Investigation of the energy barrier to the rotation of amide CN bonds in ACE inhibitors by NMR, dynamic HPLC and DFT.

The isomerizations of Enalapril, Perindopril, Enalaprilat and Lisinopril have been investigated using NMR spectroscopic, dynamic chromatographic, unified equation and DFT theoretical calculations. The thermodynamic parameters (ΔH, ΔS and ΔG) were determined by varying the temperature in the NMR experiments. At the coalescence temperature, we can evaluate the isomerization barrier to the rotation (ΔG(≠)) around the amide bond. Using dynamics chromatography and an unified equation introduced by Trap, we can determine isomerization rate constants and Gibbs activation energies. Molecular mechanics calculations also provided evidence for the presence of low energy conformers for the ACE due to restricted amide rotation. With the value of barriers (ΔE) between them of the order of (20kJmol(-1)), which is in agreement with the dynamic NMR results and DFT calculations.

A Soluble Guanylate Cyclase Activator Inhibits the Progression of Diabetic Nephropathy in the ZSF1 Rat.

Therapies that restore renal cGMP levels are hypothesized to slow the progression of diabetic nephropathy. We investigated the effect of BI 703704, a soluble guanylate cyclase (sGC) activator, on disease progression in obese ZSF1 rats. BI 703704 was administered at doses of 0.3, 1, 3, and 10 mg/kg/d to male ZSF1 rats for 15 weeks, during which mean arterial pressure (MAP), heart rate (HR), and urinary protein excretion (UPE) were determined. Histologic assessment of glomerular and interstitial lesions was also performed. Renal cGMP levels were quantified as an indicator of target modulation. BI 703704 resulted in sGC activation, as evidenced by dose-dependent increases in renal cGMP levels. After 15 weeks of treatment, sGC activation resulted in dose-dependent decreases in UPE (from 463 ± 58 mg/d in vehicle controls to 328 ± 55, 348 ± 23, 283 ± 45, and 108 ± 23 mg/d in BI 703704-treated rats at 0.3, 1, 3, and 10 mg/kg, respectively). These effects were accompanied by a significant reduction in the incidence of glomerulosclerosis and interstitial lesions. Decreases in MAP and increases in HR were only observed at the high dose of BI 703704. These results are the first demonstration of renal protection with sGC activation in a nephropathy model induced by type 2 diabetes. Importantly, beneficial effects were observed at doses that did not significantly alter MAP and HR.

Simultaneous quantitative and qualitative analysis of aliskiren, enalapril and its active metabolite enalaprilat in undiluted human urine utilizing LC-ESI-MS/MS.

The benefit-risk ratio of combined blocking by the direct renin inhibitor aliskiren and an angiotensin-converting enzyme inhibitor (e.g. enalapril) on the renin-angiotensin-aldosterone system is discussed. No method was available for simultaneous determination of both drugs in urine. A novel sensitive method for simultaneous quantification in undiluted human urine was developed which enables systematic pharmacokinetic investigations, especially in poorly investigated populations like children. Matrix effects were clearly reduced by applying solid-phase extraction followed by a chromatographic separation on Xselect(TM) C18 CSH columns. Mobile phase consisted of methanol and water, both acidified with formic acid. Under gradient conditions and a flow rate of 0.4 mL/min the column effluent was monitored by tandem mass spectrometry with electrospray ionization. Calibration curves were constructed in the range of 9.4-9600 ng/mL regarding aliskiren, 11.6-12000 ng/mL for enalapril and 8.8-9000 ng/mL for enalaprilat. All curves were analyzed utilizing 1/x(2) -weighted quadratic squared regression. Intra-run and inter-run precision were 3.2-5.8% and 6.1-10.3% for aliskiren, 2.4-6.1% and 3.9-7.9% for enalapril as well as 3.1-9.4% and 4.7-12.7% regarding enalaprilat. Selectivity, accuracy and stability results comply with current international bioanalysis guidelines. The fully validated method was successfully applied to a pharmacokinetic investigation in healthy volunteers.

Greener bioanalytical approach for LC/MS-MS assay of enalapril and enalaprilat in human plasma with total replacement of acetonitrile throughout all analytical stages.

