Interaction of ovokinin(2–7) with vascular bradykinin 2 receptors

Hypotensive Activity of Transgenic Rice Seed Accumulating Multiple Antihypertensive Peptides

Peptides derived from food protein have the potential to become antihypertensive agents with relatively few negative side effects. Herein, multiple antihypertensive peptides, extracted from the transgenic rice seed, were administered intragastrically into spontaneously hypertensive rats (SHRs) with different dosages, resulting in a significant decrease in the systolic blood pressure (SBP). Furthermore, for a period of 5 weeks, daily intragastric administration of the transgenic rice flour also significantly reduced the SBP of SHRs but not the Wistar Kyoto normotensive rats (WNRs), most importantly, which did not affect the growth, development, or serum chemistry of SHRs or WNRs and did not cause any pathological changes. Our work provides an alternative source of natural antihypertensive agents.

Bioactive Egg Proteins

The nutritional excellence of chicken egg is derived from its task as a life-giving medium, supplying the necessary nutrients to the hen's embryo while protecting it from external threats. Additionally, egg proteins possess unique biological activities above and beyond their known functional and nutritional roles. In the last few decades, extensive research has been done to evaluate the various biological activities of egg proteins and protein-derived peptides. Egg proteins and protein-derived peptides have been attributed to diverse biological activities, the most well-known being their antimicrobial properties. However, egg proteins and peptides have been shown to have other biological activities, such as antihypertensive, antioxidant, anticancer, immunomodulatory, and protease inhibitory activity. Egg-derived bioactive proteins have had a relevant scientific impact and exhibit promising applicability as an ingredient for the development of functional foods and nutraceuticals. However, it is critical to understand the effects of these proteins in signaling pathways to delineate their molecular mechanisms of action. Further studies are required to fill the current knowledge gaps. Therefore, the purpose of the chapter is to illustrate the present knowledge of the bioactivity of different egg proteins and their physiological effects.

Egg Protein-Derived Bioactive Peptides: Preparation, Efficacy, and Absorption

The hen's egg is an important protein source of human diet. On average one large egg contains ~6g protein, which contributes to ~11% of daily protein intake. As a high-quality protein, egg proteins are well recognized as excellent sources of bioactive peptides. The objectives of this chapter are to introduce generation, bioactivities, and absorption of egg protein-derived bioactive peptides. Research on egg protein-derived bioactive peptides has been progressed during the past decades. Enzymatic hydrolysis is the major technique to prepare bioactive peptides from egg protein. Quantitative structure-activity relationships-aided in silico prediction is increasingly applied as a promising tool for efficient prediction of novel bioactive peptides. A number of bioactive peptides from egg proteins have been characterized for antioxidant, immunomodulatory, antihypertensive, antidiabetic, anticancer, and antimicrobial activities. Egg protein-derived peptides that can improve bone health have been reported as well. However, molecular mechanisms of many peptides are not fully understood. The stability and absorption routes, bioavailability, safety, and production of bioactive peptides await further investigation.

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.

Bioactive peptides derived from egg proteins: A review

Egg proteins have various functional and biological activities which make them potential precursor proteins for bioactive peptide production. Simulated in vitro gastrointestinal digestion and enzymatic hydrolysis using non-gastrointestinal proteases have been used as tools to produce these peptides. Bioactive peptides derived from egg proteins are reported to display various biological activities, including angiotensin I-converting enzyme (ACE) inhibitory (antihypertensive), antioxidant, antimicrobial, anti-inflammatory, antidiabetic and iron-/calcium-binding activities. More importantly, simulated in vitro gastrointestinal digestion has indicated that consumption of egg proteins has physiological benefits due to the release of such multifunctional peptides. This review encompasses studies reported to date on the bioactive peptide production from egg proteins.

Egg-derived bioactive peptides with ACE-inhibitory properties: a literature update

Egg proteins contain a wide set of peptide sequences which have an impact on cardiovascular health.

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.

Bioactive peptides from egg: a review

Purpose

– The aim of the article was to focus on various peptides identified in the egg and their probable application as novel ingredients in the development of functional food products. Bioactive peptides of egg origin have attracted increasing interest as one of the prominent candidates for development of various health-promoting functional and designer foods.

Design/methodology/approach

– Traditionally known as a source of highly valuable proteins in human nutrition, eggs are nowadays also considered as an important source of many bioactive peptides which may find wide application in medicine and food production. These specific protein fragments from egg proteins which, above and beyond their nutritional capabilities, have a positive impact on the body’s function or condition by affecting the digestive, endocrine, cardiovascular, immune and nervous systems, and may ultimately influence health.

