New potent inhibitors of angiotensin converting enzyme

Sequential allylic C-H amination/vinylic C-H arylation: a strategy for unnatural amino acid synthesis from α-olefins

Tandem reaction sequences that selectively convert multiple C-H bonds of abundant hydrocarbon feedstocks to functionalized materials enable rapid buildup of molecular complexity in an economical way. A tandem C-H amination/vinylic C-H arylation reaction sequence is described under Pd(II)/sulfoxide-catalysis that furnishes a wide range of α- and β-homophenylalanine precursors from commodity α-olefins and readily available aryl boronic acids. General routes to enantiopure amino acid esters and densely functionalized homophenylalanine derivatives are demonstrated.

Structure determination of enalapril maleate form II from high-resolution X-ray powder diffraction data

The crystal structure of polymorphic Form II of enalapril maleate, a potent angiotensin-converting enzyme inhibitor, was determined from high-resolution X-ray diffraction data using the direct space method. Enalapril maleate Form II crystallizes in space group P2(1)2(1)2(1), Z = 4, with unit cell parameters a = 33.9898(3) A, b = 11.2109(1) A, c = 6.64195(7) A, and V = 2530.96(5) A(3). By treating the molecules as rigid bodies and using the bond lengths and angles obtained from the X-ray single crystal structures of Form I, which were solved almost 20 years ago, the total degrees of freedom of enalapril maleate were reduced from 25 to 12. This reduction in total degrees of freedom allowed the simulated annealing to complete within a reasonable computation time. In the crystal structure of Form II, the crystal packing, hydrogen-bonding pattern, and conformation of enalapril maleate resemble those in the structure of Form I. The crystal packing and conformation of enalapril maleate in the two polymorphic forms may explain the similarity of the thermal properties, (13)C nuclear magnetic resonance, Fourier transform infrared, and Raman spectra of Forms I and II. In both structures, the conformations of the main peptide chains, which are considered responsible for binding the active angiotensin-converting enzyme sites, remain largely unchanged. Lattice energy calculation showed that Form II is slightly more stable than Form I by 3.5 kcal/mole.

Age-dependent hypertension in Mpv17-deficient mice, a transgenic model of glomerulosclerosis and inner ear disease

The mutant mouse strain Mpv17-/-, carries a retroviral germline integration that inactivates the Mpv17 gene. Mpv17-deficient mice develop progressive glomerulosclerosis and sensineural deafness at early age. Characteristic basement membrane alterations are found in both sites of pathology. Mpv17 is a peroxisomal protein involved in the metabolism of reactive oxygen species, yet its molecular function is unknown. Dysregulation of antioxidant enzymes and basal membrane components has been established in this model and successful therapeutic intervention with antioxidants prove the causal role of reactive oxygen species in the development of the disease phenotype. We here investigated if the Mpv17-/- mice might be hypertensive. Indeed, our study revealed that Mpv17-/- mice developed significant systemic hypertension and tachycardia between 4 weeks and 5 months of age, accompanied by polyuria and elevated natriuresis. Judging from serum and urine parameters, the hypertensive condition develops concomitantly with the renal disease. Biochemical and pharmacological studies that used the endothelin receptor antagonist bosentan and the angiotensin converting enzyme inhibitor cilazapril indicated no involvement of the endothelin and renin-angiotensin systems in this hypertension, suggesting a potential novel mechanism of blood pressure regulation in this new murine hypertension model. Thus, Mpv17-/- mice unravel an intriguing new association between a defect in reactive oxygen metabolism and the age-dependent development of hypertension.

Effects of cilazapril on the retinal vessels in spontaneously hypertensive rats: corrosion cast and scanning electron microscopic study

