Transepithelial Transport Characteristics of the Antihypertensive Peptide, Lys-Val-Leu-Pro-Val-Pro, in Human Intestinal Caco-2 Cell Monolayers

Absorption, transport, blood-brain barrier penetration, and neuroprotection of walnut peptides LR and LPI

The prerequisite for neuroprotective peptides to exert physiological effect is that they can across intestinal epithelial barrier and blood-brain barrier (BBB). The study was aimed to investigate the absorption, transportation and BBB permeability of walnut neuroprotective peptides LR and LPI using Caco-2 cell monolayer and in vivo imaging, and further to evaluate their underlying mechanisms through transcriptome sequencing analysis of zebrafish brain. Results showed that LR and LPI improved learning and memory impairment in scopolamine-induced zebrafish. Both peptides could be intactly transported in Caco-2 cells but via different mechanisms. LR was transported via both PepT1-mediated active route and tight junction-regulated passive paracellular route, while LPI was via PepT1 route only, with apparent permeability coefficient (30.18 ± 1.94) × 10-7 cm/s and (51.91 ± 3.49) × 10-7 cm/s, respectively. In vivo imaging of nude mice after FITC-labeling peptides administration further consolidated their ability of absorption, metabolic stability, and BBB penetration. Interestingly, LR exhibited better brain influx than that of LPI in nude mice. Additionally, transcriptome sequencing analysis demonstrated that LR and LPI improved learning and memory capacity by intervening cholinergic system, synaptic development and plasticity, neurotrophins, and oxidative stress, which were subsequent verified by biochemical measurement of zebrafish brain.

Digestion, absorption, and transport properties of soy-fermented douchi hypoglycemic peptides VY and SFLLR under simulated gastrointestinal digestion and Caco-2 cell monolayers

Two novel hypoglycemic peptides VY and SFLLR were identified from douchi as the major peptides responsible for the glucose uptake activity. The present work aimed to elucidate their digestion, absorption and transport properties using simulated digestion and Caco-2 cell monolayers transport models. Besides, the effects of digestion and absorption on the structure and activity were also studied. The results showed that VY was resistant to gastrointestinal tract digestion and could cross Caco-2 cell monolayers intactly via both TJs-mediated passive paracellular pathway and PepT1-mediated active route. In comparison, SFLLR was partially degraded into small fragments of SFLL, SFL, and SF by the digestive system, leading to increased glucose uptake activity. Notably, SFLLR, SFLL, and SFL were partly hydrolyzed by aminopeptidase N or dipeptidyl peptidase IV during transport, but they were transported intact. SFL was transported via both paracellular diffusion and PepT1-mediated routes, while SFLLR and SFLL were via paracellular route only.

Assessment of Novel Oligopeptides from Rapeseed Napin (Brassica napus) in Protecting HepG2 Cells from Insulin Resistance and Oxidative Stress

Oligopeptides (Thr-His-Leu-Pro-Lys (THLPK), His-Pro-Leu-Lys (HPLK), Leu-Pro-Lys (LPK), His-Leu-Lys (HLK), and Leu-His-Lys (LHK)) are newly identified from rapeseed napin (Brassica napus) protein-derived hydrolysates with the capability of upregulating glucose transporter-4 (GLUT4) expression and translocation. However, whether each of them enhances GLUT4 expression and translocation and their specific mechanisms remain unclear. Here, we assess the effects of the oligopeptides against insulin resistance (IR) and oxidative stress in hepatocytes and screen out the most antidiabetic one. Specifically, compared with other oligopeptides, LPK not only remarkably elevated glucose consumption to 8.45 mmol/L protein; superoxide dismutase (SOD) activity to 319 U/mg protein; GLUT4 expression and translocation; and phosphorylated level of insulin receptor substrate-1 (IRS-1), phosphatidylinositol 3-kinase (PI3K), and protein kinase B (Akt) (P < 0.05) but also remarkably attenuated the reactive oxygen species (ROS) level to 2255, lactate dehydrogenase (LDH) activity to 20.5 U/mg protein, malondialdehyde (MDA) content to 241 nmol/mg protein, and NO content to 1302 μmol/mL protein (P < 0.05). These findings demonstrated that antidiabetic oligopeptide LPK possessed the most potential to protect HepG2 cells from IR and oxidative stress via activating IRS-1/PI3K/Akt/GLUT4 and regulating common oxidative markers in vitro.

