Dual inhibition of metallopeptidases ACE and NEP by extracts, and iridoids from Ligustrum vulgare L

Antioxidant activity and inhibitory effects on angiotensin I-converting enzyme and α-glucosidase of trans-p-coumaroyl-secologanoside (comselogoside) and its inclusion complex with β-cyclodextrin. Bioaccessibility during simulated in vitro gastrointestinal digestion

This study explored the impact of complexing comselogoside (COM) with β-cyclodextrin (β-CD) on antioxidant capacity and investigated its in vitro inhibitory effects against α-glucosidase and angiotensin I-converting enzyme (ACE). The COM: β-CD complex in three molar ratios (1:2, 1:1, and 2:1) showed significantly higher antioxidant activity compared to free COM, assessed by DPPH and ferric reducing power assays. COM exhibited weak to moderate α-glucosidase inhibition (IC50 1221 μM) and notable ACE inhibition (IC50 119.4 μM). Encapsulation improved ACE inhibition notably for the 1:2 and 2:1 M ratios. The cleavage of secoiridoid moiety of COM by β-glucosidase further enhanced ACE inhibition from IC50 of 63.91 to 41.75 μg/mL in the hydrolysed mixture. In vitro gastrointestinal digestion revealed 34-40% bioaccessibility of COM and its β-CD complex. This study demonstrates the potential of encapsulated COM as a functional food or supplement for preventing and treating diabetes, hypertension, and oxidative stress-related diseases.

Oleacein: A comprehensive review of its extraction, purification, absorption, metabolism, and health effects

Extra virgin olive oil (EVOO) consumption reduces the risk of cardiovascular disease in high-risk groups and the polyphenols in EVOO play an important health effect on it. As one of the most abundant polyphenols in EVOO, oleacein (OLEA) has many health benefits. However, there is no review article that focus comprehensively on OLEA, and most articles have limited data and information on OLEA. The purpose of this review is to summarize the results of all available studies, to present and compare the main traditional and novel techniques for the extraction and isolation and purification of OLEA, to elucidate the absorption and metabolic pathways of OLEA, and finally, to illustrate the health-promoting properties. Hopefully, this review can promote the use of OLEA in functional foods and therapeutic fields.

Hydroxytyrosol oleate: A promising neuroprotective nanocarrier delivery system of oleuropein and derivatives

Olive Phenols (OPs) are known to be potent antioxidants and possess various bioactivities and health benefits. Epidemiological studies suggested that consumption of olive oil reduces the risk of different diseases exerting a protective effect against certain malignant tumors (prostate, breast, digestive tract, endothelium, etc.). However, extremely low absorption rate of olive phenolic compounds restricts their bioactivity. In this context, solid lipid nanoparticles (SLNs) are a promising solution because they provide higher drug stability and can incorporate both lipophilic and hydrophilic drugs. Interesting experimental results have been obtained using hydroxytyrosol oleate (HtyOle) as a main component of a nanoparticle delivery system containing oleuropein (OL), oleuropein aglycone (3,4-DHPEA-EA), or hydroxytyrosol itself (Hty). In this work, hydroxytyrosol oleate (HtyOle) and hydroxytyrosol oleate (HtyOle)-based solid lipid nanoparticles were prepared and characterized. In addition, we evaluatedin vitro their antioxidant activity by DPPH assays and by ROS formation using the SH-SY5Y cell line.

Effects of oleuropein on rat's atria and thoracic aorta: a study of antihypertensive mechanisms

Oleuropein (OLE) is the main bioactive ingredient in the leaves of the olive plant Olea europaea L. (Oleaceae), which has proven beneficial due to the antiinflammatory, antiatherogenic, anticancer, antimicrobial, and antiviral effects. This study aimed to investigate the antihypertensive and vasodilator potential of OLE by analyzing its acute effects on spontaneous atrial contractions and vasomotor responses of the isolated thoracic aorta in rats. We showed that the application of OLE induces negative chronotropic and inotropic effects on the heart. OLE also causes mild aortic vasodilation given that the maximal reduction in tension of intact aortic rings precontracted with phenylephrine was approximately 30%. This vasodilation is likely dependent on the nitric oxide released from the endothelium based on the effect obtained on denuded and phenylephrine precontracted aortic rings and responses reordered following vasoconstriction induced by high concentrations of K⁺ and heparin. Our findings provide a basis for further testing of OLE cardiovascular effects, which may lead to subsequent clinical research for its application in the treatment of hypertension and heart disease.

