Detection of Mutated Angiotensin I-Converting Enzyme by Serum/Plasma Analysis Using a Pair of Monoclonal Antibodies

Abstract

Angiotensin I-converting enzyme (ACE; CD143) is a Zn2+ carboxydipeptidase that plays a key role in the regulation of blood pressure and in the development of vascular pathology and remodeling (1)(2)(3). ACE is constitutively expressed on the surface of endothelial cells, macrophages, dendritic cells, and various other cell types (4)(5). Somatic ACE contains two homologous domains, N- and C-terminal, each with a catalytic center (2)(6). ACE has been accepted as a CD marker, CD143 (4)(6). Soluble serum ACE originates from endothelial cells by proteolytic cleavage by an unidentified protease of the Arg1203–Ser1204 peptide bond in the stalk region near the C-terminal transmembrane sequence of the ACE molecule (7)(8)(9)(10)(11). At physiologic conditions, the concentration of ACE in blood is very stable (12), whereas the ACE concentration in serum is often significantly increased in granulomatous diseases (in particular, sarcoidosis) or Gaucher disease (13)(14)(15)(16)(17)(18). We described a Pro1199Leu mutation, located in the juxtamembrane stalk region of ACE (19)(20), that explained a considerable familial increase in blood ACE activity in individuals from several Dutch families (19). The same phenotype and autosomal-dominant inheritance pattern have been described in Japan (21) and Italy(22). Despite the fact that patients with this mutation at first scrutiny do not have clinical abnormalities (19), the finding of increased ACE has led to confusion for treating physicians (23)(24). We recently observed reduced binding of soluble ACE in Dutch patients with a Pro1199Leu substitution detected by a new monoclonal antibody (mAb), 1B3, which recognizes a Pro1199-containing epitope in the C-terminal region of soluble ACE (25). We therefore set out to develop …