Liquid chromatographic determination of hippuric acid for the evaluation of ethacrynic acid as angiotensin converting enzyme inhibitor

The Potential Angiotensin-Converting Enzyme Inhibitory Activity of Oleanolic Acid in the Hydroethanolic Extract of Crataegus monogyna Jacq

The hydroethanolic extract of Crataegus monogyna was studied for its chemical constitution and angiotensin-converting enzyme (ACE) inhibitory activity. The extract contained triterpenic acids, flavonoids and coumarins. The ACE inhibitory activity was studied using captropril, as a control drug, and oleanolic acid, as a constituent of the hydroethanolic extract and a member of the triterpenic acid group. The hydroethanolic extract and oleanolic acid showed higher IC50 values (335.00 μg/mL and 3.61 μM, respectively) in comparison to captopril (46.9 nM). However, these results indicate the anti-ACE activity of oleanolic acid and the triterpenic acids, which has not been demonstrated earlier for hawthorn extracts. In previous studies, the ACE inhibitory activity of C. monogyna extracts was always attributed to flavonoids and proanthocyanidins.

Bioactivity-Guided Fractionation of Pine Needle Reveals Catechin as an Anti-hypertension Agent via Inhibiting Angiotensin-Converting Enzyme

Hypertension has been recognized as one of the highest risk factors for cardiovascular diseases. Anti-hypertension agent screening and development has been recognized as a pharmaceutical therapy approach for the cardiovascular diseases treatment. Many kinds of traditional Chinese medicines, such as pine needle, have been used for the treatment of hypertension for a long time, but the bioactive ingredients which responsible for their therapeutic effectiveness are remain unclear. Therefore, screening bioactive chemicals in natural sources is still the most straightforward strategy for novel Angiotensin-converting enzyme inhibitor (ACEi)-based anti-hypertension agents discovery. In this study, we demonstrated a bioactivity-guided fractionation strategy for identifying bioactive fractions and chemicals from pine needle based on LC/MS assay as well as elucidating their mechanisms of pharmacological activity. And we found out the compound in pine needle extracts being ACE-inhibitory active is catechin. When ACE activity was assayed in rat tissue membranes, it was observed that catechin demonstrate ACE inhibition in kidney, lung and testes tissue. All these presents catechin in pine needle could be a potential cardiovascular medicine.

Review of Angiotensin-converting Enzyme Inhibitory Assay: Rapid Method in Drug Discovery of Herbal Plants

The renin-angiotensin-aldosterone system is a signaling pathway which responsible in the blood pressure regulation. Angiotensin-converting enzyme (ACE) is one of the key elements responsible for the hypertensive mechanism. It converts angiotensin-I to angiotensin-II. The discovery history of the ACE inhibitory activity assay method has been through a long stage for decades and development continues until today. The ACE inhibitory activity has become an effective screening method in the search for new antihypertensive agents from herbal plants. Some of in vitro assay methods were used to examine the activity of ACE inhibitors based on the substrate usage, such as; Cushman and Cheung Method using a substrate hippuryl-histidyl-leucine (HHL), Holmquist method using a substrate furanacryloyl-tripeptide, Elbl and Wagner method using a substrate benzoil-[l-14C] glicyl-L-histidine-L-leucine, Carmel and Yaron method using a substrate o-aminobenzoylglycyl-p-nitrophenylalanilproline, and Lam method using 3-hydroxybutyrylglycyl-glycyl-glycine as substrate. Several different methods to measure the results of enzymatic reactions or separating substrate with products, including spectrophotometric, fluorometric, high-performance liquid chromatography, electrophoresis, and radiochemistry. Application of the test method for screening the ACE inhibitors activity and investigation of active compounds from natural products can be done easily with this method, it is very helpful in research because the results obtained are simple, accurate, and rapid.