Bioavailability of Peptides Derived from the In Vitro Digestion of Human Milk Assessed by Caco-2 Cell Monolayers

Human milk-protein-derived peptides exhibit an array of bioactivities. Certain bioactivities cannot be exerted unless the peptides are absorbed across the gastrointestinal lumen into the bloodstream. The purpose of study was to determine which peptides derived from in vitro digestion of human milk could cross human intestinal Caco-2 cell monolayers. Our results showed that the numbers of peptides absorbed by the Caco-2 cell monolayer were different at different concentrations (44 peptides out of 169 peptides detected at 10 μg/mL, 124 peptides out of 204 peptides detected at 100 μg/mL, and 175 peptides out of 236 peptides detected at 1000 μg/mL). Four peptides (NLHLPLP (β-casein [138-144]), PLAPVHNPI (β-casein [216-224]), PLMQQVPQPIPQ (β-casein [148-159]), and FDPQIPK (β-casein [126-132])) crossed to the basolateral chamber of the Caco-2 monolayer incubated with peptides at all three concentrations. Among the peptides identified in the basolateral chambers, three peptides (NLHLPLP (β-casein [138-144]), LENLHLPLP (β-casein [136-144]), and QVVPYPQ (β-casein [182-188])) are known ACE-inhibitors; one peptide (LLNQELLLNPTHQIYPV (β-casein [197-213])) is antimicrobial, and another peptide (QVVPYPQ (β-casein [182-188])) has antioxidant activity. These findings indicate that specific milk peptides may be able to reach the bloodstream and exert bioactivity.

Pharmacokinetics and Transport of an Osteogenic Dodecapeptide

A dodecapeptide with the amino acid sequence of IEELEEELEAER (PIE), identified from Mytilus edulis proteolysis hydrolysates, has shown good bone-forming activity in previous studies. The pharmacokinetics and transport of the PIE peptide in vivo or in vitro were investigated in this study. The results showed that the PIE peptide can be transported into monolayer Caco-2 cells, and the PIE peptide was identified in the serum after the mice reached the highest value of 173.60 ± 60.30 ng/mL, in which it was quantified by an optimized mass spectrometry method. In addition, the PIE peptide has a promoting effect on the bone morphogenetic protein pathway at the gene and protein levels. According to the distribution of PIE-FITC in ovariectomized mice after orally administrated PIE-FITC, it was confirmed that it can enter the gastrointestinal tract and serum, and reach the bones. Taken together, the PIE peptide can be absorbed well both in vitro and in vivo, and it could promote pre-osteoblast differentiation factors.

Transepithelial Transport Characteristics of the Cholesterol- Lowing Soybean Peptide, WGAPSL, in Caco-2 Cell Monolayers

Recent studies have shown that soybean protein and its peptides have cholesterol-lowering activities. However, it is not clear whether these peptides could overcome physiological barriers, such as phase II metabolism in gastrointestinal tract and poor permeability, to reach the blood stream in its intact form. Therefore, the transepithelial transport characteristics of soybean peptide Trp-Gly-Ala-Pro-Ser-Leu (WGAPSL) with cholesterol- lowering activity were investigated in Caco-2 cells. In this study; the transepithelial absorption of WGAPSL was studied using human intestinal Caco-2 cell monolayers. The results showed that WGAPSL had good stability (83.9% ±1.98%) after simulated gastric and intestinal digestion. During the apical (AP) side to basolateral (BL) side transport, WGAPSL was absorbed intact through Caco-2 cell monolayers with apparent permeability coefficient (Papp) values of 4.4 × 10-8 to 1.2 × 10-8 cm/s. Cytochalasin D loosened the tight junctions of Caco-2 cell monolayers and significantly (p < 0.05) improved the transport process. Sodium azide, wortmannin, and Gly-Pro had minimal effects on transport, demonstrating that the major transport route of WGAPVL was paracellular via tight junctions. Finally, LC-MS analysis showed that Gly-Ala-Pro (GAP) was the important part for the intact absorption of WGAPVL and Trp (W) was the most unstable amino acid residue.

