Affinity chromatography and some properties of the angiotensin-converting enzyme from human heart

Conformational Fingerprinting Using Monoclonal Antibodies (on the Example of Angiotensin I-Converting Enzyme-ACE)

During the past 30 years my laboratory has generated 40+ monoclonal antibodies (mAbs) directed to structural and conformational epitopes on human ACE as well as ACE from rats, mice and other species. These mAbs were successfully used for detection and quantification of ACE by ELISA, Western blotting, flow cytometry and immunohistochemistry. In all these applications mainly single mAbs were used. We hypothesized that we can obtain a completely new kind of information about ACE structure and function if we use the whole set of mAbs directed to different epitopes on the ACE molecule. When we finished epitope mapping of all mAbs to ACE (and especially, those recognizing conformational epitopes), we realized that we had obtained a new tool to study ACE. First, we demonstrated that binding of some mAbs is very sensitive to local conformational changes on the ACE surface—due to local denaturation, inactivation, ACE inhibitor or mAbs binding or due to diseases. Second, we were able to detect, localize and characterize several human ACE mutations. And, finally, we established a new concept—conformational fingerprinting of ACE using mAbs that in turn allowed us to obtain evidence for tissue specificity of ACE, which has promising scientific and diagnostic perspectives. The initial goal for the generation of mAbs to ACE 30 years ago was obtaining mAbs to organ-specific endothelial cells, which could be used for organ-specific drug delivery. Our systematic work on characterization of mAbs to numerous epitopes on ACE during these years has lead not only to the generation of the most effective mAbs for specific drug/gene delivery into the lung capillaries, but also to the establishment of the concept of conformational fingerprinting of ACE, which in turn gives a theoretical base for the generation of mAbs, specific for ACE from different organs. We believe that this concept could be applicable for any glycoprotein against which there is a set of mAbs to different epitopes.

Sperm angiotensin-converting enzyme activity in Chernobyl victims and patients with chronic prostatitis

The method for determination of angiotensin-converting enzyme activity in human spermatozoa and seminal plasma was developed. The number of total and active-motile spermatozoa was shown to be lower in Chernobyl victims than in healthy donors. The specific activity of angiotensin-converting enzyme in spermatozoa from Chernobyl victims was 12 times higher than that in donors. Similar results, although to a lesser extent, were observed in patients with chronic prostatitis. In contrast, the enzyme activity in blood serum and seminal plasma was identical for all subjects investigated.

Ventricular dilatation and remodeling after myocardial infarction

OBJECTIVE

To discuss the important predictors of ventricular enlargement after myocardial infarction and the appropriate time frame for the initiation of medical and pharmacologic therapy.

DESIGN

A review of the important contributions relative to the process known as "postinfarction ventricular remodeling" is provided; current clinical implications and areas for future investigation are discussed.

MATERIAL AND METHODS

Ventricular dilatation is an important factor in the prognosis after infarction. Stretching and thinning of the myocardium within the infarct region can be seen within hours after the acute event and may be accompanied by delayed but potentially progressive stretching and thinning in the noninfarct regions. Development of left ventricular hypertrophy in the nonischemic myocardium, in response to increased wall stress, can be observed but may be insufficient for proper compensation. This process is referred to as postinfarction remodeling and can result in progressive and long-term changes in ventricular architecture and function in the absence of additional ischemic injury.

RESULTS

The most effective way to limit the extent of postinfarction ventricular remodeling is to limit infarct size by prompt medical intervention within the first few hours. In addition to traditional post-infarction medications such as beta-blockers, nitrates, and aspirin, long-term benefit may be derived by use of adjunctive pharmacologic therapy such as angiotensin converting enzyme inhibitors, which have been shown to be valuable in limiting the extent of ventricular chamber dilatation after infarction. Studies in animal models and conclusions from clinical trials have shown that angiotensin converting enzyme inhibitors also decrease late mortality and cardiac morbidity after infarction, likely through favorable effects on both hemodynamic and neurohumoral factors specific to this class of medication.

