Angiotensin I converting enzyme (ACE) inhibitory activity of hetero-chitooligosaccharides prepared from partially different deacetylated chitosans

Impacts of chitosan and its nanoformulations on the metabolic syndromes: a review

A significant public health issue worldwide is metabolic syndrome, a cluster of metabolic illnesses that comprises insulin resistance, obesity, dyslipidemia, hyperglycemia, and hypertension. The creation of natural treatments and preventions for metabolic syndrome is crucial. Chitosan, along with its nanoformulations, is an oligomer of chitin, the second-most prevalent polymer in nature, which is created via deacetylation. Due to its plentiful biological actions in recent years, chitosan and its nanoformulations have drawn much interest. Recently, the chitosan nanoparticle-based delivery of CRISPR-Cas9 has been applied in treating metabolic syndromes. The benefits of chitosan and its nanoformulations on insulin resistance, obesity, diabetes mellitus, dyslipidemia, hyperglycemia, and hypertension will be outlined in the present review, highlighting potential mechanisms for the avoidance and medication of the metabolic syndromes by chitosan and its nanoformulations.

Potential Medical Applications of Chitooligosaccharides

Chitooligosaccharides, also known as chitosan oligomers or chitooligomers, are made up of chitosan with a degree of polymerization (DP) that is less than 20 and an average molecular weight (MW) that is lower than 3.9 kDa. COS can be produced through enzymatic conversions using chitinases, physical and chemical applications, or a combination of these strategies. COS is of significant interest for pharmacological and medical applications due to its increased water solubility and non-toxicity, with a wide range of bioactivities, including antibacterial, anti-inflammatory, anti-obesity, neuroprotective, anticancer, and antioxidant effects. This review aims to outline the recent advances and potential applications of COS in various diseases and conditions based on the available literature, mainly from preclinical research. The prospects of further in vivo studies and translational research on COS in the medical field are highlighted.

The Role of Chitosan Oligosaccharide in Metabolic Syndrome: A Review of Possible Mechanisms

Metabolic syndrome, a cluster of metabolic disorders including central obesity, insulin resistance, hyperglycemia, dyslipidemia, and hypertension, has become a major public health problem worldwide. It is of great significance to develop natural products to prevent and treat metabolic syndrome. Chitosan oligosaccharide (COS) is an oligomer of chitosan prepared by the deacetylation of chitin, which is the second most abundant polymer in nature. In recent years, COS has received widespread attention due to its various biological activities. The present review will summarize the evidence from both in vitro and in vivo studies of the beneficial effects of COS on obesity, dyslipidemia, diabetes mellitus, hyperglycemia, and hypertension, and focus attention on possible mechanisms of the prevention and treatment of metabolic syndrome by COS.

The potential roles of chitosan oligosaccharide in prevention of kidney injury in obese and diabetic conditions

Obesity is closely associated with insulin resistance (IR). The most likely links between the two are obesity-mediated systemic low-grade chronic inflammation, endoplasmic reticulum stress and mitochondrial dysfunction, which are all known to contribute to the development of type 2 diabetes (T2DM) and eventually diabetic nephropathy (DN). Chitosan oligosaccharide (COS) is an oligomer of chitosan prepared by the deacetylation of chitin commonly found in exoskeletons of crustaceans such as shrimp and crab as well as the cell walls of fungi. COS has various biological effects including lipid lowering, anti-inflammation, anti-diabetes, and anti-oxidant effects. Therefore, COS is a potential new therapeutic agent for treatment of the obesity-induced DN condition. It is an abundant natural polymer and therefore freely available. This review includes information regarding the relationship between obesity, IR, T2DM, and DN as well as the potential usefulness of COS in controlling lipid and cholesterol metabolism, T2DM and kidney injury models in both in vivo and in vitro studies. However, evidence is limited regarding the effect of COS on the DN model. Further studies, especially in obesity-induced DN, are needed to support the mechanisms proposed in this review.