Peptidome characterization and bioactivity analysis of donkey milk

Donkey milk is an interesting commercial product for its nutritional values, which make it the most suitable mammalian milk for human consumption, and for the bioactivity associated with it and derivative products. To further mine the characterization of donkey milk, an extensive peptidomic study was performed. Two peptide purification strategies were compared to remove native proteins and lipids and enrich the peptide fraction. In one case the whole protein content was precipitated by organic solvent using cold acetone. In the other one the precipitation of the most abundant milk proteins, caseins, was performed under acidic conditions by acetic acid at pH4.6, instead. The procedures were compared and proved to be partially complementary. Considered together they provided 1330 peptide identifications for donkey milk, mainly coming from the most abundant proteins in milk. The bioactivity of the isolated peptides was also investigated, both by angiotensin-converting-enzyme inhibitory and antioxidant activity assays and by bioinformatics, proving that the isolated peptides did have the tested biological activities.

BIOLOGICAL SIGNIFICANCE

The rationale behind this study is that peptides in food matrices often play an important biological role and, despite the extensive study of the protein composition of different samples, they remain poorly characterized. In fact, in a typical shotgun proteomics study endogenous peptides are not properly characterized. In proteomics workflows one limiting point is the isolation process: if it is specific for the purification of proteins, it often comprises a precipitation step which aims at isolating pure protein pellets and remove unwonted interferent compounds. In this way endogenous peptides, which are not effectively precipitated as well as proteins, are removed too and not analyzed at the end of the process. Moreover, endogenous peptides do often originate from precursor proteins, but in phenomena which are independent of the shotgun digestion protocol, thus they can be obtained from cleavage specificities other than trypsin's, which is the main proteolytic enzyme employed in proteomic experiments. For this reason, in the end, database search will not be effective for identification of these peptides, thus the need to provide different workflows for peptide analysis. In the work presented in this paper this issue is considered for the first time for the analysis of the peptides isolated in donkey milk samples, which have been chosen for its nutritional interest. This study provides additional knowledge on this milk, already characterized by traditional proteomics studies and peptidomic studies after simulated digestion. This type of study is not just a description of the naturally occurring peptidome of a sample, but also represents a starting point to discover and characterize those naturally occurring peptides responsible for the observed bioactivities of biological samples, as in the case of donkey milk, which would remain uncharacterized by other approaches. In this paper an analytical protocol was described for the efficient isolation and purification of peptides in donkey milk, assessing the effect of the purification protocol on the final identifications. Purified peptide samples were also checked to empirically elucidate any ACE inhibitory or antioxidant activity. Finally, the peptidomic results were also further mined by a bioinformatic-driven approach for bioactive peptide identification in the donkey milk samples. In our opinion, the main strengths of this study are related to the improved analytical workflow (either as purification protocol comparison or analytical platform development) which provides a high number of identified peptides, for which the biological significance as potential bioactive peptides has also been investigated.

Discovery of new angiotensin converting enzyme (ACE) inhibitors from medicinal plants to treat hypertension using an in vitro assay

BACKGROUND AND PURPOSE OF THE STUDY

Angiotensin converting enzyme (ACE) inhibitors plays a critical role in treating hypertension. The purpose of the present investigation was to evaluate ACE inhibition activity of 50 Iranian medicinal plants using an in vitro assay.

METHODS

The ACE activity was evaluated by determining the hydrolysis rate of substrate, hippuryl-L-histidyl-L-leucine (HHL), using reverse phase high performance liquid chromatography (RP-HPLC). Total phenolic content and antioxidant activity were determined by Folin-Ciocalteu colorimetric method and DPPH radical scavenging assay respectively.

RESULTS

Six extracts revealed > 50% ACE inhibition activity at 330 μg/ml concentration. They were Berberis integerrima Bunge. (Berberidaceae) (88.2 ± 1.7%), Crataegus microphylla C. Koch (Rosaceae) (80.9 ± 1.3%), Nymphaea alba L. (Nymphaeaceae) (66.3 ± 1.2%), Onopordon acanthium L. (Asteraceae) (80.2 ± 2.0%), Quercus infectoria G. Olivier. (Fagaceae) (93.9 ± 2.5%) and Rubus sp. (Rosaceae) (51.3 ± 1.0%). Q. infectoria possessed the highest total phenolic content with 7410 ± 101 mg gallic acid/100 g dry plant. Antioxidant activity of Q. infectoria (IC50 value 1.7 ± 0.03 μg/ml) was more than that of BHT (IC50 value of 10.3 ± 0.15 μg/ml) and Trolox (IC50 value of 3.2 ± 0.06 μg/ml) as the positive controls.

