Angiotensin I-converting Enzyme Activity Research Articles

Effects of Aloe vera components on the Renin‐Angiotensin System in human mesangial cells

The local Renin‐Angiotensin System (RAS) is related to the development of diabetic nephropathy. Studies show that Aloe vera has hipoglicemic and antioxidant effects. Aloe emodin (AE), a component of A. vera, increases glycogen synthesis and also glucose transport via the PKI3 intracellular pathway. We evaluate if the Aloe vera components have effects on angiotensin I‐converting enzyme (ACE) activity in human mesangial cells exposed to normal (NG) and high glucose (HG) medium. Two components, P9 and P9a, were semi‐purified from A. vera by High Performance Liquid Chromatography (HPLC) and were eluated at the same retention time of the standard AE. Cells were treated with insulin, P9, P9a and AE at 1, 100 and 1000 pg/mL and ACE activity was evaluated using Z‐Phe‐His‐Leu‐OH as substrate. All treatments were compared to control. Cells under NG treated with P9, P9a and AE showed decreased ACE activity. In HG, high doses of P9 increased ACE activity and AE tend to present the same profile. These data suggest that the semi‐purified fractions contain the Aloe emodin component. Further studies are needed to elucidate the role of A. vera over RAS under physiological and pathological conditions, which may occur by sinergistic or isolated compound action. It could be important in A. vera terapeutic effects research, for instance, in diabetic nephropathy.

Clinical impact of an angiotensin I-converting enzyme insertion/deletion and kinin B2 receptor +9/-9 polymorphisms in the prognosis of renal transplantation

There is a consensus in the scientific literature that supports the importance of the kallikrein kinin and renin angiotensin systems in renal physiology, but few studies have investigated their importance after renal transplantation. The aim of this study was to investigate the clinical effects of the insertion/deletion polymorphism in the angiotensin I-converting enzyme (ACE) gene and the +9/-9 polymorphism in the kinin B2 receptor (B2R) gene in kidney-transplanted patients (n=215 ACE, n=203 B2R) compared with 443 healthy individuals. Demographic results showed that there is a higher frequency of the D allele (high plasma ACE activity) and +9 allele (lower B2R expression) in transplant patients compared with control individuals. We also observed a higher frequency of these alleles in patients who had an elevated level of plasma creatinine. At day 7 post-transplantation, we found a higher prevalence of individuals with the DD genotype with elevated plasma creatinine level. Furthermore, individuals with the DD genotype had a higher chronic allograft dysfunction and graft loss compared with the II patient genotype, which showed no loss of graft. Taken together, our data suggest that the DD genotype is an indicator of an unfavorable prognosis following renal transplantation and could be related to kinin modulation.

The chronic blockade of angiotensin I-converting enzyme eliminates the sex differences of serum cytokine levels of spontaneously hypertensive rats

Sex hormones modulate the action of both cytokines and the renin-angiotensin system. However, the effects of angiotensin I-converting enzyme (ACE) on the proinflammatory and anti-inflammatory cytokine levels in male and female spontaneously hypertensive rats (SHR) are unclear. We determined the relationship between ACE activity, cytokine levels and sex differences in SHR. Female (F) and male (M) SHR were divided into 4 experimental groups each (n = 7): sham + vehicle (SV), sham + enalapril (10 mg/kg body weight by gavage), castrated + vehicle, and castrated + enalapril. Treatment began 21 days after castration and continued for 30 days. Serum cytokine levels (ELISA) and ACE activity (fluorimetry) were measured. Male rats exhibited a higher serum ACE activity than female rats. Castration reduced serum ACE in males but did not affect it in females. Enalapril reduced serum ACE in all groups. IL-10 (FSV = 16.4 ± 1.1 pg/mL; MSV = 12.8 ± 1.2 pg/mL), TNF-α (FSV = 16.6 ± 1.2 pg/mL; MSV = 12.8 ± 1 pg/mL) and IL-6 (FSV = 10.3 ± 0.2 pg/mL; MSV = 7.2 ± 0.2 pg/mL) levels were higher in females than in males. Ovariectomy reduced all cytokine levels and orchiectomy reduced IL-6 but increased IL-10 concentrations in males. Castration eliminated the differences in all inflammatory cytokine levels (IL-6 and TNF-α) between males and females. Enalapril increased IL-10 in all groups and reduced IL-6 in SV rats. In conclusion, serum ACE inhibition by enalapril eliminated the sexual dimorphisms of cytokine levels in SV animals, which suggests that enalapril exerts systemic anti-inflammatory and anti-hypertensive effects.