Green bioanalytical approaches are oriented toward minimization or elimination of hazardous chemicals associated to bioanalytical applications. LC/MS-MS assay of enalapril and enalaprilat in human plasma was achieved by elimination of acetonitrile from both sample preparation and chromatographic separation stages. Protein precipitation (PP) by acetonitrile addition was replaced by liquid-liquid extraction (LLE) in 1-octanol followed by direct large volume injection of the organic layer in the chromatographic column operated under reversed phase (RP) separation mechanism. At the mean time, acetonitrile used as organic modifier in the mobile phase was successfully replaced by a mixture of propylene carbonate/ethanol (7/3, v/v). Three analytical alternatives ((I) acetonitrile PP+acetonitrile based chromatographic elution; (II) 1-octanol LLE+acetonitrile based chromatographic elution; (III) 1-octanol LLE+propylene carbonate/ethanol based chromatographic elution) were validated and the quality characteristics were compared. Comparison between these alternative analytical approaches was also based on results obtained on incurred samples taken during a bioequivalence study, through application of the Bland-Altman procedure.

Determination of enalapril and enalaprilat in small human serum quantities for pediatric trials by HPLC-tandem mass spectrometry.

The angiotensin converting enzyme-inhibitor enalapril is the prodrug of enalaprilat and used in the treatment pediatric hypertension and chronic heart failure. Pharmacokinetic data are lacking to provide adequate dosing and for pediatric pharmacotherapeutical trials it is imperative to minimize sample volume. Therefore an HPLC-tandem mass spectrometry (MS) method for the determination of enalapril and enalaprilat in 100 µL of human serum was developed and validated with benazepril as internal standard (IS). After solid-phase extraction, chromatography was performed on a Luna(®) RP-C(18) (2) column with methanol-water-formic acid (65:35:1, v/v/v) as mobile phase and a flow rate of 0.4 mL/min. The MS was set to positive-mode electrospray ionization and multiple reaction monitoring, analyzing the m/z transitions channels 377.3 → 234.2, 349.3 → 206.1 and 425.3 → 351.2 for enalapril, enalaprilat and IS. Calibration curves were linear in the range of 1.61-206 ng/mL (enalapril) and 1.84-236 ng/mL (enalaprilat) with coefficients of determination >0.99. Relative standard deviations of intra- and inter-run precisions were below 7% and relative errors were below 6 ± 7% for both analytes. Also stabilities were acceptable for both analytes. As an application example, concentrations of enalapril and enalaprilat in serum after oral administration of 20 mg enalapril maleat in a healthy volunteer were determined.

Inhibitor and substrate binding by angiotensin-converting enzyme: quantum mechanical/molecular mechanical molecular dynamics studies.

Angiotensin-converting enzyme (ACE) is an important zinc-dependent hydrolase responsible for converting the inactive angiotensin I to the vasoconstrictor angiotensin II and for inactivating the vasodilator bradykinin. However, the substrate binding mode of ACE has not been completely understood. In this work, we propose a model for an ACE Michaelis complex based on two known X-ray structures of inhibitor-enzyme complexes. Specifically, the human testis angiotensin-converting enzyme (tACE) complexed with two clinic drugs were first investigated using a combined quantum mechanical and molecular mechanical (QM/MM) approach. The structural parameters obtained from the 550 ps molecular dynamics simulations are in excellent agreement with the X-ray structures, validating the QM/MM approach. Based on these structures, a model for the Michaelis complex was proposed and simulated using the same computational protocol. Implications to ACE catalysis are discussed.

Enalaprilat and enalapril maleate eyedrops lower intraocular pressure in rabbits.

