Angiotensin converting enzyme (ACE) inhibitors activity from purified compounds Fructus Phaleria macrocarpa (Scheff) Boerl.

BACKGROUND: Mahkota Dewa [Phaleria macrocarpa (Scheff) Boerl.] fruit in vitro and in- vivo can decrease and prevent elevation of the blood pressure, lower plasma glucose levels, possess an antioxidant effect, and recover liver and kidney damage in rats. This study aimed to determine the structure and inhibitory activity of angiotensin-converting enzyme inhibitors (ACE) from the Mahkota Dewa fruit. METHODS: The fruit powder was macerated using methanol and then partitioned by hexane, ethyl acetate, n-butanol, and water. The fractions were chromatographed on the column chromatography and incorporated with TLC and recrystallization to give pure compounds. The structures of isolated compounds were determined by UV-Visible, FT-IR, MS, proton (1H-NMR), carbon (13C-NMR), and 2D-NMR techniques encompassing HMQC and HMBC spectra. The compounds were evaluated for their ACE inhibitory activity, and the strongest compound was determined by the kinetics enzyme inhibition. RESULTS: Based on the spectral data, the isolated compounds were determined as 6,4-dihydroxy-4-methoxybenzophenone-2-O-ß-D-glucopyranoside (1), 4,4'-dihydroxy-6-methoxybenzophenone-2-O-ß-D-glucopyranoside (2) and mangiferin (3). IC50 values of the isolated compounds 1, 2 and 3 were 0.055, 0.07, and 0.025 mM, respectively. CONCLUSION: The three compounds have ACE inhibitor and mangiferin demonstrated the best ACE inhibitory activity with competitive inhibition on ACE with the type of inhibition kinetics is competitive inhibition.

In vitro anti-hypertensive activity of Jasminum grandiflorum subsp. floribundum (Oleaceae) in relation to its metabolite profile as revealed via UPLC-HRMS analysis.

Jasminum is an important genus in the olive family (Oleaceae), comprising about 200 species distributed all over the world. In the current study, the methanolic extract of Jasminum grandiflorum subsp. floribundum aerial parts and its respective fractions; dichloromethane and n-butanol fractions were analyzed using ultra-performance liquid chromatography coupled to high resolution mass (UPLC-HRMS) for profiling and characterization of the plant metabolites. More than seventy metabolites were identified belonging to different classes including phenolic acids, flavonoids, secoiridoids, iridoids, lignans, fatty acids, and triterpenes. The samples were also assessed for their angiotensin-I-converting enzyme (ACE) and renin inhibitory activity along with their antioxidant potential using five complementary assays: TAC (total antioxidant capacity), DPPH (1,1-diphenyl-2-picrylhydrazyl), ABTS (2,2'-azino-bis-3-ethylbenzthiazoline-6-sulphonic acid), FRAP (ferric reducing antioxidant power) and iron reducing power. The results revealed that the n-butanol fraction showed a potent ACE and renin inhibition as compared to Lisinopril and Aliskiren standard drugs (24.66 ± 2.41 ng/mL vs. 18.37 ± 1.21 ng/mL and 141.14 ± 5.28 ng/mL vs. 447.87 ± 3.2 ng/mL, respectively) and also a strong antioxidant activity. Interestingly, the secoiridoids, dominated metabolites detected in the n-butanol fraction, revealed the potential of them for management of the hypertension diseases. The total extract and fractions were also standardized using HPLC analysis of the major secoiridoid glycoside; oleuropein. Finally, J. grandiflorum standardized extract could be considered as a target for further studies to discover a new therapeutic anti-hypertensive drug.

Bioactive properties of probiotic set-yogurt supplemented with Siraitia grosvenorii fruit extract.

