility, which were further increased by brining. After storage, the number of modified peptides from myosin heavy chain (MHC) increased over 10-fold in NaCl-treated samples (2.0 M). Various types of side-chain modifications in amino acids were identified, such as di-oxidation, α-aminoadipic semialdehyde (AAS), γ-glutamic semialdehyde (GGS), and protein-malondialdehyde (MDA) adducts, mainly originating from MHC. The Lysine/Arginine-MDA adducts, AAS, and GGS decreased protein digestibility and their intestinal transportation. These findings suggest that oxidation impacts protein digestion and should be considered in food processing and preservation strategies.

Compound small peptide of Chinese medicine alleviates cyclophosphamide induced immunosuppression in mice by Th17/Treg and jejunum intestinal flora

The aim of this study was to explore the efficacy of Compound small peptide of Chinese medicine (CSPCM) on cyclophosphamide (CTX) induced immunosuppression in mice. The 100 male Kunming mice were divided into 5 groups: group A (control group), group B (model group), group C (100 mg/kg.bw CSPCM), group D (200 mg/kg.bw CSPCM) and group E (400 mg/kg.bw CSPCM). At 1–3 days, mice of group B, C, D and E were intraperitoneally injected with 80 mg/kg.bw CTX. The results showed that compared with group A, the immune organ index, body weight change, RORγ T gene expression, RORγ T protein expression, CD3+ cell number, Th17 number and Alpha index, white blood cell count, lymphocyte count and monocyte count were significantly decreased in group B (p &lt; 0.05), while Foxp3 gene expression, Foxp3 protein expression and Treg cell number were significantly increased (p &lt; 0.05), CSPCM has a good therapeutic effect on the above abnormalities caused by CTX. CTX caused the decrease of intestinal flora richness and the abnormal structure of intestinal flora, and CSPCM could change the intestinal flora destroyed by CTX to the direction of intestinal flora of healthy mice. On the whole, CSPCM has a good therapeutic effect on CTX-induced immunosuppression in mice, which is reflected in the index of immune organs, the number of T lymphocytes and Th17 cells increased, the number of Treg cells decreased and the structure of intestinal flora was reconstructed.

Transepithelial transport and cytoprotection of novel antioxidant peptides isolated from simulated gastrointestinal digestion of Xuanwei ham

As a traditional fermented meat product, dry-cured Xuanwei ham could be a rich source of bioactive peptides. This study intended to investigate the transepithelial transport and cytoprotection of antioxidant peptides isolated from simulated gastrointestinal digestion of Xuanwei ham. Through ultrafiltration and gel filtration chromatography after simulated digestion, five new antioxidative cell-penetrating peptides (CPPs) with 16-27 amino acid residues were identified, and protective effects of the pretreatment with GHYTEGAELVDSVLDVVRK (GK-19) and TDEFQLHTNVNDGTEFGGSIYQK (TK-23) on H₂O₂-induced damaged HepG2 cells were investigated. The results showed that the peptide TK-23 at 0.5 mg mL^-1 showed a good antioxidant activity through upregulating the activity of antioxidant enzymes (CAT, SOD and GR) and decreasing the MDA level in H₂O₂-induced damaged HepG2 cells with a better protective effect compared to GSH. Our observations of novel antioxidant CPPs with 16-27 amino acid residues could enrich the antioxidative CPP database, and these findings could provide data support for further study of CPPs.

Preparation, identification, and molecular docking of novel elastase inhibitory peptide from walnut (Juglans regia L.) meal

This study aimed to isolate bioactive peptides with elastase inhibitory activity from walnut meal via ultrasonic enzymatic hydrolysis. The optimal hydrolysis conditions of walnut meal protein hydrolysates (WMPHs) were obtained by response surface methodology (RSM), while a molecular weight of<3 kDa fraction was analyzed by LC-MS/MS, and 556 peptides were identified. PyRx virtual screening and Autodock Vina molecular docking revealed that the pentapeptide Phe-Phe-Val-Pro-Phe (FFVPF) could interact with elastase primarily through hydrophobic interactions, hydrogen bonds, and π-sulfur bonds, with a binding energy of -5.22 kcal/mol. The verification results of inhibitory activity showed that FFVPF had better elastase inhibitory activity, with IC₅₀ values of 0.469 ± 0.01 mg/mL. Furthermore, FFVPF exhibited specific stability in the gastric environment. These findings suggest that the pentapeptide FFVPF from defatted walnut meal could serve as a potential source of elastase inhibitors in the food, medical, and cosmetics industries.

