leucyl-prolyl-proline and valyl-prolyl-proline

Bradykinin is the main player of the kallikrein-kinin system. Bradykinin-induced vasodilatation is age-dependent; this is believed to be associated with the level of expression of the two bradykinin receptors (BR1 and BR2) in the vasculature. The aim of this study was to clarify bradykinin-induced vascular reactivity of spontaneously hypertensive rats (SHR) and age-matched Wistar-Kyoto rats (WKY) after 6 weeks' consumption of a drink containing bioactive tripeptides (Ile-Pro-Pro, Val-Pro-Pro and Leu-Pro-Pro). Two age groups were used: young (10 weeks at the end of experiment) and old (24 weeks). Blood pressure was monitored weekly by the tail-cuff method. After six weeks, vascular reactivity was assessed in vitro in mesenteric artery rings focusing on bradykinin induced activity. Blood pressure was lowered in old SHR after 6 weeks' tripeptide consumption compared to water drinking controls (P < 0.05). Blood pressure was lowered by peptide consumption also in old WKY (P < 0.05) but tripeptide consumption exerted no effect on the blood pressure of young animals. Old SHR suffered from endothelial and smooth muscle dysfunction which was not improved by these tripeptides. Interestingly, bradykinin caused vasoconstriction even in young SHR; this was blocked by a non-selective cyclooxygenase (COX) inhibitor but not by a B1 and B2 receptor antagonist. The expressions of mRNA of COX-1 and COX-2 in aorta were slightly upregulated in old SHR. ACE-1 activity in aorta and protein level in kidney, but not ACE-1 mRNA expression was upregulated in old animals (P < 0.05). To conclude, long-term feeding with a drink containing tripeptides lowers or prevents the age-associated increase in blood pressure in hypertensive and normotensive animals. ACE-1 activity, protein level but not mRNA expression are elevated in old animals. We also demonstrated that the vascular inflammation and dysfunction present in aged hypertensive animals cause bradykinin to induce vasoconstriction; this is not prevented by tripeptide feeding but involves the prostaglandin pathway.

Topics: Angiotensin-Converting Enzyme Inhibitors; Animals; Aorta; Blood Pressure; Bradykinin; Captopril; Cyclooxygenase 1; Hypertension; Kidney; Membrane Proteins; Mesenteric Arteries; Oligopeptides; Peptidyl-Dipeptidase A; Rats, Inbred SHR; Rats, Inbred WKY; Vasoconstriction; Vasodilator Agents

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.

Topics: Animals; Dietary Supplements; Female; Kidney; Liver; Oligopeptides; Swine; Tissue Distribution

Milk-based drinks containing casein-derived tripeptides isoleucine-proline-proline (Ile-Pro-Pro) and valine-proline-proline (Val-Pro-Pro) have been shown to possess antihypertensive and vascular endothelium-protecting properties in hypertensive animal models. Furthermore in clinical intervention trials they reduce blood pressure and arterial stiffness. The exact mechanisms are not known, but inhibition of angiotensin converting enzyme 1 (ACE1) has been suggested mainly to mediate these beneficial effects. The present study investigated the in vitro effects of three tripeptides: Ile-Pro-Pro, Val-Pro-Pro and leqcine-proline-proline (Leu-Pro-Pro) on four renin-angiotensin system enzymes: ACE1, ACE2, chymase, and cathepsin G. Also their effects on arginase I, a critical enzyme in L-arginine-nitric oxide pathway, were studied. It was shown, apparently for the first time, that the inhibitory effects of Ile-Pro-Pro, Val-Pro-Pro and Leu-Pro-Pro on ACE1 at micromolar concentrations are competitive in nature. Therefore the efficacy of inhibition is largely dependent on the amount of substrate present. Inhibition of ACE2 and arginase I was reached only at concentrations three orders of magnitude greater. No inhibition of chymase and cathepsin G was observed by the tripeptides. The findings support the hypothesis that Ile-Pro-Pro, Val-Pro-Pro and Leu-Pro-Pro act favourably on blood pressure mainly by selective inhibition of ACE1.

Topics: Angiotensin-Converting Enzyme Inhibitors; Antihypertensive Agents; Arginase; Caseins; Cathepsin G; Chymases; Enzymes; Humans; Oligopeptides; Peptidyl-Dipeptidase A