Siraitia grosvenorii fruit (SGF) has been used as a natural sweetener and traditional medicine in China for more than two centuries. This study evaluated the effect of SGF extract supplementation (0.5%, 1%, and 2%) on the chemical, microbial and sensory properties of probiotic yogurt. The antioxidant, angiotensin-converting-enzyme inhibitory (ACE-I) and antibacterial bioactivities were determined. SGF extract supplementation improved some of the chemical and physicochemical characteristics. Probiotic yogurt with the fruit extract had significantly more Lactobacillus casei and Lactobacillus bulgaricus, whereas there was no significant effect on the number of Streptococcus thermophiles. The bioactivities were significantly increased by SGF extract supplementation. Probiotic yogurt with 2% SGF extract showed the highest antioxidant, ACE-I, and antibacterial activities, whereas the one with 1% SGF extract conferred the highest sensory attributes score. Overall, SGF extract offers a promising option as a dietary supplement to produce novel dairy products that have high nutritional and bioactivity values.

Set-style yoghurts made from goat milk bases fortified with whey protein concentrates.

This research paper addresses the hypothesis that the fortification of goat milk base with whey protein concentrate (WPC) could affect both the textural and the biofunctional properties of set-style yoghurt. The effect of fortification of goat milk base with two different WPCs on thermophilic bacteria counts, proteolysis, physical and biofunctional properties of set-style yoghurts was studied at specific sampling points throughout a 4-week storage period. Fortification and storage did not influence thermophilic counts. Physical properties were affected significantly (P < 0.05) by the composition of the protein and the mineral fraction of the WPC but not by the storage. ACE-inhibitory activity was moderate in accordance to low lactobacilli counts and lack of proteolysis. DPPH-radical scavenging activity, Fe2+-chelating activity and superoxide scavenging activity were high. At 28 d an anti-inflammatory effect was observed, which was not affected by WPC addition.

Mass Spectrometry-Sensitive Probes Coupled with Direct Analysis in Real Time for Simultaneous Sensing of Chemical and Biological Properties of Botanical Drugs.

The development of botanical materials as therapeutic agents involves the meticulous assessment of safety, efficacy, and quality. Compared with small-molecule drugs, quality control of botanical drugs confronts with more significant challenges due to their inherent complexity. Current quality control methods for botanical drugs, either prevailing chemical tests or emerging biological assays, are not able to meet recent demands of multiplexing, sensitivity, and speed. Here, we propose an on-demand strategy based on a direct analysis in real time-mass spectrometry (DART-MS) platform, which is capable of simultaneously analyzing multiple constituents and bioactivities of botanical drugs. Notably, the bioactivities are assessed by a multiple-enzyme assay that adopts cleavable mass spectrometry probes as enzymatic substrates: these probes labeled with a piperazine tag make possible sensitive, multiplexed, and quantitative enzyme activity measurements. The concept is successfully demonstrated via a case study of Danshen (Salvia miltiorrhiza) Injection where simultaneous detection of 34 constituents and inhibitory activities on two target enzymes can be achieved in just minutes. This proof-of-concept application also gives evidence that combining MS-sensitive probes with DART-MS can provide an environmentally friendly, highly sensitive analytical approach for botanical quality control.

A method using angiotensin converting enzyme immobilized on magnetic beads for inhibitor screening.

Angiotensin converting enzyme (ACE), fusing with FLAG tag, was overexpressed in human embryonic kidney 293T cells. This recombinant FLAG-tagged ACE was immobilized on anti-FLAG antibody coated magnetic beads by affinity method in crude cell lysate for the first time. The enzyme-immobilized magnetic beads (ACE-MB), without further cleavage procedure, were used directly to establish a cost-effective and reliable method for screening ACE inhibitors by coupling with fluorescence detection. The enzymatic activity of the ACE-MB was validated based on its Michaelian kinetic behavior towards hippuryl-histidyl-leucine by UHPLC-MS/MS method firstly. Then, several conditions were optimized including amount of magnetic beads, incubation temperature and time in the procedure of ACE immobilization and amount of ACE-MB in the microplate operation. Moreover, this screening assay was validated with Z' factors between 0.71 and 0.81 using four known ACE inhibitors (captopril, lisinopril, fosinopril and fosinoprilat). The developed method was applied for the screening of ACE inhibitors from a small compound library of 45 natural products. As a result, epiberberine and fangchinoline with certain ACE inhibitory activities were screened out in the assay and validated. The results demonstrate the usefulness of this screening method using ACE immobilized on magnetic beads and the advantage of great efficiency with respect to both time and reagents for screening ACE inhibitors.