CONCLUSION

These investigations notwithstanding, further studies are necessary for a complete understanding of the pathogenesis of postinfarction ventricular remodeling and the appropriate timing of specific pharmacologic therapy intended to limit ventricular dilatation. The hemodynamic and neurohumoral interactions on and within the heart must be thoroughly understood relative to microscopic and macroscopic changes in cardiac size, shape, and function after myocardial infarction.

A comparison of the properties and enzymatic activities of three angiotensin processing enzymes: angiotensin converting enzyme, prolyl endopeptidase and neutral endopeptidase 24.11

The discovery of angiotensin-(1-7) [Ang-(1-7)] as a bioactive Ang II fragment of the renin-angiotensin system (RAS) alters the current understanding of the enzymatic components that comprise the RAS cascade. Two neutral endopeptidases, prolyl endopeptidase (E.C. 3.4.21.26) and neutral endopeptidase 24.11 (E.C. 3.4.24.11), are capable of forming Ang-(1-7) from Ang I and have been implicated in the in vivo processing of Ang I. This makes them putative Ang processing enzymes and part of the RAS cascade. This review summarizes the physical characteristics and distribution of angiotensin converting enzyme (E.C. 3.4.15.1), a known Ang I processing enzyme, and compares its features to what is known of prolyl endopeptidase and neutral endopeptidase 24.11.

Cardiac effects of local angiotensin-converting enzyme inhibition in hypertensive patients

1. The direct cardiac effects of angiotensin-converting enzyme (ACE) inhibitor in 22 hypertensive patients were investigated. Radionuclide ventriculography and echocardiography were performed to measure left ventricular function before and 60 min after administration of a subdepressor dose of captopril. 2. Since the response to ACE inhibitor is not uniform, patients were classified into 12 patients without significant blood pressure change following captopril (group I) and 10 patients with reduction of blood pressure (group II). 3. Clinical and baseline haemodynamic characteristics were similar for the two groups. 4. Ejection fraction (EF) increased without changes of heart rate and end-diastolic dimension after ACE inhibitor in group I as well as group II. The change of EF was not different for the two groups. No correlation was found between changes in EF and blood pressure in group I patients. 5. This study indicates that ACE inhibitor might directly influence left ventricular function independent of systemic haemodynamic changes.

Angiotensin-converting enzyme: clinical applications and laboratory investigations on serum and other biological fluids

Angiotensin I-converting enzyme (ACE) is a peptidyldipeptide hydrolase that is located mainly on the luminal surface of vascular endothelial cells but also in cells derived from the monocyte-macrophage system. Physiologically, ACE is a key enzyme in the renin-angiotensin system, converting angiotensin I into the potent vasopressor angiotensin II and also inactivating the vasodilator bradykinin. Increased serum ACE activity (SACE) has been reported in pathologies involving a stimulation of the monocytic cell line, primarily granulomatous diseases. Sarcoidosis is the most frequent and the better studied of these diseases; high SACE is not only a well-established marker for the diagnosis but is also a useful tool for following its course and evaluating the effect of therapy. SACE can also be increased in nonsarcoidotic pulmonary granulomatous diseases such as silicosis and asbestosis, in extrathoracic granulomatous pathologies such as Gauchers disease and leprosis, and, to a lesser extent, in nongranulomatous disorders such as hyperthyroidism or cholestasis. On the other hand, monitoring sarcoidosis obviates the measurement of ACE activity in other biological fluids, e.g., broncho-alveolar and cerebrospinal fluids, in the search of a locoregional dissemination or dis-simulation of the disease. Decreased SACE has been reported in vascular pathologies involving an endothelial abnormality, e.g., deep vein thrombosis, and in endothelium dysfunctions related to the toxicity of chemo- and radiotherapy used in cancers, leukemias, and hematopoietic or organ transplantations. SACE is also of interest for monitoring arterial hypertension treated with specific synthetic ACE inhibitors. These various reasons for determining ACE activity have led to the development of numerous methods. The most widely used is the spectrophotometric assay using hippuryl-histidyl-leucine as substrate. Fluorimetric and radiochemical assays using both classic and novel substrates have been proposed, but they are time consuming, require special apparatus, and are not suited to automation. Kinetic spectrophotometry of furylacryloyl-phenylalanyl-glycyl-glycine hydrolysis is now used extensively because it is easy to automatize. Efforts are now required to standardize one or more of these assays. Indeed, "normal" plasma values differ not only according to the substrate, but also to the method of determination and to sex and age.