Acid-Resistant Mesoporous Metal-Organic Frameworks as Carriers for Targeted Hypoglycemic Peptide Delivery: Peptide Encapsulation, Release, and Bioactivity

Oral administration of bioactive peptides with α-glucosidase inhibitory activities is a promising strategy for diabetes mellitus. The wheat germ peptide Leu-Asp-Leu-Gln-Arg (LDLQR) has been previously proven to inhibit the activity of α-glucosidase efficiently. However, it is still difficult to transport the peptide to the intestine completely due to the harsh condition of the stomach. Herein, an acid-resistant zirconium-based metal-organic framework, NU-1000, was used to immobilize LDLQR with a high encapsulation capacity (92.72%) and encapsulation efficiency (44.08%) in only 10 min. The in vitro release results showed that the acid-stable NU-1000 not only effectively protected LDLQR from degradation in the presence of stomach acid and pepsin effectively but also ensured the release of encapsulated LDLQR under simulated intestinal conditions. Furthermore, LDLQR@NU-1000 could slow down the elevated blood sugar caused by maltose in mice and the area under blood sugar curve decreased by almost 20% when compared with the control group. The inflammatory factor (IL-1β, IL-6) in vivo and cell growth in vitro were almost the same between NU-1000 treatment and normal control groups. This study indicates NU-1000 is a promising vehicle for targeted peptide-based bioactive delivery to the small intestine.

Current trends and perspectives on bioaccessibility and bioavailability of food bioactive peptides: in vitro and ex vivo studies

The bioaccessibility and bioavailability of food-derived bioactive compounds are important issues when assessing their in vivo physiological health-promoting effects. Food components such as proteins and peptides are exposed to different proteases and peptidases during gastrointestinal digestion and absorption. Different in vitro approaches have therefore been developed to evaluate the bioaccessibility and stability of bioactive peptides. The static simulated gastrointestinal digestion model (SGD) was widely reported to assess the bioaccessibility of bioactive peptides. On the other hand, although the dynamic SGD model may better simulate human digestion, it has rarely been explored in bioaccessibility studies of food bioactive peptides due to its high cost and lack of standardization. For bioavailability studies, the Caco-2 cell monolayer model has been used extensively for the assessment of food bioactive peptides. In fact, very few reports using alternative methods for determining transepithelial transport of bioactive peptides have been employed. In this sense, ex vivo tissue-based models such as the Ussing chamber and the everted sac gut have been used. Current evidence supports the fact that using SGD with cell-based models for evaluating the bioaccessibility, absorption, and bioavailability of food-derived bioactive peptides, is the most commonly used approach. Nevertheless, SGD with ex vivo tissue-based models such as the everted sac, remains to be further explored because it seems to be the model that better mimics the physiological process - it is also fast and inexpensive, and several compounds may be tested simultaneously. In the present review, we discuss information available on the different in vitro approaches for the determination of bioaccessibility and bioavailability of food-derived bioactive peptides with special emphasis on ex vivo tissue-based models such as the everted sac and the Ussing chamber models. © 2022 Society of Chemical Industry.

