a1 Institute of Biomedicine, Pharmacology, University of Helsinki, PO Box 63, 00014 University of Helsinki, Finland
a2 Valio Ltd, R&D, PO Box 30, 00039 Valio, Finland
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.
(Received November 23 2010)
(Revised January 25 2011)
(Accepted March 07 2011)
(Online publication May 10 2011)
Abbreviations: ACE, angiotensin-converting enzyme; ACh, acetylcholine; COX, cyclo-oxygenase; EDHF, endothelium-derived hyperpolarising factor; eNOS, endothelial NO synthase; fc, fold change; Ile-Pro-Pro, isoleucine-proline-proline; l-NAME, NG-nitro-l-arginine methyl ester; PE, phenylephrine; RAS, renin–angiotensin system; SBP, systolic blood pressure; SHR, spontaneously hypertensive rat; SNP, sodium nitroprusside; TRAM-34, 1-[(2-chlorophenyl)diphenylmethyl]-1H-pyrazole; Val-Pro-Pro, valine-proline-proline