Presence of angiotensin converting enzyme isoforms in larval lepidoptera (Spodoptera littoralis)

In this research the presence of angiotensin converting enzyme (ACE) in larvae of the lepidopteran Spodoptera littoralis was evaluated. Making use of the substrate Abz-FRK-(Dnp)P-OH and the specific inhibitor captopril at 10 microM, ACE activity was determined in a fluorescence assay for intact larvae, hemolymph, head, midgut and dorsal tissue. In dorsal tissue and hemolymph, ACE activity was highest. These data are consistent with a possible role for ACE in contractions of the dorsal vessel and metabolism of circulating peptide hormones in the hemolymph. After the presence of ACE was confirmed, a sequential procedure of anion exchange and size exclusion chromatography was applied to purify ACE from whole wandering larvae (last stage). With this procedure, three different ACE pools were collected that cleaved the fluorogenic substrate Abz-FRK-(Dnp)P-OH. Activity could be inhibited by a final concentration of 2.5 microM captopril. In addition, two out of three samples eluted at different salt concentration and thus ACE 1, 2 and 3 represent at least two different ACE isoforms. These data reveal that ACE is present in S. littoralis and that at least two out of three isolated ACE forms are truly isoforms.     

The peptide network regulated by angiotensin converting enzyme (ACE) in hematopoiesis

The concept of a local bone marrow renin-angiotensin system (RAS) has been introduced and accumulating evidence suggests that the local RAS is actively involved in hematopoiesis. Angiotensin converting enzyme (ACE) is a key player in the RAS and makes the final effector angiotensin II. Besides angiotensin II, ACE also regulates a panel of bioactive peptides, such as substance P, Ac-SDKP and angiotensin 1–7. These peptides have also been individually reported in the regulation of pathways of hematopoiesis. In this setting, an ACE-regulated peptide network orchestrating hematopoiesis has emerged. Here, we focus on this peptide network and discuss the roles of ACE and its peptides in aspects of hematopoiesis. Special attention is given to the recent revelation that ACE is a bona fide marker of hematopoietic stem cells.Key words: hematopoiesis, myelopoiesis, angiotensin converting enzyme (ACE), angiotensin II, AT1 receptor, renin-angiotensin system (RAS), substance P, Ac-SDKP, angiotensin 1–7     

The peptide network regulated by angiotensin converting enzyme (ACE) in hematopoiesis

The concept of a local bone marrow renin-angiotensin system (RAS) has been introduced and accumulating evidence suggests that the local RAS is actively involved in hematopoiesis. Angiotensin converting enzyme (ACE) is a key player in the RAS and makes the final effector angiotensin II. Besides angiotensin II, ACE also regulates a panel of bioactive peptides, such as substance P, Ac-SDKP and angiotensin 1-7. These peptides have also been individually reported in the regulation of pathways of hematopoiesis. In this setting, an ACE-regulated peptide network orchestrating hematopoiesis has emerged. Here, we focus on this peptide network and discuss the roles of ACE and its peptides in aspects of hematopoiesis. Special attention is given to the recent revelation that ACE is a bona fide marker of hematopoietic stem cells.     

Procyanidin structure defines the extent and specificity of angiotensin I converting enzyme inhibition

Recent reports have shown a decrease in blood pressure associated with the consumption of flavanol-containing foods. However, the mechanism behind this effect is not yet known. Previously we demonstrated that the flavanol epicatechin and its related oligomers, the procyanidins, inhibit angiotensin I converting enzyme (ACE) activity in vitro. In this study, we further characterized epicatechin monomer, dimer, tetramer and hexamer ACE inhibitory effect, by performing fluorescence quenching and kinetic assays, using angiotensin I as substrate. Assessment of ACE activity in cultured human umbilical vein endothelial cells (HUVEC) indicated that the tetramer was the most active inhibitor decreasing the formation of angiotensin II by 52% (P<0.001). When ACE activity was measured using isolated rabbit lung ACE, dimer, tetramer and hexamer inhibited angiotensin II production at IC(50) values of 97.0, 4.4, and 8.2 microM, respectively. The quenching of ACE tryptophan fluorescence was assayed to evaluate the molecular interaction between ACE and procyanidins. The hexamer was the most active quencher decreasing ACE fluorescence by 56%, followed by the tetramer and the dimer, decreasing ACE fluorescence by 37% and 36%, respectively. ACE activity was evaluated in the presence of different concentrations of the ACE activator chloride ion (Cl(-)). Increased Cl(-) concentrations reduced IC(50) values for the dimer and tetramer. Finally, ACE inhibition was determined in the presence of different albumin concentrations. The presence of albumin did not reverse the ACE inhibition by dimer and tetramer, but decreased hexamer inhibition by 65%. In summary, the inhibitory effect of procyanidins on ACE and the extent of this inhibition were largely dependent on procyanidin structure. ACE inhibition by procyanidins in vivo might provide a mechanism to explain the benefits of flavonoid consumption on cardiovascular diseases.     