PURPOSE: This study aimed to develop low-viscosity aqueous eyedrops containing enalaprilat and its prodrug enalapril maleate in solution, and to evaluate the eyedrops in rabbits. METHODS: Aqueous eyedrops with hydroxypropyl-beta-cyclodextrin containing 0.01-2.9% (w/v) enalaprilat, 1.0% (w/v) enalapril maleate with cyclodextrin or 0.5% (w/v) timolol were prepared. The eyedrops were administered to rabbits and intraocular pressure (IOP) was measured at various time intervals after the administration and the results (mean of 10 experiments +/- standard error of the mean) are expressed as the change from baseline (24.7 +/- 3.3 mmHg). RESULTS: Enalaprilat possessed sufficient stability to be formulated as an aqueous eyedrop solution with a shelf-life of several years at room temperature. The maximum decline in IOP after topical administration of one drop of 2.9% enalaprilat solution was 6.2 +/- 0.7 mmHg at 4 hours after administration. Duration of activity exceeded 10 hours. A 1% enalaprilat solution lowered IOP by 4.4 +/- 0.8 mmHg at 4 hours after administration and had similar duration, and was more potent than 0.5% timolol. The enalapril maleate eyedrops resulted in delayed action, showing maximum potency at 10-22 hours after administration and duration of up to 32 hours. CONCLUSIONS: Enalaprilat eyedrops lower IOP in rabbits. The decline in IOP is proportional to the concentration of dissolved enalaprilat in low-viscosity aqueous eyedrop formulations.

Nanocomposites coated with xyloglucan for drug delivery: In vitro studies.

Enalaprilate (Enal), an active pharmaceutical component, was intercalated into a layered double hydroxide (Mg/Al-LDH) by an ion exchange reaction. The use of a layered double hydroxide (LDH) to release active drugs is limited by the low pH of the stomach (pH approximately 1.2), in whose condition it is readily dissolved. To overcome this limitation, xyloglucan (XG) extracted from Hymenaea courbaril (jatobá) seeds, Brazilian species, was used to protect the LDH and allow the drug to pass through the gastrointestinal tract. All the materials were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, elemental analyses, transmission electronic microscopy, thermal analyses, and a kinetic study of the in vitro release was monitored by ultraviolet spectroscopy. The resulting hybrid system containing HDL-Enal-XG(3) slowly released the Enal. In an 8-h of test, the system protected 40% (w/v) of the drug. The kinetic profile showed that the drug release was a co-effect behavior, involving dissolution of inorganic material and ion exchange between the intercalated anions in the lamella and those of phosphate in the buffer solution. The nanocomposite coated protection with XG was therefore efficient in obtaining a slow release of Enal.

Simultaneous quantification of enalapril and enalaprilat in human plasma by high-performance liquid chromatography-tandem mass spectrometry and its application in a pharmacokinetic study.

A rapid, selective and sensitive high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) method was developed to simultaneously determine enalapril and enalaprilat in human plasma. With benazepril as internal standard, sample pretreatment involved in a one-step protein precipitation (PPT) with methanol of 0.2 ml plasma. Analysis was performed on an Ultimate XB-C(18) column (50 mm x 2.1 mm, i.d., 3 microm) with mobile phase consisting of methanol-water-formic acid (62:38:0.2, v/v/v). The detection was performed on a triple quadrupole tandem mass spectrometer by multiple reaction-monitoring (MRM) mode via electrospray ionization (ESI) source. Each plasma sample was chromatographed within 2.5 min. The linear calibration curves for enalapril and enalaprilat were both obtained in the concentration range of 0.638-255 ng/ml (r(2) > or = 0.99) with the lower limit of quantification (LLOQ) of 0.638 ng/ml. The intra-day precision (R.S.D.) was below 7.2% and inter-day R.S.D. was less than 14%, while accuracy (relative error R.E.) was within +/-8.7 and +/-5.5%, determined from QC samples for enalapril and enalaprilat which corresponded to requirement of the guidance of FDA. The HPLC-MS/MS method herein described was fully validated and successfully applied to the pharmacokinetic study of enalapril maleate capsules in 20 healthy male volunteers after oral administration.

[The in vitro cross-effects of inhibitors of renin-angiotensin and fibrinolytic systems on the key enzymes of these systems].

