Milk protein-derived bioactive tripeptides Ile-Pro-Pro and Val-Pro-Pro protect endothelial function in vitro in hypertensive rats

Critical Review and Perspectives on Food-Derived Antihypertensive Peptides

Food-derived peptides with antihypertensive properties have received great interest during the past 30 years. There is solid evidence of the effect of various peptide sequences in clinical trials, but their use in preventive or therapeutic treatments is not extensive. There are certain issues, such as the bioavailability or the mechanism of action, that would need to be clarified to establish a direct cause/effect relationship between the administered molecule and the observed effect. This perspective emphasizes the advances in the study of antihypertensive peptides and proposes future research topics that might encourage industry and health policy to exploit these food constituents.

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.

Bradykinin -induced vasodilatation: Role of age, ACE1-inhibitory peptide, mas- and bradykinin receptors

Bradykinin exerts its vascular actions via two types of receptors, the non-constitutively expressed bradykinin receptor type 1 (BR1) and the constitutive type 2 receptor (BR2). Bradykinin-induced vasorelaxation is age-dependent, a phenomenon related to the varying amounts of BR1 and BR2 in the vasculature. Isoleucine-proline-proline (Ile-Pro-Pro), a bioactive tripeptide, lowers elevated blood pressure and improves impaired endothelium-dependent vasorelaxation in hypertensive rats. It inhibits angiotensin converting enzyme 1 (ACE1). Other mechanisms of action have also been postulated. The aims of the study were to clarify the underlying mechanisms of the age-dependency of bradykinin-induced vasodilatation such as the roles of the two bradykinin receptors, the mas-receptor and synergism with Ile-Pro-Pro. The vascular response studies were conducted using mesenteric artery and aorta rings from normotensive 6 wk. (young) and 22 wk. (old) Wistar rats. Cumulative dosing of acetylcholine, bradykinin and angiotensin(1-7) (Ang(1-7))were tested in phenylephrine-induced vasoconstriction with or without 10min pre-incubation with antagonists against BR1-, BR2- or mas-receptors, Ang(1-7) or ACE1-inhibitors captopril and Ile-Pro-Pro. The bradykinin-induced vasorelaxation in vitro was age-dependent and it was improved by pre-incubation with Ile-Pro-Pro, especially in old rats with endothelial dysfunction. The mas-receptor antagonist, D-Pro₇-Ang(1-7) abolished bradykinin-induced relaxation totally. Interestingly, BR1 and BR2 antagonists only slightly reduced bradykinin-induced vasorelaxation, as an evidence for the involvement of other mechanisms in addition to receptor activation. In conclusion, bradykinin-induced vasorelaxation was age-dependent and Ile-Pro-Pro improved it. Mas receptor antagonist abolished relaxation while bradykinin receptor antagonist only slightly reduced it, suggesting that bradykinin-induced vasorelaxation is regulated also by other mechanisms than the classical BR1/BR2 pathway.

Antihypertensive and hypolipidemic effect of milk fermented by specific Lactococcus lactis strains

The antihypertensive and hypolipidemic effects of milk fermented by specific Lactococcus lactis strains in spontaneously hypertensive rats (SHR) were investigated. The SHR were fed ad libitum milk fermented by Lc. lactis NRRL B-50571, Lc. lactis NRRL B-50572, Captopril (40mg/kg of body weight, Sigma-Aldrich Co., St. Louis, MO) or purified water for 4 wk. Results suggested that Lc. lactis fermented milks presented a significant blood pressure-lowering effect. No significant difference was noted among milk fermented by Lc. lactis NRRL B-50571 and Captopril by the second and third week of treatment. Additionally, milk fermented by Lc. lactis strains modified SHR lipid profiles. Milk fermented by Lc. lactis NRRL B-50571 and B-50572 were able to reduce plasma low-density lipoprotein cholesterol and triglyceride contents. Thus, milk fermented by Lc. lactis strains may be a coadjuvant in the reduction of hypertension and hyperlipidemia and may be used as a functional food for better cardiovascular health.

Antihypertensive peptides: production, bioavailability and incorporation into foods

Bioactive food peptides are encrypted within the sequence of food proteins but can be released during food processing (by enzymatic hydrolysis or fermentation) or during gastrointestinal transit. Among bioactive food peptides, those with antihypertensive activity are receiving special attention due to the high prevalence of hypertension in the Western countries and its role in cardiovascular diseases. This paper reviews the current literature on antihypertensive food peptides, focusing on the main methodologies for their production, such as enzymatic hydrolysis, fermentation and the use of recombinant bacteria. This paper also describes the structure/activity relationship of angiotensin-converting enzyme (ACE)-inhibitory peptides, as well as their bioavailability, physiological effects demonstrated by both in vitro and in vivo assays, and the contribution of mechanisms of action other than ACE inhibition. Finally, current reported strategies for incorporation of antihypertensive peptides into foods and their effects on both availability and activity are revised in this manuscript.