Lactic acid bacteria: inhibition of angiotensin converting enzyme in vitro and in vivo

A total of 26 strains of wild-type lactic acid bacteria, mainly belonging to Lactococcus lactis and Lactobacillus helveticus, were assayed in vitro for their ability to produce a milk fermentate with inhibitory activity towards angiotensin converting enzyme (ACE). It was clear that the test strains in this study, in general, produce inhibitory substances in varying amounts. Using a spectrophotometric assay based on amino group derivatization with ortho-phthaldialdehyde as a measure of relative peptide content, it was shown that there is a significant correlation between peptide formation and ACE inhibition, indicating that peptide measurement constitutes a convenient selection method. The effect of active fermentates on in vivo ACE activity was demonstrated in normotensive rats. The pressor effect of angiotensin I (0.3 μg/kg) upon intravenous injection was significantly lower when rats were pre-fed with milks fermented using two strains of Lactobacillus helveticus. An increased response to bradykinin (10 μg/kg, intravenously injected) was observed using one of these fermented milks. It is concluded that Lactobacillus helveticus produces substances which in vivo can give rise to an inhibition of ACE. The inhibition in vivo was low compared to what can be achieved with classical ACE inhibitors. The clinical relevance of this finding is discussed. This work is the first in which an effect of fermented milk on ACE in vivo has been demonstrated, measured as decreased ability to convert angiotensin I to angiotensin II. This revised version was published online in June 2006 with corrections to the Cover Date.     

Different distribution of two types of angiotensin II-generating enzymes in the aortic wall

Dog, monkey and human aortic tissues contained two distinct types of angiotensin II-generating enzymes; angiotensin converting enzyme (ACE) and chymostatin-sensitive angiotensin II-generating enzyme (CAGE). Endothelium, media and adventitia of canine thoracic aortae were separated using collagenase digestion, and determined for their ACE and CAGE activity. ACE activity was assayed by hippuryl-His-Leu cleavage. CAGE activity was estimated with ANG I as substrate in the presence of inhibitors of ACE and angiotensinases. His-Leu, the common product of both enzyme reactions, was fluorimetrically quantified after o-phthalaldehyde condensation. ACE localized mainly in endothelium, while CAGE distributed predominantly in adventitia. Similar results were obtained with human and monkey aortae. Such a contrasting distribution may indicate the distinct functional role of these two enzymes.     

Isolation and characterization of a novel angiotensin I-converting enzyme inhibitory peptide derived from the edible mushroom Tricholoma giganteum

The fruiting body of Tricholoma giganteum has many pharmaceutical uses and has long been utilized as a home remedy in Asia. This study describes the extraction and characterization of the first angiotensin I-converting enzyme (ACE) inhibitory peptide from T. giganteum. The maximum ACE inhibitory activity (IC50: 0.31 mg) was obtained when the fruiting body of T. giganteum was extracted with distilled water at 30 degrees C for 3 h. After the purification of ACE inhibitory peptides with ultrafiltration, Sephadex G-25 column chromatography, and reverse-phase HPLC, an active fraction with an IC50 of 0.04 mg and a yield of 0.3% was obtained. The ACE inhibitory peptide was a novel tripeptide, showing very low similarity to other ACE inhibitory peptide sequences, and was sequenced as Gly-Glu-Pro. The purified ACE inhibitor from T. giganteum competitively inhibited ACE, and it maintained inhibitory activity even after incubation with proteases. ACE inhibitor from T. giganteum showed a clear antihypertensive effect in spontaneously hypertensive rats (SHR), at a dosage of 1 mg/kg.     