CONCLUSIONS

In this study, we introduced six medicinal plants with ACE inhibition activity. Despite the high ACE inhibition and antioxidant activity of Q. infectoria, due to its tannin content (tannins interfere in ACE activity), another plant, O. acanthium, which also had high ACE inhibition and antioxidant activity, but contained no tannin, could be utilized in further studies for isolation of active compounds.

Isolation, identification and molecular docking studies of a new isolated compound, from Onopordon acanthium: a novel angiotensin converting enzyme (ACE) inhibitor

ETHNOPHARMACOLOGICAL RELEVANCE

Onopordon acanthium (also known as Scotch thistle) is a medicinal plant of the Asteraceae family that is widely distributed in Europe and Asia. This plant has been long used in traditional medicine as a hypotensive, cardiotonic and diuretic agent.

AIM OF THE STUDY

The present study is designed to isolate an active compound with ACE inhibition activity from O. acanthium, measure antioxidant activity, predict domain specificity and pharmacokinetic properties of the isolated compound.

MATERIALS AND METHODS

Methanolic extract of O. acanthium seeds, has been subjected to a repeated column chromatography to give a pure compound with Angiotensin Converting Enzyme (ACE) inhibition activity. The ACE inhibition activity was determined using hippuryl-L-histidyl-L-leucine (HHL) as substrate in an in vitro ACE assay. Structure of the pure compound, isolated from O. acanthium has been established by spectroscopic methods, including Infrared (IR), Nuclear Magnetic Resonance (NMR) and Mass spectrum analysis. In addition, antioxidant activity of the new isolated compound, was measured using 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging assay and compared with those of BHT and Trolox as positive controls. Enzyme type inhibition and ACE-C or N domain specificity of the new compound was further evaluated through molecular modeling and docking studies.

RESULTS

Structure of the pure compound, isolated from O. acanthium (83±1% ACE inhibition activity at concentration of 330 μg/ml), has been established. The isolated compound possessed acceptable antioxidant activity (IC50 value of 2.6±0.04 μg/ml) in comparison with BHT (IC50 value of 10.3±0.15 μg/ml) and Trolox (IC50 value of 3.2±0.06 μg/ml). Molecular docking predicted competitive type enzyme inhibition and approximately similar affinity of the isolated compound for ACE-C and N domains.

CONCLUSION

The results derived from computational and in vitro experiments, confirm the potential of the isolated compound, from O. acanthium as a new antihypertensive compound and give additional scientific support to an anecdotal use of O. acanthium in traditional medicine to treat cardiovascular disease such as hypertension.

Comparison of analytical methods to assay inhibitors of angiotensin I-converting enzyme

The linearity, precision and repeatability of visible spectrophotometric (VSP) and high-performance liquid chromatography (HPLC) methods for analysis of inhibitory activity of angiotensin I-converting enzyme (ACE) were compared by using several inhibitors and Hip-His-Leu (HHL) as substrates. IC50 values (concentration at which ACE activity is inhibited by 50%) of 0.00206±0.00005 μg/mL for captopril, 192±4.53 μg/mL for soybean peptides, and 153±4.29 μg/mL for grass carp peptides determined by the VSP method, and these values were 1.07, 1.07, 1.18 and 1.44-fold, respectively, higher than those from the HPLC method. In addition, the inhibitory constant (Ki value) of captopril was determined to be 7.09 nM and 4.94 nM using VSP and HPLC method, respectively. These results showed that the HPLC method revealed a higher level of sensitivity and precision, suitable for assaying ACE inhibition activity of antihyper-sensitive peptides. In contrast, the VSP method can simultaneously measure several samples with simple operations, suitable for analysis of ACE inhibition activity of food protein enzymatic hydrolysates.