Blood-pressure-lowering effect of fermented buckwheat sprouts in spontaneously hypertensive rats

A practical antihypertensive food, neo-fermented buckwheat sprouts (neo-FBS), was produced from buckwheat sprouts by lactic fermentation. The neo-FBS preparation gave a 12.7 times better yield and had a 10 times more potent blood-pressure-lowering (BPL) effect than conventionally prepared products. Neo-FBS decreased both systolic and diastolic blood pressure in spontaneously hypertensive rats (SHRs) at a dose of 0.010mg/kg, an effect comparable to 1.0mg/kg captopril, an anti-hypertensive drug. Orally administered neo-FBS (10mg/kg) significantly decreased angiotensin I-converting enzyme (ACE) activity in the lung, thoracic aorta, heart, kidney, and liver of SHRs. Neo-FBS had a detectable relaxing effect on a phenylephrine-precontracted thoracic aorta in SHRs at 0.5μg/mL and the EC50 value was 8.3±1.4μg/mL. The ACE inhibition and vasorelaxation activities were found to be responsible for the excellent BPL effect of neo-FBS. As SHR is a standard model for human hypertension, neo-FBS may also have BPL effects in human patients.

Conformational Changes of Blood ACE in Chronic Uremia

BackgroundThe pattern of binding of monoclonal antibodies (mAbs) to 16 epitopes on human angiotensin I-converting enzyme (ACE) comprise a conformational ACE fingerprint and is a sensitive marker of subtle protein conformational changes.HypothesisToxic substances in the blood of patients with uremia due to End Stage Renal Disease (ESRD) can induce local conformational changes in the ACE protein globule and alter the efficacy of ACE inhibitors.Methodology/Principal FindingsThe recognition of ACE by 16 mAbs to the epitopes on the N and C domains of ACE was estimated using an immune-capture enzymatic plate precipitation assay. The precipitation pattern of blood ACE by a set of mAbs was substantially influenced by the presence of ACE inhibitors with the most dramatic local conformational change noted in the N-domain region recognized by mAb 1G12. The “short” ACE inhibitor enalaprilat (tripeptide analog) and “long” inhibitor teprotide (nonapeptide) produced strikingly different mAb 1G12 binding with enalaprilat strongly increasing mAb 1G12 binding and teprotide decreasing binding. Reduction in S-S bonds via glutathione and dithiothreitol treatment increased 1G12 binding to blood ACE in a manner comparable to enalaprilat. Some patients with uremia due to ESRD exhibited significantly increased mAb 1G12 binding to blood ACE and increased ACE activity towards angiotensin I accompanied by reduced ACE inhibition by inhibitory mAbs and ACE inhibitors.Conclusions/SignificanceThe estimation of relative mAb 1G12 binding to blood ACE detects a subpopulation of ESRD patients with conformationally changed ACE, which activity is less suppressible by ACE inhibitors. This parameter may potentially serve as a biomarker for those patients who may need higher concentrations of ACE inhibitors upon anti-hypertensive therapy.

Effects of Aerobic Exercise Training on Cardiac Renin-Angiotensin System in an Obese Zucker Rat Strain

ObjectiveObesity and renin angiotensin system (RAS) hyperactivity are profoundly involved in cardiovascular diseases, however aerobic exercise training (EXT) can prevent obesity and cardiac RAS activation. The study hypothesis was to investigate whether obesity and its association with EXT alter the systemic and cardiac RAS components in an obese Zucker rat strain.MethodsThe rats were divided into the following groups: Lean Zucker rats (LZR); lean Zucker rats plus EXT (LZR+EXT); obese Zucker rats (OZR) and obese Zucker rats plus EXT (OZR+EXT). EXT consisted of 10 weeks of 60-min swimming sessions, 5 days/week. At the end of the training protocol heart rate (HR), systolic blood pressure (SBP), cardiac hypertrophy (CH) and function, local and systemic components of RAS were evaluated. Also, systemic glucose, triglycerides, total cholesterol and its LDL and HDL fractions were measured.ResultsThe resting HR decreased (∼12%) for both LZR+EXT and OZR+EXT. However, only the LZR+EXT reached significance (p<0.05), while a tendency was found for OZR versus OZR+EXT (p = 0.07). In addition, exercise reduced (57%) triglycerides and (61%) LDL in the OZR+EXT. The systemic angiotensin I-converting enzyme (ACE) activity did not differ regardless of obesity and EXT, however, the OZR and OZR+EXT showed (66%) and (42%), respectively, less angiotensin II (Ang II) plasma concentration when compared with LZR. Furthermore, the results showed that EXT in the OZR prevented increase in CH, cardiac ACE activity, Ang II and AT2 receptor caused by obesity. In addition, exercise augmented cardiac ACE2 in both training groups.ConclusionDespite the unchanged ACE and lower systemic Ang II levels in obesity, the cardiac RAS was increased in OZR and EXT in obese Zucker rats reduced some of the cardiac RAS components and prevented obesity-related CH. These results show that EXT prevented the heart RAS hyperactivity and cardiac maladaptive morphological alterations in obese Zucker rats.