High blood pressure-lowering and vasoprotective effects of milk products in experimental hypertension

Milk casein-derived angiotensin-converting enzyme (ACE)-inhibitory tripeptides isoleucine-proline-proline (Ile-Pro-Pro) and valine-proline-proline (Val-Pro-Pro) have been shown to have antihypertensive effects in human subjects and to attenuate the development of hypertension in experimental models. The aim of the present study was to investigate the effect of a fermented milk product containing Ile-Pro-Pro and Val-Pro-Pro and plant sterols on already established hypertension, endothelial dysfunction and aortic gene expression. Male spontaneously hypertensive rats (SHR) with baseline systolic blood pressure (SBP) of 195 mmHg were given either active milk (tripeptides and plant sterols), milk or water ad libitum for 6 weeks. SBP was measured weekly by the tail-cuff method. The endothelial function of mesenteric arteries was investigated at the end of the study. Aortas were collected for DNA microarray study (Affymetrix Rat Gene 1.0 ST Array). The main finding was that active milk decreased SBP by 16 mmHg compared with water (178 (sem 3) v. 195 (sem 3) mmHg; P < 0·001). Milk also had an antihypertensive effect. Active milk improved mesenteric artery endothelial dysfunction by NO-dependent and endothelium-derived hyperpolarising factor-dependent mechanisms. Treatment with active milk caused mild changes in aortic gene expression; twenty-seven genes were up-regulated and eighty-two down-regulated. Using the criteria for fold change (fc) <  0·833 or > 1·2 and P < 0·05, the most affected (down-regulated) signalling pathways were hedgehog, chemokine and leucocyte transendothelial migration pathways. ACE expression was also slightly decreased (fc 0·86; P = 0·047). In conclusion, long-term treatment with fermented milk enriched with tripeptides and plant sterols decreases SBP, improves endothelial dysfunction and affects signalling pathways related to inflammatory responses in SHR.

Long-term intake of a milk casein hydrolysate attenuates the development of hypertension and involves cardiovascular benefits

Essential hypertension is considered a serious health problem and diet can play an important role in its prevention and treatment. The aim of this study was to evaluate the effect of the long-term intake of a product based on milk casein hydrolysate on the development of hypertension in spontaneously hypertensive rats (SHR). A daily dose of 800 mg/kg body weight of the casein hydrolysate product was administered dissolved in drinking water during 6 weeks. Systolic and diastolic blood pressures were measured weekly by the tail-cuff method. Endothelial function in aorta and mesenteric segments, left ventricular hypertrophy, endothelial nitric oxide synthase (eNOS) expression in aorta and plasmatic angiotensin conversion enzyme (ACE) activity were also evaluated at the end of treatment. The development of hypertension was attenuated in the group treated with the casein hydrolysate product; in this sense the systolic blood pressure increased 33±3 mmHg in control group and only 18±5 mmHg in the treated group during the experimental period. In addition, the treatment improved aorta and mesenteric acetylcholine relaxations and increased the eNOS expression in aorta. Left ventricular hypertrophy decreased in treated SHR accompanied by a significant decrease in interstitial fibrosis. These results warrant evaluation in humans to determine if the product based on a casein hydrolysate could be used as a functional food ingredient to prevent blood pressure increased with additional cardiovascular benefits.

Bioactive peptides derived from milk proteins and their health beneficial potentials: an update

It has been well recognized that dietary proteins provide a rich source of biologically active peptides. Today, milk proteins are considered the most important source of bioactive peptides and an increasing number of bioactive peptides have been identified in milk protein hydrolysates and fermented dairy products. Bioactive peptides derived from milk proteins offer a promising approach for the promotion of health by means of a tailored diet and provide interesting opportunities to the dairy industry for expansion of its field of operation. The potential health benefits of milk protein-derived peptides have been a subject of growing commercial interest in the context of health-promoting functional foods. Hence, these peptides are being incorporated in the form of ingredients in functional and novel foods, dietary supplements and even pharmaceuticals with the purpose of delivering specific health benefits.

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.

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.