Evolution of angiotensin-converting enzyme inhibitors

The renin-angiotensin system is perhaps the most important hormonal system in the regulation of blood pressure. Its influence on blood pressure is mediated by the potent vasoconstrictor angiotensin II. Since angiotensin-converting enzyme performs the last step in the biosynthesis of angiotensin II, inhibition of this enzyme has attracted the attention of many researchers as a novel approach in the control of high blood pressure. The evolution of inhibitors of this enzyme will be traced from the early snake venom peptide inhibitors to the drugs currently available for the treatment of high blood pressure and congestive heart failure.     

Inhibition of angiotensin-converting enzyme by angiotensin I analogue peptide inhibitors. A kinetic study

Angiotensin I analogues with a phosphonic acid group replacing the C-terminal carboxyl group were shown to be competitive inhibitors of angiotensin-converting enzyme. This new class of inhibitors was used to study the binding requirements of the angiotensin I-like ligands to the enzyme's active site. These studies indicate that angiotensin-converting enzyme recognizes at least five amino acid residues at the C-terminus of the peptide. The effect of pH on the binding of the most potent inhibitor peptide was compared to Captopril. The two inhibitors showed similar Ki-pH profiles despite their structural differences. Chloride enhanced the binding of the peptide inhibitor at both pH 9.0 and pH 6.5. At pH 9.0 the inhibitor peptide and the anion bind randomly to the enzyme, while at pH 6.5 the mechanism is ordered. In the latter case, the anion binds first to the enzyme.     

The C-type natriuretic peptide precursor of snake brain contains highly specific inhibitors of the angiotensin-converting enzyme

The bradykinin-potentiating peptides from Bothrops jararaca venom are the most potent natural inhibitors of the angiotensin-converting enzyme. The biochemical and biological features of these peptides were crucial to demonstrate the pivotal role of the angiotensin-converting enzyme in blood pressure regulation. In the present study, seven bradykinin-potentiating peptides were identified within the C-type natriuretic peptide precursor cloned from snake brain. The bradykinin-potentiating peptides deduced from the B. jararaca brain precursor are strong in vitro inhibitors of the angiotensin-converting enzyme (nanomolar range), and also potentiate the bradykinin effects in ex vivo and in vivo experiments. Two of these peptides are novel bradykinin-potentiating peptides, one of which displays high specificity toward the N-domain active site of the somatic angiotensin-converting enzyme. In situ hybridization studies revealed the presence of the bradykinin-potentiating peptides precursor mRNAs in distinct regions of the B. jararaca brain, such as the ventromedial hypothalamus, the paraventricular nuclei, the paraventricular organ, and the subcommissural organ. The biochemical and pharmacological properties of the brain bradykinin-potentiating peptides, their presence within the neuroendocrine regulator C-type natriuretic peptide precursor, and their expression in regions of the snake brain correlated to neuroendocrine functions, strongly suggest that these peptides belong to a novel class of endogenous vasoactive peptides.     

Congestive heart failure. New frontiers.

Congestive heart failure is a common syndrome with high mortality in its advanced stages. Current therapy includes the use of vasodilator drugs, which have been shown to prolong life. Despite current therapy, mortality remains high in patients with severe heart failure. Potent new inotropic vasodilators have improved ventricular performance but have not prolonged life in patients with end-stage heart failure. Serious arrhythmias are implicated in the sudden deaths of 30% to 40% of patients with severe heart failure, but the benefits of antiarrhythmic therapy have not been established. Upcoming trials will address this question. Ventricular remodeling and progressive dilatation after myocardial infarction commonly lead to congestive heart failure; early unloading of the ventricle with an angiotensin-converting enzyme inhibitor may attenuate these events. These findings support the concept that angiotensin-converting enzyme inhibitors may be useful in managing heart failure of all degrees of severity, including left ventricular dysfunction and end-stage heart failure. Part of the damage that may occur with acute myocardial infarction, particularly in this era of thrombolysis therapy, is reperfusion injury, which may be mediated by oxygen-derived free radicals. Better knowledge of the mechanisms and treatment of myocardial infarction, the leading cause of congestive heart failure, may help prevent or attenuate the development of this syndrome.     