Molecular recognition and regulation of human angiotensin-I converting enzyme (ACE) activity by natural inhibitory peptides

Angiotensin-I converting enzyme (ACE), a two-domain dipeptidylcarboxypeptidase, is a key regulator of blood pressure as a result of its critical role in the renin-angiotensin-aldosterone and kallikrein-kinin systems. Hence it is an important drug target in the treatment of cardiovascular diseases. ACE is primarily known for its ability to cleave angiotensin I (Ang I) to the vasoactive octapeptide angiotensin II (Ang II), but is also able to cleave a number of other substrates including the vasodilator bradykinin and N-acetyl-Ser-Asp-Lys-Pro (Ac-SDKP), a physiological modulator of hematopoiesis. For the first time we provide a detailed biochemical and structural basis for the domain selectivity of the natural peptide inhibitors of ACE, bradykinin potentiating peptide b and Ang II. Moreover, Ang II showed selective competitive inhibition of the carboxy-terminal domain of human somatic ACE providing evidence for a regulatory role in the human renin-angiotensin system (RAS).

The use of Angiotensin-I converting enzyme i/d genetic polymorphism as a biomarker of athletic performance in humans.

Angiotensin II is a key regulator of blood pressure and cardiovascular function in mammals. The conversion of angiotensin into its active form is carried out by Angiotensin I-Converting Enzyme (ACE). The measurement of ACE concentration in plasma or serum, its enzymatic activity, and the correlation between an insertion/deletion (I/D) genetic polymorphism of the ACE gene have been investigated as possible indicators of superior athletic performance in humans. In this context, other indicators of superior adaptation to exercise resulting in better athletic performance (such as ventricular hypertrophy, VO2 max, and competition results) were mostly used to study the association between ACE I/D polymorphism and improved performance. Despite the fact that the existing literature presents little consensus, there is sufficient scientific evidence to warrant further investigation on the usage of ACE activity and the I/D ACE gene polymorphism as biomarkers of superior athletic performance in humans of specific ethnicities or in athletes involved in certain sports. In this sense, a biomarker would be a substance or genetic component that could be measured to provide a degree of certainty, or an indication, of the presence of a certain trait or characteristic that would be beneficial to the athlete’s performance. Difficulties in interpreting and comparing the results of scientific research on the topic arise from dissimilar protocols and variation in study design. This review aims to investigate the current literature on the use of ACE I/D polymorphism as a biomarker of performance in humans through the comparison of scientific publications.

Angiotensin I converting enzyme (ACE) inhibitory peptides from salmon byproduct protein hydrolysate by Alcalase hydrolysis

Angiotensin I converting enzyme (ACE) inhibitory peptides were produced from salmon byproduct proteins via enzymatic hydrolysis using Alcalase, flavourzyme, neutrase, pepsin, protamex and trypsin. Among them, Alcalase hydrolysate showed the highest ACE inhibitory activity, thus ACE inhibitory peptides were purified using consecutive chromatography. The purified ACE inhibitory peptides were identified to be Val-Trp-Asp-Pro-Pro-Lys-Phe-Asp (P1), Phe-Glu-Asp-Tyr-Val-Pro-Leu-Ser-Cys-Phe (P2), and Phe-Asn-Val-Pro-Leu-Tyr-Glu (P4) by time of flight-mass spectrometry/mass spectrometry (TOF-MS) analysis. The IC50 values against ACE activity were 9.10μM (P1), 10.77μM (P2) and 7.72μM (P4). The inhibition mode of P1, P2 and P4 was analyzed using the Lineweaver–Burk plots, demonstrating P1 to be a non-competitive inhibitor, P2 and P4 having a mixed inhibition mode. Taken together, the salmon byproduct protein hydrolysate and/or its active peptides can be used in foods for its benefits against hypertension and related diseases.