Chitosan and Derivatives: Bioactivities and Application in Foods

Chitosan is a biodegradable, biocompatible, and nontoxic aminopolysaccharide. This review summarizes and discusses the structural modifications, including substitution, grafting copolymerization, cross-linking, and hydrolysis, utilized to improve the physicochemical properties and enhance the bioactivity and functionality of chitosan and related materials. This manuscript also reviews the current progress and potential of chitosan and its derivatives in body-weight management and antihyperlipidemic, antihyperglycemic, antihypertensive, antimicrobial antioxidant, anti-inflammatory, and immunostimulatory activities as well as their ability to interact with gut microbiota. In addition, the potential of chitosan and its derivatives as functional ingredients in food systems, such as film and coating materials, and delivery systems is discussed. This manuscript aims to provide up-to-date information to stimulate future discussion and research to promote the value-added utilization of chitosan in improving the safety, quality, nutritional value and health benefits, and sustainability of our food system while reducing the environmental hazards.

Phytochemical Analysis and Evaluation of Antioxidant and Biological Activities of Extracts from Three Clauseneae Plants in Northern Thailand

This study established the DNA barcoding sequences (matK and rbcL) of three plant species identified in the tribe Clauseneae, namely Clausena excavata, C. harmandiana and Murraya koenigii. The total phenolic and total flavonoid contents, together with the biological activities of the derived essential oils and methanol extracts, were also investigated. Herein, the success of obtaining sequences of these plant using two different barcode genes matK and rbcL were 62.5% and 100%, respectively. Both regions were discriminated by around 700 base pairs and these had resemblance with those of the Clausenae materials earlier deposited in Genbank at a 99–100% degree of identity. Additionally, the use of matK DNA sequences could positively confirm the identity as monophyletic. The highest total phenolic and total flavonoid content values (p < 0.05) were observed in the methanol extract of M. koenigii at 43.50 mg GAE/g extract and 66.13 mg QE/g extract, respectively. Furthermore, anethole was detected as the dominant compound in C. excavata (86.72%) and C. harmandiana (46.09%). Moreover, anethole (26.02%) and caryophyllene (21.15%) were identified as the major phytochemical compounds of M. koenigii. In terms of the biological properties, the M. koenigii methanol extract was found to display the greatest amount of antioxidant activity (DPPH; IC₅₀ 95.54 µg/mL, ABTS value 118.12 mg GAE/g extract, FRAP value 48.15 mg GAE/g extract), and also revealed the highest α-glucosidase and antihypertensive inhibitory activities with percent inhibition values of 84.55 and 84.95. Notably, no adverse effects on human peripheral blood mononuclear cells were observed with regard to all of the plant extracts. Furthermore, M. koenigii methanol extract exhibited promise against human lung cancer cells almost at 80% after 24 h and 90% over 48 h.

Enzymatic Modifications of Chitin, Chitosan, and Chitooligosaccharides

Chitin and its N-deacetylated derivative chitosan are two biological polymers that have found numerous applications in recent years, but their further deployment suffers from limitations in obtaining a defined structure of the polymers using traditional conversion methods. The disadvantages of the currently used industrial methods of chitosan manufacturing and the increasing demand for a broad range of novel chitosan oligosaccharides (COS) with a fully defined architecture increase interest in chitin and chitosan-modifying enzymes. Enzymes such as chitinases, chitosanases, chitin deacetylases, and recently discovered lytic polysaccharide monooxygenases had attracted considerable interest in recent years. These proteins are already useful tools toward the biotechnological transformation of chitin into chitosan and chitooligosaccharides, especially when a controlled non-degradative and well-defined process is required. This review describes traditional and novel enzymatic methods of modification of chitin and its derivatives. Recent advances in chitin processing, discovery of increasing number of new, well-characterized enzymes and development of genetic engineering methods result in rapid expansion of the field. Enzymatic modification of chitin and chitosan may soon become competitive to conventional conversion methods.

New insights into the role of chitosan oligosaccharide in enhancing growth performance, antioxidant capacity, immunity and intestinal development of weaned pigs

Chitosan oligosaccharide (COS), an oligomer ofd-glucosamine, is a vital growth stimulant in the pig industry.