Forced degradation of l-(+)-bornesitol, a bioactive marker of Hancornia speciosa: Development and validation of stability indicating UHPLC-MS method and effect of degraded products on ACE inhibition.

The antihypertensive activity of the medicinal plant Hancornia speciosa has been previously demonstrated by us, being the activity ascribed to polyphenols and cyclitols like l-(+)-bornesitol. We herein evaluated the stability of the bioactive marker bornesitol submitted to forced degradation conditions. Bornesitol employed in the study was isolated from H. speciosa leaves. An UHPLC-ESI-MS/MS method was developed to investigate bornesitol stability based on MRM (Multiple Reaction Monitoring) acquisition mode and negative ionization mode, employing both specific (m/z 193 → 161 Da) and confirmatory (m/z 193 → 175 Da) transitions. A gradient elution of 0.1% formic acid in water and acetonitrile was performed on a HILIC column. The method was validated and showed adequate linearity (r2 > 0.99), selectivity, specificity, accuracy, and precision (RSD < 2.9%). The method was robust for deliberate variations on dessolvation temperature, but not for changes in the flow rate and dessolvation gas. The results from the stability studies allowed us to classify bornesitol as labile for acidic and alkaline hydrolysis, but as very stable for oxidative and neutral hydrolysis exposure. Bornesitol was categorized as practically stable under photolysis degradation, whereas a considerable reduction on its contents was induced by metal ions and thermolysis exposure. Degraded samples from neutral hydrolysis and thermolysis were assayed in vitro for ACE inhibition and showed a substantial decrease in biological activity as compared to intact bornesitol. myo-Inositol was identified as the major degradation products in both matrices. This is the first report on bornesitol stability under different stress conditions and the obtained data are relevant for the development and quality control of standardized products from H. speciosa leaves.

Partial substitution of NaCl by KCl and addition of flavor enhancers on probiotic Prato cheese: A study covering manufacturing, ripening and storage time.

Cheese is a suitable matrix to deliver probiotic strains but it contains a high amount of sodium. The effect of partial substitution of NaCl by KCl and the addition of flavor enhancers (l-arginine, yeast and oregano extract) on probiotic Prato cheese was investigated after 1, 30, and 60 d of refrigerated storage (immediately after manufacturing, and during ripening and storage). Microbiological (lactic acid bacteria and probiotic Lactobacillus casei 01 counts and survival under gastrointestinal conditions), physicochemical (pH, proteolysis, fatty acids), bioactivity (antioxidant effect and angiotensin I-converting enzyme inhibitory activity), rheological, and water mobility by means of time domain low-field nuclear magnetic resonance were investigated. Significant changes in probiotic survival were observed; however, the sodium reduction and the addition of flavor enhancers did not constitute an obstacle to L. casei 01 (>108 CFU/g) during storage. Slight changes were observed in proteolysis, bioactivity, water mobility, texture profile, and fatty acids of the cheeses as a function of the flavor enhancer added. The sodium reduction and the supplementation of Prato cheese with probiotic cultures may be an effective alternative to the production of a potentially functional cheese.

New potentially antihypertensive peptides liberated in milk during fermentation with selected lactic acid bacteria and kombucha cultures.