Tissue and plasma angiotensin converting enzyme and the response to ACE inhibitor drugs

1. There is a body of circumstantial and direct evidence supporting the existence and functional importance of a tissue based RAS at a variety of sites. 2. The relation between circulatory and tissue based systems is complex. The relative importance of the two in determining haemodynamic effects is unknown. 3. Despite the wide range of ACE inhibitors already available, it remains unclear whether there are genuine differences related to tissue specificity. 4. Pathological states such as chronic cardiac failure need to be explored with regard to the contribution of tissue based ACE activities in generating acute and chronic haemodynamic responses to ACE inhibitors. 5. The role of tissue vs plasma ACE activity may be clarified by study of the relation between drug concentration and haemodynamic effect, provided that the temporal dissociation is examined and linked to circulating and tissue based changes in ACE activity, angiotensin peptides and sympathetic hormones.

Characterization of cardiac angiotensin converting enzyme (ACE) and in vivo inhibition following oral quinapril to rats

1. Angiotensin converting enzyme (ACE) from the rat heart and lung was studied by use of the radioligand [125I]-351A. 2. Displacement of the bound radioinhibitor [125I]-351A was used to assess the relative potency of six ACE inhibitors in rat heart and lung homogenates and estimate the binding association constant (KA). 3. The KA for atrial preparations was significantly higher than that of the lung (P less than 0.025) and also the ventricles (P less than 0.005). Ventricular preparations and preparations from the lung also differed significantly (P less than 0.05). These differences in KA were noted for all six ACE inhibitors used to displace the radioligand. 4. The rank order of potency of the ACE inhibitors was quinaprilat = benazeprilat greater than perindoprilat greater than 351A greater than lisinopril greater than fosinoprilat. 5. Cardiac ACE inhibition was studied ex vivo following oral administration of quinapril to rats. Following 0.3 mg kg-1 quinapril, the time course and degree of inhibition of ventricular and atrial ACE were similar. 6. These results suggest that the detected differences in KA noted have only a limited potential biological significance. The difference in KA may reflect variations in the structure or conformation of ACE in different tissues.

Angiotensin II-forming pathways in normal and failing human hearts

Reduced preload and afterload to the heart are important effects of angiotensin converting enzyme (ACE) inhibitors in the treatment of congestive heart failure. However, since angiotensin II (Ang II) directly increases the strength of myocardial contraction, suppression of Ang II formation by ACE inhibitors could potentially reduce the beneficial effects of Ang II on the failing heart. To study how ACE inhibition suppresses cardiac Ang II formation in man, we characterized ACE-dependent and ACE-independent Ang II-forming pathways in eight normal and 24 failing human hearts obtained at cardiac transplantation. Ang II-forming activity in left ventricular (LV) membrane preparations was assessed by measuring the conversion of [125I]angiotensin I (Ang I) to [125I]Ang II. LV [125I]Ang II-forming activity in normal hearts (35.5 +/- 2.7 fmol/min/mg, n = 8) was not different from that in hearts from patients with ischemic cardiomyopathy (25.5 +/- 2.9 fmol/min/mg, n = 9) and was 48% lower (p less than 0.001) in hearts from patients with idiopathic cardiomyopathy (18.5 +/- 1.9 fmol/min/mg, n = 15).(ABSTRACT TRUNCATED AT 250 WORDS)

Angiotensin converting enzyme in the rat heart: studies of its inhibition in vitro and ex vivo

1. The pharmacokinetics of angiotensin converting enzyme (ACE) inhibition in rat heart and lung was evaluated in vitro and ex vivo. 2. Radioinhibitor [125I]-351A binding displacement was used to assess the relative potency of six ACE-inhibitors (CI906, CGS14831, S9780, 351A, MK521, SQ27519) in rat heart and lung homogenates, and estimate equilibrium association constant (Ka). 3. Following oral administration of 0.3 mg/kg of Quinapril (CI928) specific binding of [125I]-351A to ACE was measured in rat heart. 4. Ka for binding to ACE of each inhibitor was significantly higher in right and left atrium than in lung (P less than 0.05) or the right and left ventricle (P less than 0.005). These differences did not affect the degree or time course of inhibition in vivo in the rat myocardial ACE following Quinapril treatment. 5. Rank order of potency of the ACE inhibitors tested was CI906 = CGS14831 greater than S9780 greater than 351A greater than MK521 greater than SQ27519