Flavonoids-Rich Orthosiphon stamineus Extract as New Candidate for Angiotensin I-Converting Enzyme Inhibition: A Molecular Docking Study

This study aims to evaluate the in vitro angiotensin-converting enzyme (ACE) inhibition activity of different extracts of Orthosiphon stamineus (OS) leaves and their main flavonoids, namely rosmarinic acid (RA), sinensetin (SIN), eupatorin (EUP) and 3′-hydroxy-5,6,7,4′-tetramethoxyflavone (TMF). Furthermore, to identify possible mechanisms of action based on structure–activity relationships and molecular docking. The in vitro ACE inhibition activity relied on determining hippuric acid (HA) formation from ACE-specific substrate (hippuryl-histidyl-leucine (HHL)) by the action of ACE enzyme. A High Performance Liquid Chromatography method combined with UV detection was developed and validated for measurement the concentration of produced HA. The chelation ability of OS extract and its reference compounds was evaluated by tetramethylmurexide reagent. Furthermore, molecular docking study was performed by LeadIT-FlexX: BioSolveIT’s LeadIT program. OS ethanolic extract (OS-E) exhibited highest inhibition and lowest IC₅₀ value (45.77 ± 1.17 µg/mL) against ACE compared to the other extracts. Among the tested reference compounds, EUP with IC₅₀ 15.35 ± 4.49 µg/mL had highest inhibition against ACE and binding ability with Zn (II) (56.03% ± 1.26%) compared to RA, TMF and SIN. Molecular docking studies also confirmed that flavonoids inhibit ACE via interaction with the zinc ion and this interaction is stabilized by other interactions with amino acids in the active site. In this study, we have demonstrated that changes in flavonoids active core affect their capacity to inhibit ACE. Moreover, we showed that ACE inhibition activity of flavonoids compounds is directly related to their ability to bind with zinc ion in the active site of ACE enzyme. It was also revealed that OS extract contained high amount of flavonoids other than RA, TMF, SIN and EUP. As such, application of OS extract is useful as inhibitors of ACE.

Chitosan oligosaccharide: Biological activities and potential therapeutic applications

Chitosan oligosaccharide (COS) is an oligomer of β-(1➔4)-linked d-glucosamine. COS can be prepared from the deacetylation and hydrolysis of chitin, which is commonly found in the exoskeletons of arthropods and insects and the cell walls of fungi. COS is water soluble, non-cytotoxic, readily absorbed through the intestine and mainly excreted in the urine. Of particular importance, COS and its derivatives have been demonstrated to possess several biological activities including anti-inflammation, immunostimulation, anti-tumor, anti-obesity, anti-hypertension, anti-Alzheimer's disease, tissue regeneration promotion, drug and DNA delivery enhancement, anti-microbial, anti-oxidation and calcium-absorption enhancement. The mechanisms of actions of COS have been found to involve the modulation of several important pathways including the suppression of nuclear factor kappa B (NF-κB) and mitogen-activated protein kinases (MAPK) and the activation of AMP-activated protein kinase (AMPK). This review summarizes the current knowledge of the preparation methods, pharmacokinetic profiles, biological activities, potential therapeutic applications and safety profiles of COS and its derivatives. In addition, future research directions are discussed.

Identification of bioactive peptide from Oreochromis niloticus skin gelatin

Fish skin, one type of wastes generated from Nile tilapia processing, is still a good source of collagen and gelatin. Bioactive peptides can be obtained from Nile tilapia skin gelatin by trypsin digestion. Trypsin hydrolysate was subsequently purified by gel filtration chromatography. Trypsin A fraction showed the greatest reducing power (5.138 ± 1.060 μM trolox/mg peptide) among all hydrolysate fractions, while trypsin B fraction from gel filtration column was found to exhibit the best radical scavenging and angiotensin-I-converting enzyme (ACE) inhibitory activities 8.16 ± 2.18 μg trolox/mg peptide and 59.32 ± 9.97 % inhibition, respectively. The most active fraction was subjected to MALDI-TOF/TOF MS/MS. After annotation by Mascot sequence matching software (Matrix Science) with Ludwig NR Database, two peptide sequences were identified; GPEGPAGAR (MW 810.87 Da) and GETGPAGPAGAAGPAGPR (MW 1490.61 Da). The docking analysis suggested that the shape of the shorter peptide may be slightly more proper, to fit into the binding cleft of the ACE. However, the binding affinities calculated from the docking showed no significant difference between the two peptides. In good agreement with the in silico data, results from the in vitro ACE inhibitory activity with synthetic peptides also showed no significant difference. Both peptides are thus interesting novel candidates suitable for further development as ACE inhibitory and antioxidant agents from the natural source.