Active Peptide AR-9 From Eupolyphaga sinensis Reduces Blood Lipid and Hepatic Lipid Accumulation by Restoring Gut Flora and Its Metabolites in a High Fat Diet–Induced Hyperlipidemia Rat

The dysbiosis of gut flora and its metabolites plays important roles in the progression of hyperlipidemia (HL), and some bioactive peptides are available for HL treatment. In this study, we aimed to isolate an active peptide (AR-9) from active peptides of E. sinensis (APE) and determine whether AR-9 could improve many symptoms of a HL rat induced by a high-fat diet (HFD) by modulating gut flora and its metabolites. Above all, AR-9 was derived from APE using ion-exchange chromatography, and its structure was deconstructed by Fourier transform infrared spectrometer (FT-IR), circular dichroism (CD) spectroscopy, and UHPLC-Q-Exactive-Orbitrap MS. Then, an HFD-induced HL model in SD rats was established and used to clarify the regulatory effects of AR-9 (dose of 3 mg/kg) on HL. Normal diet–fed rats were taken as the control. The plasma samples and liver were harvested for biochemical and histopathological examinations. 16S rRNA gene sequencing and untargeted metabolomics were sequenced to assess changes in gut flora and its metabolites from rat fecal samples. Finally, Spearman’s correlation analysis was used to assess the relationship between lipid-related factors, gut flora, and its metabolites so as to evaluate the mechanism of AR-9 against HL. The results of the separation experiments showed that the amino acid sequence of AR-9 was AVFPSIVGR, which was a fragment of the actin protein from Blattaria insects. Moreover, HFD rats developed exaltation of index factors, liver lipid accumulation, and simple fibrosis for 8 weeks, and the profiles of gut flora and its metabolites were significantly altered. After treatment, AR-9 decreased the levels of lipid factors in plasma and the extent of liver damage. 16S rRNA gene sequencing results indicated that AR-9 significantly increased the relative abundance of beneficial bacteria Bacteroidetes and reduced the relative abundance of the obesity-associated bacteria Firmicutes. Furthermore, AR-9 changed gut microbiota composition and increased the relative abundance of beneficial bacteria: Lactobacillus, Clostridium, Dehalobacterium, and Candidatus arthromitus. Fecal metabolomics showed that the pathway regulated by AR-9 was “arginine biosynthesis”, in which the contents were citrulline and ornithine. Spearman’s correlation analysis revealed that two metabolites (ornithine and citrulline) showed significantly negative correlations with obesity-related parameters and positive correlations with the gut genera (Clostridium) enriched by AR-9. Overall, our results suggested interactions between gut microbial shifts and fecal amino acid/lipid metabolism and revealed the mechanisms underlying the anti-HL effect of AR-9. The abovementioned results not only reveal the initial anti-HL mechanism of AR-9 but also provide a theoretical basis for the continued development of AR-9.

Effects of compound small peptides of Chinese medicine on intestinal immunity and cecal intestinal flora in CTX immunosuppressed mice

The study was designed to explore the improvement effect of CSPCM (compound small peptide of Chinese medicine) on intestinal immunity and microflora through the treatment of different doses of CSPCM. A total of 100 male Kunming mice were weighed and divided into five groups, namely, group A (control group), group B (model group), group C (0.1 g/kg·bw CSPCM), group D (0.2 g/kg·bw CSPCM), and group E (0.4 g/kg·bw CSPCM). The use of CTX (cyclophosphamide) caused a series of negative effects: the secretion of IL-2, IL-22, TNF-α, sIgA, length of the villi, and the area of Pey's node were significantly reduced (P < 0.05); the depth of crypt and the percent of CD3⁺ and CD4⁺ cells were significantly increased (P < 0.05); the cecal flora taxa decreased; the abundance of Firmicutes and Lactobacillus increased; and the abundance of Bacteroidetes, Deferribacteres, Proteobacteria, Mucispirillum, Bacteroides, and Flexisprra decreased. The addition of CSPCM improved the secretion of cytokines and the development of intestinal villi, crypts, and Pey's node. The number of CD3⁺ and CD4⁺ cells in groups C, D, and E was significantly higher than that in group B (P < 0.05). Compared with group B, the abundance of Firmicutes in groups C, D, and E was decreased, and the Bacteroidetes, Deferribacteres, and Proteobacteria increased. The abundance of Lactobacillus decreased, while that of Mucispirillum, Bacteroides, and Flexisprra increased. It is concluded that cyclophosphamide is extremely destructive to the intestinal area and has a great negative impact on the development of the small intestine, the intestinal immune system, and the intestinal flora. The CSPCM can improve the negative effects of CTX.