Diversity of secoiridoid glycosides in leaves of UK and Danish ash provide new insight for ash dieback management

Secoiridoid glycosides are anti-feeding deterrents of the Oleaceae family recently highlighted as potential biomarkers in Danish ash trees to differentiate between those tolerant and susceptible to the fungal disease ash dieback. With the knowledge that emerald ash borer has recently entered Europe from Russia, and that extensive selection trials are ongoing in Europe for ash dieback tolerant European ash (Fraxinus excelsior), we undertook comprehensive screening of secoiridoid glycosides in leaf extracts of trees tolerant and susceptible to ash dieback sampled from sites in the UK and Denmark. Here we report an unexpected diversity of secoiridoid glycosides in UK trees and higher levels of secoiridoid glycosides in the UK sample group. While it is unlikely that secoiridoid glycosides generally can serve as reliable markers for ash dieback susceptibility, there are differences between tolerant and susceptible groups for specific secoiridoids. We predict that the high levels-and structural diversity-of secoiridoids present in the UK group may provide a robust reservoir of anti-feeding deterrents to mitigate future herbivore threats such as the Emerald ash borer.

In vitro α-amylase and pancreatic lipase inhibitory activity of Cornus mas L. and Cornus alba L. fruit extracts

Less-common fruits from Cornus spp. (Cornaceae), also named dogwoods, have shown antidiabetic, antibacterial and anti-allergic properties and are thus considered a source of phytochemicals that are beneficial to human health. The study aimed to compare the chemical compositions of the aqueous and ethanolic extracts of lyophilized fresh-picked and commercially available dried fruits of Cornus mas (Cm, cornelian cherry) and Cornus alba (Ca) fruits using HPLC-DAD-MS/MS method. Simultaneously, the a-amylase and pancreatic lipase (PL) inhibitory activities of the prepared extracts were compared by in vitro fluorescence assay based on the kinetic hydrolysis of starch or oleate ester of 4-methylumbelliferone (MUO), respectively. Additionally, a bio-assay guided identification of compounds potentially responsible for the inhibition of pancreatic enzymes was performed. Iridoids (loganic acid, cornuside) and anthocyanins (pelargonidin 3-O-galactoside) were identified in the Cmfruit extracts. Flavonoids, such as quercetin and kaempferol derivatives, were detected in the Ca fruit extracts. The chromatographic separation of the constituents of Ca fruit provided a fraction containing phenolic acids derivatives, which inhibited PL activity by 69.9 ± 4.5% at a concentration of 7.5 μg·mL⁻¹. The IC₅₀ of hydroxytyrosol glucoside, isolated from the most active Ca fraction, was 0.99 ± 0.10 mg·mL⁻¹ indicating other constituents responsible for the fraction activity. The most active subfraction from Cm fruit (7.5 μg·mL⁻¹), which inhibited PL activity by 28.3 ± 1.5%, contained pelargonidin 3-O-galactoside. Loganic acid and cornuside in highly pure form did not inhibit lipase activity. The phytochemical constituents of Cm, and particularly of Ca fruit extracts, can inhibit pancreatic enzymes and thus might be considered effective preparations in the prevention and control of hyperlipidemia related diseases.

Inhibitory effect of Ligustrum vulgare leaf extract on the development of neuropathic pain in a streptozotocin-induced rat model of diabetes

BACKGROUND

Chronic hyperalgesia and allodynia associated with progressive damage of peripheral neurons are the most prevalent complications of diabetes mellitus. Plants belonging to the family of Oleaceae were traditionally used in folk medicine for the management of diabetes.

HYPOTHESIS/PURPOSE

The aim of this study was to investigate whether an aqueous extract from the leaves of Ligustrum vulgare (common privet) could be useful to target neuropathic pain in a rat streptozotocin (STZ) model of diabetes.