Stability and Transport of Spent Hen-Derived ACE-Inhibitory Peptides IWHHT, IWH, and IW in Human Intestinal Caco-2 Cell Monolayers

Ile-Trp-His-His-Thr (IWHHT), initially identified as an ACE inhibitory peptide, was shown to have antioxidant and anti-inflammatory activities in cells and blood pressure lowering activity in animals. IWHHT was degraded into IWH and IW during simulated gastrointestinal digestion. The purpose of this study was to investigate the stability, permeability, and transport pathways of IWHHT, IWH, and IW across intestinal epithelium using human intestinal Caco-2 cell monolayers. IWHHT, IWH, and IW were partly degraded by aminopeptidase N or dipeptidyl peptidase IV, but they were transported intact, with apparent permeability coefficients of (22.0 ± 1.42) × 10^-8, (37.5 ± 1.11) × 10^-8, and (19.6 ± 0.62) × 10^-8 cm s^-1, respectively. The results firstly evidenced an important role of aminopeptidase N in cleaving small ACE inhibitory peptides during transport. IWH was transported via both peptide transporter 1 (PepT1) and paracellular route, while IW was via PepT1 and IWHHT was via paracellular route only. Transport of IW implied that hydrophobic peptides (even with a small size), consisting of only highly hydrophobic amino acid residues, might not be transported via paracellular diffusion. This study suggested that all three peptides could pass through the intestinal epithelium and that the degraded IWH and IW might also contribute to the antihypertensive activity of IWHHT.

Transport of ACE Inhibitory Peptides Ile-Gln-Pro and Val-Glu-Pro Derived from Spirulina platensis Across Caco-2 Monolayers

This study evaluated transepithelial transport mechanisms of Ile-Gln-Pro (IQP) and Val-Glu-Pro (VEP), two ACE-inhibitory peptides derived from Spirulina platensis, using human intestinal Caco-2 cell monolayers. IQP and VEP were absorbed intact through Caco-2 cell monolayers with P_app values of 7.48 ± 0.58 × 10^-6 and 5.05 ± 0.74 × 10^-6 cm/s, respectively. The transport of IQP and VEP were affected neither by Gly-Pro nor by wortmannin, indicating that they were not PepT1-mediated and did not involve endocytosis. However, transport of IQP and VEP were increased significantly by sodium deoxycholate, suggesting that the major transport mechanism was paracellular. In addition, the increased transport of VEP and IQP were followed with the addition of sodium azide, suggesting influence of energy to the process. The transport of VEP was also increased by verapamil, indicating an apical-to-basolateral flux mediated by P-gp.

PRACTICAL APPLICATION

Bioactive peptides derived from food proteins have been considered as potentially ideal products to reduce hypertension because of their safety and positive impacts on health. IQP and VEP are the 2 ACE inhibitory peptides derived from Spirulina platensis, a kind of edible cyanobacteria with rich nutrition and multiple physiological functions, and were demonstrated to inhibit ACE and lower blood pressure in spontaneously hypertensive rats. However, it is prerequisite that such bioactive peptides must be absorbed intact across the intestinal epithelium, so as to exert antihypertensive effects in vivo. This study evaluated transepithelial transport mechanisms of IQP and VEP. It contributes to the study of Spirulina in lowering blood pressure and supports the development of bioactive peptide products.

Molecular interactions, bioavailability, and cellular mechanisms of angiotensin-converting enzyme inhibitory peptides

Food-derived angiotensin-converting enzyme inhibitory (ACEi) peptides have gained substantial interest as potential alternatives to synthetic drugs in the management of hypertension. Peptide size and sequence are two critical factors that determine their potency, bioavailability, and cellular mechanisms. Molecular interaction studies between ACE and ACEi peptides support that potent ACEi peptides are generally composed of hydrophobic, positively charged, and aromatic or cyclic amino acid residues at the third, second, and first position from the C-terminus, respectively. Small peptides containing N-terminal Tyr and/or C-terminal Pro could improve their stability against enterocyte peptidases, thus their bioavailability. Different ACEi peptides can reduce aberrant cellular proliferation, excessive inflammation, and oxidative stress but through different mechanisms. Further understanding the structure-activity-bioavailability relationships will help design novel potent ACEi peptides with improved bioavailability and in vivo efficacy. PRACTICAL APPLICATIONS: ACEi peptides have the potential for uses as functional food ingredients against hypertension.