Current Trends and Applications of Food-derived Antihypertensive Peptides for the Management of Cardiovascular Disease

Abstract:

Food derived Antihypertensive peptides is considered as a natural supplement for controlling the hypertension. Food protein not only serve as a macronutrient but also act as raw material for biosynthesis of physiologically active peptides. Food sources like milk and milk products, animal protein such as meat, chicken, fish, eggs and plant derived proteins from soy, rice, wheat, mushroom, pumpkins contain high amount of antihypertensive peptides. The food derived antihypertensive peptides has ability to supress the action of rennin and Angiotesin converting enzyme (ACE) which is mainly involved in regulation of blood pressure by RAS. The biosynthesis of endothelial nitric oxide synthase is also improved by ACE inhibitory peptides which increase the production of nitric oxide in vascular walls and encourage vasodilation. Interaction between the angiotensin II and its receptor is also inhibited by the peptides which help to reduce hypertension. This review will explore the novel sources and applications of food derived peptides for the management of hypertension.

Purification and Characterization of a Novel Calcium-Binding Heptapeptide from the Hydrolysate of Tilapia Bone with Its Osteogenic Activity

In this study, a calcium-binding peptide was obtained by hydrolyzing tilapia bone and its osteogenic activity was evaluated. Animal protease was selected from nine enzymes, and its hydrolysate was purified through preparative and semi-preparative reverse phase high-performance liquid chromatography. The purified peptide was identified as DGPSGPK (656.32 Da) and its calcium-binding capacity reached 111.98 µg/mg. The peptide calcium chelate (DGPSGPK-Ca) was obtained, and its structure was characterized through Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM), and mass spectrometry (MS). The results of XRD and SEM showed that DGPSGPK-Ca was formed as a new compound. The carboxyl and amino groups of Lys and Asp residues may be the chelating sites of DGPSGPK according to the FTIR and MS results. The molecular simulation showed the carbonyl groups of Asp, Pro, Ser, and Lys residues involved in the binding of calcium. The interaction of DGPSGPK and different integrins was evaluated by molecular docking simulation, and the main forces involved were electrostatic interaction forces, hydrogen bonding and hydrophobic interactions. Furthermore, DGPSGPK could inhibit the differentiation of osteoclast and promote the proliferation, differentiation and mineralization of osteoblasts.

A Novel Gelatinase from Marine Flocculibacter collagenilyticus SM1988: Characterization and Potential Application in Collagen Oligopeptide-Rich Hydrolysate Preparation

Although the S8 family in the MEROPS database contains many peptidases, only a few S8 peptidases have been applied in the preparation of bioactive oligopeptides. Bovine bone collagen is a good source for preparing collagen oligopeptides, but has been so far rarely applied in collagen peptide preparation. Here, we characterized a novel S8 gelatinase, Aa2_1884, from marine bacterium Flocculibacter collagenilyticus SM1988^T, and evaluated its potential application in the preparation of collagen oligopeptides from bovine bone collagen. Aa2_1884 is a multimodular S8 peptidase with a distinct domain architecture from other reported peptidases. The recombinant Aa2_1884 over-expressed in Escherichia coli showed high activity toward gelatin and denatured collagens, but no activity toward natural collagens, indicating that Aa2_1884 is a gelatinase. To evaluate the potential of Aa2_1884 in the preparation of collagen oligopeptides from bovine bone collagen, three enzymatic hydrolysis parameters, hydrolysis temperature, hydrolysis time and enzyme-substrate ratio (E/S), were optimized by single factor experiments, and the optimal hydrolysis conditions were determined to be reaction at 60 ℃ for 3 h with an E/S of 400 U/g. Under these conditions, the hydrolysis efficiency of bovine bone collagen by Aa2_1884 reached 95.3%. The resultant hydrolysate contained 97.8% peptides, in which peptides with a molecular weight lower than 1000 Da and 500 Da accounted for 55.1% and 39.5%, respectively, indicating that the hydrolysate was rich in oligopeptides. These results indicate that Aa2_1884 likely has a promising potential application in the preparation of collagen oligopeptide-rich hydrolysate from bovine bone collagen, which may provide a feasible way for the high-value utilization of bovine bone collagen.