Rapid and simple colorimetric assay for screening angiotensin I-converting enzyme inhibitors

CONTEXT

Angiotensin-converting enzyme (ACE) is one of the main regulators of blood pressure through its action on the renin-angiotensin system. ACE inhibitory peptides from natural materials inhibit ACE activity and have considerable importance as antihypertensive agents.

OBJECTIVE

A new chromogenic reaction method for determining hippuric acid (HA) and angiotensin I-converting enzyme (ACE) inhibitor activity was developed.

MATERIALS AND METHODS

This method is based on the reaction of HA with p-dimethylaminobenzaldehyde in the presence of quinoline, acetate, and acetic anhydride. The red-orange formation product in the reaction has a stable absorbance in the visible region and it was determined at 478 nm. The assay conditions were optimized and by using an ACE concentration of 12 mU/mL in enzymatic reaction, the method was applied to monitor the IC(50) values (the concentration of inhibitor required to inhibit 50% of the ACE activity) for captopril and Saurida elongata (Synodontidae) muscle protein hydrolyzate.

RESULTS

With the proposed method, IC(50) values for captopril and Saurida elongata muscle protein hydrolyzate were determined as 0.0123 µM and 0.1648 mg/mL, respectively. Those results correspond to the IC(50) values of 0.0109 µM and 0.1820 mg/mL obtained by high-performance liquid chromatography (HPLC) method.

DISCUSSION AND CONCLUSION

The proposed method is rapid, accurate, reproducible and convenient, and suitable for screening ACE inhibitor peptides from food materials while it does not require HA extraction from the components of the ACE activity assay reaction.

Antihypertensive peptides: production, bioavailability and incorporation into foods

Bioactive food peptides are encrypted within the sequence of food proteins but can be released during food processing (by enzymatic hydrolysis or fermentation) or during gastrointestinal transit. Among bioactive food peptides, those with antihypertensive activity are receiving special attention due to the high prevalence of hypertension in the Western countries and its role in cardiovascular diseases. This paper reviews the current literature on antihypertensive food peptides, focusing on the main methodologies for their production, such as enzymatic hydrolysis, fermentation and the use of recombinant bacteria. This paper also describes the structure/activity relationship of angiotensin-converting enzyme (ACE)-inhibitory peptides, as well as their bioavailability, physiological effects demonstrated by both in vitro and in vivo assays, and the contribution of mechanisms of action other than ACE inhibition. Finally, current reported strategies for incorporation of antihypertensive peptides into foods and their effects on both availability and activity are revised in this manuscript.

Development of a fast liquid chromatography/mass spectrometry screening method for angiotensin-converting enzyme (ACE) inhibitors in complex natural mixtures like snake venom

A new robust high-performance liquid chromatography/electrospray ionization mass spectrometry (HPLC/ESI-MS)-based screening method for angiotensin-converting enzyme (ACE)-inhibiting substances in crude samples is described. The ACE assay is carried out in a typical offline setup by incubation of the samples with ACE and angiotensin I (AI), followed by stopping the reaction with acetonitrile containing val(5)-AI serving as internal standard (I.S.). AI and the product angiotensin II (AII) are extracted from the incubation mixture by turbulent-flow chromatography (TFC) applied in backflush mode as online solid-phase extraction and are directly quantified by ESI(+)-MS. The presence of ACE inhibitors (ACEi) is detected by an increase in AI signal intensity and a corresponding decrease of AII signal, as compared to the blank assay. The overall time of analysis of the TFC/ESI-MS method was 5 min, thus making the described setup suitable for a rapid screening method. The assay was validated using a known ACE inhibitor and the IC(50) values found were in good accordance with a common HPLC/UV method and literature data. The method was successfully applied for the screening of size-exclusion chromatography fractions of the venom of the pitviper Bothrops moojeni. Three of 18 analyzed fractions inhibited ACE, due to peptides present as components of this snake venom. These compounds were extracted from the two most-active fractions by means of TFC and isolated by means of HPLC. Three peptides with ACE inhibitory activity were characterized and their structures were elucidated with ESI-MS/MS-based de novo sequencing to be ZKWPPGKVPP, ZKWPRPGPEIPP and ZNWPRPGPEIPP, respectively (Z = pyroglutamic acid).