An active local renin-angiotensin system (RAS) has recently been found in the human eye. The aim of the present study was to compare the activities of central RAS enzymes (ACE1 and 2) in porcine ocular tissues, morphologically and physiologically close to the human eye. In addition, the effects of three ACE-inhibitory tripeptides on these enzymes were evaluated.. Enucleated fresh porcine eyes were used. Activities of ACE1 and ACE2 and their inhibition by bioactive tripeptides (Ile-Pro-Pro, Val-Pro-Pro, Leu-Pro-Pro) as well as by a standard ACE-inhibitor captopril were assayed in the vitreous body, the retina and the ciliary body using fluorometric detection methods.. Activity of ACE1 as well as ACE2 was found in all tissues evaluated. ACE1 activity was markedly higher in the ciliary body (3.7 +/- 0.7 mU/mg protein) than in retina (0.2 +/- 0.02 mU/mg), whereas ACE2 activities in the ciliary body (0.2 +/- 0.02 mU/mg) and retina (0.2 +/- 0.01 mU/mg) were at the same level. In the vitreous body ACE1 activity (8.2 +/- 0.31 nmol/min/mL) was manifold compared to that of ACE2 (0.1 +/- 0.02 nmol/min/mL). The tripeptides inhibited ACE1 at one-thousandth of the concentration needed to inhibit ACE2. All peptides studied evinced about equal inhibitory activities.. To our knowledge the present findings constitute the first evidence of ACE2 activity in the ciliary and vitreous bodies, in addition to previously described activity in the retina. The known favorable effects of ACE2 products vs. those of ACE1 suggest a counterbalancing interaction of these two enzyme homologues in physiological regulation of ocular circulation and pressure and possible protective role in certain ophthalmic disorders such as glaucoma and diabetic retinopathy.

Topics: Angiotensin-Converting Enzyme 2; Angiotensin-Converting Enzyme Inhibitors; Animals; Captopril; Ciliary Body; In Vitro Techniques; Oligopeptides; Peptidyl-Dipeptidase A; Retina; Swine; Vitreous Body

The effect of chronic treatment with fermented milk products containing bioactive tripeptides and plant sterols on blood pressure and vascular function was investigated in spontaneously hypertensive rats (SHR). Six-weeks old male SHR (n=36) were randomized into 4 groups by body weight and blood pressure to receive either Lactobacillus helveticus fermented standard milk product (containing tripeptides Ile-Pro-Pro, Val-Pro-Pro and Leu-Pro-Pro), test product with enzymatically produced tripeptides without or with plant sterols or control product without the active constituents for 8 weeks. Systolic blood pressure (SBP) was measured weekly using the tail-cuff method. Thoracic aorta and mesenteric artery were excised for vascular response measurements. At the end, SBP values vs. control product group were: standard product group -14 mmHg (P<0.05), test product group -12 mmHg and test product +sterols group -7 mmHg. The average daily tripeptide dose was 2.8-5.2 mg/kg. Total serum cholesterol in the test product +sterols group tended to be lower than in the test product group (P=0.10) whereas serum plant sterol (campesterol, sitosterol) concentrations were higher (P<0.001). In conclusion, bioactive tripeptide-containing milk products attenuated the blood pressure development in SHR. The plant sterols did not improve this effect. Vascular responses did not markedly differ between the groups, except that endothelium-derived hyperpolarizing factor (EDHF) -related aortic relaxation was demonstrated in the test product +sterols group.

Topics: Acetylcholinesterase; Animals; Antihypertensive Agents; Arteries; Blood Pressure; Caseins; Cholesterol; Cultured Milk Products; Hypertension; Lactobacillus helveticus; Male; Oligopeptides; Phytosterols; Random Allocation; Rats; Rats, Inbred SHR; Time Factors

Tripeptides may possess bioactive properties. For instance, blood pressure lowering is attributed to the proline-rich tripeptides Ile-Pro-Pro (IPP), Leu-Pro-Pro (LPP), and Val-Pro-Pro (VPP). However, little is known about their absorption, distribution, and elimination characteristics. The aim of this study was to characterize the pharmacokinetic behavior of IPP, LPP, and VPP in a conscious pig model. Synthetic IPP, LPP, and VPP were administered intravenously or intragastrically (4.0 mg kg(-1) BW in saline) to 10 piglets (approximately 25 kg body weight) in the postabsorptive state. After intravenous dosing, the elimination half-life for IPP was significantly higher (P<0.001) than for LPP and VPP (2.5+/-0.1, 1.9+/-0.1, and 2.0+/-0.1 min, respectively). After intragastric dosing, however, the elimination half-lives were not significantly different between the peptides (9+/-1, 15+/-4, and 12+/-6 min, respectively). Maximum plasma concentrations were about 10 nmol l(-1) for the three tripeptides. The fraction dose absorbed was 0.077+/-0.010, 0.059+/-0.009, and 0.073+/-0.015%, for IPP, LPP, and VPP, respectively. Proline-rich tripeptides reach the blood circulation intact, with an absolute bioavailability of about 0.1% when administered via a saline solution. Because half-lives of absorption and elimination were maximally about 5 and 15 min, respectively, this suggests that under these conditions a bioactive effect of these tripeptides would be rather acute.

Topics: Animals; Antihypertensive Agents; Female; Oligopeptides; Swine