METHODS

The chemical composition of the aqueous extract from privet leaf was characterized with the UHPLC-DAD-MS method and the analytical quantification of its constituents was performed with HPLC-DAD. Mechanical hyperalgesia and allodynia were evaluated with the Randall-Selitto and von Frey tests.

RESULTS

Our investigation revealed the presence of secoiridoids: oleacein (23.48 ± 0.87 mg/g), oleocanthal (8.44 ± 0.08 mg/g), oleuropein (1.50 ± 0.01 mg/g), as well as phenylpropanoids: echinacoside (6.46 ± 0.07 mg/g), verbascoside (4.03 ± 0.04 mg/g) and p-coumaroyl glucarates in the dried aqueous extract of privet leaves. Behavioral data indicated that chronic intraperitoneal administration of the extract (50-200 mg/kg) for 21 days resulted in a decrease in diabetes-induced hyperalgesia and allodynia. Blood glucose levels remained unaltered, while body weight and water intake decreased significantly.

CONCLUSION

The aqueous privet leaf extract could serve useful in facilitating treatment of painful diabetic neuropathy. Additionally, the study showed that the antihyperalgesic activity of Ligustrum vulgare leaf extract is not likely related to its antihyperglycemic properties.

Biosynthesis of Silver Nanoparticles Using Ligustrum Ovalifolium Fruits and Their Cytotoxic Effects

The present study reports for the first time the efficacy of bioactive compounds from Ligustrum ovalifolium L. fruit extract as reducing and capping agents of silver nanoparticles (AgNPs), developing a green, zero energetic, cost effective and simple synthesis method of AgNPs. The obtained nanoparticles were characterized by UV-Vis spectroscopy, transmission electron microscopy (TEM), X-ray diffraction (XRD) and Fourier Transform Infrared spectroscopy (FTIR), confirming that nanoparticles were crystalline in nature, spherical in shape, with an average size of 7 nm. The FTIR spectroscopy analysis demonstrated that the AgNPs were capped and stabilized by bioactive molecules from the fruit extract. The cytotoxicity of the biosynthesized AgNPs was in vitro evaluated against ovarian carcinoma cells and there were found to be effective at low concentration levels.

Synthesis and antioxidant evaluation of lipophilic oleuropein aglycone derivatives

Oleuropein is the most important phenolic compound present in olive cultivars, but it is scarcely present in extra virgin olive oil (EVOO) due to its high hydrophilicity and degradability. Thus, a set of oleuropein aglycone derivatives were synthesized by transacetylation under mild conditions with the aim of circumventing these drawbacks and making the active moiety in oleuropein suitable to be added to food fats. The oleuropein aglycone (closed ring form) is obtained by hydrolyzing oleuropein using Lewis acid catalysis. Then, the permeation profiles as well as the antioxidant capacity of the oleuropein aglycone derivatives were evaluated by ORAC, DPPH assays and by ROS formation using the SH-SY5Y cell line. The biological activities of the obtained compounds exhibited a dependence on their level of lipophilicity.

Oleacein may inhibit destabilization of carotid plaques from hypertensive patients. Impact on high mobility group protein-1

BACKGROUND

In patients with hypertension the haemorrhage into carotid atherosclerotic plaque increases risk of plaque destabilization and rupture. Our previous study showed that oleacein, a secoiridoid present in extra virgin olive oil, enhanced uptake of haemoglobin-haptoglobin complex and change macrophage phenotype from pro-inflammatory M1 to anti-inflammatory M2.

PURPOSE

The aim this study was to investigate a potential role of oleacein in attenuation of carotid plaque destabilisation ex vivo.

METHODS

Samples of atherosclerotic plaque were harvested from 20 patients with hypertension /11 women and 9 men/, who underwent carotid endarterectomy after transient ischemic attacks. Matching pieces of each plaque were incubated with increased concentration of pure oleacein /range 0-20 µM/ for 24 h. HMGB1, MMP-9, MMP-9/NGAL, TF and IL-10, as well as HO-1 secretion from plaque was measured by enzyme-linked immunosorbent assay /ELISA/. Statistical significance was set at P < 0.05 and P < 0.001.