Findings

– Several peptides that are released in vitro or in vivo from egg proteins have been attributed to different health effects, including antihypertensive effects, antimicrobial properties, antioxidant activities, anticancer activity, immunomodulating activity, antiadhesive properties and enhancement of nutrient absorption and/or bioavailability. Extensive research has been undertaken to identify and characterize these biologically active peptides of egg origin which has changed the image of egg as a new source of biologically active ingredients for the development of functional foods with specific benefits for human health and treatment and prevention of diseases.

Originality/value

– The paper mainly describes the above-stated properties of bioactive peptides derived from egg proteins.

Vascular effects of egg white-derived peptides in resistance arteries from rats. Structure-activity relationships

BACKGROUND

The vasodilator properties of several peptide sequences derived from egg white proteins were screened in mesenteric resistance arteries from Wistar-Kyoto rats. For this, third-order branches of the mesenteric arteries from 6-month-old male rats were used. The vasodilator responses, with or without endothelium, to several peptides (0.1 mmol L(-1)) were analysed in an isometric myograph. Moreover, the effect of nitric oxide (NO) synthase (L-NAME, 100 micromol L(-1)) and cyclooxygenase (indomethacin, 10 micromol L(-1)) inhibitors on the vasodilator response was tested.

RESULTS

The peptides Arg-Ala-Asp-His-Pro-Phe-Leu, Arg-Ala-Asp-His-Pro-Phe, Arg-Ala-Asp-His-Pro, Tyr-Arg-Gly-Gly-Leu-Glu-Pro-Ile-Asn-Phe, Arg-Asp-Ile-Leu-Asn-Gln and Val-Pro-Pro showed a high endothelium-dependent vasorelaxation, whereas Phe-Arg-Ala-Asp-His-Pro-Phe-Leu was only partially endothelium-dependent. The relaxation induced by Arg-Ala-Asp-His-Pro-Phe-Leu, Arg-Ala-Asp-His-Pro-Phe, Arg-Ala-Asp-His-Pro, Arg-Asp-Ile-Leu-Asn-Gln and Val-Pro-Pro was mainly mediated by NO, since the response was inhibited only by L-NAME, while both L-NAME and indomethacin inhibited the vasodilator response induced by Phe-Arg-Ala-Asp-His-Pro-Phe-Leu and Tyr-Arg-Gly-Gly-Leu-Glu-Pro-Ile-Asn-Phe. The presence of Arg or Tyr at the N-terminal position could be related to the vasodilator activity of these compounds in this vascular bed. The well-known angiotensin-converting enzyme inhibitor captopril showed only a slight vasodilator effect.

CONCLUSION

These peptides could reduce the vascular resistance and be used as functional ingredients in the prevention and/or treatment of hypertension and other associated disorders.

Hypotensive activity of novokinin, a potent analogue of ovokinin(2-7), is mediated by angiotensin AT(2) receptor and prostaglandin IP receptor

Novokinin (Arg-Pro-Leu-Lys-Pro-Trp) is a potent hypotensive peptide previously designed based on the structure of ovokinin(2-7) (Arg-Ala-Asp-His-Pro-Phe), a vasorelaxing and hypotensive peptide derived from ovalbumin. Novokinin exhibited an affinity for the angiotensin AT(2) receptor (Ki=7.35 microM). Novokinin significantly lowered systolic blood pressure at a dose of 0.03 and 0.1 mg/kg after intravenous and oral administration, respectively, in spontaneously hypertensive rats (SHRs), and the hypotensive activity was blocked by PD123319, an antagonist of the AT(2) receptor. Novokinin lowered blood pressure in C57BL/6J mice after oral administration at a dose of 50 mg/kg. However, in AT(2) receptor-deficient mice, novokinin did not reduce blood pressure. These results demonstrate that the hypotensive activity of novokinin is mediated by the AT(2) receptor. The hypotensive activity of novokinin in SHRs was completely blocked by indomethacin and CAY10441, an inhibitor of cyclooxygenase and an antagonist of the prostaglandin IP receptor, respectively. These suggest that the hypotensive activity is mediated by prostacyclin and the IP receptor downstream of the AT(2) receptor.

