Potent Angiotensin Converting Enzyme Inhibitor Research Articles

Angiotensin converting enzyme inhibitors: Comparative structure, pharmacokinetics, and pharmacodynamics

Angiotensin converting enzyme (ACE) inhibitors are a novel class of antihypertensive and anticongestive heart failure agents with wide patient and physician acceptability. By blocking the formation of angiotensin II in blood and tissue, all ACE inhibitors significantly lower systemic vascular resistance, lower blood pressure, and improve cardiac function, while maintaining or enhancing perfusion of vital organs: kidneys, brain, and heart. Captopril is the first oral ACE inhibitor with an active sulfhydryl group. Enalapril and lisinopril are potent nonsulfhydryl inhibitors of ACE characterized by weak chelating properties. The side effects of skin rashes, pruritus, taste abnormalities, oral ulcers, pemphigus, and blood dyscrasias have been considered to be strongly characteristic of penicillaminelike drugs, including the sulfhydryl ACE inhibitors. The class effects of cough, angio-edema, hyperkalemia, nonoliguric functional renal insufficiency, and hypotension can occur with equal frequency with all ACE inhibitors. It is unclear whether the many yet investigational ACE inhibitors would have distinct advantages over captopril, enalapril, lisinopril, and enalaprilat. This paper reviews the comparative structure and clinical pharmacology of the three commercially available but chemically different oral ACE inhibitors.

Angiotensin-converting enzyme inhibitors: Synthesis and biological activity of N-substituted tripeptide inhibitors.

A new series of highly potent angiotensin-converting enzyme (ACE) inhibitors, 1-(N2-substituted L-lysyl-gamma-D-glutamyl)octahydro-1H-indole-2-carboxylic acids, was synthesized; various acyl groups were introduced at the alpha-amino group of the N-terminal P1 Lys. The effect of the N2-acyl groups on in vitro inhibitory activity and oral antihypertensive effect was examined. All of the synthesized N-acyl tripeptides were found to have in vitro inhibitory activity at an approximately nanomolar level, and showed antihypertensive potency in renal hypertensive rats at a dose of 10 mg/kg, when administered orally. Among them, compounds 7e, g and 9f, i, m showed potent and long-lasting antihypertensive effects compared with enalapril (2a). Their structure-activity relationships are also discussed.

Loss of striatal angiotensin-converting enzyme following intrastriatal AF64A is not related to destruction of cholinergic interneurons

The potent angiotensin-converting enzyme (ACE) inhibitor 351 A was radioiodinated ( 125I-351A) and used to quantitate ACE in the striatum of rats treated with the cholinergic neurotoxin AF64A. Unilateral administration of 4nmol of AF64A into the striatum, which caused a 42% reduction in striatal choline acetyltransferase (ChAT) activity, reduced binding of 125I-351A in the lesioned striatum by 37% relative to the untreated striatum. The AF64A treatment also reduced the dopamine (DA) concentration by 59% in the lesioned striatum, but did not significantly reduce the serotonin (5-HT) concentration. Despite the reductions in ACE and these neurochemical markers, there was no significant correlation between the extent of reduction of the specific neurochemical markers and ACE. These results suggest that the AF64A treatment caused non-specific damage to striatal non-cholinergic neurons as well as destroying cholinergic neurons, and that ACE is contained in non-cholinergic neurons.

Heart muscle contains a potent heat and acid stable inhibitor of angiotensin-converting enzyme: B. Netopil, W. Quinkler, W. Schaper, Max-Planck-Institute, Dept. Exp. Cardiology, Bad Nauheim, F. R. Germany

Heart muscle contains a potent heat and acid stable inhibitor of angiotensin-converting enzyme: B. Netopil, W. Quinkler, W. Schaper, Max-Planck-Institute, Dept. Exp. Cardiology, Bad Nauheim, F. R. Germany

A review of the preclinical cardiovascular pharmacology of cilazapril, a new angiotensin converting enzyme inhibitor.