Antioxidant and antihypertensive activity of gelatin hydrolysate from Nile tilapia skin

Fish skin, a by-product from fish processing industries, still contains a significant amount of protein-rich material. Gelatin was extracted from Nile tilapia skin with the yield 20.77 ± 0.80 % wet weight. Gelatin was then separately hydrolyzed by proteases, including bromelain, papain, trypsin, flavourzyme, alcalase and neutrase. Low molecular weight gelatin hydrolysate (<10 kDa) has a great potential as an antioxidant agent. Flavourzyme hydrolysate has potent activity on ABTS radical scavenging (1,413.61 ± 88.74 μg trolox/mg protein) and also inhibits the oxidation of linoleic acid at a high level (59.74 ± 16.57 % inhibition). The greatest reducing power is in alcalase hydrolysate (4.951 ± 1.577 mM trolox/mg protein). While, bromelain hydrolysate has the highest ferrous ion chelating activity (86.895 ± 0.061 %). Evaluation of the angiotensin-I-converting enzyme's inhibitory activity indicates that all hydrolysates have great potency as an antihypertensive agent. All studied tilapia skin gelatin hydrolysates contain potent antioxidant and anti-hypertensive effects.

Chitooligosaccharide and its derivatives: preparation and biological applications

Chitin is a natural polysaccharide of major importance. This biopolymer is synthesized by an enormous number of living organisms; considering the amount of chitin produced annually in the world, it is the most abundant polymer after cellulose. The most important derivative of chitin is chitosan, obtained by partial deacetylation of chitin under alkaline conditions or by enzymatic hydrolysis. Chitin and chitosan are known to have important functional activities but poor solubility makes them difficult to use in food and biomedicinal applications. Chitooligosaccharides (COS) are the degraded products of chitosan or chitin prepared by enzymatic or chemical hydrolysis of chitosan. The greater solubility and low viscosity of COS have attracted the interest of many researchers to utilize COS and their derivatives for various biomedical applications. In light of the recent interest in the biomedical applications of chitin, chitosan, and their derivatives, this review focuses on the preparation and biological activities of chitin, chitosan, COS, and their derivatives.

Inhibition of angiotensin-converting enzyme by aqueous extract of tomato

PURPOSE

To investigate the presence of anti-angiotensin converting enzyme (ACE) factors in aqueous extract of tomato.

METHODS

The bio-guided fractionation of the aqueous extract of tomato produced a sugar-free, heat-stable fraction with molecular mass <1,000 Da from tomatoes. The sugar-free tomato extract (TE) was tested for its anti-ACE activity using human plasma and rabbit lung pure ACE. In addition, its effect on human platelet aggregation induced by ADP, collagen or arachidonic acid was determined. The mechanism of platelet inhibitory action of TE was investigated by measuring platelet factor 4 (PF4) release and cAMP synthesis by platelets.

RESULTS

Typically, 100 g tomatoes produced 72.2 ± 4.7 mg of TE. This extract inhibited both platelet aggregation and plasma ACE activity in a dose-dependent manner. It inhibited platelet aggregation in response to ADP, collagen or arachidonic acid, and inhibitory action was mediated in part by reducing platelet PF4 release and by stimulating cAMP synthesis. The IC50 value of TE for ADP-induced platelet aggregation was 0.4 ± 0.02 mg/ml, whereas the IC50 value for ACE enzyme inhibition was 1.40 ± 0.04 mg/ml. Both the TE and commercially available sugar-free TE, Fruitflow(®)-2 had similar amount of catechin, and also had equal inhibitory potencies against platelet aggregation and plasma ACE activity.

CONCLUSION

Together these data indicate that aqueous extract of tomatoes contain anti-ACE factors in addition to previously described anti-platelet factors.