The effects of the long-term oral angiotensin-converting enzyme inhibitor, cilazapril, on retinal circulation in stroke-prone spontaneously hypertensive (SHR-SP) rats were assessed by scanning electron microscopy (SEM), corrosion casts and transmission electron microscopy (TEM). Two groups of 20 male SHR-SP rats were compared. One group was treated with 10 mg/kg/day of cilazapril from 4 to 40 weeks of age, and the other group received no treatment. A third group of male Wistar-Kyoto (WKY) rats served as age-matched controls. At regular intervals the rats were weighed, and their systolic blood pressure was measured. Cilazapril normalized systolic arterial pressure to 121+/-2.7 mm Hg (SD) in the treated SHR-SP rats. There was no significant difference in body weight between the two groups of SHR-SP. In the 40-week-old SHR-SP rats without treatment corrosion cast and SEM revealed hypertensive retinal vascular changes. In the 40-week-old SHR-SP rats treated with cilazapril, these changes were markedly decreased to the level seen in WKY rats. The differences in caliber of retinal capillaries between the treated SHR-SP and untreated SHR-SP rats were statistically significant (p<.0001). TEM in the cilazapril-treated SHR-SP rats revealed intact basement membranes (0.29+/-0.057 microm) of the endothelial cells and pericytes, but in the untreated SHR-SP rats the basement membrane was thickened (0.51+/-0.123 microm) (p<.0001) and the pericytes damaged. Our results show that the long-term administration of cilazapril decreased systolic arterial pressure to a nearly normal level and prevented hypertensive retinal vascular changes, probably by improving endothelial function. The effects of cilazapril on the retinal vasculature are described for the first time. SEM of corrosion casts is a valuable technique for showing the effects of some drugs on the vasculature easily, precisely and three-dimensionally.

Effect of renin-angiotensin inhibition on glomerular injuries in DOCA-salt hypertensive rats

To determine whether growth factors in the glomerulus are induced in the renin suppressed hypertensive model, we examined the mRNA expressions of platelet-derived growth factor (PDGF) B-chain, transforming growth factor (TGF)-beta 1 and angiotensin II type 1 (AT1) receptors in the glomeruli of deoxycorticosterone acetate (DOCA)-salt-treated hypertensive rats (DOCA-treated rats). We also examined the effects of treatment with cilazapril, an angiotensin I-converting enzyme inhibitor (ACEI), and L-158,809, an AT1 receptor antagonist, on these expressions in DOCA-treated rats. We administered oral 10 mg/kg of cilazapril (CILAZA group) and 1 mg/kg of L-158,809 (L158 group) to DOCA-treated rats daily. Systolic blood pressure in the two groups was not decreased compared with that in DOCA-treated rats given saline. The mRNA expressions were examined using reverse transcriptase polymerase chain reaction (RT-PCR) methods. The mRNA expressions of these genes were higher in DOCA-treated rats than in age-matched control rats. After treatment with these agents for 4 weeks, the mRNA expressions of growth factors were suppressed in both the CILAZA and L158 groups. Mesangial expansion and cell proliferation observed in DOCA-treated rats were suppressed in both the CILAZA and L158 groups. Decreases in the size of the glomerulus were observed only in the CILAZA group. These findings suggested that suppression of growth factors and glomerular proliferative changes of these agents are mediated by blocking tissue renin-angiotensin system (RAS) in the renin-suppressed model.

Quantitative characterization of insulin-glucose response in Watanabe heritable hyperlipidemic and cholesterol-fed rabbits and the effect of cilazapril

A great deal of evidence suggests that insulin resistance, via hyperinsulinemia, contributes to hyperlipoproteinemia and coronary atherosclerosis. When Watanabe heritable hyperlipidemic (WHHL) rabbits, an animal model of familial hypercholesterolemia (FH), are compared with normolipidemic Japanese White (JW) rabbits, an elevated fasting plasma insulin level and a heightened plasma insulin response to an intravenous (i.v.) glucose challenge are found. To elucidate the mechanism behind this phenomenon, a two-compartment model of the glucose/insulin system was fitted to empirical time courses of glucose and insulin concentrations during an i.v. glucose tolerance test (IVGTT) by nonlinear least-square regression, and the model parameters such as the glucose utilization rate constant, insulin degradation rate constant, and pancreas sensitivity were determined. WHHL rabbits showed decreased values of glucose utilization and insulin degradation rate constants and slightly higher values of pancreas sensitivity. This suggests that insulin resistance occurs in extrapancreatic tissues, and that this may be attributable to insulin receptor and/or post-insulin receptor abnormalities. Cholesterol feeding did not significantly change glucose tolerance or insulin action in JW rabbits. The effects of an angiotensin-converting enzyme (ACE) inhibitor, cilazapril, on insulin resistance were also examined in WHHL and JW rabbits. A decreased insulin response to an i.v. glucose challenge and increased glucose utilization and insulin degradation rate constants were observed in WHHL rabbits that had been treated with cilazapril, indicating that cilazapril improved insulin resistance in WHHL rabbits, possibly by increasing the number of insulin receptors. No significant differences were found in glucose tolerance and insulin action in JW rabbits before and after cilazapril administration.(ABSTRACT TRUNCATED AT 250 WORDS)