Current knowledge of intestinal absorption of bioactive peptides

Peptides have been demonstrated as potentially beneficial compounds against several life-style related diseases such as hypertension, hypercholesterolemia, and atherosclerosis, among others. However, limited research has been carried out on peptide absorption, resulting in a lack of understanding and control of this process. Therefore, this review discusses the recent insights gathered on in vitro and in vivo absorption of peptides across intestinal membranes, into blood circulation. Briefly, some di-/tripeptides permeate through intestinal membranes in their intact forms via peptide transporter systems, while others are vulnerable to protease degradation. Oligopeptides (>tetrapeptides) show a lower transport ability than di-/tripeptides, possibly due to the presence of paracellular tight junctions. The hydrophobicity of peptides (log P) does not seem to influence absorption, while peptide length and degradation of peptides (and peptide sequences) by intestinal proteases may be determinant factors of the absorption process.

Hydrolysis and transepithelial transport of two corn gluten derived bioactive peptides in human Caco-2 cell monolayers

The objective of this paper was to investigate the transepithelial transport of two novel corn gluten-derived antioxidant peptides, YFCLT and GLLLPH, using Caco-2 cell monolayers. Results showed that both of YFCLT and GLLLPH could transport in intact form across Caco-2 cell monolayers with apparent permeability coefficient (P_app) values of (1.10±0.16)×10^-7cm/s and (1.98±0.23)×10^-7cm/s, respectively. However, it was found that the two peptides were susceptible and easily hydrolyzed by brush border membrane peptidases. In the presence of diprotin A, an inhibitor of dipeptidyl peptidase IV (DPPIV), the hydrolysis of YFCLT and GLLLPH decreased and their permeabilities increased significantly compared to control group (P<0.05). The results of transport routes revealed that Gly-Sar, a peptide transporter 1 (PepT1) substrate, had little effects on the transepithelial permeability (P>0.05), suggesting that the transport of YFCLT and GLLLPH across Caco-2 cell monolayers was not mediated by PepT1. However, it was found that cytochalasin d, a tight junctions (TJs) disruptor, increased the permeability significantly (P<0.05). While wortmannin, a transcytosis inhibitor, and sodium azide, an ATP synthesis inhibitor, both decreased the permeability significantly (P<0.05). It indicated that the TJs-mediated paracellular pathway and energy-dependent transcytosis were involved in the transport of YFCLT and GLLLPH across Caco-2 cell monolayers.

Production, optimisation and characterisation of angiotensin converting enzyme inhibitory peptides from sea cucumber (Stichopus japonicus) gonad

The purification, characterization, and molecular docking study of a novel ACE inhibitory peptide (NAPHMR) derived from sea cucumber gonad hydrolysates.

Effects of natural peptides from food proteins on angiotensin converting enzyme activity and hypertension

Cardiovascular diseases are the leading cause of death. The underlying pathophysiology is largely contributed by an overactivation of the renin-angiotensin-aldosterone-system (RAAS). Herein, angiotensin II (AngII) is a key mediator not only in blood pressure control and vascular tone regulation, but also involved in inflammation, endothelial dysfunction, atherosclerosis, hypertension and congestive heart failure. Since more than three decades suppression of AngII generation by inhibition of the angiotensin-converting enzyme (ACE) or blockade of the AngII-receptor has shown clinical benefit by reducing hypertension, atherosclerosis and other inflammation-associated cardiovascular diseases. Besides pharmaceutical ACE-inhibitors some natural peptides derived from food proteins reduce in vitro ACE activity. Several animal studies and a few human clinical trials have shown antihypertensive effects of such peptides, which might be attractive as food additives to prevent age-related RAAS activation. However, their inhibitory potency on in vitro ACE activity does not always correlate with an antihypertensive impact. While some peptides with high inhibitory activity on ACE-activity in vitro show no antihypertensive effect in vivo, other peptides with only a moderate ACE inhibitory activity in vitro cause such effects. The explanation for this conflicting phenomenon between inhibitory activity and antihypertensive effect remains unclear to date. This review shall critically address the effects of natural peptides derived from different food proteins on the cardiovascular system and the possible underlying mechanisms. A central aspect will be to point to conceptual gaps in the current understanding of the action of these peptides with respect to in vivo blood pressure lowering effects.