The effects of hypotensive agents (captopril, enalaprilate, and lisinopril) on the activities of components of the fibrinolytic system (FS) and the effects of antifibrinolytic agents (6-aminohexanoic acid (6-AHA) and tranexamic acid (t-AMCHA)) on the activities of angiotensin converting enzyme (ACE) were studied in vitro. Enalaprilate did not affect the FS activity. Captopril considerably inhibited the amidase activities of urokinase (u-PA), plasminogen tissue activator (t-PA), and plasmin ([I]50 (2.0-2.6) +/- 0.1 mM), and the activation of Glu-plasminogen affected by t-PA and u-PA ([I]50 (1.50-1.80) +/- 0.06 mM), which may be due to the presence of a mercapto group in the inhibitor molecule. Lisinopril did not affect the amidase activities of FS enzymes, but stimulated Glu-plasminogen and u-PA activation and inhibited activation of t-PA-fibrin-bound Glu-plasminogen ([I]50 (12.0 +/- 0.5) mM). Presumably, these effects can be explained by the presence in lisinopril of a Lys side residue, whose binding to lysine-binding Glu-plasminogen centers resulted, on the one hand, in the transformation of its closed conformation to a semi-open one and, on the other hand, in its desorption from fibrin. Unspecific inhibition of the activity of ACE, a key enzyme of the renin-angiotensin system, in the presence of 6-AHA and t-AMCHA ([I]50 10.0 +/- 0.5 and 7.5 +/- 0.4 mM, respectively) was found. A decrease in the ACE activity along with the growth of the fibrin monomer concentration was revealed. The data demonstrate that, along with endogenous mediated interactions, relations based on the direct interactions of exogenous inhibitors of one system affecting the activities of components of another system can take place.

The sensitivity of the cis/trans-isomerization of enalapril and enalaprilat to solvent conditions.

The cis- and trans-isomers of enalapril and enalaprilat can be resolved by HPLC and by capillary electrophoresis. The isomeric content of enalapril is perturbed by the ionization of both its carboxyl and amine groups, while the isomeric content of enalaprilat is only perturbed by the ionization of its amine group. Increasing the hydrophobicity of the analyte solvent, as reflected in its molar polarization, increases the Z (cis) content of enalapril and markedly decreases the kinetics for isomerization. Far UV circular dichroic measurements suggest that the increase in Z (cis) content of enalapril is due to protonation of its carboxylate group. Taken together, the in-vitro properties of enalapril and enalaprilat suggest that the in-vivo transformation of the prodrug enalapril to the inhibitor enalaprilat and its delivery to angiotensin-converting enzyme should not be significantly limited by cis/trans-isomerization.

Structural details on the binding of antihypertensive drugs captopril and enalaprilat to human testicular angiotensin I-converting enzyme.

Angiotensin converting enzyme (ACE) plays a critical role in the circulating or endocrine renin-angiotensin system (RAS) as well as the local regulation that exists in tissues such as the myocardium and skeletal muscle. Here we report the high-resolution crystal structures of testis ACE (tACE) in complex with the first successfully designed ACE inhibitor captopril and enalaprilat, the Phe-Ala-Pro analogue. We have compared these structures with the recently reported structure of a tACE-lisinopril complex [Natesh et al. (2003) Nature 421, 551-554]. The analyses reveal that all three inhibitors make direct interactions with the catalytic Zn(2+) ion at the active site of the enzyme: the thiol group of captopril and the carboxylate group of enalaprilat and lisinopril. Subtle differences are also observed at other regions of the binding pocket. These are compared with N-domain models and discussed with reference to published biochemical data. The chloride coordination geometries of the three structures are discussed and compared with other ACE analogues. It is anticipated that the molecular details provided by these structures will be used to improve the binding and/or the design of new, more potent domain-specific inhibitors of ACE that could serve as new generation antihypertensive drugs.

Simultaneous quantitation of enalapril and enalaprilat in human plasma by 96-well solid-phase extraction and liquid chromatography/tandem mass spectrometry.

A sensitive and rapid method based on liquid chromatography/tandem mass spectrometry (LC/MS/MS) combined with rapid solid-phase extraction (SPE) has been developed and validated for the quantitative determination of enalapril and its active metabolite enalaprilat in human plasma. After addition of internal standard to human plasma, samples were extracted by 96-well SPE cartridge. The extracts were analyzed by HPLC with the detection of the analyte in the multiple reaction monitoring (MRM) mode. This method for the simultaneous determination of enalapril and enalaprilat was accurate and reproducible, with respective limits of quantitation of 0.2 and 1.0 ng/mL in plasma. The standard calibration curves for both enalapril and enalaprilat were linear (r(2) = 0.9978 and 0.9998) over the concentration ranges 0.2-200 and 1.0-100 ng/mL in human plasma, respectively. The intra- and inter-day precision over the concentration range for enalapril and enalaprilat were lower than 13.3 and 15.4% (relative standard deviation, %RSD), and accuracy was between 89.2-105.0 and 91.9-104.7%, respectively.