Reversible impairment of renal function associated with enalapril in a diabetic patient

Acute renal failure and hyperkalemia due to angiotensin-converting enzyme inhibitors have been described in diabetic patients with other predisposing conditions. The case reported here involves a patient with type 1 diabetes mellitus, microalbuminuria and normal renal function who was treated with enalapril. Two years after initiation of this therapy, at a time when glycemic control was poor, he presented with symptomatic hyperkalemia and impaired renal function accompanied by hyporeninemic hypoaldosteronism. This case illustrates that reversible impairment of renal function and hyperkalemia can present after 2 years of treatment with angiotensin-converting enzyme inhibitors in patients with precipitating factors.     

How long should angiotensin-converting enzyme inhibitors be given to patients following myocardial infarction: implications of the HOPE trial

Long-term treatment with angiotensin-converting enzyme inhibitors reduces post-infarction morbidity and mortality in patients with left ventricular (LV) systolic dysfunction or symptomatic heart failure. Until recently, the effect of such treatment in patients with preserved LV function has not been known. The results from the Heart Outcome Prevention Evaluation trial have indicated that long-term treatment with ramipril leads to a significant reduction in cardiovascular events in patients with atherosclerotic disease, including those with prior myocardial infarction and preserved LV function. These results suggest that long-term angiotensin-converting enzyme inhibition should also be considered in post-infarction patients with normal cardiac function.     

Sialosylglobotetraosylceramide: a marker for amyotropic lateral sclerosis

Modification of alanyl proline by introduction of both zinc coordinating and S1 subsite binding interactions affords potent new carboxy- and mercapto-acyl dipeptide angiotensin-converting enzyme (ACE) inhibitors. Design of these inhibitors was guided by an extension of the hypothetical ACE active site model originally used to derive captopril. Significant increases in ACE inhibitory activity were observed by introduction of conformation constraint into acyclic acyl dipeptides, thus further defining the three dimensional structure of the ACE active site.     

Azapeptides: a new class of angiotensin-converting enzyme inhibitors

A class of potent inhibitors of angiotensin-converting enzyme (dipeptidyl carboxypeptidase, E.C. 3.4.15.1) is reported, in which an alpha-aza substitution into the substituted N-carboxymethyl dipeptide structure of enalapril is made. The inhibitors 2 exhibit striking alterations in their conformational and acid-base properties due to the aza substitution, as is clear from pKa data and the x-ray crystal structure of a model azapeptide. In spite of this, they bind tightly to the enzyme, with inhibitor potency comparable to that of captopril.     

Controlling oxidative stress as a novel molecular approach to protecting the vascular wall in diabetes

PURPOSE OF REVIEW: In diabetes, oxidative stress plays a key role in the pathogenesis of vascular complications; therefore an antioxidant therapy would be of great interest in this disease. RECENT FINDINGS: Hyperglycemia directly promotes an endothelial dysfunction--inducing process of overproduction of superoxide at the mitochondrial level. This is the first and key event able to activate all the pathways involved in the development of vascular complications of diabetes. It has recently been shown that statins, angiotensin-converting enzyme inhibitors, angiotensin II type 1 blockers, calcium channel blockers, and thiazolidinediones have a strong intracellular antioxidant activity. SUMMARY: Classic antioxidants, such as vitamin E, failed to show beneficial effects on diabetic complications probably because their action is only "symptomatic". The preventive activity against hyperglycemia-induced oxidative stress shown by statins, angiotensin-converting enzyme inhibitors, angiotensin II type 1 blockers, calcium channel blockers, and thiazolidinediones justifies use of these compounds for preventing complications in patients with diabetes, in whom antioxidant defences have been shown to be defective.     

Proteases as drug targets

The effective management of AIDS with HIV protease inhibitors, or the use of angiotensin-converting enzyme inhibitors to treat hypertension, indicates that proteases do make good drug targets. On the other hand, matrix metalloproteinase (MMP) inhibitors from several companies have failed in both cancer and rheumatoid arthritis clinical trials. Mindful of the MMP inhibitor experience, this chapter explores how tractable proteases are as drug targets from a chemistry perspective. It examines the recent success of other classes of drug for the treatment of rheumatoid arthritis, and highlights the need to consider where putative targets lie on pathophysiological pathways--regardless of what kind of therapeutic entity would be required to target them. With genome research yielding many possible new drug targets, it explores the likelihood of discovering proteolytic enzymes that are causally responsible for disease processes and that might therefore make better targets, especially if they lead to the development of drugs that can be administered orally. It also considers the impact that biologics are having on drug discovery, and in particular whether biologically derived therapeutics such as antibodies are likely to significantly alter the way we view proteases as targets and the methods used to discover therapeutic inhibitors.     