Antihypertensive activity of orally consumed ACE-I inhibitory peptides

Food proteins are sources for ACE-I inhibitory peptides that can be extracted by enzymatic hydrolysis exhibiting anti-hypertensive activity. However, these peptides are prone to further degradation by gastrointestinal enzymes during oral consumption. Bio-activity of these peptides is dependent on the resultant peptide post gastrointestinal digestion. To exhibit the bio-activity, they need to be absorbed in intact form. Although studies suggest di and tri-peptides show better ACE-I inhibitory activity, few peptides show altered IC₅₀ values under simulated gastrointestinal digestion. Moreover, ACE-I inhibitory peptides with low IC₅₀ values have not shown effective anti-hypertensive activity in spontaneously hypertensive rats when administered orally. Few ACE-I inhibitory peptides have reported effective reduction in systolic blood-pressure when administered through intravenously. During oral consumption of such peptides, the actual peptide sequence responsible for reducing blood-pressure is a result of breakdown in gastrointestinal tract. The fate of targeted peptides during digestion depends on amino acid sequence of the protein containing the specific site for cleavage where the action of digestive enzymes takes place. Therefore, this review attempts to explain the factors that affect the anti-hypertensive activity of ACE-I inhibitory peptides during oral consumption. It also highlights subsequent absorption of ACE-I inhibitory peptides after gastrointestinal digestion.

In vitro and in silico characterization of adiponectin-receptor agonist dipeptides

The aim of this study is to develop a dipeptide showing an adiponectin receptor 1 (AdipoR1) agonistic effect in skeletal muscle L6 myotubes. Based on the structure of the AdipoR1 agonist, AdipoRon, 15 synthetic dipeptides were targeted to promote glucose uptake in L6 myotubes. Tyr-Pro showed a significant increase in glucose uptake among the dipeptides, while other dipeptides, including Pro-Tyr, failed to exert this effect. Tyr-Pro induces glucose transporter 4 (Glut4) expression in the plasma membrane, along with adenosine monophosphate-activated protein kinase (AMPK) activation. In AdipoR1-knocked down cells, the promotion by Tyr-Pro was ameliorated, indicating that Tyr-Pro may directly interact with AdipoR1 as an agonist, followed by the activation of AMPK/Glut4 translocation in L6 myotubes. Molecular dynamics simulations revealed that a Tyr-Pro molecule was stably positioned in the two potential binding pockets (sites 1 and 2) of the seven-transmembrane receptor, AdipoR1, anchored in a virtual 1-palmitoyl-2-oleoyl-phosphatidylcholine membrane. In conclusion, we demonstrated the antidiabetic function of the Tyr-Pro dipeptide as a possible AdipoR1 agonist.

Characteristics of Electrospray-Ionization Detection of Synthetic Di- to Penta-Oligopeptides by Amine Derivatizations

Chemical derivatizations have been extensively developed for highly sensitive detection of bioactive small peptides; however, their advantages from the viewpoint of longer oligopeptides remain unverified. In this study, electrospray-ionization (ESI)-mass spectrometric (MS) detection of synthetic di- to pentapeptides consisting of glycine and sarcosine were characterized by four amine derivatization methods. It was concluded that the ESI-MS detection of di- to pentapeptides was characterized by the molecular surface area of derivatized peptide moieties with an optimal value of 250 - 300 Ų, regardless of hydrophobicity and derivatization methods.

Measuring the oral bioavailability of protein hydrolysates derived from food sources: A critical review of current bioassays

BACKGROUND

Food proteins are a source of hydrolysates with potentially useful biological attributes. Bioactive peptides from food-derived proteins are released from hydrolysates using exogenous industrial processes or endogenous intestinal enzymes. Current in vitro permeability assays have limitations in predicting the oral bioavailability (BA) of bioactive peptides in humans. There are also difficulties in relating the low blood levels of food-derived bioactive peptides detected in preclinical in vivo models to pharmacodynamic read-outs relevant for humans.