Cardiac mitochondrial function and tissue remodelling are improved by a non-antihypertensive dose of enalapril in spontaneously hypertensive rats

Renal and cardiac benefits of renin-angiotensin system inhibition exceed blood pressure (BP) reduction and seem to involve mitochondrial function. It has been shown that RAS inhibition prevented mitochondrial dysfunction in spontaneously hypertensive rats (SHR) kidneys. Here, it is investigated whether a non-antihypertensive enalapril dose protects cardiac tissue and mitochondria function. Three-month-old SHR received water containing enalapril (10 mg/kg/day, SHR+Enal) or no additions (SHR-C) for 5 months. Wistar-Kyoto rats (WKY) were normotensive controls. At month 5, BP was similar in SHR+Enal and SHR-C. In SHR+Enal and WKY, heart weight and myocardial fibrosis were lower than in SHR-C. Matrix metalloprotease-2 activity was lower in SHR+Enal with respect to SHR-C and WKY. In SHR+Enal and WKY, NADH/cytochrome c oxidoreductase activity, eNOS protein and activity and mtNOS activity were higher and Mn-SOD activity was lower than in SHR-C. In summary, enalapril at a non-antihypertensive dose prevented cardiac hypertrophy and modifies parameters of cardiac mitochondrial dysfunction in SHR.

A high-throughput fluorimetric assay for angiotensin I-converting enzyme

Angiotensin I-converting enzyme (ACE) assays are commonly used for measuring enzymatic activity in clinical and biological samples. The fluorimetric procedure described is sensitive, rapid and involves unsophisticated procedures and inexpensive reagents. It uses the substrate hippuryl-L-histidyl-L-leucine, and the fluorescent adduct of the enzyme-catalyzed product L-histidyl-L-leucine is quantified fluorimetrically. This assay has been adapted for a 96-well plate format that produces comparable data to previously described assays and has the advantage of greater efficiency with respect to both time and reagents. The protocol can be used for routine purposes or for more detailed kinetic analyses. The apparent Km and kcat values for purified testis ACE determined from a double reciprocal plot were 3.0 mM and 195.7 s(-1), respectively. The protocol can be completed within 4 h.

Inhibition of angiotensin converting enzyme activity by flavanol-rich foods

Angiotensin converting enzyme (ACE) activity was evaluated in the presence of flavanol-rich foods, i.e., wines, chocolates, and teas, and of purified flavonoids. All foods assayed inhibited ACE activity, red wines being more effective than white wine, and green tea more effective than black tea. The inhibition of ACE activity was associated with both phenolic and flavanol content in the foods. When isolated polyphenols were assayed, procyanidins (dimer and hexamer) and epigallocatechin significantly inhibited enzyme activity; similar concentrations of (+)-catechin, (-)-epicatechin, gallic acid, chlorogenic acid, caffeic acid, quercetin, kaempferol, and resveratrol were ineffective. When ACE activity was assayed in rat kidney membranes in the presence of chocolate extracts or purified procyanidins, it was observed that the inhibition depended on the chocolate content of flavanols and the number of flavanol units constituting the procyanidin. These experiments demonstrate that flavanols either isolated or present in foods could inhibit ACE activity. The occurrence of such inhibition in vivo needs to be determined, although is supported by the association between the consumption of flavanol-rich foods and reductions in blood pressure observed in several experimental models.