Influence of the physico-chemical characteristics of chito-oligosaccharides (COS) on antioxidant activity

Chito-oligosaccharides (COS) are being used as important functional materials for many applications due to their bioactivities. The aim of this research has been to assess the relationship between the physico-chemical characteristics, average molecular weight (Mw), acetylation degree (DA), polymerization degree (DP) and specially sequence composition determined by MALDI-TOF MS and the antioxidant properties of COS. These oligosaccharides were obtained by enzymatic depolymerization with chitosanase and lysozyme using a specific chitosan and its reacetylated product. The COS fraction below 5 kDa obtained from chitosanase depolymerization showed the highest capacity to scavenge DPPH radicals and to reduce Fe(3+). A correlation was found between the relative amount of molecules with a given A/D (acetylated vs deacetylated units) ratio within the COS and their antioxidant activity, which could be used to predict the antioxidant behavior of a fraction of chito-oligosaccharides.

The changes of calretinin immunoreactivity in paraquat-induced nephrotoxic rats

Calcium-binding proteins are present in the kidneys: calbindin D-28k in the distal tubules and calretinin in the proximal tubules. Since paraquat causes degeneration in the brush border-bearing proximal tubule cells in rat kidneys, we investigated the changes of calretinin immunoreactivity in the proximal tubule cells of paraquat-induced nephrotoxicity in experimental male Sprague-Dawley rats following chitosan oligosaccharide pretreatment to investigate its protective properties. Paraquat (60 mg/kg) was administered intraperitoneally with or without chitosan oligosaccharide (500 mg/kg, p.o.) pretreatment. The changes on calretinin were compared with those of calbindin D-28k by immunohistochemistry and Western Blot analysis. Calretinin was immunolocalized on the apical surface of proximal tubule cells in the deeper cortex of normal kidney, and disappeared after paraquat administration with minor changes of calbindin D-28k immunoreactivity in the distal tubules and collecting ducts. Chitosan oligosaccharide pretreatment caused increased expression of calretinin and calbindin D-28k before paraquat injection and helped preserve proximal tubules after paraquat treatment. However, Western blot analysis on calretinin and calbindin D-28k could not explain the degeneration of the proximal tubule cells in paraquat-induced nephrotoxicity. These findings suggested that calretinin is a possible and more useful histopathological marker for proximal tubule cells in paraquat-induced nephrotoxic rats.

Inhibition of angiotensin-converting enzyme activity by flavonoids: structure-activity relationship studies

Previous studies have demonstrated that certain flavonoids can have an inhibitory effect on angiotensin-converting enzyme (ACE) activity, which plays a key role in the regulation of arterial blood pressure. In the present study, 17 flavonoids belonging to five structural subtypes were evaluated in vitro for their ability to inhibit ACE in order to establish the structural basis of their bioactivity. The ACE inhibitory (ACEI) activity of these 17 flavonoids was determined by fluorimetric method at two concentrations (500 µM and 100 µM). Their inhibitory potencies ranged from 17 to 95% at 500 µM and from 0 to 57% at 100 µM. In both cases, the highest ACEI activity was obtained for luteolin. Following the determination of ACEI activity, the flavonoids with higher ACEI activity (i.e., ACEI >60% at 500 µM) were selected for further IC₅₀ determination. The IC₅₀ values for luteolin, quercetin, rutin, kaempferol, rhoifolin and apigenin K were 23, 43, 64, 178, 183 and 196 µM, respectively. Our results suggest that flavonoids are an excellent source of functional antihypertensive products. Furthermore, our structure-activity relationship studies show that the combination of sub-structures on the flavonoid skeleton that increase ACEI activity is made up of the following elements: (a) the catechol group in the B-ring, (b) the double bond between C2 and C3 at the C-ring, and (c) the cetone group in C4 at the C-ring. Protein-ligand docking studies are used to understand the molecular basis for these results.