SCOPE AND APPROACH

In this review, we describe in vitro assays of digestion, permeation, and metabolism as indirect predictors of the potential oral BA of hydrolysates and their constituent bioactive peptides. We discuss the relationship between industrial hydrolysis processes and the oral BA of hydrolysates and their peptide by-products.

KEY FINDINGS

Hydrolysates are challenging for analytical detection methods due to capacity for enzymatic generation of peptides with novel sequences and also new modifications of these peptides during digestion. Mass spectrometry and peptidomics can improve the capacity to detect individual peptides released from complex hydrolysates in biological milieu.

Oral intake of rice overexpressing ubiquitin ligase inhibitory pentapeptide prevents atrophy in denervated skeletal muscle

We previously reported that intramuscular injections of ubiquitin ligase CBLB inhibitory pentapeptide (Cblin; Asp-Gly-pTyr-Met-Pro) restored lost muscle mass caused by sciatic denervation. Here, we detected Cblin on the basolateral side of Caco-2 cells after being placed on the apical side, and found that cytochalasin D, a tight junction opener, enhanced Cblin transport. Orally administered Cblin was found in rat plasma, indicating that intact Cblin was absorbed in vitro and in vivo. Furthermore, transgenic Cblin peptide-enriched rice (CbR) prevented the denervation-induced loss of muscle mass and the upregulation of muscle atrophy-related ubiquitin ligases in mice. These findings indicated that CbR could serve as an alternative treatment for muscle atrophy.

Dietary egg white protein hydrolysate improves orotic acid-induced fatty liver in rats by promoting hepatic phospholipid synthesis and microsomal triglyceride transfer protein expression

We investigated the effects of egg white protein hydrolysates (EWH) on orotic acid (OA)-induced nonalcoholic fatty liver (NAFL) in rats. Effects of the egg white protein (EWP) and EWH were also compared. Four groups of male Sprague-Dawley rats were separately fed AIN-76-based diets, supplemented with 20% casein for control, or with 1% OA, together with either 20% casein (OA), 20% EWP, or 20% EWH, respectively, for 3 d (developing stage) and 14 d (developed stage). In both feeding periods, animals from the OA group showed higher accumulation hepatic triacylglycerol (TAG) compared with those from the control group. In the 14-d experiment, dietary EWP and EWH significantly reduced the hepatic TAG levels. Intake of EWP reduced liver fat in OA-fed rats by 61%, while EWH reduced it by 92%. In addition, EWH restored the OA-induced high serum-TAG level to that seen in the control group. The 3 d experiment showed that consumption of EWH improved the expression of hepatic MTP, that was reduced by OA, without changing Mttp gene expression. It also increased the hepatic synthesis of PC and PE by enhancing the transcription of Pcyt1 and Pemt genes. Inclusion of EWP and EWH in the diet improves the OA-induced NAFL. EWH reduces the liver TAG better than EWP, and works more rapidly. Dietary EWH ameliorates OA-induced NAFL by promoting the secretion of hepatic TAG.

Dairy-originated digestion-resistant and bioactive peptides increase the risk of hypertension: Tehran Lipid and Glucose Study

Milk-protein-derived bioactive peptides (BPs) have been proposed as modulators of different regulatory processes involved in blood pressure regulation. Studies on the long-term effects of BPs on blood pressure have not yet been conducted. We aimed to investigate the association of dairy-originated BPs with the risk of hypertension (HTN) in the Tehran Lipid and Glucose Cohort Study (TLGS). In this cohort study, 4378 subjects with a mean follow-up period of 3.1 years were included in the final analysis. Dietary intake, physical activity, demographic, and anthropometric data and blood pressure measurements were obtained for all participants. Various types of dairy-originated BPs were determined by an in silico method. High intake of total digestion-resistant and bioactive peptides (OR: 1.31, CI 95%: 1.01-1.70), dipeptides (OR: 1.33, CI 95%: 1.03-1.73), peptides with more than seven residues (OR: 1.32, CI 95%: 1.01-1.71), glycosylated residues (OR: 1.39, CI 95%: 1.07-1.80), highly hydrophilic peptides (OR: 1.32, CI 95%: 1.01-1.71), and low hydrophobic peptides (OR: 1.32, CI 95%: 1.01-1.71) was associated with an increased risk of HTN in the adjusted model. In addition, subjects in the higher tertile of anti-HTN peptide (OR: 1.33, CI 95%: 1.02-1.72) and antidiabetic peptide (OR: 1.35, CI 95%: 1.04-1.76) intake had a higher risk of HTN than those in the lower tertile. No significant association emerged between calcium intake from dairy and incident risk of HTN. Our results showed that the intake of some forms of digestion-resistant and BPs, such as anti-HTN peptides, dipeptides, and peptides with more than seven residues, can increase the risk of HTN in the TLGS population.