Structure and physiological importance of angiotensin converting enzyme domains

Somatic angiotensin converting enzyme (ACE) consists of two homologous catalytic domains (N- and C-domain), exhibiting different biochemical properties. The catalytically active ACE isoforms consisted of just one domain have been also detected in mammals. Substantial progress in ACE domain research was achieved during the last years, when their crystal structures were determined. The crystal structures of domains in complex with diverse potent ACE inhibitors provided new insights into structure-based differences of the domain active sites. Physiological functions of ACE are not limited by regulation of the cardiovascular system. Recent evidence suggests that the ACE domains may be also involved into control of different physiological functions. The C-terminal catalytic domain plays an important role in the regulation of blood pressure: it catalyzes angiotensin I cleavage in vivo. The N-domain contributes to the processing of other bioactive peptides for which it exhibits high affinity. The role of the N-domain is not ultimately associated with functioning of the rennin-angiotensin system and it contributes processing of other bioactive peptides for which it exhibits high affinity (goralatide, luliberin, enkephalin heptapeptide, beta-amyloid peptide). Domain-selective inhibitors selectively blocking either the N- or C-domain of ACE have been developed.     

Characterization of new milk-derived inhibitors of angiotensin converting enzyme in vitro and in vivo

Inhibition of angiotensin converting enzyme (ACE) has been observed with a variety of different peptides, and peptide fragments with inhibitory capabilities have been identified within many different proteins, including milk proteins. The purpose of this study therefore was to identify new short peptides with inhibitory properties from the primary structure of milk proteins and to characterize them in vitro and in vivo, since no milk derived ACE inhibitors have previously been evaluated for their ability to inhibit ACE in vivo. In vitro, 8 of 9 dipeptides were found to be competitive inhibitors of ACE. The IC50 was significantly lower when an angiotensin I-like substrate was used, than when a bradykinin-like substrate was used. Using three different in vivo models for ACE inhibition, a very moderate effect was observed for three of the new peptides, but only for up to 6 or 12 minutes. Nothing was observed with two reference compounds that are reported to be hypotensive ACE-inhibitors derived from milk proteins. This raises the question whether the mechanism of hypotensive action is straightforward inhibition of ACE in vivo.     

Modulation of renin angiotensin system components by high glucose levels in the culture of collecting duct cells

Diabetes mellitus and its complications have become a major health concern in Western countries. Increased activity of the intrarenal renin–angiotensin system (RAS) contributes to diabetic nephropathy (DN). We previously reported that in mesangial cells, the high glucose concentration (HG) leads to upregulation of angiotensin-converting enzyme (ACE) messenger RNA, suggesting that ACE was modulated by angiotensin II (Ang II) release. However, this relation in the collecting duct has not yet been studied. We, therefore, aimed to evaluate RAS modulation in inner medullary collecting duct cells (IMCD) exposed to HG. The IMCD were divided into normal glucose (5 mM D -glucose, NG), high glucose (30 mM, HG), and mannitol (30 mM, M) groups. The cells were cultured 48 hr in their respective media. The intracellular and extracellular ACE activity was measured using hippuryl-His-Leu as substrate via a fluorimetric assay and expression was analyzed using western blot analysis. ACE activity, intracellular (27%) and extracellular (22%), was significantly lower in the HG group than in NG and M. ACE2 activity and Ang 1–7 levels were higher in the intracellular compartment. Our data suggest that the HG cannot modify ACE synthesis in IMCD cells but can modulate its activity. The decrease in ACE activity may result in decreased levels of Ang II to protect the IMCD against proliferative and inflammatory deleterious effects of this peptide. Conversely, the increase of ACE2 generating high levels of Ang 1–7, a vasodilator peptide, suggesting that this peptide can induce glucose uptake and protect cells against oxidative stress, which can elicit insulin resistance.     

Isolated liver granulomas of murine Schistosoma mansoni contain components of the angiotensin system

Angiotensin I (AI) and angiotensin II/III (AII/III) were detected by radioimmunoassay in homogenates of isolated liver granulomas from mice infected for 8 wk with Schistosoma mansoni. Angiotensin I converting enzyme (ACE) activity, which could be completely inhibited by captopril, a specific ACE inhibitor, was also present as determined by radioassay. Spontaneous angiotensin I-generating activity was detected in homogenates that received supplemental angiotensinogen (protein renin substrate). This activity was partly inhibited by pepstatin, an acid protease inhibitor, indicating the presence of angiotensinogenase(s). Trypsinization of homogenates resulted in some AI generation, which suggests that homogenates had AI precursor. Treatment of infected mice with MK421, another specific ACE inhibitor, decreased granuloma ACE activity and AII content and size. AII, and to a lesser extent AIII, inhibited mouse peritoneal macrophage migration in an in vitro assay. These data support the contention that components of the angiotensin system are in the granuloma and may serve a function in regulation of the inflammation.     