Importance of Terminal Amino Acid Residues to the Transport of Oligopeptides across the Caco-2 Cell Monolayer

The objective of this paper was to investigate the effects of terminal amino acids on the transport of oligopeptides across the Caco-2 cell monolayer. Ala-based tetra- and pentapeptides were designed, and the N- or C-terminal amino acid residues were replaced by different amino acids. The results showed that the oligopeptides had a wide range of transport permeability across the Caco-2 cell monolayer and could be divided into four categories: non-/poor permeability, low permeability, intermediate permeability, and good permeability. Tetrapeptides with N-terminal Leu, Pro, Ile, Cys, Met, and Val or C-terminal Val showed the highest permeability, with apparent permeability coefficient (P_app) values over 10 × 10^-6 cm/s (p < 0.05), suggesting that nonpolar hydrophobic aliphatic amino acids or polar sulfur-containing amino acids were the best for the transport of tetrapeptides. Pentapeptides with N- or C-terminal Tyr also showed high permeability levels, with P_app values of about 10 × 10^-6 cm/s. The amino acids Glu, Asn, and Thr at the N terminus or Lys, Asp, and Arg at the C terminus were also beneficial for the transport of tetra- and pentapeptides, with P_app values ranging from 1 × 10^-6 to 10 × 10^-6 cm/s. In addition, peptides with amino acids replaced at the N terminus generally showed higher permeability than those with amino acids replaced at the C terminus (p < 0.05), suggesting that N-terminal amino acids were more important for the transport of oligopeptides across the Caco-2 cell monolayer.

Transport Study of Egg-Derived Antihypertensive Peptides (LKP and IQW) Using Caco-2 and HT29 Coculture Monolayers

The objective of this study was to investigate the mechanisms of the transport of antihypertensive tripeptides LKP (Leu-Lys-Pro) and IQW (Ile-Gln-Trp) derived from egg white using a coculture system of Caco-2 and HT29 cell monolayers. The results revealed that LKP and IQW have no cytotoxicity to the cell viability after 2 h incubation, could be transported intact across coculture monolayers (apparent permeability coefficient: (18.11 ± 1.57) × 10^-8 and (13.21 ± 1.12) × 10^-8 cm/s, respectively), and were resistant to peptidase secreted by enterocytes. In addition, the transports were significantly inhibited by dipeptide Gly-Pro (P < 0.05), a competitive substance of peptide transporter 1 (PepT1). The transports from apical to basolateral side were significantly higher than that of the reverse direction (P < 0.05). These results suggest that PepT1 is involved in LKP and IQW transports. The transports were also significantly decreased by theaflavin-3'-O-gallate (P < 0.05), an enhancer of tight junction (TJ) and increased by cytochalasin D (P < 0.05), a disruptor of TJ but not influenced by wortamanin, a transcytosis inhibitor, suggesting that passive paracellular route via TJs is also involved in LKP and IQW transports but not transcytosis. In addition, siRNA was also used to knockdown the expression of PepT1 and significantly inhibited the transport (P < 0.05), confirming that PepT1 is involved in transport process. Therefore, both passive paracellular route via TJ and active route via PepT1 coexist in the transport of antihypertensive LKP and IQW across Caco-2/HT29 coculture monolayers.

Therapeutic potential of dairy bioactive peptides: A contemporary perspective

Dairy products are associated with numerous health benefits. These are a good source of nutrients such as carbohydrates, protein (bioactive peptides), lipids, minerals, and vitamins, which are essential for growth, development, and maintenance of the human body. Accordingly, dairy bioactive peptides are one of the targeted compounds present in different dairy products. Dairy bioactive compounds can be classified as antihypertensive, anti-oxidative, immmunomodulant, anti-mutagenic, antimicrobial, opoid, anti-thrombotic, anti-obesity, and mineral-binding agents, depending upon biological functions. These bioactive peptides can easily be produced by enzymatic hydrolysis, and during fermentation and gastrointestinal digestion. For this reason, fermented dairy products, such as yogurt, cheese, and sour milk, are gaining popularity worldwide, and are considered excellent source of dairy peptides. Furthermore, fermented and non-fermented dairy products are associated with lower risks of hypertension, coagulopathy, stroke, and cancer insurgences. The current review article is an attempt to disseminate general information about dairy peptides and their health claims to scientists, allied stakeholders, and, certainly, readers.