Transport of Dietary Anti-Inflammatory Peptide, γ-Glutamyl Valine (γ-EV), across the Intestinal Caco-2 Monolayer

The present study analyzed the transepithelial transport of the dietary anti-inflammatory peptide, γ-glutamyl valine (γ-EV). γ-EV is naturally found in dry edible beans. Our previous study demonstrated the anti-inflammatory potency of γ-EV against vascular inflammation at a concentration of 1mM, and that it can transport with the apparent permeability coefficient (P_app) of 1.56 × 10^-6 ± 0.7 × 10^-6 cm/s across the intestinal Caco-2 cells. The purpose of the current study was to explore whether the permeability of the peptide could be enhanced and to elucidate the mechanism of transport of γ-EV across Caco-2 cells. The initial results indicated that γ-EV was nontoxic to the Caco-2 cells up to 5 mM concentration and could be transported across the intestinal cells intact. During apical-to-basolateral transport, a higher peptide dose (5 mM) significantly (p < 0.01) enhanced the transport rate to 2.5 × 10^-6 ± 0.6 × 10^-6 cm/s. Cytochalasin-D disintegrated the tight-junction proteins of the Caco-2 monolayer and increased the P_app of γ-EV to 4.36 × 10^-6 ± 0.16 × 10^-6 cm/s (p < 0.001), while theaflavin 3'-gallate and Gly-Sar significantly decreased the P_app (p < 0.05), with wortmannin having no effects on the peptide transport, indicating that the transport route of γ-EV could be via both PepT1-mediated and paracellular.

Characterising the efficacy and bioavailability of bioactive peptides identified for attenuating muscle atrophy within a Vicia faba-derived functional ingredient

Characterising key components within functional ingredients as well as assessing efficacy and bioavailability is an important step in validating nutritional interventions. Machine learning can assess large and complex data sets, such as proteomic data from plants sources, and so offers a prime opportunity to predict key bioactive components within a larger matrix. Using machine learning, we identified two potentially bioactive peptides within a Vicia faba derived hydrolysate, NPN_1, an ingredient which was previously identified for preventing muscle loss in a murine disuse model. We investigated the predicted efficacy of these peptides in vitro and observed that HLPSYSPSPQ and TIKIPAGT were capable of increasing protein synthesis and reducing TNF-α secretion, respectively. Following confirmation of efficacy, we assessed bioavailability and stability of these predicted peptides and found that as part of NPN_1, both HLPSYSPSPQ and TIKIPAGT survived upper gut digestion, were transported across the intestinal barrier and exhibited notable stability in human plasma. This work is a first step in utilising machine learning to untangle the complex nature of functional ingredients to predict active components, followed by subsequent assessment of their efficacy, bioavailability and human plasma stability in an effort to assist in the characterisation of nutritional interventions.

Identification of peptides in blood following oral administration of β-conglycinin to Wistar rats

In this study, β-conglycinin (100 mg/kg) was orally administered to Wistar rats in order to identify peptides that may be derived from the protein in the blood. Plasma samples taken from the tail vein up to 8 h after administration were analyzed by matrix-assisted laser desorption/ionization (MALDI) and liquid chromatography-time-of-flight (LC-TOF) mass spectrometry (MS). In total, 126 signals were detected by MALDI-MS. Among the signals, nine oligopeptides (SEL, KGPL, SILGA, DSEL, GDANI, SYFV, CLQSC, GEQPRPF, and LVINEGDA) were successfully identified as β-conglycinin-derived peptides by LC-TOF/MS at a plasma concentration of 0.75-756 pmol/mL. The results demonstrated that β-conglycinin could be the dietary source protein for the oligopeptides produced prior to entering the circulating bloodstream of rats.