1. Cilazapril is the monoethyl ester prodrug form of the di-acid cilazaprilat, a new angiotensin converting enzyme (ACE) inhibitor. Cilazaprilat has an IC50 of 1.9 nM as an inhibitor of rabbit lung ACE in vitro making it one of the most potent ACE inhibitors currently available. Studies on a wide range of other enzymes show that the inhibition is highly specific. 2. An oral dose of 0.1 mg kg-1 cilazapril evoked the same maximum degree of plasma ACE inhibition (approximately 76%) in the rat as 0.25 mg kg-1 enalapril. Cilazapril (0.25 mg kg-1 p.o.) inhibited plasma ACE by greater than 95%. The rate of recovery of ACE activity was slower with cilazapril (5-6% h-1) than with enalapril (10% h-1). 3. In anaesthetised rats cilazaprilat was equipotent with ramiprilat and slightly more potent (1.5x) than enalaprilat as an inhibitor of the angiotensin I pressor response. 4. Following oral administration to conscious rats and intravenous administration to anaesthetised dogs, cilazapril was 2-4.5x more potent than enalapril as an ACE inhibitor. 5. In cats cilazapril (0.1 and 0.3 mg kg-1 p.o.) dose dependently decreased plasma ACE activity and the angiotensin pressor response. Peak effects occurred at 2 h after dosing and plasma ACE inhibition was maintained at greater than or equal to 50% for up to 18 h. Mean arterial pressure was also decreased dose dependently with a peak effect at 3-4 h. 6. Daily oral dosing of cilazapril (30 mg kg-1 p.o.) to spontaneously hypertensive rats evoked a progressive and prolonged (24 h) antihypertensive response with a maximum decrease in systolic blood pressure of 110 mm Hg. 7. Cilazapril (10 mg kg-1 p.o. twice daily for 3.5 days) progressively decreased blood pressure in volume depleted renal hypertensive dogs. The maximum fall in systolic pressure was 39 +/- 6 mm Hg. 8. Haemodynamic studies in open chest anaesthetised dogs showed that the hypotensive response to intravenous cilazapril was accompanied by a reduction in total peripheral resistance. Small decreases in cardiac output and myocardial contractile force were seen at high doses. 9. Cilazapril had no adverse effect on cardiovascular reflexes. There was no impairment of the baroreflex in rats. Exercise-induced tachycardia and pressor responses in conscious cats were unchanged. 10. Cilazapril is exceptionally well absorbed by the oral route (98% in rats).

Antihypertensive effects and pharmacokinetics of single and consecutive doses of cilazapril in hypertensive patients with normal or impaired renal function.

1. A 1.25 mg dose of cilazapril, a new angiotensin-converting enzyme (ACE) inhibitor, was administered orally to two groups of hypertensive patients, five with normal renal function (NRF) and seven with impaired renal function (IRF), once daily for 5 or 8 consecutive days. Blood pressure, heart rate and serum ACE activity were measured up to 24 h following the initial and the last dose. Plasma level profiles of cilazapril and its active diacid were also evaluated on the first and the last day of treatment. 2. Cilazapril induced significant falls in both systolic and diastolic blood pressures without increasing heart rate. The antihypertensive effect was evident within 1 h after drug administration and was sustained for up to 24 h, particularly after consecutive dosing. 3. Serum ACE activity was markedly suppressed over 24 h. The recovery of ACE activity was delayed in the IRF group when compared with the NRF group. 4. Plasma concentrations of the active diacid in the IRF group were higher than in the NRF group with significant differences in the peak concentrations and area under the plasma concentration-time curve (AUC). The plasma concentration profile for the parent drug was similar for both the NRF and IRF groups. 5. A significant inverse correlation was found between the creatinine clearance and the AUC for the diacid. 6. Cilazapril is a potent ACE inhibitor with a prolonged duration of antihypertensive effect and is a useful agent for controlling blood pressure in hypertensives either with NRF or IRF. In patients with severe renal impairment the dose of cilazapril should be reduced.

A peptidyl dipeptidase-4 from Pseudomonas maltophilia: Purification and properties

A peptidyl dipeptidase-4 (bacterial PDP-4) was purified to near homogeneity from a supernatant of Pseudomonas maltophilia extracellular medium. Bacterial PDP-4 is a single-polypeptide-chain enzyme, 82 kDa, with an alkaline isoelectric point. Peptides susceptible to hydrolysis by bacterial PDP-4 include angiotensin 1, bradykinin, enkephalins, atriopeptin 2, and smaller synthetic peptides. N-acylated tripeptides are hydrolyzed, but free tripeptides are not. A free carboxy terminus is required for hydrolysis. Peptides with ultimate and penultimate Pro residues are not hydrolyzed. The enzyme does not require an anion for activity. Bacterial PDP-4 was inhibited by EDTA and the dipeptide Phe-Arg. Thiorphan was an inhibitor only at levels well above those required for inhibition of neutral metalloendopeptidase (NEP), an enzyme for which thiorphan is specific. A second NEP and thermolysin inhibitor, phosphoramidon, did not inhibit bacterial PDP-4. The potent angiotensin-converting enzyme inhibitor lisinopril was not inhibitory. Bacterial PDP-4 is distinguished from a similar enzyme from Escherichia coli, which is not susceptible to EDTA inhibition, and one from Corynebacterium equi, which hydrolyzes free tripeptides. These data indicate that the bacterial PDP-4 catalytic site is unlike those of other enzymes that function either wholly or in part as peptidyl dipeptidases.