The role of apurinic/apyrimidinic endonuclease on the progression of streptozotocin-induced diabetic nephropathy in rats

Apurinic/apyrimidinic endonuclease (APE) acts as a regulator of p53 or vice versa in the cellular response to oxidative stress. Since oxidative stress-induced apoptosis is suggested in the pathophysiology of diabetic nephropathy, we proposed that APE may have a feasible role in the progression of diabetic complications. We investigated the interrelationship between APE and p53 in streptozotocin-induced diabetic rat kidneys. Variable parameters on kidneys were checked 12 weeks after streptozotocin administration with or without chitosan oligosaccharide (COS) treatment. Streptozotocin administration caused changes as seen in early diabetic nephropathy with increased kidney size, increased p53, decreased APE, and increased cleaved caspase-3. COS was not suspected as being detrimental to renal measurements, and caused the augmentation of APE after streptozotocin administration. The augmented APE, in association with increased p53, suppressed cleaved caspase-3. 8-OHdG was mainly immunolocalized in the distal tubules, but also in the proximal tubules after streptozotocin administration without COS treatment, while APE was observed in proximal tubules in all groups. These results suggested that p53-dependent apoptosis resulting in suppressed APE might be an underlying mechanism of streptozotocin-induced nephropathy.

WITHDRAWN: Bioactive peptides derived from meat proteins

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β-secretase inhibitory activity of phenolic acid conjugated chitooligosaccharides

Eight kinds of phenolic acid conjugated chitooligosaccharides (COSs) were synthesized using hydroxyl benzoic acid and hydroxyl cinnamic acid. These phenolic acid conjugated-COSs with different substitution groups, including p-hydroxyl, 3,4-dihydroxyl, 3-methoxyl-4-hydroxyl and 3,5-dimethoxyl-4-hydroxy groups, were evaluated for their inhibitory activities against β-site amyloid precursor protein (APP)-cleaving enzyme (BACE) and inhibited BACE with a ratio of 50.8%, 74.8%, 62.1%, 64.8% and 42.6%, respectively at the concentration of 1,000 μg/mL. BACE is a critical component to reduce the levels of Aβ amyloid peptide in Alzheimer's disease (AD) which is based on the amyloid cascade theory in the brain, as this protease initiates the first step in Aβ production. Among them, Caffeic acid conjugated-COS (CFA-COS) was further analysed to determine mode of inhibition of BACE and it showed non-competitive inhibition. Hence in this study, we suggest that CFA-COS derivatives have potential to be used as novel BACE inhibitors to reduce the risk of AD.

Membrane bioreactor technology for the development of functional materials from sea-food processing wastes and their potential health benefits

Sea-food processing wastes and underutilized species of fish are a potential source of functional and bioactive compounds. A large number of bioactive substances can be produced through enzyme-mediated hydrolysis. Suitable enzymes and the appropriate bioreactor system are needed to incubate the waste materials. Membrane separation is a useful technique to extract, concentrate, separate or fractionate the compounds. The use of membrane bioreactors to integrate a reaction vessel with a membrane separation unit is emerging as a beneficial method for producing bioactive materials such as peptides, chitooligosaccharides and polyunsaturated fatty acids from diverse seafood-related wastes. These bioactive compounds from membrane bioreactor technology show diverse biological activities such as antihypertensive, antimicrobial, antitumor, anticoagulant, antioxidant and radical scavenging properties. This review discusses the application of membrane bioreactor technology for the production of value-added functional materials from sea-food processing wastes and their biological activities in relation to health benefits.

Chitosanase Immobilization Using Composite Carrier of Sodium Alginate/Cellulose

Sodium alginate and cellulose were combined to use as a composite carrier forPseudomonassp. CUY8 chitosanase immobilization. For free enzyme, immobilized chitosanase within different carriers of sodium alginate and composite carrier, Km values were 1.919, 9.27, and 5.91µM, respectively. The increase of Km value of immobilized chitosanase with composite carrier was lower than that of single carrier. This indicates that the composite carrier of sodium alginate/ cellulose improves the affinity of chitosanase to the substrate. Furthermore, chitosanase immobilization using composite carrier shows improved thermal stability ranging from 65 to 80°C, and enzyme residual activities were more than 75%. The effects of ratio of enzyme to substrate on chitooligosaccharides (COS) production were determined, and COS yields with composite carrier was 68% at optimum ratio of 1:1. Since the immobilization process using composite carrier is simple and effective, this method could be used for the industrial production of COS.