Inhibitors of enkephalin-degrading enzymes as potential therapeutic agents

A limited number of enzymes such as membrane metalloendopeptidase (enkephalinase) and angiotensin converting enzyme appear to be involved in deactivation and modulation of circulatory regulatory peptides. Peptides such as the enkephalins are also involved in a large number of physiological processes. This multiplicity of physiological roles has made it difficult to establish the therapeutic role of enkephalin-degrading enzyme inhibitors. Other factors such as difficulty in quantification and thus measurement of processes involved in pain and mental illness have also hindered the process of establishing any therapeutic role of enkephalin-degrading enzyme inhibitors in these conditions. However, they have proved to be useful pharmacological 'tools'. The most likely therapeutic role at present appears to be in the treatment of cardiovascular disorders. As a 'profile' of pharmacological actions of enkephalin-degrading enzymes emerges, it is becoming apparent that bioavailability rather than a high degree of specificity or inhibitory potency may be the most important factor. This may be used to an advantage in future developments by the use of less specific or combined inhibitors in the form of prodrugs, designed to be active at specific sites such as the central nervous system.

Effect of cilazapril on regional left ventricular wall thickness and chamber dimension following acute myocardial infarction: in vivo assessment using MRI

The primary goal of the current study was to assess in situ, using magnetic resonance imaging, the effect of a new angiotensin-converting enzyme inhibitor, cilazapril, in reducing left ventricular remodeling after acute myocardial infarction. Three groups of animals were investigated: (1) sham-operated rats (n = 19); (2) infarcted rats receiving no treatment (n = 23); and (3) infarcted rats receiving cilazapril (100 mg/L drinking water, n = 20). Treatment with cilazapril began on the third day postocclusion and continued for 3 to 4 months. Myocardial infarction was produced by ligation of the left coronary artery, and electrocardiographic (ECG)-gated short-axis images were acquired 3 to 4 months later. Sham-operated animals were subjected to the same procedure but the left coronary artery was not ligated. From the image acquired in the middle of the left ventricle (equatorial slice), left ventricular wall thicknesses, chamber diameters, and surface area measurements of the cavities were determined. At autopsy examination, infarct size and tissue water content were determined. The results demonstrate that magnetic resonance imaging has the potential to assess in situ the alterations of left ventricular dimensions and mass after acute myocardial infarction and can be used to document the influence of therapeutic interventions. Cilazapril provided protection against the deleterious remodeling changes such as ventricular dilation and wall thinning consequent to acute myocardial infarction.

The pharmacokinetics of benazepril relative to other ACE inhibitors

Benazepril is a prodrug that, following rapid conversion to benazeprilat, is a potent nonsulfhydryl inhibitor of angiotensin-converting enzyme. The absorption, bioactivation, distribution, and elimination of benazepril and benazeprilat have been evaluated in healthy subjects, hypertensive patients, and patients with characteristics known to alter the pharmacokinetic disposition of ACE inhibitors, such as renal impairment, hepatic impairment, and advanced age. Following oral administration, benazepril is absorbed and transformed into benazeprilat in the liver. Coadministration of benazepril with food delays absorption slightly but does not affect the ultimate bioavailability of benazeprilat. Severe hepatic impairment slows conversion of benazepril to benazeprilat but does not affect the overall bioavailability of benazeprilat; thus dosage adjustment is not necessary in the hepatically impaired population. Mild-to-moderate renal impairment (creatinine clearance greater than 30 ml/min) slightly increases benazeprilat concentrations; severe renal impairment (creatinine clearance less than 30 ml/min) reduces benazeprilat elimination and requires dosage reduction. In elderly patients, benazepril disposition is the same as in younger patients, although benazeprilat clearance is slightly reduced. No clinically significant drug-drug interactions occur with benazepril and many other medications commonly prescribed to elderly hypertensive patients. The pharmacokinetic characteristics of benazepril are stable over a wide range of conditions, and dosage adjustments for pharmacokinetic reasons are required infrequently.