Constrained search of conformational hyperspace.

We introduce a new method for determining pharmacophore or active site geometries by analysis of the structures of a series of active compounds. The method, constrained search, and the key concepts on which it is based, is described and illustrated by its application to 28 potent inhibitors of angiotensin-converting enzyme (ACE). The data set is one utilized by Mayer et al. [J. Comput.-Aided Mol. Design, 1 (1987) 3-16] to determine a unique geometry for the active site. Our experiment validated the previously reported results, obtained by a systematic search, while reducing the computer time requirement by more than two orders of magnitude. The experiment also identified a previously unrecognized alternative active site geometry for the ACE series.

Definition of the effective dose of the converting-enzyme inhibitor benazepril

Benazepril was shown in preclinical studies to be a potent and specific inhibitor of angiotensin-converting enzyme with a benign toxicologic profile. Its onset and duration of action and the dose-response relationship of its antihypertensive effect have been evaluated. The results of these studies show that 20 mg of benazepril once daily lowers blood pressure by a clinically important amount, which was statistically superior to placebo in three double-blind studies. Doses as low as 10 mg once daily may be effective in individual patients. Doses of 40 and 80 mg once daily have been evaluated and provide small further reductions beyond those seen with the 20 mg dose. Adverse effects are uncommon and generally not dose related. Thiazide diuretics add to the antihypertensive action of benazepril, which has little effect on blood chemistry, apart from a slight rise in serum potassium.

High-Affinity Binding of the Converting Enzyme Inhibitor, Ramiprilat, to Isolated Human Glomeruli

Evidence for effects of angiotensin converting enzyme (ACE) on isolated human glomeruli was provided using specific binding of tritium-labeled ramiprilat, a potent inhibitor of ACE. [3H]ramiprilat bound to isolated glomeruli, depending on time and temperature, displaying a KD of 3.8 nmol/L and a Bmax of 853 fmol/mg protein. Specific binding represented more than 90% of total binding. Dissociation occurred rapidly after dilution of the sample with incubation buffer or after addition of an excess of unlabeled inhibitor. Binding of [3H]ramiprilat was also inhibited by increasing concentrations of enalaprilat, another ACE inhibitor. ACE is a zinc-containing enzyme. Addition of EGTA to the assay, which chelates zinc ions, completely prevented binding. This was reversed by divalent Zn2+ and Ca2+ ions, but not by magnesium. Binding of [3H]ramiprilat to isolated glomeruli was maximal at pH 8, which also is optimal for ACE activity. The binding of [3H]ramiprilat to isolated human glomeruli is specific, and resembles the characteristics which have been found earlier for enzyme activity of ACE. Thus, binding of [3H]ramiprilat to isolated glomeruli can be assumed to be directed to ACE.

Studies on the nötropic potential of some angiotensin converting enzyme inhibitors in the mouse

1. 1. The effects of captopril, epicaptopril and fosenopril were compared with codergine mesylate in a number of tests which may be predicative of potential nöotropic activity. None of the drugs tested protected against KCN induced hypoxic seizures. However, in the acute atropine sulphate induced hyperactivity test, in which the behaviour of the mice in the ‘open field’ apparatus was assessed, both captopril and codergine mesylate were found to reverse the atropine induced hyper-motility. The effect of captopril would not appear to be a direct reflection of its angiotensin converting enzyme (ACE) inhibitory activity as fosenopril is also a potent ACE inhibitor. 2. 2. Only codergine mesylate was found to reverse the atropine sulphate induced amnesia in a one trial avoidance task, captopril and its analogues being inactive in such a test. 3. 3. Chronically administered codergine mesylate, captopril and its analogues reversed the hypermobility in the ‘open field’ apparatus that occurred following the injection of a single dose of the neurotoxin trimethyltin. 4. 4. None of the changes in locomotor activity would appear to be due to adverse effect of the drugs on motor coordination. 5. 5. It is concluded that captopril may be worthy of more detailed studies as a potential nöotropic agent.

Effects of inhibition of angiotensin converting enzyme and carbonic anhydrase on fluid production by ciliary process, choroid plexus, and pancreas.