Novel angiotensin I-converting enzyme inhibitory peptides produced in fermented milk by specific wild Lactococcus lactis strains

The ability of specific wild Lactococcus lactis strains to hydrolyze milk proteins to release angiotensin I-converting enzyme (ACE) inhibitory peptides was evaluated. The peptide profiles were obtained from the <3kDa water-soluble extract and subsequently fractionated by reversed-phase HPLC. The fractions with the lowest half-maximal inhibitory concentration estimated values (peptide concentration necessary to inhibit ACE activity by 50%) were Lc. lactis NRRL B-50571 fraction (F)1 (0.034±0.002μg/mL; mean ± SD) and Lc. lactis NRRL B-50572B F 0005 (0.041±0.003μg/mL; mean ± SD). All peptide fractions were analyzed by reversed-phase HPLC tandem mass spectrometry. Twenty-one novel peptide sequences associated with ACE inhibitory (ACEI) activity were identified. Several novel ACEI peptides presented peptides encrypted with proven hypotensive activity. In conclusion, specific wild Lc. lactis strains were able to hydrolyze milk proteins to generate potent ACEI peptides. However, further studies are necessary to find out the relationship between Lc. lactis strain proteolytic systems and their ability to biogenerate hypotensive peptides.

Hypotensive and heart rate-lowering effects in rats receiving milk fermented by specific Lactococcus lactis strains

Previous studies have demonstrated that milk fermented by specific Lactococcus lactis strains significantly inhibits the activity of angiotensin I-converting enzyme (ACE). However, the relationship between the ACE inhibitor and its in vivo action has revealed discrepancies. Therefore, the aim of the present study was to investigate the antihypertensive and heart rate (HR)-lowering effect of milk fermented by specific L. lactis in a murine model. Spontaneously hypertensive male rats (271 (SD14) g) were randomised into four treatment groups that were orally administered with milk fermented by L. lactis NRRL B-50 571 or L. lactis NRRL B-50 572 at 35 or 50 mg protein/kg body weight (BW), respectively. Further, two more groups were fed with different solutions as controls: a saline solution as the negative control and Captopril (40 mg/kg BW), a proven ACE inhibitor, as the positive control. Blood pressure and HR were monitored by the tail-cuff method before the treatments and at 2, 4, 6 and 24 h post-oral administration. The results demonstrated that milk fermented by L. lactis NRRL B-50 571 as well as by L. lactis NRRL B-50 572 presented an important systolic and diastolic blood pressure- and HR-lowering effect. Thus, milk fermented by specific L. lactis strains may present potential benefits in the prevention and treatment of CVD associated with hypertension in humans.

Inhibition mechanism and model of an angiotensin I-converting enzyme (ACE)-inhibitory hexapeptide from yeast (Saccharomyces cerevisiae).

Angiotensin I-converting enzyme (ACE) has an important function in blood pressure regulation. ACE-inhibitory peptides can lower blood pressure by inhibiting ACE activity. Based on the sequence of an ACE-inhibitory hexapeptide (TPTQQS) purified from yeast, enzyme kinetics experiments, isothermal titration calorimetry (ITC), and a docking simulation were performed. The hexapeptide was found to inhibit ACE in a non-competitive manner, as supported by the structural model. The hexapeptide bound to ACE via interactions of the N-terminal Thr1, Thr3, and Gln4 residues with the residues on the lid structure of ACE, and the C-terminal Ser6 attracted the zinc ion, which is vital for ACE catalysis. The displacement of the zinc ion from the active site resulted in the inhibition of ACE activity. The structural model based on the docking simulation was supported by experiments in which the peptide was modified. This study provides a new inhibitory mechanism of ACE by a peptide which broads our knowledge for drug designing against enzyme targets.

