The lactotripeptides isoleucine-proline-proline and valine-proline-proline do not inhibit the N-terminal or C-terminal angiotensin converting enzyme active sites in humans

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.

Identification and quantification of ACE-inhibiting peptides in enzymatic hydrolysates of plant proteins

Enzymatic hydrolysis of proteins from rice, soy, pea and wheat, with both chymotrypsin and thermolysin, resulted in hydrolysates, which are efficient inhibitors of the angiotensin-converting enzyme (ACE). IC50 values of the hydrolysates were between 27 and 39mg/l, which is comparable to enzymatically hydrolysed whey protein. A significant increase of the ACE-inhibiting effect was observed following butanol extraction due to accumulation of hydrophobic peptides (IC50 between 12 and 21mg/l). Based on the identification and quantification of individual tryptophan-, tyrosine- and phenylalanine-containing dipeptides, 50-80% of the total ACE-inhibiting potential of butanol extracts from plant protein hydrolysates could be explained. Compared to hydrolysates from whey protein, where the inhibitory effect can almost exclusively be attributed to Ile-Trp, the ACE inhibition by plant protein hydrolysates is caused by a variety of peptides, in particular tyrosine-containing peptides. Hydrolysates of plant proteins are promising ingredients for the development of functional foods.

Enhanced Lacto-Tri-Peptide Bio-Availability by Co-Ingestion of Macronutrients

Some food-derived peptides possess bioactive properties, and may affect health positively. For example, the C-terminal lacto-tri-peptides Ile-Pro-Pro (IPP), Leu-Pro-Pro (LPP) and Val-Pro-Pro (VPP) (together named here XPP) are described to lower blood pressure. The bioactivity depends on their availability at the site of action. Quantitative trans-organ availability/kinetic measurements will provide more insight in C-terminal tri-peptides behavior in the body. We hypothesize that the composition of the meal will modify their systemic availability. We studied trans-organ XPP fluxes in catheterized pigs (25 kg; n=10) to determine systemic and portal availability, as well as renal and hepatic uptake of a water-based single dose of synthetic XPP and a XPP containing protein matrix (casein hydrolyte, CasH). In a second experiment (n=10), we compared the CasH-containing protein matrix with a CasH-containing meal matrix and the modifying effects of macronutrients in a meal on the availability (high carbohydrates, low quality protein, high fat, and fiber). Portal availability of synthetic XPP was 0.08 ± 0.01% of intake and increased when a protein matrix was present (respectively 3.1, 1.8 and 83 times for IPP, LPP and VPP). Difference between individual XPP was probably due to release from longer peptides. CasH prolonged portal bioavailability with 18 min (absorption half-life, synthetic XPP: 15 ± 2 min, CasH: 33 ± 3 min, p<0.0001) and increased systemic elimination with 20 min (synthetic XPP: 12 ± 2 min; CasH: 32 ± 3 min, p<0.0001). Subsequent renal and hepatic uptake is about 75% of the portal release. A meal containing CasH, increased portal 1.8 and systemic bioavailability 1.2 times. Low protein quality and fiber increased XPP systemic bioavailability further (respectively 1.5 and 1.4 times). We conclude that the amount and quality of the protein, and the presence of fiber in a meal, are the main factors that increase the systemic bioavailability of food-derived XPP.

Does the cis/trans configuration of peptide bonds in bioactive tripeptides play a role in ACE-1 enzyme inhibition?

Background

The milk casein-derived bioactive tripeptides isoleucine-proline-proline (IPP) and valine-proline-proline (VPP) have been shown to prevent development of hypertension in animal models and to lower blood pressure in moderately hypertensive subjects in most but not all clinical trials. Inhibition of angiotensin-converting enzyme 1 (ACE-1) has been suggested as the explanation for these antihypertensive and beneficial vascular effects. Previously, human umbilical vein endothelial cells (HUVEC) have not been used to test ACE-1 inhibiting properties of casein derived tripeptides in vasculature.

Purpose

We focused on the cis/trans configurations of the peptide bonds in proline-containing tripeptides in order to discover whether the different structural properties of these peptides influence their activity in ACE-1 inhibition. We hypothesized that the configuration of proline-containing peptides plays a significant role in enzyme inhibition.

Methods

AutoDock 4.2 docking software was used to predict suitable peptide bond configurations of the tripeptides. Besides modeling studies, we completed ACE-1 activity measurements in vitro using HUVEC cultures.

Results

In HUVEC cells, both IPP and VPP inhibited ACE-1. Based on molecular docking studies, we propose that in ACE-1 inhibition IPP and VPP share a similar cis configuration between the first aliphatic (isoleucine or valine) and the second (proline) amino acid residues and more different configurations between two proline residues. In vivo experiments are needed to validate the significance of the present findings.