Compounds with the ability to inhibit angiotensin-converting enzyme (ACE) are used medically to treat human hypertension. The presence of such compounds naturally in food is potentially useful for treating the disease state. The goal of this study was to screen lactic acid bacteria, including species commonly used as dairy starter cultures, for the ability to produce new potent ACE-inhibiting peptides during milk fermentation. Strains of Lactobacillus acidophilus, Lactobacillus casei, Lactobacillus delbrueckii ssp. bulgaricus, Lactobacillus helveticus, Lactobacillus paracasei, Lactococcus lactis, Leuconostoc mesenteroides, and Pediococcus acidilactici were tested in this study. Additionally, a symbiotic consortium of yeast and bacteria, used commercially to produce kombucha tea, was tested. Commercially sterile milk was inoculated with lactic acid bacteria strains and kombucha culture and incubated at 37°C for up to 72 h, and the liberation of ACE-inhibiting compounds during fermentation was monitored. Fermented milk was centrifuged and the supernatant (crude extract) was subjected to ultrafiltration using 3- and 10-kDa cut-off filters. Crude and ultrafiltered extracts were tested for ACE-inhibitory activity. The 10-kDa filtrate resulting from L. casei ATCC 7469 and kombucha culture fermentations (72 h) showed the highest ACE-inhibitory activity. Two-step purification of these filtrates was done using HPLC equipped with a reverse-phase column. Analysis of HPLC-purified fractions by liquid chromatography-mass spectrometry/mass spectrometry identified several new peptides with potent ACE-inhibitory activities. Some of these peptides were synthesized, and their ACE-inhibitory activities were confirmed. Use of organisms producing these unique peptides in food fermentations could contribute positively to human health.

Nutritional and Functional Bioactivity Value of Selected Azorean Macroalgae: Ulva compressa, Ulva rigida, Gelidium microdon, and Pterocladiella capillacea.

This study presents information on the biochemical composition (dry weight basis), nutritional aspects, and angiotensin I-converting enzyme (ACE) inhibitory properties of selected macroalgae (Ulva compressa, Ulva rigida, Gelidium microdon, and Pterocladiella capillacea) from Azores. Moisture content was very high (83.2% to 90.0% of fresh weight). Total dietary fiber (33.7% to 41.0%) that presented a good balance of both soluble and insoluble fibers (15.5% to 19.2% and 18.2% to 21.8%, respectively) was the most abundant component in these macroalgae. Protein and ash (ranged from 15.7% to 23.4% and 10.7% to 20.7%, respectively) were the 2nd most abundant components in red and green macroalgae, respectively. Moderate soluble carbohydrate contents (14.5% to 19.8%) were found in all species. Lipid contents were low (1.0% to 4.3%), particularly in Ulva species (1.0% to 1.7%), but contained higher unsaturated fatty acids (FAs) (7.5% to 32.9% and 29.6% to 69.2% of total FA for monounsaturated fatty acid and polyunsaturated fatty acid groups, respectively) than saturated fatty acid (23.3% to 46.8% of total FA) contents. All the macroalgal proteins had high digestibility in vitro (82.2% to 89.4%, relatively to sodium caseinate), contained high quantity of essential amino acids (45.3% to 58.1% of total amino acids), but in different proportions, and were rich in aspartic and glutamic acids that together account for 17.2% to 36.2% of the total amino acids. These results suggested that regular consumption of the selected macroalgae may improve human health and revealed that they can be used for producing food supplements for human and animal nutrition and/or pharmaceuticals with potential effect on the regional economy. Furthermore, the ACE-inhibitory IC50 values of 0.095 to 0.695 mg/mL for the <1 kDa protein hydrolysate fraction revealed a potential impact on hypertension disorder.

Identification and quantification of ACE-inhibiting peptides in enzymatic hydrolysates of plant proteins.

Enzymatic hydrolysis of proteins from rice, soy, pea and wheat, with both chymotrypsin and thermolysin, resulted in hydrolysates, which are efficient inhibitors of the angiotensin-converting enzyme (ACE). IC50 values of the hydrolysates were between 27 and 39mg/l, which is comparable to enzymatically hydrolysed whey protein. A significant increase of the ACE-inhibiting effect was observed following butanol extraction due to accumulation of hydrophobic peptides (IC50 between 12 and 21mg/l). Based on the identification and quantification of individual tryptophan-, tyrosine- and phenylalanine-containing dipeptides, 50-80% of the total ACE-inhibiting potential of butanol extracts from plant protein hydrolysates could be explained. Compared to hydrolysates from whey protein, where the inhibitory effect can almost exclusively be attributed to Ile-Trp, the ACE inhibition by plant protein hydrolysates is caused by a variety of peptides, in particular tyrosine-containing peptides. Hydrolysates of plant proteins are promising ingredients for the development of functional foods.