Efficient production of (R)-(−)-2-hydroxy-4-phenylbutyric acid by recombinant Pichia pastoris expressing engineered d-lactate dehydrogenase from Lactobacillus plantarum with a single-site mutation

Bioprocess and Biosystems Engineering - (R)-2-hydroxy-4-phenylbutyric acid (R-HPBA) is a valuable intermediate for the synthesis of angiotensin-converting enzyme inhibitors. The asymmetric...     

Citrullyl-Hydroxyprolyl-Proline (ChPP): An Artificially Synthesized Tripeptide as Potent ACE Inhibitor

International Journal of Peptide Research and Therapeutics - Currently bioactive peptides are the main focus in attempts to identify novel angiotensin-converting enzyme inhibitors (ACEIs) for the...     

Inhibitor analysis of angiotensin I-converting and kinin-degrading activities of bovine lung and testicular angiotensin-converting enzyme.

Inhibition of bovine lung and testicular angiotensin-converting enzyme (ACE) by some well-known ACE inhibitors (lisinopril, captopril, enalapril), new substances (Nalpha-carboxyalkyl dipeptides PP-09, PP-35, and PP-36), and phosphoramidon was investigated using Cbz-Phe-His-Leu and FA-Phe-Phe-Arg (C-terminal analogs of angiotensin I and bradykinin, respectively) as the substrates. The somatic (two domains) and testicular (single domain) isoenzymes demonstrated different kinetic parameters for hydrolysis of these substrates. All of the inhibitors were competitive inhibitors of both ACE isoforms, and the Ki values were substrate-independent. The relative potencies of the inhibitors for both enzymes were: lisinopril > captopril > PP-09 > enalapril > PP-36 > PP-35 > phosphoramidon. The inhibition efficiency of PP-09 was comparable with those of the well-known ACE inhibitors. Captopril was more effectively bound to the somatic ACE (Ki = 0.5 nM) than to the testicular isoform (Ki = 6.5 nM).     

Debate: PCI vs CABG: a moving target, but we are gaining

The treatment of patients with coronary artery disease continues to evolve; all three strategies – medical therapy, surgical revascularization, and percutaneous coronary intervention – have changed. Medical therapy with intense risk-factor modification and treatment with a statin, aspirin, and angiotensin-converting enzyme (ACE) inhibitors, should be used unless contraindicated. Surgical therapy has also changed with the introduction of minimally invasive, beating heart surgery. Percutaneous coronary intervention has perhaps changed the most radically with adjunctive therapy – glycoprotein IIb/IIIa inhibitors, thienopyridines, and reliance on stent implantation. The future, with new distal protection devices and drug-coated stents, should continue to see increased numbers of patients who can benefit from percutaneous intervention.     

Design of tripeptide modeled inhibitors of angiotensin-converting enzyme: Studies on the role of the N-terminal acylamino group

Several series of tripeptide modeled angiotensin-converting enzyme (ACE) inhibitors have been reported which contain an N-terminal acylamino substituent as an essential structural component for conservation of biological activity. The results of a study aimed at defining the role served by this group in enzyme/inhibitor binding by examining the consequences of systematic chemical modifications are described. The benzamido N atom is shown to play a critical function in enzyme binding of ketomethylene ACE inhibitors. Evidence is also presented to implicate the benzamido carbonyl and phenyl ring in productive enzyme binding interactions.     

Purification of angiotensin-converting enzyme from rabbit lung and human plasma by affinity chromatography

Lisinopril (N alpha-[(S)-1-carboxy-3-phenylpropyl]L-lysyl-L-proline), a potent angiotensin-converting enzyme inhibitor, is an exceptionally selective affinity chromatography ligand for this enzyme. Affinity chromatography furnishes electrophoretically homogeneous enzyme directly from crude homogenates of rabbit lung tissue, a 1,000-fold purification; also, it affords a 100,000-fold enrichment of the more rare human plasma enzyme in a single step. The affinity of angiotensin-converting enzyme for the Sepharose-spacer-lisinopril matrix (Ki matrix = 1 X 10(-5) M) is weak compared to its affinity for free lisinopril (Ki = 1 X 10(-10) M). The capacity of the affinity column is described quantitatively as a function of Ki matrix, lisinopril, and enzyme concentrations. The recovery of bound enzyme is low in chromatography of crude tissue samples (10-40%), although it approaches a reversible process (70-100%) with pure enzyme. The holoenzyme is converted to Zn2+-free apoenzyme to effect removal of lisinopril. In this process, the rate constant for spontaneous dissociation of Zn2+ from free enzyme is 1 X 10(-2) s-1 (t 1/2 = 1 min), which places a lower limit of 3 X 10(-10) M on the dissociation constant of Zn2+ at neutral pH from angiotensin-converting enzyme. The exceptional selectivity of lisinopril as an affinity chromatography ligand for angiotensin-converting enzyme suggests it is among the most specific inhibitors designed for any enzyme.     