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.

A rapid assay for angiotensin-converting enzyme activity using ultra-performance liquid chromatography-mass spectrometry

Angiotensin-converting enzyme (ACE) plays an important role in the renin-angiotensin system and ACE activity is usually assayed in vitro by monitoring the transformation from a substrate to the product catalyzed by ACE. A rapid and sensitive analysis method or ACE activity by quantifying simultaneously the substrate hippuryl-histidyl-leucine and its product hippuric acid using an ultra-performance liquid chromatography coupled with electrospray ionization-mass spectrometry (UPLC-MS) was first developed and applied to assay the inhibitory activities against ACE of several natural phenolic compounds. The established UPLC-MS method showed obvious advantages over the conventional HPLC analysis in shortened running time (3.5 min), lower limit of detection (5 pg) and limit of quantification (18 pg), and high selectivity aided by MS detection in selected ion monitoring (SIM) mode. Among the six natural products screened, five compounds, caffeic acid, caffeoyl acetate, ferulic acid, chlorogenic acid and resveratrol indicated potent in vitro ACE inhibitory activity with IC(50) values of 2.527 +/- 0.032, 3.129 +/- 0.016, 10.898 +/- 0.430, 15.076 +/- 1.211 and 6.359 +/- 0.086 mm, respectively. A structure-activity relationship estimation suggested that the number and the situation of the hydroxyls on the benzene rings and the acrylic acid groups may play the most predominant role in their ACE inhibitory activity.

Angiotensin-I-converting enzyme (ACE) inhibitors from marine resources: prospects in the pharmaceutical industry

Hypertension or high blood pressure is one of the major independent risk factors for cardiovascular diseases. Angiotensin-I-converting enzyme (EC 3.4.15.1; ACE) plays an important physiological role in regulation of blood pressure by converting angiotensin I to angiotensin II, a potent vasoconstrictor. Therefore, the inhibition of ACE activity is a major target in the prevention of hypertension. Recently, the search for natural ACE inhibitors as alternatives to synthetic drugs is of great interest to prevent several side effects and a number of novel compounds such as bioactive peptides, chitooligosaccharide derivatives (COS) and phlorotannins have been derived from marine organisms as potential ACE inhibitors. These inhibitory derivatives can be developed as nutraceuticals and pharmaceuticals with potential to prevent hypertension. Hence, the aim of this review is to discuss the marine-derived ACE inhibitors and their future prospects as novel therapeutic drug candidates for treat hypertension.

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).

Preparation, characterization and applications of low-molecular-weight alginate-oligochitosan nanocapsules

The development of drug-delivering nanoparticles from natural materials for various biomedical applications is an area of great promise. However, the contradictory data on their uncontrollable diameter, unstable structure and toxic effects, highlight the need to study their preparation, characterization and cytotoxic effects in cells. In this work, nanocapsules are made from a type of W/O microemulsion system with low-molecular-weight alginate (LMWALG) and oligochitosan (OCS). The particles possess excellent biocompatibility and good biodegradability. The size of capsules is controlled and optimized by carefully adjusting the molecular weight and concentration of LMWALG and OCS. We found, from orthogonal experiments, the encapsulation time leading to a uniform size distribution with an average diameter of 136 nm. Furthermore, we found that molecular weights of LMWALG and OCS significantly influence the stability and size of capsules. The optimized nanocapsules are further used to study the drug release of BSA. Results show that the efficiency of encapsulation approximately reaches 88.4% and the concentration of BSA in phosphate-buffered solution (PBS, pH = 7.4) is well maintained at a level of 35 to 40% from 12 h to 48 h, due to the stable and slow degradation of the nanocapusules. The biocompatibility of LMWALG/OCS nanocapsules is cross-examined by cytotoxicity experiments and acute systemic toxicological tests, and they were found to enhance the survival rate of the cells from 80.30 to 95.39% in 7 days. The synthesized nanocapsules exhibit high biocompatibility, non-toxicity, biodegradation, and uniform size, providing a new potential candidate for drug releases in clinic experiments.