title: New perspectives in the renin-angiotensin-aldosterone system (RAAS) I: endogenous angiotensin converting enzyme (ACE) inhibition.
abstract: Angiotensin-converting enzyme (ACE) inhibitors represent the fifth most often prescribed drugs. ACE inhibitors decrease 5-year mortality by approximately one-fifth in cardiovascular patients. Surprisingly, there are reports dating back to 1979 suggesting the existence of endogenous ACE inhibitors, which endogenous inhibitory effects are much less characterized than that for the clinically administered ACE inhibitors. Here we aimed to investigate this endogenous ACE inhibition in human sera. It was hypothesized that ACE activity is masked by an endogenous inhibitor, which dissociates from the ACE when its concentration decreases upon dilution. ACE activity was measured by FAPGG hydrolysis first. The specific (dilution corrected) enzyme activities significantly increased by dilution of human serum samples (23.2 ± 0.7 U/L at 4-fold dilution, 51.4 ± 0.3 U/L at 32-fold dilution, n = 3, p = 0.001), suggesting the presence of an endogenous inhibitor. In accordance, specific enzyme activities did not changed by dilution when purified renal ACE was used, where no endogenous inhibitor was present (655 ± 145 U/L, 605 ± 42 U/L, n = 3, p = 0.715, respectively). FAPGG conversion strongly correlated with angiotensin I conversion suggesting that this feature is not related to the artificial substrate. Serum samples were ultra-filtered to separate ACE (MW: 180 kDa) and the hypothesized inhibitor. Filtering through 50 kDa filters was without effect, while filtering through 100 kDa filters eliminated the inhibiting factor (ACE activity after <100 kDa filtering: 56.4 ± 2.4 U/L, n = 4, control: 26.4 ± 0.7 U/L, n = 4, p<0.001). Lineweaver-Burk plot indicated non-competitive inhibition of ACE by this endogenous factor. The endogenous inhibitor had higher potency on the C-terminal active site than N-terminal active site of ACE. Finally, this endogenous ACE inhibition was also present in mouse, donkey, goat, bovine sera besides men (increasing of specific ACE activity from 4-fold to 32-fold dilution: 2.8-fold, 1.7-fold, 1.5-fold, 1.8-fold, 2.6-fold, respectively). We report here the existence of an evolutionary conserved mechanism suppressing circulating ACE activity, in vivo, similarly to ACE inhibitory drugs.
authors.affiliation: Division of Clinical Physiology, Institute of Cardiology, University of Debrecen, Debrecen, Hungary.
authors.forename: Miklós
authors.initials: M
authors.lastname: Fagyas
authors.affiliation: Division of Clinical Physiology, Institute of Cardiology, University of Debrecen, Debrecen, Hungary.
authors.forename: Katalin
authors.initials: K
authors.lastname: Úri
authors.affiliation: Division of Clinical Physiology, Institute of Cardiology, University of Debrecen, Debrecen, Hungary.
authors.forename: Ivetta M
authors.initials: IM
authors.lastname: Siket
authors.affiliation: Division of Clinical Physiology, Institute of Cardiology, University of Debrecen, Debrecen, Hungary.
authors.forename: Andrea
authors.initials: A
authors.lastname: Daragó
authors.affiliation: Department of Neurology, University of Debrecen, Debrecen, Hungary.
authors.forename: Judit
authors.initials: J
authors.lastname: Boczán
authors.affiliation: Institute of Internal Medicine, Division of Nephrology, University of Debrecen, Debrecen, Hungary.
authors.forename: Emese
authors.initials: E
authors.lastname: Bányai
authors.affiliation: Division of Clinical Physiology, Institute of Cardiology, University of Debrecen, Debrecen, Hungary.
authors.forename: István
authors.initials: I
authors.lastname: Édes
authors.affiliation: Division of Clinical Physiology, Institute of Cardiology, University of Debrecen, Debrecen, Hungary.
authors.forename: Zoltán
authors.initials: Z
authors.lastname: Papp
authors.affiliation: Division of Clinical Physiology, Institute of Cardiology, University of Debrecen, Debrecen, Hungary.
authors.forename: Attila
authors.initials: A
authors.lastname: Tóth
mesh_terms: D000803:Angiotensin I / Q000378:metabolism; D000806:Angiotensin-Converting Enzyme Inhibitors / Q000494:pharmacology*; D002216:Captopril / Q000494:pharmacology; D020134:Catalytic Domain; D017124:Conserved Sequence; D019143:Evolution, Molecular; D006801:Humans; D006863:Hydrogen-Ion Concentration; D006868:Hydrolysis; D008954:Models, Biological; D008970:Molecular Weight; D009842:Oligopeptides / Q000378:metabolism; D009994:Osmolar Concentration; D007703:Peptidyl-Dipeptidase A / Q000097:blood*; D012084:Renin-Angiotensin System / Q000187:drug effects*
chemical_list: D000806:Angiotensin-Converting Enzyme Inhibitors; D009842:Oligopeptides; C038275:2-furanacryloyl-phenylalanyl-glycyl-glycine; D000803:Angiotensin I; D002216:Captopril; C488034:ACE protein, human; D007703:Peptidyl-Dipeptidase A