The impact of milk proteins and peptides on blood pressure and vascular function: a review of evidence from human intervention studies

CVD are the leading cause of death worldwide. Hypertension, a major controllable risk factor of CVD, is intimately associated with vascular dysfunction, a defect which is also now recognised to be a major, modifiable risk factor for the development of CVD. The purpose of the present review was to critically evaluate the evidence for the effects of milk proteins and their associated peptides on blood pressure (BP) and vascular dysfunction. After a detailed literature search, the number of human trials evaluating the antihypertensive effects of casein-derived peptides (excluding isoleucine-proline-proline and valine-proline-proline) was found to be limited; the studies were preliminary with substantial methodological limitations. Likewise, the data from human trials that examined the effects of whey protein and peptides were also scarce and inconsistent. To date, only one study has conducted a comparative investigation on the relative effects of the two main intact milk proteins on BP and vascular function. While both milk proteins were shown to reduce BP, only whey protein improved measures of arterial stiffness. In contrast, a growing number of human trials have produced evidence to support beneficial effects of both milk proteins and peptides on vascular health. However, comparison of the relative outcomes from these trials is difficult owing to variation in the forms of assessment and measures of vascular function. In conclusion, there is an accumulating body of evidence to support positive effects of milk proteins in improving and/or maintaining cardiovascular health. However, the variable quality of the studies that produced this evidence, and the lack of robust, randomised controlled intervention trials, undermines the formulation of firm conclusions on the potential benefits of milk proteins and peptides on vascular health.

Lactotripeptides intake and blood pressure management: a meta-analysis of randomised controlled clinical trials

BACKGROUND AND AIMS

Lactotripeptides (LTPs, including IPP and VPP) have held promise in the framework of lifestyle modification for prevention and control of hypertension - a cardiovascular risk factor, as LTPs are reported to have an inhibitory effect on angiotensin-converting enzyme. While the number of clinical trials to test the efficacy of LTP continues to increase, the results have been inconsistent, especially in the last few years. The purpose of the present meta-analysis is to precisely estimate the pooled mean effect of LTPs on conventional blood pressure (BP) generally and on 24-h ambulatory BP (ABP) particularly, as well as the change of BP in relation to baseline BP, race, and study design, to better reflect the evolving field.

DATA SYNTHESIS

In general analysis of 24 studies with 28 trials on 1919 human subjects, there are small reductions in both systolic BP (SBP) and diastolic BP (DBP) with the pooled mean effects of 1.66 (95% confidence interval (CI): -2.48 and -0.84) and 0.76 mmHg (-1.31 and -0.20) in response to LTP administration. In analysis of 24-h ABP response to LTP intervention, the reductions of SBP and DBP are 1.30 (-2.49 and -0.11) and 0.57 mmHg (-1.49 and 0.35). In subgroup analysis, the anti-hypertensive efficacy appears to be related to baseline BP, ethnic differences, treatment duration and double versus not double-blind design.

CONCLUSIONS

The present findings indicate that the BP-lowering effect of LTP is statistically significant, though small in magnitude. More clinical investigations (especially randomized double-blind trials with ABP) are warranted to determine the anti-hypertensive efficacy of LTP conclusively.

Predictors of the short-term effect of isoleucine-proline-proline/valine-proline-proline lactotripeptides from casein on office and ambulatory blood pressure in subjects with pharmacologically untreated high-normal blood pressure or first-degree hypertension

Our aim was to evaluate the predictors of Isoleucine-Proline-Proline/Valine-Proline-Proline (IPP-VPP) lactotripeptides (LTPs) antihypertensive effect in the context of a short-term large double-blind randomized clinical trial involving 164 pharmacologically untreated subjects in primary prevention for cardiovascular disease. When compared with the baseline, office systolic blood pressure (SBP) (-3.42 mm Hg, P < .001) and diastolic blood pressure (DBP) (-2.35 mm Hg, P < .001) significantly decreased, in the LTP-treated patients only. No significant change in predictors during the study of ambulatory blood pressure measurement (ABPM) parameters was observed. A short-term supplementation with LTPs significantly improves the office SBP and DBP, especially in male subjects. The main predictor of LTP antihypertensive effect was the baseline BP.

Possible role of milk-derived bioactive peptides in the treatment and prevention of metabolic syndrome

The growing prevalence of metabolic syndrome as well as its impact on public health has garnered increased attention in recent years. As a result, metabolic syndrome is now considered one of the world's leading public health problems. Bioactive peptides deriving from milk proteins may play an important role in the prevention and treatment of metabolic syndrome and its complications via several mechanisms, such as the satiety response, the regulation of insulinemia levels and blood pressure, the uptake of free radicals, and alteration of the lipid profile. These peptides can be incorporated into functional foods or administered via nutraceuticals to decrease the risk of obesity, atherogenesis, arterial hypertension, and type 2 diabetes. Recent findings have generated considerable scientific and commercial interest in milk-derived bioactive peptides, leading to numerous publications on the effectiveness of these substances. This review summarizes the current knowledge on bioactive peptides derived from milk proteins and examines the potential value of these peptides in the treatment and prevention of metabolic syndrome and its complications.

