title: Activities of angiotensin-converting enzymes ACE1 and ACE2 and inhibition by bioactive peptides in porcine ocular tissues.
abstract: OBJECTIVE
  An active local renin-angiotensin system (RAS) has recently been found in the human eye. The aim of the present study was to compare the activities of central RAS enzymes (ACE1 and 2) in porcine ocular tissues, morphologically and physiologically close to the human eye. In addition, the effects of three ACE-inhibitory tripeptides on these enzymes were evaluated.
  
  
  METHODS
  Enucleated fresh porcine eyes were used. Activities of ACE1 and ACE2 and their inhibition by bioactive tripeptides (Ile-Pro-Pro, Val-Pro-Pro, Leu-Pro-Pro) as well as by a standard ACE-inhibitor captopril were assayed in the vitreous body, the retina and the ciliary body using fluorometric detection methods.
  
  
  RESULTS
  Activity of ACE1 as well as ACE2 was found in all tissues evaluated. ACE1 activity was markedly higher in the ciliary body (3.7 +/- 0.7 mU/mg protein) than in retina (0.2 +/- 0.02 mU/mg), whereas ACE2 activities in the ciliary body (0.2 +/- 0.02 mU/mg) and retina (0.2 +/- 0.01 mU/mg) were at the same level. In the vitreous body ACE1 activity (8.2 +/- 0.31 nmol/min/mL) was manifold compared to that of ACE2 (0.1 +/- 0.02 nmol/min/mL). The tripeptides inhibited ACE1 at one-thousandth of the concentration needed to inhibit ACE2. All peptides studied evinced about equal inhibitory activities.
  
  
  CONCLUSIONS
  To our knowledge the present findings constitute the first evidence of ACE2 activity in the ciliary and vitreous bodies, in addition to previously described activity in the retina. The known favorable effects of ACE2 products vs. those of ACE1 suggest a counterbalancing interaction of these two enzyme homologues in physiological regulation of ocular circulation and pressure and possible protective role in certain ophthalmic disorders such as glaucoma and diabetic retinopathy.
authors.affiliation: Division of Biotechnology, Department of Biological and Environmental Science, University of Jyväskylä, Finland.
authors.forename: Satu
authors.initials: S
authors.lastname: Luhtala
authors.forename: Anu
authors.initials: A
authors.lastname: Vaajanen
authors.forename: Olli
authors.initials: O
authors.lastname: Oksala
authors.forename: Jarkko
authors.initials: J
authors.lastname: Valjakka
authors.forename: Heikki
authors.initials: H
authors.lastname: Vapaatalo
mesh_terms: D000085962:Angiotensin-Converting Enzyme 2; D000806:Angiotensin-Converting Enzyme Inhibitors / Q000494:pharmacology*; D000818:Animals; D002216:Captopril / Q000494:pharmacology; D002924:Ciliary Body / Q000187:drug effects / Q000201:enzymology*; D066298:In Vitro Techniques; D009842:Oligopeptides / Q000494:pharmacology; D007703:Peptidyl-Dipeptidase A / Q000378:metabolism*; D012160:Retina / Q000187:drug effects / Q000201:enzymology*; D013552:Swine; D014822:Vitreous Body / Q000187:drug effects / Q000201:enzymology*
chemical_list: D000806:Angiotensin-Converting Enzyme Inhibitors; D009842:Oligopeptides; C489032:isoleucyl-prolyl-proline; C535179:leucyl-prolyl-proline; C489031:valyl-prolyl-proline; D002216:Captopril; D007703:Peptidyl-Dipeptidase A; C000705307:ACE2 protein, human; D000085962:Angiotensin-Converting Enzyme 2