Inhibitors of angiotensin converting enzyme (ACE) (1) and of carbonic anhydrase (CA) (2,3) decrease intraocular pressure (IOP) in conscious rabbits. We asked whether ACE inhibition decreases IOP through effects on CA-dependent flow of aqueous humor (AH) and whether ACE inhibitors decrease other CA-dependent secretions. We show in anesthetized rabbits (a) that topical inhibitors of ACE decrease both IOP and AH flow as much as systemic inhibitors of CA; (b) that the maximal effects of ACE and CA inhibition are not additive, therefore these treatments may affect one or more components of a single system for fluid production; and that (c) ACE inhibitors do not work through inhibition of CA. Looking at other fluid production systems, we find (d) that cerebrospinal fluid (CSF) production is increased after ventriculocisternal perfusion with a potent ACE inhibitor and (e) that flow of pancreatic juice (PJ) is increased after systemic ACE inhibition.

Direct formation of angiotensin II without renin or converting enzyme in the ischemic dog heart.

An in vivo study was done to determine whether angiotensin II is directly formed by kallikrein or kallikrein-like proteases. Dogs were bilaterally nephrectomized 24 hours before ligation of the coronary artery. This acute coronary artery occlusion led to a regionally increased acidic state in the ischemic tissue and resulted in an elevation of immunoreactive angiotensin II (IR-Angiotensin II) levels in the coronary sinus blood, but not in systemic aortic blood. Elevation of the IR-Angiotensin II level was specifically inhibited by aprotinin, a kallikrein inhibitor. It was not affected by either captopril, a potent angiotensin converting enzyme inhibitor, or by pepstatin, a renin inhibitor. The concentrations of immunoreactive angiotensin I (IR-Angiotensin I), plasma renin activity and angiotensin converting enzyme activity remained unaltered in the presence of coronary artery occlusion. These results suggest that IR-Angiotensin II in the ischemic heart may be generated directly by kallikrein or kallikrein-like proteases, independently of the systemic renin angiotensin system.

A practical and diastereoselective synthesis of angiotensin converting enzyme inhibitors.

The diastereoselective synthesis of a series of potent angiotensin converting enzyme (ACE) inhibitors is described. The optically active intermediate, N-carbamyl (R)-2-amino-4-phenylbutyric acid (2) leading to (R)-2-halogeno or (R)-2-hydroxy-4-phenylbutyric acid was prepared by asymmetric hydrolysis of DL-5-phenethylhydantoin (1) by microbial hydantoinase. The halogenoester was subjected to SN2 reaction with L-amino acid derivatives to afford N-substituted amino acids, which were easily converted to ACE inhibitors or intermediates by deprotection.

Synthesis of 1,4-Thiazepine Derivatives Having Angiotensin-Converting Enzyme Inhibitory Property

Abstract Reduction of (6R)-6-amino-6,7-dihydro-2-thienyl-1,4-thiazepin-5(4H)-one derivatives with Mg–MeOH gave the corresponding perhydrothiazepinones. Protection with trityl group at the 6-amino group gave predominantly the 2S,6R isomer which was converted to the potent angiotensin-converting enzyme (ACE) inhibitor. The ACE inhibitor having the 6,7-dihydro-l,4-thiazepin-5(4H)-one ring was also prepared.

High affinity binding of ramiprilat on isolated human glomeruli

Evidence for angiotensin-converting enzyme (ACE) on isolated human glomeruli was furnished by specific binding of tritium-labeled ramiprilat, a potent inhibitor of ACE. 3H-ramprilat bound to isolated glomeruli, depending on time and temperature displaying a K D of 3.8 nmol/l and a B max of 853 fmol/mg protein. Specific binding represented more than 90% of total binding. Dissociation occurred rapidly after dilution of the sample with incubation buffer or after addition of an excess of unlabeled inhibitor. Binding of 3H-ramiprilat was also inhibited by increasing concentrations of enalaprilat, another ACE-inhibitor or by preincubation of the glomeruli with polyclonal antibodies against ACE. ACE is a zinc-containing enzyme. Addition of EGTA to the assay, which chelates zinc ions, completely inhibited binding. This inhibitory effect of EGTA was reversed by divalent Zn 2+ and Ca 2+ ions but not by magnesium. Binding of 3H-ramiprilat to isolated glomeruli was maximal when the pH of the assay medium was brought to pH 8. In conclusion, the binding of 3H-ramiprilat to isolated human glomeruli is specific and resembles the characteristics which have been found earlier for enzyme activity of ACE. Thus, binding of 3H-ramiprilat to isolated glomeruli can be assumed to be directed to ACE.

