Kinetics of the inhibition of renin and angiotensin I-converting enzyme by flaxseed protein hydrolysate fractions

January 1, 2009 Human Health and Nutrition Data 0 Comments

Kinetics of the inhibition of renin and angiotensin I-converting enzyme by flaxseed protein hydrolysate fractions

Year: 2009
Authors: Udenigwe, C.C. lin, Y.-S. Hou, W.-C. Aluko, R.E.
Publication Name: Journal of Functional Foods
Publication Details: Volume 1; Pages 199-207.


Enzymatic hydrolysates from flaxseed protein were investigated for in vitro inhibition of angiotensin I-converting enzyme (ACE) and renin activities. Pepsin, ficin, trypsin, papain, thermolysin, pancreatin and Alcalase were used to hydrolyze flaxseed proteins followed by fractionation using ultrafiltration to isolate low-molecular-weight peptides, and separation of the Alcalase hydrolysate into cationic peptide fractions. Using N-(3-[2-furyl]acryloyl)-phenylalanylglycylglycine as substrate, the protein hydrolysates showed a concentration-dependent ACE inhibition (IC50, 0.0275 +/- 0.151 mg/ml) with thermolysin hydrolysate and Alcalase cationic peptide fraction I (FI) showing the most potent activity. Flaxseed peptide fractions also showed no or moderate inhibitory activities against human recombinant renin (IC50, 1.22 +/- 2.81 mg/ml). Kinetics studies showed that the thermolysin hydrolysate and FI exhibited mixed-type pattern of ACE inhibition whereas cationic peptide fraction II inhibited renin in uncompetitive fashion. These results show that the protein components of flaxseed meal possess peptide amino acid sequences that can be exploited as potential food sources of anti-hypertensive agents. (Author's abstract)
The renin angiotensin aldoresterone system (RAAS) is a target for the development of anti-hypertensive agents.  The RAAS pathway comprises a series of reactions that produce molecules capable of regulating blood pressure in humans; renin and angiotensin I-converting enzyme (ACE). Renin catalyzes the initial and rate-limiting step by converting angiotensionogen to angiotensin I (AT-I). ACE catalyzes the conversion of AT-I into a potent vasoconstrictor angiotensin II (AT-II), and also degrades bradykinin, a vasodilator. ACE inhibitors  block or suppress the formation of ATII. Several food protein hydrolysates and constituent peptides have been shown to display in vitro inhibition of ACE activity resulting in the lowering of elevated blood pressure in hypertensive humans. Crude flaxseed protein hydrolysate prepared using Flavourzyme inhibited ACE in vitro and displayed antioxidant properties in scavenging hydroxyl radical and lipid peroxyl radical.  The objective of this study was to determine the potential ACE and renin inhibitory activities of low-molecular-weight (LMW) flaxseed protein hydrolysates produced from hydrolysis of isolated flaxseed proteins using different food-grade proteases. The inhibition of the activities of ACE and human recombinant renin observed in this study was dependent on the ability of the different proteases used for hydrolysis to release bioactive peptide sequences from flaxseed proteins rather than the protein yield of low-molecular-weight peptides. The authors suggest that flaxseed peptide fractions that inhibited both ACE and renin activities possess  potentially could provide better in vivo lowering of blood pressure when compared to peptides that inhibit ACE alone. Further work is on-going to characterize the effects of these flaxseed protein hydrolysate and cationic peptide fractions in lowering of blood pressure, and to identify their constituent bioactive peptides. (Editor's comments)

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