Structural Design of Oligopeptides for Intestinal Transport Model

Glycyl-sarcosine (Gly-Sar) is a well-known model substrate for the intestinal uptake of dipeptides through peptide transporter 1 (PepT1). However, there are no other model peptides larger than tripeptides to evaluate their intestinal transport ability. In this study, we designed new oligopeptides based on the Gly-Sar structure in terms of protease resistance. Gly-Sar-Sar was found to be an appropriate transport model for tripeptides because it does not degrade during the transport across the rat intestinal membrane, while Gly-Gly-Sar was degraded to Gly-Sar during the 60 min transport. Caco-2 cell transport experiments revealed that the designed oligopeptides based on Gly-Sar-Sar showed a significantly (p < 0.05) lower transport ability by factors of 1/10-, 1/25-, and 1/40-fold for Gly-Sar-Sar, Gly-Sar-Sar-Sar, and Gly-Sar-Sar-Sar-Sar, respectively, compared to Gly-Sar (apparent permeability coefficient: 38.6 ± 11.4 cm/s). Cell experiments also showed that the designed tripeptide and Gly-Sar were transported across Caco-2 cell via PepT1, whereas the tetra- and pentapeptides were transported through the paracellular tight-junction pathway.

Transport of Antihypertensive Peptide RVPSL, Ovotransferrin 328-332, in Human Intestinal Caco-2 Cell Monolayers

The objective of this study was to investigate the transepithelial transport of RVPSL (Arg-Val-Pro-Ser-Leu), an egg-white-derived peptide with angiotensin I-converting enzyme (ACE) inhibitory and antihypertensive activity, in human intestinal Caco-2 cell monolayers. Results revealed that RVPSL could be passively transported across Caco-2 cell monolayers. However, during the process of transport, 36.31% ± 1.22% of the initial RVPSL added to the apical side was degraded, but this degradation decreased to 23.49% ± 0.68% when the Caco-2 cell monolayers were preincubated with diprotin A (P < 0.001), suggesting that RVPSL had a low resistance to various brush border membrane peptidases. When transport from the apical side to the basolateral side was investigated, the apparent permeability coefficient (Papp) was (6.97 ± 1.11) × 10(-6) cm/s. The transport route of RVPSL appears to be the paracellular pathway via tight junctions, as only cytochalasin D, a disruptor of tight junctions (TJs), significantly increased the transport rate (P < 0.001). In addition, the relationship between the structure of RVPSL and transport across Caco-2 cell monolayers was studied by mutation of RVPSL. It was found that N-terminal Pro residues were more beneficial for transport of pentapeptides across Caco-2 cell monolayers than Arg and Val. Furthermore, RVPSL could be more easily transported as smaller peptides, especially in the form of dipeptides and tripeptides.

Transport of Egg White ACE-Inhibitory Peptide, Gln-Ile-Gly-Leu-Phe, in Human Intestinal Caco-2 Cell Monolayers with Cytoprotective Effect

The purpose of this study was to investigate the transepithelial transport and cytoprotective effect of Gln-Ile-Gly-Leu-Phe (QIGLF), an ACE-inhibitory peptide derived from egg white ovalbumin, in human intestinal Caco-2 cell monolayers. The results showed that QIGLF could be absorbed intact through Caco-2 cell monolayers with a P_app value of (9.11 ± 0.19) × 10^-7 cm/s (transport kinetic parameters: K_m, 32.37 ± 12.59 mM; V_max, 1.23 ± 0.49 μM/min cm²). The transport was not significantly decreased by sodium azide and Gly-Pro, an ATP synthesis inhibitor and a peptide transporter 1 (PepT1) substrate, respectively, suggesting that transport of QIGLF was not energy-dependent and carrier-mediated. In addition, wortmannin, a transcytosis inhibitor, had little effect on the transport, suggesting that endocytosis was not involved in the transport of QIGLF. However, the transport of QIGLF was increased significantly in the presence of cytochalasin D, a tight junction disruptor, suggesting that paracellular transport via tight junctions was the major transport mechanism for intact QIGLF across Caco-2 cell monolayers. Moreover, QIGLF was added to Caco-2 cells followed by addition of H₂O₂, and exhibited significant cytoprotective effect in Caco-2 cells against oxidative stress induced by H₂O₂.