RP-HPLC and NMR study of cis-trans isomerization of enalaprilat.

The angiotensin converting enzyme inhibitor, enalaprilat can exist in solution as cis and trans conformers which interconvert around the amide bond at room temperature. A HPLC with UV detection was performed to study the influence of various chromatographic operational conditions on both rotamers separation and elution of enalaprilat as a single peak. In addition nuclear overhauser enhancement difference was used for the identification of the conformers. The isomer ratio integrated from the obtained 1H NMR result were 71.5:28.5 and 76:24 at 298 and 279 K, respectively where the trans was the major form.

Effect of column temperature on the behaviour of some angiotensin converting enzyme inhibitors during high-performance liquid chromatographic analysis.

The chromatographic behaviour of the ACE inhibitors lisinopril, enalapril and its two degradation products, enalaprilat (hydrolytic degradation product) and diketopiperazine (DKP) (cyclization degradation product) was studied as a function of column temperature and pH of the mobile phase. The rate of isomerization (which influences the peak shape or even peak splitting during chromatographic analysis) increases with temperature. The shape of the chromatographic peak for enalapril, enalaprilat and lisinopril is also pH dependent. At high temperature (80 degrees C) and low pH (pH=2) all studied compounds appear on the chromatogram as a narrow chromatographic peak. Chromatographic peaks become broader or they split by lowering the column temperature. Enalapril appears at 6 degrees C on the chromatogram in two peaks which belong to its cis- and trans-rotation isomers. Separation of the rotamers was confirmed by NMR spectroscopy.

In vitro characterization of human intact erythrocytes loaded by enalaprilat.

In vitro characteristics of the human erythrocytes loaded by enalaprilat have been evaluated. Erythrocytes obtained from a healthy volunteer were loaded by enalaprilat using the hypotonic preswelling method, and the loading parameters, drug-release kinetics, hematological indices, particle size distribution, scanning electron microscopy view, osmotic and turbulence fragilities, and deformability of the resulting carrier cells were determined along with the sham encapsulated and unloaded cells. Carrier erythrocytes, having acceptable loading parameters, released their drug content according to zero-order kinetics. Mean corpuscular hemoglobin and mean corpuscular hemoglobin content values of the cells decreased, particle size dispersion increased, the cells transformed to cup-form, the erythrocytes became more fragile against osmotic pressure and turbulent flow, and, finally, the deformability of the cells decreased significantly upon drug loading.

Design, synthesis and enzyme inhibitory activities of new trifluoromethyl-containing inhibitors for angiotensin converting enzyme.

A series of trifluoromethyl-containing analogs of captopril as well as analogs and homologs of enalaprilat were synthesized and evaluated for inhibition of angiotensin converting enzyme (ACE). It was found that direct substitution of trifluoromethyl for methyl produced a very potent captopril analog with an IC50 of 3 x 10(-10) M in vitro. Hydrophobicity and conformational effects of trifluoromethyl group are among the reasons accounting for this activity. Structure-activity relationship is studied based on molecular mechanics calculations using a II-SCF-molecular mechanics program (PIMM) as well as SYBYL molecular mechanics program. It was found that simultaneous incorporation of trifluoromethyl and an indoline residue unexpectedly yielded a less potent captopril analog (IC50 = 8 x 10(-8) M). Enalaprilat analogs derived from replacement of the alanine residue with trifluoronorvaline and trifluoronorleucine residues gave moderately potent compounds (IC50 = 2-6 x 10(-8) M). The structure-activity relationship for these fluoroenalaprilat analogs is discussed in comparison with known analogs.

Compatibility of enalaprilat with dobutamine, dopamine, heparin, nitroglycerin, potassium chloride and nitroprusside.

The physical and chemical compatibility of enalaprilat in admixtures of dobutamine, dopamine, heparin, nitroglycerin, potassium chloride, or sodium nitroprusside, in 5% dextrose, were studied at room temperature over a 24-h period. Enalaprilat was found to be physically compatible and chemically stable in all admixture solutions tested.