Angiotensin-Converting Enzyme Modulates Dopamine Turnover in the Striatum

Abstract: The effect of chronic inhibition of the angiotensin-converting enzyme on dopamine content and release in the striatum was investigated using in vivo microdialysis in awake, freely moving rats. Rats were treated for 1 week with the angiotensin-converting enzyme inhibitor perindopril (1 mg/kg) via the drinking water, whereas the controls were given water alone. One week after perindopril treatment, striatal dopamine dialysate levels in the treated group were markedly elevated compared with control values: control, 233 ± 43 pg/ml; perindopril, 635 ± 53 pg/ml ( p < 0.001). These results were confirmed by a complementary study in which dopamine content was measured in striatal extracts (3.5 ± 0.4 µg of dopamine/g of tissue for controls compared with 9.2 ± 2.4 µg of dopamine/g of tissue for the treated group; p < 0.05). In the rats that were dialyzed, angiotensin-converting enzyme levels in the striatum were decreased by 50% after perindopril treatment. Levels of dopamine D₁ and D₂ receptors and of preprotachykinin and tyrosine hydroxylase mRNAs were unchanged after angiotensin-converting enzyme inhibition. A small, but significant, increase was detected in striatal preproenkephalin mRNA levels in the angiotensin-converting enzyme inhibitor-treated group. These results indicate that peripherally administered angiotensin-converting enzyme inhibitors penetrate the blood-brain barrier when given chronically and modulate extracellular dopamine and striatal neuropeptide levels.     

Purification of human serum angiotensin I-converting enzyme by affinity chromatography

A relatively simple procedure is described for purifying human serum angiotensin-converting enzyme. The enzyme was purified 130,000-fold to electrophoretic homogeneity using affinity chromatography as the principal purification step. The ligand was an immobilized competitive inhibitor, d-cysteinyl-l-proline. A six-carbon spacer arm was satisfactory for trapping the enzyme; 80% of the bound enzyme was eluted with 3 m urea-1.0 m NaCl-0.1 m Tris, pH 8.3. The specific activity was 39 units/mg protein and the molecular weight (155,000), isoelectric point (4.7), kinetic properties, and the effect of various inhibitors are in agreement with published reports.     

The use of 1H-NMR-spectroscopy for the study of peptide degradation by angiotensin-converting enzyme

A new method for continuous registration of enzymatic hydrolysis of peptides involving 1H-NMR spectroscopy was developed. The advantages of the method were demonstrated, using dalargin (Tyr-D-Ala-Gly-Phe-Leu-Arg) hydrolysis catalyzed by human kidney angiotensin-converting enzyme as an example. It was shown that the maximal activity of the enzyme towards dalargin is observed at pH 7.8; Km is 0.35 mM. The enzyme is inhibited by the substrate (Kd = 0.55 mM). Cl- do not influence the catalytic activity of the enzyme with respect to dalargin. The stereospecificity of the angiotensin-converting enzyme towards dalargin diasteriomers was studied.     

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

Human heart angiotensin-converting enzyme has been purified by affinity chromatography on immobilized N-[1(S)-carboxy-5-aminopentyl]-Gly-Gly. The isolation procedure permitted a 1650-fold-purified enzyme to be obtained. The specific activity of angiotensin-converting enzyme was 38 units per mg protein. The molecular weight of enzyme determined by polyacrylamide gel electrophoresis in denaturing conditions was 150,000. The isoelectric point (5.3) of the enzyme was determined by chromatofocusing. The Km values of the enzyme for Bz-Gly-His-Leu and angiotensin I are 1.2 mM and 10 microM, respectively. Substrate inhibition of heart angiotensin-converting enzyme with a K's of 14 mM has been shown. The human heart enzyme is inhibited by SQ 20881 (IC50 = 40 nM). It was shown that NaCl, CaCl2 as well as Na2SO4 in the absence of Cl- are activators of the heart angiotensin-converting enzyme, whereas CH3COONa and NaNO3 have no effect on a catalytic activity of the enzyme.