Casein-derived tripeptide Ile-Pro-Pro improves angiotensin-(1-7)- and bradykinin-induced rat mesenteric artery relaxation

AIMS

Milk casein-derived bioactive tripeptides isoleucine-proline-proline (Ile-Pro-Pro) and valine-proline-proline (Val-Pro-Pro) lower blood pressure in animal models of hypertension and humans. In some studies, their angiotensin-converting enzyme (ACE)-inhibitory effect has been demonstrated. Besides classical ACE-angiotensin II-AT(1)-receptor pathway (ACE-Ang II- AT(1)), the significance of ACE2-angiotensin-(1-7)-Mas-receptor (ACE2-Ang-(1-7)-Mas) axis in the blood pressure regulation has now been acknowledged. The present study was aimed to further evaluate the renin-angiotensin system (RAS)-related vascular effects of Ile-Pro-Pro in vitro using rat mesenteric arteries.

MAIN METHODS

Superior mesenteric arteries of spontaneously hypertensive rat (SHR) were isolated, cut into rings and mounted in standard organ bath chambers. Endothelium-intact arterial rings were incubated in Krebs solution either with Ile-Pro-Pro, proline-proline (Pro-Pro), isoleucine (Ile), proline (Pro) or captopril for 6h at +37°C and vascular reactivity was measured.

KEY FINDINGS

In the presence of AT(1)-antagonist valsartan, Ang II induced vasodilatation, which was more pronounced in the arteries incubated with Ile-Pro-Pro (P<0.05) compared to the other compounds. Ang-(1-7)-induced vasodilatation was augmented by Ile-Pro-Pro or Pro (P<0.001 vs. control). Mas-receptor antagonist A-779 did not alter the responses. Ile-Pro-Pro and Pro augmented also bradykinin-induced relaxations (P<0.001 vs. control). Control arteries and arteries incubated with captopril showed only slight relaxations at higher bradykinin concentrations.

SIGNIFICANCE

Casein-derived tripeptide Ile-Pro-Pro and amino acid Pro enhance the vasodilatory effect of Ang-(1-7) and bradykinin. The role of ACE2-Ang-(1-7)-Mas axis in the modulation of vascular tone by these compounds seems probable.

Lactopeptides and human blood pressure

PURPOSE OF REVIEW

Since the mid-1990s, a number of randomized controlled trials have been published that showed an antihypertensive effect of peptides derived from milk. Research has mainly focused on isoleucine-proline-proline and valine-proline-proline (IPP + VPP), two lactotripeptides that can inhibit the angiotensin-converting enzyme (ACE) in vitro. In Finnish and Japanese subjects with (mild) hypertension, systolic blood pressure (SBP) reductions of approximately 5 mmHg were reported during 4-12 weeks of IPP + VPP supplementation. This review was performed to summarize new data from human intervention studies.

RECENT FINDINGS

The effect of lactotripeptides on blood pressure has recently been examined in six double-blind, placebo-controlled trials that involved a total of 780 subjects with high-normal blood pressure or untreated hypertension from the UK and The Netherlands. Intervention periods lasted 4-8 weeks, and IPP + VPP intake ranged from 2 to 10 mg/day. Contrary to earlier trials, there was little evidence for an antihypertensive effect of IPP + VPP. Furthermore, no ACE inhibition was observed in vivo.

SUMMARY

Recent data do not support a role for lactotripeptides in blood pressure regulation. However, we cannot exclude a beneficial effect in hypertensive subjects from specific populations (e.g. Finland, Japan). Should this be confirmed, more research is needed on mechanisms other than the renin-angiotensin-aldosterone system that could be involved.

Antihypertensive Peptides from Milk Proteins

Dietary proteins possess a wide range of nutritional and functional properties. They are used as a source of energy and amino acids, which are needed for growth and development. Many dietary proteins, especially milk proteins, contain physiologically active peptides encrypted in the protein sequence. These peptides may be released during gastrointestinal digestion or food processing and once liberated, cause different physiological functions. Milk-derived bioactive peptides are shown to have antihypertensive, antimicrobial, immunomodulatory, antioxidative and mineral-binding properties. During the fermentation of milk with certain lactobacilli, two interesting tripeptides Ile-Pro-Pro and Val-Pro-Pro are released from casein to the final product. These lactotripeptides have attenuated the development of hypertension in several animal models and lowered blood pressure in clinical studies. They inhibit ACE in vitro at micromolar concentrations, protect endothelial function in vitro and reduce arterial stiffness in humans. Thus, milk as a traditional food product can after certain processing serve as a functional food and carry specific health-promoting effects, providing an option to control blood pressure.