Angiotensin-converting enzyme inhibitors: a comparative review

The chemistry, pharmacology, pharmacokinetics, adverse effects, and dosages of the three currently available angiotensin-converting enzyme (ACE) inhibitors are reviewed. This class of agents effectively inhibits the conversion of angiotensin I to the active vasoconstrictor angiotensin II, a hormone that also promotes, via aldosterone stimulation, increased sodium and water retention. The ACE inhibitors, therefore, are capable of lowering blood pressure primarily by promoting vasodilatation and reducing intravascular fluid volume. Captopril, the first orally active, commercially available ACE inhibitor, is a sulfhydryl-containing compound. Captopril was followed by the introduction of enalapril and lisinopril, two non-sulfhydryl ACE inhibitors. The pharmacokinetic profiles of these three ACE inhibitors differ. Captopril has rapid onset with relatively short duration of action, whereas enalapril and lisinopril have slower onset and relatively long duration of action. Captopril is an active ACE inhibitor in its orally absorbable parent form. In contrast, enalapril must be deesterified in the liver to the metabolite enalaprilat in order to inhibit the converting enzyme; this accounts for its delayed onset of action. Lisinopril does not require metabolic activation to be effective; however, a slow and incomplete absorption pattern explains the delay in onset of activity. Captopril and its disulfide metabolites are primarily excreted in the urine with minor elimination in the feces. Approximately two-thirds of an administered enalapril dose is excreted in the urine as both the parent drug and the metabolite enalaprilat; the remainder of these two substances are excreted in the feces. Lisinopril does not undergo measurable metabolism and approximately one-third is excreted unchanged in the urine with the remaining parent drug being excreted in the feces. The ACE inhibitors lower systemic vascular resistance with a resultant decrease in blood pressure. Their efficacy is comparable to diuretics and beta-blockers in treating patients with mild, moderate, or severe essential and renovascular hypertension. In those patients with severe congestive heart failure (CHF) the ACE inhibitors produce a reduction in systemic vascular resistance, blood pressure, pulmonary capillary wedge pressure, and pulmonary artery pressure. These drugs may produce improvement in cardiac output and stroke volume and, with chronic administration, may promote regression of left ventricular hypertrophy. The antihypertensive effects of the ACE inhibitors are enhanced when these agents are combined with a diuretic. Captopril and enalapril have been shown to be of particular benefits as adjunctive therapy in patients with congestive heart failure, both in terms of subjective improvement of patient symptoms, and in improving overall hemodynamic status.(ABSTRACT TRUNCATED AT 400 WORDS)

Conformationally restricted peptides through short-range cyclizations

The various types of conformationally restricted peptides obtained by short-range cyclizations, from residue i to residue i + 1, are presented. Relevant examples of N in equilibrium C alpha, C' in equilibrium C alpha, N in equilibrium C', C alpha in equilibrium C alpha, C' in equilibrium C', and N in equilibrium N cyclizations are reported and the pertinent literature listed. In the discussion emphasis is place on the conformational consequences for peptides from the incorporation of such ring structures.

Effects of cilazapril on the cerebral circulation in spontaneously hypertensive rats

Chronic hypertension is associated with a lower cerebral vascular reserve due to thickening of the media of cerebral vessels. The goal of the present study was to determine if long-term inhibition of angiotensin converting enzyme with cilazapril, a new long-acting angiotensin converting enzyme inhibitor, could improve cerebral vascular reserve. For this purpose, two groups of 12 spontaneously hypertensive rats were compared. One group was treated with 10 mg/kg/day cilazapril from 14 weeks to 33 weeks of age and was compared with a group treated with placebo. A third group of 12 Wistar-Kyoto rats treated with placebo was used as reference. At the end of the treatment period, cerebral vascular reserve was evaluated by measuring cerebral blood flow (radioactive microspheres) at rest and during maximal vasodilation induced by seizures provoked by bicuculline. Then, the rats were perfusion-fixed, and morphometry of the cerebral vasculature was performed. Cerebral vascular reserve was severely impaired in the spontaneously hypertensive rats since their maximal cerebral blood flow was decreased by 52% compared with the Wistar-Kyoto rats. Cilazapril normalized cerebral blood flow reserve. This normalization was associated with a decreased thickness of the medial layer in the carotid artery, the middle cerebral artery, and in the pial arteries larger than 100 microns. Further studies are required to determine whether this decreased medial thickness is due to the normalization of blood pressure induced by cilazapril or to the reduction of trophic factors such as angiotensin II.