Calcium ionophore A23187 elevates angiotensin-converting enzyme in cultured bovine endothelial cells

Calcium ionophore A23187 (0.3-0.4 microM) elevated cellular angiotensin-converting enzyme activity (ACE) 2-7-fold after 48 h incubation with bovine pulmonary artery endothelial cells in culture. Cycloheximide (0.1 micrograms/ml) blocked the elevation in ACE produced by A23187. The increase in ACE was inhibited by 0.2 mM EGTA, 50 microM verapamil and 50 microM nifedipine, and was not associated with changes in cellular cAMP. Melittin, a phospholipase A2 activator, or addition of exogenous arachidonic acid failed to reproduce the elevation, and indomethacin only partially blocked the A23187 effect. The elevation of ACE was also inhibited by the calcium-calmodulin inhibitor, calmidazolium. Thus, we postulate that the ionophore A23187 elevates ACE in endothelial cells through a calcium-dependent mechanism other than phospholipase A2 activation. The elevation depends on new protein synthesis and involves calcium-calmodulin-dependent cellular mechanisms.

Kinetic and inhibitory characteristics of serum angiotensin-converting enzyme from nine mammalian species

1. Serum angiotensin-converting enzyme activities were obtained from nine mammalian species: rat, mouse, horse, sheep, guinea pig, hamster, rabbit, dog and man. 2. Kinetic constants (Km and Vmax) using hippuryl-L-histidyl-L-leucine as substrate and inhibitory constants (I50 and Ki) for captopril were determined for the serum ACE of each species. 3. There were important differences in the kinetic and inhibitory constants (Kms went from 6.6 mM to 1.21 mM for hamster and guinea pig; I50 ranged from 2100 nM to 3 nM for mouse and sheep) as well as differences in enzyme activity of the different species (values varied from 938 to 13 nmol hippuric acid/ml/min for guinea pig and dog serum).

Microbial synthesis of metabolites with antihypertensive activity: aspects of fermentation derived inhibitors of angiotensin-converting enzyme (ACE)

In this review the microbial angiotensin-converting enzyme inhibitors are described. Especially from the microbiological point of view the characteristics of these metabolites are given, e.g. occurrence, fermentation physiology and specificity. Besides these data, the structure, assays and some isolation problems are summarised. Apart from ACE inhibition the different biological activities of these secondary metabolites are discussed.

Atriopeptin 2 is hydrolysed by cardiac but not pulmonary isozyme of angiotensin-converting enzyme

Hydrolysis of Bz-Gly-Ser-Phe-Arg, C-terminal fragment of atriopeptin 2, by human cardiac angiotensin-converting enzyme has been studied. The KM for the reaction was 10(-4) M. The effect of concentration of NaCl on activity of cardiac angiotensin-converting enzyme has been determined, which allowed to regard Bz-Gly-Ser-Phe-Arg as bradykinin-like substrates. It was demonstrated that cardiac, but not pulmonary isozyme of angiotensin-converting enzyme specifically hydrolyses atriopeptin 2.

Immunohistochemical study of angiotensin-converting enzyme in human tissues using monoclonal antibodies

The localization of angiotensin-converting enzyme (ACE) in human tissues has been studied by the PAP-method with the use of monoclonal antibody 9 B9 against human lung ACE. The enzyme was detected on the surface of endothelial cells in lung, myocardium, liver, intestine and testis as well as in the epithelial cells of the kidney proximal tubules and intestine. The monoclonal antibody 9 B9 did not react with ACE in the epithelial cells of the testis seminiferous tubules. These data suggest that the antibody 9 B9 recognizes epitope which is shared by the ACE molecule of endothelial cells and renal and intestinal epithelial cells but is not present in testicular ACE, or is not accessible there to the antibody.