Production of angiotensin‐I‐converting enzyme inhibitory peptides from β‐lactoglobulin‐ and casein‐derived peptides: An integrative approach

Angiotensin I-converting enzyme (ACE) inhibition is one of the mechanisms by which reduction in blood pressure is exerted. Whey proteins are a rich source of ACE inhibitory peptides and have shown a blood pressure reduction effect i.e. antihypertensive activity. The aim of this work was to develop a simplified process using a combination of adsorption and microfiltration steps for the production of hydrolysates from whey with high ACE inhibitory activity and potency; the latter was measured as the IC50, which is the peptide concentration required to reduce ACE activity by half. This process integrates the selective separation of β-lactoglobulin- and casein-derived peptides (CDP) from rennet whey and their hydrolysis, which results in partially pure, less complex hydrolysates with high bioactive potency. Hydrolysis was carried out with protease N "Amano" in a thermostatically controlled membrane reactor operated in a batch mode. By applying the integrative approach it was possible to produce from the same feedstock two different hydrolysates that exhibited high ACE inhibition. One hydrolysate was mainly composed of casein-derived peptides with IC50=285 μg/mL. In this hydrolysate we identified the well-known potent ACE-inhibitor and antihypertensive tripeptide Ile-Pro-Pro (IPP) and another novel octapeptide Gln-Asp-Lys-Thr-Glu-Ile-Pro-Thr (QDKTEIPT). The second hydrolysate was mainly composed of β-lactoglobulin derived peptides with IC50=28 μg/mL. This hydrolysate contained a tetrapeptide (Ile-Ile-Ala-Glu) IIAE as one of the two major peptides. A further advantage to this process is that enzyme activity was substantially increased as enzyme product inhibition was reduced.

Biological activity from the gelatin hydrolysates of duck skin by-products

In this study, free radical scavengers and angiotensin I converting enzyme (ACE) inhibitors from the gelatin hyrdolysates of duck skin by-products were examined. Gelatin was obtained by pretreating duck skin by-products with acid and alkaline and hydrolysis using nine proteases (Alcalase, Collaganase, Flavourzyme, Neutrase, Protamex, papain, pepsin, trypsin and α-chymotrypsin). Of the various hydrolysates produced, the pepsin hydrolysate exhibited the highest free radical scavenging activity. The DPPH, hydroxyl and alkyl radical scavenging activity of pepsin was the most prominent with IC50 values of 1.230, 0.554 and 1.193mg/ml respectively, which were measured using an electron spin resonance (ESR) spectrometer. However, when the gelatin was hydrolyzed as a combination of two enzymes, Collaganase and pepsin, the DPPH, hydroxyl and alkyl radical scavenging activity increased as the IC50 decreased to 0.632, 0.222 and 0.708mg/ml, respectively. In addition, the ability of pepsin hydrolysates from the gelatin of duck skin by-products to inhibit oxidative damage to DNA was assessed in vitro by measuring the conversion of supercoiled pBR322 plasmid DNA to the open circular form. The enzymatic hydrolysates from the gelatin of duck skin by-products significantly protected hydroxyl radical-induced DNA damage in a dose-dependent manner, while also inhibiting the ACE activity of the α-chymotrypsin hydrolysates.These results indicate that enzymatic hydrolysates from the gelatin of duck skin by-products may be a beneficial ingredient in functional foods and/or pharmaceuticals.

A variant peptide of buffalo colostrum β-lactoglobulin inhibits angiotensin I-converting enzyme activity

β-lactoglobulin is a rich source of bioactive peptides. The LC-MS separated tryptic peptides of buffalo colostrum β-lactoglobulin (BLG-col) were computed based on MS–MS fragmentation for de novo sequencing. Among the selected peptides (P1–P8), a variant was detected with methionine at position 74 instead of glutamate. The sequences of two peptides were identical to hypocholesterolemic peptides whereas the remaining peptides were in accordance with buffalo milk β-lactoglobulin. Comparative sequence analysis of BLG-col to milk β-lactoglobulin was carried out using CLUSTALW2 and a molecular model for BLG-col was constructed (PMDB ID-PM0076812). The synthesized variant pentapeptide (IIAMK, m/z-576 Da) was found to inhibit angiotensin I-converting enzyme (ACE) with an IC50 of 498 ± 2 μM, which was rationalized through docking simulations using Molgrow virtual docker.