Drying Methods Alter Angiotensin-I Converting Enzyme Inhibitory Activity, Antioxidant Properties, and Phenolic Constituents of African Mistletoe (Loranthus bengwensis L) Leaves.

This study investigated the most appropriate drying method (sun drying, oven drying, or air drying) for mistletoe leaves obtained from almond tree. The phenolic constituents were characterized using high-performance liquid chromatography-diode array detector, while the inhibitory effect of the aqueous extracts of the leaves on angiotensin-I converting enzyme (ACE) was determined in vitro as also the antioxidant properties. Oven-dried extract (kidney [276.09 µg/mL] and lungs [303.41 µg/mL]) had the highest inhibitory effect on ACE, while air-dried mistletoe extract (kidney [304.47 µg/mL] and lungs [438.72 µg/mL]) had the least. Furthermore, the extracts dose-dependently inhibited Fe(2+) and sodium nitroprusside-induced lipid peroxidation in rat's heart and kidney. Also, all extracts exhibited antioxidative properties as typified by their radical scavenging and Fe-chelating ability. Findings from this study revealed that oven drying is the best of the 3 drying methods used for mistletoe obtained from almond host tree, thus confirming that diversity in drying methods leads to variation in phenolic constituents and biological activity of plants.

[Application of reversed-phase liquid chromatography-tandem mass spectrometry in the identification of protein and bioactivity peptides from rape bee pollen].

Based on the shotgun proteomic method, rape bee pollen protein was prepared with ultrasonic extraction and digested by trypsin, then separated and sequenced by reversed-phase liquid chromatography-tandem mass spectrometry (RPLC-MS/MS), followed by protein database searching. After the above analysis, 353 peptides were identified and the molecular biological functions of 239 proteins have been known. The identified molecular biological functions of these proteins mainly included binding activity, enzyme activity, transporter activity, inhibitor activity and so on. Five peptides were obtained after the screening and appropriate amino acid modification among the identified 353 peptides, according to the relationship between the sequence structure of the bioactivity peptide and angiotensin converting enzyme (ACE) inhibitor activity. The five peptides were speculated to have ACE inhibitor activity and synthesized to detect ACE inhibitor activity. The results showed that all of the five peptides had good ACE inhibitor activity. The peptides of AELDIVLALF and LAVNLIPFP among the five peptides displayed especially good ACE inhibition with half maximal inhibitory concentration (IC50) of (10.65 +/- 0.50) micromol/L and (23.66 +/- 1.08) micromol/L, respectively. This method is rapid, low-cost and achieves the goal of high-throughput screening of bioactivity peptides that greatly shorten the period of identification compared with traditional methods.

Bio-functional pickles that reduce blood pressure of rats.

Addition of γ-aminobutyric acid (GABA) and angiotensin converting enzyme (ACE)-inhibitory peptides to the pickles was studied in order to develop a new type of pickles that reduce blood pressure. Based on the outcome of these studies, a new type of fermentation bed composed of rice bran and white miso has been successfully developed. The advantage of such pickles is that they not only contain both GABA and ACE-inhibitory peptides, but also that their taste and flavor are excellent, with colors close to the original ones. The new type of pickles could temporarily reduce blood pressure in two types of rats, spontaneously hypertensive rats and NaCl-sensitive model rats. Thus, the newly developed pickles appear to be beneficial for pickle business.

Proposal of a new degradation mechanism of enalapril maleate and improvement of enalapril maleate stability in tablet formulation with different stabilizers.