Techniques, perspectives, and challenges of bioactive peptide generation: A comprehensive systematic review

Due to the digestible refractory and absorbable structures of bioactive peptides (BPs), they could induce notable biological impacts on the living organism. In this regard, the current study was devoted to providing an overview regarding the available methods for BPs generation by the aid of a systematic review conducted on the published articles up to April 2019. In this context, the PubMed and Scopus databases were screened to retrieve the related publications. According to the results, although the characterization of BPs mainly has been performed using enzymatic and microbial in-vitro methods, they cannot be considered as suitable techniques for further stimulation of digestion in the gastrointestinal tract. Therefore, new approaches for both in-vivo and in-silico methods for BPs identification should be developed to overcome the obstacles that belonged to the current methods. The purpose of this review was to compile the recent analytical methods applied for studying various aspects of food-derived biopeptides, and emphasizing generation at in vitro, in vivo, and in silico.

Gastrointestinal Digestion of Food Proteins under the Effects of Released Bioactive Peptides on Digestive Health

The gastrointestinal tract represents a specialized interface between the organism and the external environment. Because of its direct contact with lumen substances, the modulation of digestive functions by dietary substances is supported by a growing body of evidence. Food-derived bioactive peptides have demonstrated a plethora of activities in the organism with increasing interest toward their impact over the digestive system and related physiological effects. This review updates the biological effects of food proteins, specifically milk and soybean proteins, associated to gastrointestinal health and highlights the study of digestion products and released peptides, the identification of the active form/s, and the evaluation of the mechanisms of action underlying their relationship with the digestive cells and receptors. The approach toward the modifications that food proteins and peptides undergo during gastrointestinal digestion and their bioavailability is a crucial step for current investigations on the field. The recent literature on the regulation of digestive functions by peptides has been mostly considered in terms of their influence on gastrointestinal motility and signaling, oxidative damage and inflammation, and malignant cellular proliferation. A final section regarding the actual challenges and future perspectives in this scientific topic is critically discussed.

Assessment of the DPP-IV inhibitory activity of a novel octapeptide derived from rapeseed using Caco-2 cell monolayers and molecular docking analysis

The Octapeptide ELHQEEPL, which was identified from the rapeseed protein napin showed prominent Dipeptidyl peptidase-IV (DPP-IV) inhibitory activity. The objective of this study was to investigate the DPP-IV inhibitory activity and transepithelial transport of ELHQEEPL in an approaching intestinal condition using Caco-2 cell monolayers. ELHQEEPL and its degraded fragments EL, HQEEP, and methylated ELHQEEPL were transported across Caco-2 cell monolayers through different pathways. Compared with the nonbiological enzyme inhibition test, the in vitro experiment on Caco-2 cell monolayers showed that the IC50 value of DPP-IV inhibition increased by 43.11% for ELHQEEPL. There was no significant change in DPP-IV gene expression in the Caco-2 cell monolayers upon treatment with ELHQEEPL. Furthermore, molecular docking predicted that the weaker binding between inhibitory peptide and enzyme for the degradation products from ELHQEEPL during transepithelial transport greatly limited its role in inhibiting DPP-IV. PRACTICAL APPLICATIONS: The DPP-IV inhibitory activity of ELHQEEPL was confirmed using Caco-2 cell monolayers as a novel assessment tool, although its potency was reduced by metabolic degradation. In general, this study reported the use of Caco-2 cell monolayers as a tool for comprehensively studying peptides as sources of DPP-IV inhibitors. A Caco-2 cell-based approach with molecular docking can be adapted for the investigation of intestinal absorption and activity attenuation of food peptides being considered for enzymatic action. Moreover, since the Caco-2 cells express a wide range of enzymes, this method can be used for screening for other active food peptides such as for the inhibitors of ACE and a-glucosidase.