Influence of the structure and composition of the País grape proanthocyanidins on the inhibition of angiotensin I-converting enzyme (ACE)

The influence of polymerisation (number of subunits), galloylation (content of esterified gallates) and type of subunit in the polymeric chain of proanthocyanidins (PAs) in skin and seed extracts of Vitis vinifera L. cv. Pais on the inhibition of angiotensin I-converting enzyme (ACE) was evaluated. Gel permeation chromatography was used to purify the extracts, which were characterised by acid-catalysis depolymerisation followed by HPLC. ACE activity was tested by quantitative HPLC, measuring the hippuric acid (HA) produced from hippuryl-l-histidyl-l-leucine (HHL) hydrolysis by ACE. The inhibitory activity on ACE was verified for all the obtained fractions, although the PAs’ molecular size and structural composition affected the ACE inhibition. The higher inhibitory power of skin extract was associated with greater –OH availability, higher mean degree of polymerisation (mDP) and the presence of epicatechin-gallate (ECG) expressed as percentage of galloylation (%G). However, comparing only the structural composition (for samples with similar mDP), % epicatechin (EC) and ECG, <3 %G appeared to be the most important characteristic when considering inhibitory effect of both tissues. Thus, these results indicate that the ACE inhibition by grape PAs depend on the stereochemical configuration of the studied flavanols.

Carbamazepine inhibits angiotensin I-converting enzyme, linking it to the pathogenesis of temporal lobe epilepsy

We find that a common mutation that increases angiotensin I-converting enzyme activity occurs with higher frequency in male patients suffering from refractory temporal lobe epilepsy. However, in their brains, the activity of the enzyme is downregulated. As an explanation, we surprisingly find that carbamazepine, commonly used to treat epilepsy, is an inhibitor of the enzyme, thus providing a direct link between epilepsy and the renin–angiotensin and kallikrein–kinin systems.

Hypertension-attenuating effect of whey protein hydrolysate on spontaneously hypertensive rats

The angiotensin I-converting enzyme (ACE)-inhibitory activity and antihypertensive effect of whey protein hydrolysate (WPH) after single oral administration (short term) or continuous administration for 20 d (long term) were investigated. In the case of short term administration, the systolic and diastolic blood pressure of spontaneously hypertensive rats (SHRs) in captopril and WPH-supplemented groups significantly decreased from 6 to 8 h post-administration compared to the negative control group. In the case of long term administration, WPH supplementation lowered the blood pressure and affected the heart rate of SHRs in a dose-dependent manner, the lowest systolic blood pressure was obtained at the dose of 240 mg WPH/kg b.w. Furthermore, the ACE activity in plasma, lung, kidney and abdominal aorta of the WPH-administered groups decreased in a dose-related manner, and was significantly lower than that of the negative control group. These results suggest that WPH with an ACE-inhibitory activity could potentially suppress the development of hypertension in SHRs.

Isolation and Identification of an Angiotensin-I Converting Enzyme Inhibitory Peptide from Yeast (Saccharomyces cerevisiae)

Angiotensin-I converting enzyme (ACE) has an important function in blood pressure regulation. ACEinhibitory peptides can lower blood pressure by inhibiting ACE activity. In this investigation, water-soluble proteins were extracted from yeast (Saccharomyces cerevisiae) and hydrolyzed by yeast protein extraction enzyme to isolate ACEinhibitory peptides. Peptides with ACE-inhibitory activity were further separated and purified by ultrafiltration and fast protein liquid chromatography (FPLC). A hexapeptide, Thr-Pro-Thr-Gln-Gln-Ser, with a calculated molecular weight of 660Da, was purified and identified by MALDI-TOF-MS. The hexapeptide showed remarkable ACE-inhibitory activity, with an IC50 of 73.25 μg/mL. The level of ACE-inhibitory activity of the hexapeptide indicated that it is a good candidate for development of a hypotension drug or functional food.

Antihypertensive effect of mulberry leaf aqueous extract containing γ-aminobutyric acid in spontaneously hypertensive rats

We hypothesised that mulberry leaves (ML) exert their antihypertensive effect through γ-aminobutyric acid (GABA) and that the antihypertensive activity of ML extract would be comparable to GABA alone in spontaneously hypertensive rats (SHR). We found that single administration of a water extract from leaves of Morus alba L. (WEML) lowered systolic blood pressure (SBP) transiently in a dose-dependent manner. Interestingly, the SBP-lowering effect of WEML was significantly higher than after treatment with GABA alone. We further found that WEML strongly inhibited angiotensin I-converting enzyme (ACE) activity in vitro with an IC50 value of 29.8mg/ml. These results suggest that WEML has a transient antihypertensive effect in vivo that may involve a mechanism of ACE inhibition in addition to GABA.