Enalapril maleate (EM) is unstable in poorly designed tablet formulations. To improve the stability of EM, the degradation mechanism should be elucidated. In this study, we found that several commonly used excipients promoted the degradants of EM, particularly a diketopiperazine derivative (DKP). We propose two degradation pathways in which both acid and alkali can promote the formation of DKP, although previous reports suggested that DKP is produced mainly in acidic media. Based on the degradation pathways, we believe that subtle control of the microenvironmental pH can inhibit the formation of DKP. This was confirmed by the observation that the degradation rate became slower when certain organic acids were added to the binary mixtures of EM and excipient. The data showed that the stability of EM in the ternary mixtures was much higher than that in binary mixtures. It was further proved that tablets containing these organic acids produced less DKP after the accelerated test. We also found that the formation of DKP in tablets varied with different ratios of tartaric acid, which was used as a model organic acid. This illustrated that an optimum ratio of tartaric acid is required. These results indicated that the stability of EM in tablet formulation is closely associated with microenvironmental pH and the addition of a suitable organic acid based on the reaction mechanism is an effective strategy for improving the stability of EM.

Application of taste sensing system for characterisation of enzymatic hydrolysates from shrimp processing by-products.

The objective of this study was to investigate the potential of an instrumental taste-sensing system to distinguish between shrimp processing by-products hydrolysates produced using different proteases and hydrolysis conditions, and the possible association of taste sensor outputs with human gustatory assessment, salt content, and bioactivity. Principal component analysis of taste sensor output data categorised samples according to the proteases used for hydrolysis. High umami sensor outputs were characteristic of bromelain- and Flavourzyme-produced hydrolysates, compared to low saltiness and high bitterness outputs of Alcalase-produced hydrolysates, and high saltiness and low umami outputs of Protamex-produced hydrolysates. Extensively hydrolysed samples showed higher sourness outputs. Saltiness sensor outputs were correlated with conductivity and sodium content, while umami sensor responses were related to gustatory sweetness, bitterness and umami, as well as angiotensin-I converting enzyme inhibitory activity. Further research should explore the dose dependence and sensitivity of each taste sensor to specific amino acids and peptides.

Activity-guided discovery of (S)-malic acid 1'-O-ß-gentiobioside as an angiotensin I-converting enzyme inhibitor in lettuce (Lactuca sativa).

Angiotensin-converting enzyme (ACE), playing a crucial role in the renin angiotensin aldosterone system, is well-known to catalyze the conversion of the decapeptide angiotensin I into the physiologically active octapeptide angiotensin II, triggering blood pressure increasing mechanisms. To meet the demand for natural phytochemicals as antihypertensive agents in functional food development, extracts prepared from a series of vegetables were screened for their ACE-inhibitory activity by means of a LC-MS/MS-based in vitro assay. By far the highest ACE inhibition was found for a lettuce extract, in which the most active compound was located by means of activity-guided fractionation. LC-MS, NMR spectroscopy, and hydrolysis experiments followed by ion chromatography led to the unequivocal identification of the ACE inhibitor as the previously not reported (S)-malic acid 1'-O-ß-gentiobioside. This glycoside represents a novel class of ACE-inhibiting phytochemicals with a low IC(50) value of 27.8 µM. First incubation experiments in saliva and aqueous hydrochloric acid demonstrated the stability of (S)-malic acid 1'-O-ß-gentiobioside against salivary glycosidases and stomach acid.

Chemical composition, angiotensin-converting enzyme-inhibitory activity and antioxidant activities of few-flower wild rice (Zizania latifolia Turcz.).