Direct spectrophotometric measurement of angiotensin I-converting enzyme inhibitory activity for screening bioactive peptides

A direct, extraction-free spectrophotometric assay was developed for determination of angiotensin I-converting enzyme activity (ACE) in the presence of ACE inhibitors using hippuryl-l-histidyl-l-leucine (HHL) as the ACE-specific substrate. This method relies on previously published spectrophotometric determination of hippuric acid (HA) content in the urine, the method of which was based on the specific colorimetric reaction of HA with benzene sulfonyl chloride (BSC) in the presence of quinoline. The proposed ACE inhibition assay was applied to the measurement of the ACE inhibitory activity of Captopril. IC(50) value of Captopril corresponded well with literature data. Furthermore, Alcalase hydrolysates of mung bean and rice protein isolates were assessed for ACE inhibitory activity by this method. These two hydrolysates showed high ACE inhibitory activity. This method proposed here was shown to be direct, sensitive, accurate, reproducible, and less expensive without separation of HA from ACE reaction mixture, and can be used for the screening of ACE inhibitory peptides derived from food proteins.

Modification of the furanacryloyl-l-phenylalanylglycylglycine assay for determination of angiotensin-I-converting enzyme inhibitory activity

Angiotensin-I-converting enzyme (ACE, EC 3.4.15.1) plays a central role in the regulation of blood pressure in man. The objective of this study was to evaluate and modify the furanacryloyl-L-phenylalanylglycylglycine (FAPGG) assay method for quantification of ACE activity. The fixed time conditions developed for assay of ACE activity were as follows: 0.8 mM FAPGG, 175 + or - 10 units l(-1) ACE, incubation at 37 degrees C for 30 min and enzyme inactivation with 100 mM ethylenediaminetetra-acetic acid (EDTA). Hydrolysis of FAPGG to FAP and GG was quantified by measuring the decrease in absorbance at 340 nm. It was shown that increasing the level ACE activity in the assay from 155 to 221 + or - 15 units l(-1) resulted in a corresponding increase in the apparent IC(50) value for Captopril from 9.10 to 39.40 nM. Similar trends in the apparent IC50 values for a whey protein hydrolysate were obtained. The results demonstrate the requirement for carefully controlling ACE activity levels in the assay in order to obtained comparable and reproducible values for the inhibitory potency of ACE inhibitors.

Hypotensive peptides from milk proteins

Hypertension is the major controllable risk factor associated with cardiovascular disease (CVD) events such as myocardial infarction, stroke, heart failure, and end-stage diabetes. A 5 mm Hg decrease in blood pressure has been equated with approximately 16% decrease in CVD. In the U.S. alone current annual antihypertensive drug costs are approximately dollars 15 billion. The renin-angiotensin-aldosterone system is a target for blood pressure control. Cleavage of angiotensinogen by renin produces angiotensin I which is subsequently hydrolyzed by angiotensin-I-converting enzyme (ACE) to angiotensin II (a potent vasoconstrictor). Various side effects are associated with the use of ACE inhibitory drugs in the control of blood pressure including hypotension, increased potassium levels, reduced renal function, cough, angioedema, skin rashes, and fetal abnormalities. Milk proteins, both caseins and whey proteins, are a rich source of ACE inhibitory peptides. Several studies in spontaneously hypertensive rats show that these casokinins and lactokinins can significantly reduce blood pressure. Furthermore, a limited number of human studies have associated milk protein-derived peptides with statistically significant hypotensive effects (i.e., lower systolic and diastolic pressures). The advent of effective milk protein based functional food ingredients/nutraceuticals for the prevention/control of blood pressure therefore has the potential to significantly reduce global healthcare cost.

Inhibition of angiotensin converting enzyme (ACE) activity by flavan-3-ols and procyanidins

It was determined that flavan-3-ols and procyanidins have an inhibitory effect on angiotensin I converting enzyme (ACE) activity, and the effect was dependent on the number of epicatechin units forming the procyanidin. The inhibition by flavan-3-ols and procyanidins was competitive with the two substrates assayed: N-hippuryl-L-histidyl-L-leucine (HHL) and N-[3-(2-furyl)acryloyl]-L-phenylalanylglycylglycine (FAPGG). Tetramer and hexamer fractions were the more potent inhibitors, showing Ki of 5.6 and 4.7 microM, respectively. As ACE is a membrane protein, the interaction of flavanols and procyanidins with the enzyme could be related to the number of hydroxyl groups on the procyanidins, which determine their capacity to be adsorbed on the membrane surface.