Lactotripeptides Inhibiting ACE1 Elevate the Plasma Bradykinin Concentration Acutely in a Placebo-Controlled, Double-Blind, Cross-Over, 4-Week Trial in Healthy Volunteers

Abstract

This placebo-controlled, double-blind, cross-over intervention with twelve normotensive healthy volunteers tested the effects of milk products contain ing either 5 or 50 mg of ACE1-inhibitory lactotripeptides (isolecine-proline-proline, Ile-Pro-Pro, and valine-proline-proline, Val-Pro-Pro) and placebo milk drink (with similar taste) on plasma bradykinin levels. The subjects consumed one of the three test products in a random order, double-blinded, and four-week trial. On the first day (day 1) and on the last day (day 29) i.e. after four weeks ’ treatment with one of the products, the acute effect with the same single dose was assayed. Other markers of the renin-angiotensin-aldosterone system (RAAS) were measured from plasma four times on the same days when we also assessed daytime urinary excretion of biomarkers of endothelial function. Neither acute nor prolonged administration of the ACE-1 inhibiting peptide drinks significantly lowered blood pressure of the normotensive subjects. The most important finding was the dose-dependent, and linear increase in plasma bradykinin concentrations after acute dosing on the first day; it was nearly statistically significant also on the day 29 (p < 0.06). Other indicators of RAAS or endothelial function did not differ from those of placebo after the acute or prolonged treatments. Our results suggest that even weak inhibitors of ACE-1, such as the lactotripeptides Ile-Pro-Pro and Val-Pro-Pro, are able to diminish the breakdown of bradykinin and therefore increase plasma bradykinin levels. This may partly explain the blood pressure lowering and vasodilatory effects of lactotripeptides, shown by us earlier in mildly hypertensive subjects.