Chemical design of cilazapril

1. The three dimensional requirements for inhibition of ACE (angiotensin converting enzyme) were investigated in order to facilitate design of a more potent and selective antihypertensive agent. 2. All compounds designed possessed a bicyclic unit incorporating carboxylate and amidic carbonyl groups together with a thiol-bearing side chain. 3. NMR spectroscopy of the bicyclic units and molecular mechanics calculations enabled the possible positions of the thiol group to be studied. 4. Determination of the positions of the thiol group conferring best inhibition in the active site of ACE permitted the probable location of the active site zinc ion to be identified. The intention was to replace the thiol side chain with a homophenylalanine unit to bind to the zinc ion and also to occupy the S1 site which fits the Phe8 side chain of angiotensin I. 5. Examination of a torsional angle psi in a compound possessing poor inhibitory potency indicated correspondence to a high energy conformation of alanylproline. The bicyclic unit was modified to incorporate a seven-instead of a six-membered ring to bring psi into the range of an accessible conformation of alanylproline. The corresponding IC50 resulting indicated that psi was closer to that of the active conformations of enalaprilat and captopril. 6. Removal of one carbonyl improved the ACE inhibitory potency further. 7. The postulated active conformation of cilazaprilat is presented.

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.

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.

Effects of acute and chronic cilazapril treatment in spontaneously hypertensive rats

1. The effects of acute and chronic treatment with cilazapril, a new ACE inhibitor, on peripheral vasculature and renal excretory function were assessed in spontaneously hypertensive rats. Regional blood flow and cardiac output were measured by the radioactive microspheres technique. 2. Acute treatment (3 mg kg-1 intravenously) reduced mean arterial blood pressure from 171 +/- 7 to 140 241 +/- 7 mm Hg (P less than 0.001), chronic treatment (1 x 10 mg kg-1 day-1 orally for 9 weeks) from 191 +/- 5 to 122 +/- 3 mm Hg P less than 0.001). With both kinds of treatments cardiac output was unchanged. Heart rate was slightly decreased (-9%, P less than 0.05) with chronic treatment. Acutely, the main effect of cilazapril was a decrease of the renal vascular resistance (-41%, P less than 0.001) associated with an increase of the fraction of the cardiac output distributed to the kidney (+46%, P less than 0.001). Chronically, cilazapril decreased regional vascular resistance in most of the peripheral vascular beds except the heart. 3. With a high dose of cilazapril (10 mg kg-1 orally) both acute and chronic treatment increased diuresis (+107% and +92%, P less than 0.001) and natriuresis (/124% and +111%, P less than 0.001) with a slight increase in kaliuresis. However, with a low dose (1 mg kg-1 orally) the kidneys responded only to chronic treatment. 4. It is concluded that chronic treatment with cilazapril decreases arterial blood pressure more than acute treatment. This effect seems to be due to a greater peripheral vasodilation.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of chronic heart failure on the responsiveness to angiotensin I and to angiotensin converting enzyme inhibition with cilazapril in rats

1. The effects of heart failure due to chronic myocardial infarction on the responsiveness to injected angiotensin I and ACE inhibition by intravenous cilazapril (1 mg kg-1) were evaluated. 2. For this purpose one group of 17 rats with a 4-week old myocardial infarction was compared with a group of 10 sham operated rats. 3. Heart failure increased markedly the responsiveness of the renal and mesenteric vascular beds to ACE inhibition which produced a vasodilation in these two vascular beds. 4. This increased responsiveness was most likely due to a stimulation of the renin-angiotensin system without any change of sensitivity to angiotensin I of the renal and mesenteric vascular beds. 5. Cilazapril produced the same level of ACE inhibition in both groups of rats.