Preparation and in vitro/in vivo characterization of enteric-coated nanoparticles loaded with the antihypertensive peptide VLPVPR

Our previous study revealed that the peptide Val-Leu-Pro-Val-Pro-Arg (VLPVPR), which was prepared using deoxyribonucleic acid recombinant technology, effectively decreased the blood pressure of spontaneous hypertensive rats; however, the effect only lasts 6 hours, likely due to its low absorption in the gastrointestinal tract. To overcome this problem, the purpose of this study was to characterize (methoxy-polyethylene glycol)-b-poly(D,L-lactide-co-glycolide)-b-poly(L-lysine) nanoparticles as in vitro and in vivo carriers for the effective delivery of VLPVPR. In our study, the VLPVPR nanoparticles were prepared using a double emulsion method, coated with Eudragit S100, and freeze-dried to produce enteric-coated nanoparticles. The optimized parameters from the double emulsion method was obtained from orthogonal experiments, including drug loading (DL) and encapsulated ratio (ER) at 6.12% and 86.94%, respectively, and the average particle size was below 100 nm. The release experiment demonstrated that the nanoparticles were sensitive to pH: almost completely released at pH 7.4 after 8 hours, but demonstrated much less release at pH 4.5 or pH 1.0 in the same amount of time. Therefore, the nanoparticles are suitable for enteric release. In vivo compared with the untreated group, the medium and high doses of orally administered VLPVPR nanoparticles reduced blood pressure for more than 30 hours, demonstrating that these nanoparticles have long-lasting and significant antihypertensive effects in spontaneously hypertensive rats.

Release of angiotensin I-converting enzyme inhibitory peptides from flaxseed (Linum usitatissimum L.) protein under simulated gastrointestinal digestion

The scope of this study was to determine the ability of flaxseed (Linum usitatissimum L.) proteins to release angiotensin I-converting enzyme inhibitory (ACEI) peptides during simulated gastrointestinal (GI) digestion using a static (SM; no absorption in the intestinal phase) and a dynamic model (DM; simultaneous absorption of digested products in the intestinal phase via passive diffusion). Gastric and gastric + small intestinal digests of flaxseed proteins of both models possessed ACEI activity. The ACEI activity of the gastric + small intestinal digest in the DM (IC(50) unabsorbed, 0.05 mg N/mL; IC(50) absorbed, 0.04 mg N/mL) was significantly higher (p < 0.05) than that of the SM (IC(50), 0.39 mg N/mL). Two peptides, a pentapeptide (Trp-Asn-Ile/Leu-Asn-Ala) and a hexapeptide (Asn-Ile/Leu-Asp-Thr-Asp-Ile/Leu), were identified in the most active ACEI fraction (0.5-1 kDa) of the absorbable flaxseed protein digest by de novo sequencing.

Bioactive peptides from muscle sources: meat and fish

Bioactive peptides have been identified in a range of foods, including plant, milk and muscle, e.g., beef, chicken, pork and fish muscle proteins. Bioactive peptides from food proteins offer major potential for incorporation into functional foods and nutraceuticals. The aim of this paper is to present an outline of the bioactive peptides identified in the muscle protein of meat to date, with a focus on muscle protein from domestic animals and fish. The majority of research on bioactives from meat sources has focused on angiotensin-1-converting enzyme (ACE) inhibitory and antioxidant peptides.

The bioavailable octapeptide Gly-Ala-Hyp-Gly-Leu-Hyp-Gly-Pro stimulates nitric oxide synthesis in vascular endothelial cells

Gly-Ala-Hyp-Gly-Leu-Hyp-Gly-Pro (GAXGLXGP, X: Hyp), an octapeptide contained in chicken collagen hydrolysate, inhibits angiotensin I-converting enzyme activity in vitro. Intestinal Caco-2 and bovine aortic endothelial cells (BAECs) were used to investigate whether the transported GAXGLXGP improves vascular function. When GAXGLXGP was added to the apical side of Caco-2 monolayers, the intact form of GAXGLXGP was released to the basolateral side without incorporation into the cells. This transport was energy-independent but was associated with tight junction permeability. GAXGLXGP was then added to BAECs, and endothelial nitric oxide (NO) synthase (eNOS) activation was examined. GAXGLXGP at a concentration of 10 microM stimulated production of NO during a 1 h incubation. This event involved phosphorylation of eNOS at Ser(1179) without a change in the total eNOS protein level. These findings indicate that GAXGLXGP absorbed intact through the intestinal epithelium has direct effects on eNOS activity in vascular endothelial cells, leading to NO synthesis, thereby suggesting the potential for improvement in vascular function.