BACKGROUND: The chemical compositions of the stem and leaf sheath of few-flower wild rice were analysed. In addition, their extracts were evaluated for diphenylpicrylhydrazyl (DPPH) free radical-scavenging activity, ferric-reducing antioxidant power and angiotensin-converting enzyme (ACE)-inhibitory activity, since these are important properties of sources of nutraceuticals or functional foods. RESULTS: The stems contained more ascorbic acid (0.06 g kg(-1) fresh weight), protein (28.18 g kg(-1) dry weight (DW)), reducing sugars (308.54 g kg(-1) DW), water-soluble pectin (20.63 g kg(-1) DW), Na(2) CO(3) -soluble pectin (44.14 g kg(-1) DW), K (8 g kg(-1) dry matter (DM), S (6 g kg(-1) DM) and P (5 g kg(-1) DM) but less starch, total dietary fibre, Si, Na and Ca than the leaf sheaths. The DPPH free radical-scavenging IC(50) values of the stem and leaf sheath extracts were 19.28 and 21.22 mg mL(-1) respectively. In addition, the ACE-inhibitory IC(50) value of the stem extracts was 38.54 mg mL(-1). CONCLUSION: Both the stem and leaf sheath extracts exhibited good antioxidant properties, while good ACE-inhibitory activity was detected only in the phosphate buffer solution extracts of the stem. Few-flower wild rice could be processed into formula feeds for fish, poultry, etc. or functional foods for persons with high blood pressure.

[Establishment of three screening models of angiotensin converting enzyme inhibitors].

OBJECTIVE: To establish and compare three in vitro screening models of angiotensin converting enzyme inhibitors (ACEI), and provide methodological basis for screening ACEI drugs from Chinese herbal medicine. METHOD: Three screening models were established using rat serum, pure angiotensin converting enzyme (ACE) and crude extract enzyme from rabbit lung as enzyme sources, respectively, with corresponding testing methods, and captopril as the positive drug. RESULT: The IC50 of captopril was 2.30 nmol x L(-1) using rat serum as the enzyme; and 1.04 nmol x L(-1) for ACE pure enzyme; and 1.40 nmol x L(-1) for crude extract enzyme from rabbit lung. CONCLUSION: Results from the three screening models were all in accordance with literature reports. These models can be applied to in vitro pharmaceutical screening. The selection of suitable screening model depend on the experimental situation and the inherent characters of models.

Antihypertensive effects of isoquercitrin and extracts from Tropaeolum majus L.: evidence for the inhibition of angiotensin converting enzyme.

AIM OF THE STUDY: Previous studies have shown that the extracts obtained from Tropaeolum majus L. exhibit pronounced diuretic properties. In the present study, we assessed whether the hypotensive and/or antihypertensive mechanism of hydroethanolic extract (HETM), semi-purified fraction (TMLR) obtained from T. majus and the flavonoids isoquercitrin (ISQ) and kaempferol (KPF) can be mediated by their interaction with angiotensin converting enzyme (ACE). METHODS AND METHODS: Firstly, to evaluate changes in mean arterial pressure (MAP), different groups of normotensive and spontaneously hypertensive rats (SHR) were orally and intraduodenally treated with HETM (10-300 mg/kg) and TMLR (12.5-100mg/kg) and intravenously treated with ISQ and KPF being later anesthetized with ketamine (100mg/kg) and xylazine (20mg/kg). The left femoral vein and the right carotid artery were isolated, and polyethylene catheters were inserted for ISQ and KPF (0.5-4 mg/kg) administration and blood pressure recording, respectively. The plasmatic ACE activity was evaluated to indirect fluorimetry, in serum samples after orally treatment with HETM, TMLR, ISQ and KPF. RESULTS: The oral administration of the HETM and its TMLR significantly reduced, in a dose-dependent manner, the MAP in both normotensive and SHR. In addition, these preparations significantly decreased the MAP for up to 3h after the administration of the extract. Additionally, the intravenous administration of ISQ, but not KPF, decreased MAP in rats. Otherwise, neither the extracts nor ISQ affected the heart rate. The oral administration of the HETM, TMLR or ISQ reduced ACE activity in serum samples at 90 min after administration. Finally, the intravenous administration of ISQ caused a significant reduction in the hypertensive response to angiotensin I, but not angiotensin II in normotensive rats. CONCLUSION: Our results show that the hypotensive effects caused by the HETM, as well as by its TMLR, may be associated with the high levels of the flavonoid ISQ found in this plant. In addition, ISQ-induced hypotension in rats is an event dependent on the inhibition of angiotensin II generation by ACE.