Enzyme immunoassay discrimination of a new angiotensin-converting enzyme (ACE) inhibitor, cilazapril, and its active metabolite

Simple and sensitive enzyme immunoassays (EIAs), discriminating a new angiotensin-converting enzyme (ACE) inhibitor, cilazapril [9(s) - [1(s)-(ethoxycarbonyl)-3-phenylpropylamino]-octahydro-10-oxo-6H- pyridazo[1,2-a] [1,2]diazepine-1(s)carboxylic acid] and its active metabolite [9(s)-[1(s)-carboxy-3-phenylpropylamino]-octahydro-10-oxo-6H- pyridazo[1,2-a][1,2]diazepine-1(s)carboxylic acid] were developed for pharmacokinetic studies of this drug which is used as an antihypertensive agent. These assays can be performed directly on serum or plasma specimens without pretreatment. The EIA for cilazapril (prodrug) allowed the determination of as little as 30 pg/mL, while a 1000-times greater concentration of its active metabolite was required to achieve the same extent of inhibition. The EIA for the active metabolite exhibited a sensitivity and specificity similar to those of the prodrug. Plasma specimens from a human volunteer study and a marmoset subacute toxicity study were assayed by these two newly developed EIAs. The plasma levels of active metabolite determined by the EIA were compared with those assayed by radioenzymatic assay, and a good correlation was observed between them.

Difference in response of vascular angiotensin converting enzyme activity to cilazapril in SHR

Angiotensin I converting enzyme (ACE) activity was found in all rat arteries and veins examined, considerably varied among these vessels, and usually higher in arteries than in corresponding veins except for femoral and subclavian pairs. Decrease of vascular ACE activity in response to cilazapril at hypotensive doses varied in vessels and was not dependent on their ACE activity levels.

Preclinical studies on angiotensin converting enzyme inhibitors

The identification of the renin-angiotensin-aldosterone system in the control of blood pressure, and the preclinical development of the angiotensin converting enzyme inhibitors for therapeutic use are reviewed. The properties of these compounds are discussed with respect to their in vitro enzyme inhibitory potency; prevention of the pharmacological effects of angiotensin I; potentiation of those of bradykinin; tissue enzyme inhibition; mechanism of effect on blood pressure both alone and in combination with other antihypertensive agents; and effect on cardiac parameters.

Enalapril. A review of its pharmacodynamic and pharmacokinetic properties, and therapeutic use in hypertension and congestive heart failure

Enalapril maleate is an orally active angiotensin-converting enzyme inhibitor. It lowers peripheral vascular resistance without causing an increase in heart rate. Enalapril 10 to 40 mg/day administered either once or twice daily is effective in lowering blood pressure in all grades of essential and renovascular hypertension, and shows similar efficacy to usual therapeutic dosages of hydrochlorothiazide, beta-blockers (propranolol, atenolol and metoprolol) and captopril. Most patients achieve adequate blood pressure control on enalapril alone or with hydrochlorothiazide. In patients with severe congestive heart failure resistant to conventional therapy, enalapril improves cardiac performance by a reduction in both preload and afterload, and improves clinical status long term. Enalapril appears to be well tolerated, with few serious adverse effects being reported. It does not induce the bradycardia associated with beta-blockers or the adverse effects of diuretics on some laboratory values. In fact, the hypokalaemic effect of hydrochlorothiazide is attenuated by the addition of enalapril. The incidence of the main (but rare) side effects of hypotension in hypovolaemic patients and reduced renal function in certain patients with renovascular hypertension, which are also seen with captopril, might be reduced by careful dosage titration, discontinuation of diuretics, and monitoring of at-risk patients. Thus, enalapril is a particularly worthwhile addition to the antihypertensive armamentarium, as an alternative for treatment of all grades of essential and renovascular hypertension. It also shows promise in the treatment of congestive heart failure.

Recent developments in the design of angiotensin-converting enzyme inhibitors

Orally-active angiotensin-converting enzyme inhibitors are rapidly establishing themselves in the therapy of hypertension and congestive heart failure. Concerted efforts in a number of laboratories have now led to the discovery or synthesis of an unparalleled variety of potent inhibitors. The manner in which several of these inhibitors bind to ACE is beginning to be understood. It is hoped that some of the insights to be derived from the SAR and structural studies done with ACE inhibitors will be applicable to other enzyme targets as well. The success of ACE inhibitors as pharmacological tools and in the clinic will also quite certainly encourage future efforts to develop new enzyme inhibitor approaches to drug therapy.