Identification of essential tyrosine and lysine residues in angiotensin converting enzyme: evidence for a single active site

Inactivation of rabbit lung angiotensin converting enzyme (ACE) by 1-fluoro-2,4-dinitrobenzene (Dnp-F) has been shown to be due primarily to the modification of a tyrosine residue [Bünning, P., Kleeman, S.G., & Riordan, J.F. (1990) Biochemistry (preceding paper in this issue)]. Rabbit testicular ACE is also inactivated by Dnp-F. The specific site of modification has been identified by peptide mapping of tryptic digests of the Dnp-modified protein. Two principal 340-nm-absorbing peaks, not observed with protein modified in the presence of inhibitor, have been characterized. Amino acid and sequence analyses show that these peptides contain two distinct residues that have been selectively modified. The sequence of the major (greater than 90% of the total) modified peptide is YVEFTNK with the Dnp group on tyrosine. The sequence of the second, minor peptide is KVQDLQR with the Dnp group on lysine. Identical peptides were obtained from Dnp-modified rabbit lung ACE. These modified amino acids correspond to residues 200 and 118, respectively, in testicular ACE (human enzyme numbering). Both peptides are present only in the carboxy-terminal half-domain of lung ACE, corresponding to residues 776 and 694, respectively. These results indicate that the Dnp-F sensitive, catalytically functional active site is located in the "testicular" half of lung ACE.     

Purification of angiotensin I converting enzyme from pig lung using concanavalin-A sepharose chromatography

Angiotensin I converting enzyme (ACE) plays a major role in blood pressure regulation, catalyzing the conversion of angiotensin I to the vasoconstrictor angiotensin II. In this report we describe a two-step affinity chromatography method for preparative purification of ACE from pig lung using Concanavalin-A Sepharose 4B and affinity chromatography on Lisinopril Sepharose 6B. The same purification scheme was used to obtain Cobalt-ACE, where zinc ion located at the active site is replaced by cobalt. Cobalt-ACE visible spectrum shows a characteristic broad peak from 500 to 600 nm. The shape and maximum absorptivity of this peak changes in presence of ACE inhibitors that bind at the catalytic site.     

Latent production of angiotensin I-converting enzyme inhibitors from buckwheat protein.

The latent production of angiotensin I-converting enzyme (ACE) Inhibitors from tartary buckwheat (BW) was investigated, and the peptides responsible for ACE inhibition characterized. Intact buckwheat was found to exhibit ACE inhibitory activity having an IC50 value of 3.0 mg/ml. The activity of the protein fraction (IC50: 0.36 mg protein/ml) was not enhanced by pepsin treatment. Pepsin, followed by chymotrypsin and trypsin hydrolysis, resulted in a significant increase in the ACE inhibitory activity (IC50: 0.14 mg protein/ml). The rutin contained in the buckwheat did not exhibit any ACE inhibition. A single oral administration of BW digest lowered the systolic blood pressure of a spontaneously hypertensive rat. Thus, BW proteins offer a potential resource for producing ACE inhibitory peptides during the digestion process. From the di-/tri-peptide fraction (DTPF) of the BW digest, inhibitory peptides were identified. The magnitude (%) of the total ACE inhibitory contribution of each identified peptide, relative to the overall inhibition of the DTPF, was about 41%.     

Differential response of human cardiac fibroblasts to angiotensin I and angiotensin II

The vasoactive peptide angiotensin II (Ang II) has been implicated as a mediator of myocardial fibrosis. We carried out a comparative investigation of the effects of Ang II and its precursor Ang I on collagen metabolism and proliferation in cultured human cardiac fibroblasts. Cardiac fibroblasts responded to both Ang I and Ang II with concentration-dependent increases in collagen synthesis but no proliferation. The stimulatory effect of Ang II was abolished by the AT(1) receptor antagonist losartan but not the AT(2) receptor antagonist PD123319. The response to Ang I was not affected by either antagonist, nor by the angiotensin-converting enzyme (ACE) inhibitor captopril. In conclusion, Both Ang I and Ang II stimulate collagen synthesis of human cardiac fibroblasts, the effect of Ang II occurring via the AT(1) receptor whilst Ang I appears to exert a direct effect through non-Ang II-dependent mechanisms. These results suggest distinct roles for angiotensin peptides in the development of cardiac fibrosis.     