Enalapril Therapy in Patients With Renal Function Impairment

The angiotensin-converting enzyme inhibitor (ACEI), enalapril maleate, is a nonsulfydryl group—containing compound. Accordingly, it is said to be less associated with side effects such as taste disturbance, rashes, proteinuria, and interstitial nephritis; these side effects having been observed with captopril, and attributed to its sulfydryl group. Enalapril is a pro-drug. Because the active compound, enalaprilic acid, is poorly absorbed, the drug is given as an absorbable ester, which is then hydrolyzed to the active compound. This results in a more gradual onset of antihypertensive effect than may be seen with captopril. However, enalapril is a more potent ACEI than captopril, and its pharmacologic half-life is prolonged, permitting once daily dosage. See also p 2358. The consequences of ACEI therapy are complex, multidimensional, and imperfectly understood. 1 The inhibition of the enzyme that converts the inactive decapeptide angiotensin-I into the potent pressor agent angiotensin-II has systemic and intrarenal consequences. Systemically, decreased

Characterization of angiotensin converting enzyme (ACE) in the testis and assessment of the in vivo effects of the ACE inhibitor perindopril.

Angiotensin converting enzyme (ACE) was characterized by radioligand studies utilizing the potent ACE inhibitor 351A, a derivative of lisinopril. Ligand binding characteristics were similar for ACE derived from testis, lung, and kidney, despite known differences in structure between ACe from these sources. This observation suggests that the ACE active enzymatic site is similar in different tissues. The effect of the orally active ACE inhibitor perindopril was studied ex vivo in tissues of the rat after oral gavage. Radioligand bound to tissue ACE was reduced after perindopril treatment, in tissue homogenates of lung and kidney, but not testis. Autoradiographs of radioligand binding to tissue sections obtained ex vivo after oral perindopril showed inhibition of ACE in the aorta, lung, and kidney, but did not reveal any inhibition of ACE in the testis. ACE in small vessels of the testis was inhibited as in the aorta, while at the same time testicular ACE was unaffected. ACE in rat testis appears to have a similar enzymatic binding site to ACE from the lung and kidney. Perindopril inhibited ACE in the lung and kidney but did not affect ACE in the testis, suggesting the drug is limited in testicular penetration by the blood-testis barrier. This may explain the lack of any reports of adverse effects of ACE inhibitors on testicular function.

Synthesis and biological activity of ketomethylene-containing nonapeptide analogues of snake venom angiotensin converting enzyme inhibitors.

Two ketomethylene-containing nonapeptide analogues were synthesized to determine if ketomethylene analogues of the nonapeptide venom inhibitors of angiotensin converting enzyme (ACE) would have oral ACE inhibition activity. Both ketomethylene-containing nonapeptides 18 and 19 were potent inhibitors of rabbit lung ACE with I50s of 3.4 and 8.0 nM, respectively, compared to 340 nM for their parent nonapeptide and 450 nM for captopril. Peptide 18 was rapidly cleaved by trypsin, but 19 was reasonably stable to all enzyme degradation systems tested with maximum degradation of 50% by pepsin in 3 h. Both 18 and 19 when given iv to normotensive rats were between 3 and 10 times more potent than captopril in inhibiting an angiotensin I induced blood pressure increase. Peptide 19 showed no ACE inhibition activity in unanesthetized normotensive rats when administered orally at doses of 10 or 100 mg/kg. Experiments were conducted to determine whether 19 is adsorbed from the gastrointestinal track following oral administration. These experiments indicated that 19 is adsorbed. It is concluded that the lack of oral activity of 19 is probably due to its rapid excretion, probably into the bile.

A radioimmunoassay for MC-838 (altiopril calcium), a novel angiotensin-converting enzyme inhibitor.

A radioimmunoassay was developed for a new, potent inhibitor of angiotensin-converting enzyme (ACE; EC 3.4.15.1), calcium(-)-N-[(S)-3-[(N-cyclohexylcarbonyl-D-alanyl)thio]-2-methyl- propionyl]-L-prolinate (MC-838, altiopril calcium). The antiserum was obtained by immunizing rabbits with MC-838-bovine serum albumin (BSA) conjugate. MC-838-L-tyrosine labeled with 125I and purified by thin-layer chromatography was used as a tracer. The assay sensitivity was 0.1 ng/ml, the average intra-assay coefficient of variation was 7.9%, and the average inter-assay coefficient of variation was 13.7%. The antiserum was specific for MC-838, showing only slight crossreactivity with degradation products of MC-838. After a single oral dose of MC-838 (2 mg/kg), radioimmunoassay of MC-838 canine serum demonstrated rapid absorption from the gastrointestinal tract with a peak level of 40.6 ng/ml. The decline in serum concentration was a biphasic decay, with a half-life of 80 min during rapid falloff followed by a slower decline.