Antihypertensive effects of lactoferrin hydrolyzates: Inhibition of angiotensin- and endothelin-converting enzymes

Abstract

The potential of bovine lactoferrin (LF) as a source of antihypertensive peptides acting on the renin–angiotensin system (RAS) and the endothelin (ET) system as dual vasopeptidase inhibitors has been examined. For this purpose enzymatic LF hydrolyzates (LFHs) were generated by trypsin and proteinase K digestions. Permeate fractions with molecular masses lower than 3kDa (LFH <3kDa) were orally administered to spontaneously hypertensive rats (SHRs). Although both LFHs <3kDa showed in vitro angiotensin I-converting enzyme (ACE)-inhibitory activity, only proteinase K LFH <3kDa exerted an in vivo antihypertensive effect. The proteinase K LFH <3kDa and a previously characterized pepsin LFH <3kDa with ACE-inhibitory and antihypertensive effects were tested in ex vivo functional assays as inhibitors of ACE-dependent vasoconstriction. Pepsin LFH <3kDa but not proteinase K LFH <3kDa inhibited ACE-dependent vasoconstriction. When tested as inhibitors towards endothelin-converting enzyme (ECE), both LFHs <3kDa exerted in vitro inhibitory effects on ECE activity and inhibited ECE-dependent vasoconstriction. Most abundant peptides in proteinase K LFH <3kDa were identified by using an ion trap mass spectrometer. Based on peptide abundance, two peptides (GILRPY and REPYFGY) were chemically synthesized and their ECE-inhibitory activity was tested. Both exerted in vitro inhibitory effects on ECE activity. In conclusion, orally effective antihypertensive LFHs <3kDa may act as dual vasopeptidase (ACE/ECE) or as single ECE inhibitors with different antivasoconstrictor effects depending on the protease used to release bioactive peptide sequences.