Presence and comparison of angiotensin converting enzyme in commercial cell culture sera

This study was conducted to determine the presence of the angiotensin converting enzyme in commercial sera used in cell culture medium. The aim of the research was to bring the presence of proteinases (angiotensin converting enzyme) to cell culture users' knowledge and to give some data for solving problems about the development of peptides as useful drugs. The enzymes, purified from foetal bovine, adult bovine, foetal equine, adult equine, and human sera, showed molecular weights of about 170 kDa. Captopril and lisinopril inhibited enzyme activities at nanomolar concentrations. The enzymes were able to hydrolyze, with different efficiency, angiotensin I, bradykinin and epidermal mitosis inhibiting pentapeptide. The heat inactivation of commercial sera at 56 degrees C for 30 min showed a reduction of ACE activity of about 35-80%. Therefore, the presence of ACE activity in commercial sera can influence the activity of biological peptides tested on cell lines cultured "in vitro."     

Characterization of new antihypertensive angiotensin I-converting enzyme inhibitory peptides from Korean traditional rice wine

This study describes the characterization of a new angiotensin I-converting enzyme (ACE) inhibitory peptide from a Korean traditional rice wine. After purification of the ACE inhibitor peptides with ultrafiltration, Sephadex G-25 column chromatography, and successively C?? and SCX solid-phase extraction, reverse-phase HPLC, and size exculsion chromatography, two types of the purified ACE inhibitors with IC?? values of 0.34 mg/ml and 1.23 mg/ml were finally obtained. The two purified ACE inhibitors (F-1 and F-2) were found to have two kinds of novel oligopeptides, showing very little similarity to other ACE inhibitory peptide sequences. The amino acid sequences of the two purified oligopeptides were found to be Gln- Phe-Tyr-Ala-Val (F-1) and Ala-Gly-Pro-Val-Leu-Leu (F-2), and their molecular masses were estimated to be 468.7 Da (F-1) and 357.7 Da (F-2), respectively. They all showed a clear antihypertensive effect on spontaneously hypertensive rats at a dosage of 500 mg/kg.     

Size of the aliphatic chain of sodium houttuyfonate analogs determines their affinity for renin and angiotensin I converting enzyme

Sodium houttuyfonate analogs (SHAs), CH(3)-(CH(2))(n)-CO-CH(2)-CH(OH)SO(3)Na, (n=6-14) were synthesized and their molecular interactions with renin and angiotensin I converting enzyme (ACE) studied using fluorescence quenching techniques. Unlike renin, inhibition of ACE activity was not directly proportional to the aliphatic chain length of SHAs. Ability of SHAs to inhibit enzyme activities and quench protein fluorescence was greater with renin than with ACE. The presence of an ACE substrate (angiotensin I) did not reduce quenching ability of SHAs, suggesting that enzyme-inhibitor interactions did not involve the active site or the substrate was displaced by inhibitor molecules. The results showed that renin is a more sensitive target than ACE for the potential antihypertensive ability of SHAs.     

Isolation and characterization of an angiotensin converting enzyme substrate from vitellogenic ovaries of Neobellieria bullata

Vitellogenic ovaries of the gray fleshfly Neobellieria bullata contain a variety of unidentified substances that interact, either as a substrate or as an inhibitor, with angiotensin converting enzyme (ACE). We here report the isolation and characterization of the first ACE interactive compound hereof. This 1312.7 Da peptide with the sequence NKLKPSQWISL, is substrate to both insect and human ACE. It is a novel peptide that shows high sequence similarity to a sequence at the N-terminal part of dipteran yolk polypeptides (YPs). We propose to call it N. bullata ovary-derived ACE interactive factor or Neb-ODAIF. Both insect and human ACE hydrolyze Neb-ODAIF by sequentially cleaving off two C-terminal dipeptides. K(m) values of Neb-ODAIF and Neb-ODAIF(1-9) (NKLKPSQWI) for human somatic ACE (sACE) are 17 and 81 microM, respectively. Additionally, Neb-ODAIF(1-7) (NKLKPSQ) also interacts with sACE (K(m/i)=90 microM). These affinity-constants are in range with those of the physiological ACE substrates and suggest the importance of Neb-ODAIF and its cleavage products in the elucidation of the physiological role of insect ACE. Alternatively, they can serve as lead compounds in the development of new drugs against ACE-related diseases in humans.