Vasodilator effects of peptides derived from egg white proteins

The aim of this work was to investigate the effect of several peptides, identified before and after simulated gastrointestinal digestion of an egg white hydrolysate, on the vascular function, in rat aorta. The sequences IVF, RADHPFL and YAEERYPIL (0.1 mM) induced vasodilatation in intact aortic rings, with the maximum percentage of dilation corresponding to RADHPFL (40.5+/-7.0%). Two of the end products of the gastrointestinal digestion, RADHP and YPI, also showed vasodilator activity with degrees of relaxation higher than 50%. However, all these peptides failed to induce relaxation in endothelium-denuded aortic rings. The relaxation induced by RADHP was concentration-dependent and it was partially blocked by the nitric oxide synthase inhibitor L-NAME (100 microM) and by the B(1) bradykinin receptor antagonist Des-HOE 140 (30 nM), thus showing that it was mediated by NO production through the activation of B(1) bradykinin receptors. These findings suggest that these peptides could reduce the vascular resistance and could be used as functional food ingredients in the prevention and treatment of hypertension.

Effect of beta-lactotensin on acute stress and fear memory

beta-Lactotensin (beta-LT) is a bioactive peptide derived from bovine milk beta-lactoglobulin and is a natural ligand for neurotensin receptors. We examined the effect of beta-LT on restraint stress and fear memory in mice. Mice subjected to acute restraint stress exhibited a decreased number of head-dips and increased head-dip latency compared to non-stressed controls in the hole-board test, reflecting increased stress-induced behaviors. However, prior administration of beta-LT improved the behaviors caused by stress. The anti-stress effect of beta-LT was blocked by levocabastine, a neurotensin receptor subtype 2 (NTR2) antagonist. In the fear-conditioning test, the duration of freezing responses by cued fear conditioning was significantly reduced in mice administered beta-LT compared with control mice. These results suggest that beta-LT has an anti-stress effect and promotes the extinction of fear memory, which may be mediated by NTR2.

Antihypertensive peptides derived from egg proteins

There have been studies of antihypertensive peptides derived from food proteins, but very few described the production of bioactive peptides from egg proteins. The first 2 antihypertensive peptides isolated in egg were obtained by enzymatic hydrolysis of ovalbumin. They correspond to the sequences Phe-Arg-Ala-Asp-His-Pro-Phe-Leu (ovokinin) and Arg-Ala-Asp-His-Phe-Leu (ovokinin 2-7). Both exhibited endothelium-dependent vasodilatory activity. Ovokinin (2-7) had higher antihypertensive potency than ovokinin in spontaneously hypertensive rats (SHR). Modifications in the sequence of ovokinin (2-7) improved the bioavailability of this peptide. It was also demonstrated that different ovalbumin hydrolysates can inhibit angiotensin I-converting enzyme (ACE). We recently obtained an egg white hydrolysate that inhibited the enzyme in vitro. It was obtained by treating egg white with pepsin and it exhibited antihypertensive activity in SHR. Some ACE-inhibitory peptides obtained from this hydrolysate (Tyr-Arg-Glu-Glu-Arg-Tyr-Pro-Ile-Leu, Arg-Ala-Asp-His-Pro-Phe-Leu, and Ile-Val-Phe) also showed antihypertensive activity in these rats. The egg products mentioned could be used as functional food ingredients with potential therapeutic benefit in the prevention and treatment of hypertension.

Effect of simulated gastrointestinal digestion on the antihypertensive properties of ACE-inhibitory peptides derived from ovalbumin

Food-derived bioactive peptides with ACE-inhibitory properties are receiving special attention due to their beneficial effects in the treatment of hypertension. In this work we evaluate the impact of a simulated gastrointestinal digestion on the stability and activity of two bioactive peptides that derive from ovalbumin by enzymatic hydrolysis, YAEERYPIL and RADHPFL. These peptides possess in vitro ACE-inhibitory activity and antihypertensive activity in spontaneously hypertensive rats (SHR). The results showed that YAEERYPIL and RADHPFL were susceptible to proteolytic degradation after incubation with pepsin and a pancreatic extract. In addition, their ACE-inhibitory activity in vitro decreased after the simulated digestion. The antihypertensive activity on SHR of the end products of the gastrointestinal hydrolysis, YAEER, YPI, and RADHP, was evaluated. The fragments YPI and RADHP significantly decreased blood pressure, 2 h after administration, at doses of 2 mg/kg, but they probably did not exert their antihypertensive effect through an ACE-inhibitory mechanism. It is likely that RADHP is also the active end product of the gastrointestinal digestion of the antihypertensive peptides FRADHPFL (ovokinin) and RADHPF (ovokinin 2-7).