RESULTS

Oleacein at the concentrations of 10 and 20 µM significantly (P < 0.001) decreased secretion of HMGB1 (up 90%), MMP-9 (up to 80%), MMP-9/NGAL complex (up to 80%) and TF (more than 90%) from the treated plaque, as compared to control. At the same time IL-10 and HO-1 release increased by more than 80% (P < 0.001).

CONCLUSION

Our results indicate that oleacein possess ability to attenuate the destabilization of carotid plaque and could be potentially useful in the reduction of ischemic stroke risk.

Inhibition of Angiotensin Converting Enzyme, Angiotensin II Receptor Blocking, and Blood Pressure Lowering Bioactivity across Plant Families

Hypertension is a major risk factor for coronary heart disease, kidney disease, and stroke. Interest in medicinal or nutraceutical plant bioactives to reduce hypertension has increased dramatically. The main biological regulation of mammalian blood pressure is via the renin-angiotensin-aldosterone system. The key enzyme is angiotensin converting enzyme (ACE) that converts angiotensin I into the powerful vasoconstrictor, angiotensin II. Angiotensin II binds to its receptors (AT1) on smooth muscle cells of the arteriole vasculature causing vasoconstriction and elevation of blood pressure. This review focuses on the in vitro and in vivo reports of plant-derived extracts that inhibit ACE activity, block angiotensin II receptor binding and demonstrate hypotensive activity in animal or human studies. We describe 74 families of plants that exhibited significant ACE inhibitory activity and 16 plant families with potential AT1 receptor blocking activity, according to in vitro studies. From 43 plant families including some of those with in vitro bioactivity, the extracts from 73 plant species lowered blood pressure in various normotensive or hypertensive in vivo models by the oral route. Of these, 19 species from 15 families lowered human BP when administered orally. Some of the active plant extracts, isolated bioactives and BP-lowering mechanisms are discussed.

Quantitative Determination of Secoiridoids and Phenylpropanoids in Different Extracts of Ligustrum Vulgare L. Leaves by a Validated HPTLC-Photodensitometry Method

INTRODUCTION

The genus Ligustrum (Oleaceae) is distributed in Europe and Asia (south China and Korea), where it is used to prevent hypertension, sore throats, inflammation and diabetes. The main groups of compounds in extracts of Ligustrum vulgare are biologically active secoiridoids and phenylpropanoids.

OBJECTIVES

The aim of the study was primarily the development and validation of a HPTLC-photodensitometry method for separation and determination of secoiridoids (oleacein, oleuropein) and phenylpropanoids (echinacoside) in different extracts prepared from leaves of L. vulgare. A secondary issue was the quantitative screening of oleacein, oleuropein and echinacoside in extracts from leaves collected at different stages of plant growth (from May to September).

METHODS

A HPTLC-photodensitometry method was developed and validated for quantification of oleuropein, oleacein and echinacoside in plant extracts (aqueous and ethanolic extract, decoction, infusion). Silica gel was used as the stationary phase and dichloromethane:methanol:formic acid:water (80:25:1.5:4, v/v/v/v) as the mobile phase.

RESULTS

The HPTLC-photodensitometry method developed for quantification of oleacein, oleuropein and echinacoside was specific, accurate and precise. The presence of oleacein was detected in aqueous extracts, whereas oleuropein was present, in particular, in ethanolic extracts, decoctions and infusions. Echinacoside was detected in all the extracts prepared. The content of secoiridoids was variable from May to September, whereas the amount of echinacoside increased in this term.

CONCLUSION

The developed and validated HPTLC-photodensitometry method allowed performing fast screening of quantitative profiles of oleacein, oleuropein and echinacoside in preparations of privet leaves.

Oleuropein offers cardioprotection in rats with simultaneous type 2 diabetes and renal hypertension

Objectives:

The study aimed at examining the role of oxidative stress in cadioprotective effects of oleuropein in a rat model of simultaneous type 2 diabetes and renal hypertension.

Materials and Methods:

Five groups of male Sprague-Dawley rats including a control group, a diabetic-hypertensive group receiving vehicle, and three diabetic-hypertensive groups receiving oleuropein at 20, 40, or 60 mg/kg/day were used. Blood pressure and glucose, serum malondialdehyde, and erythrocyte superoxide dismutase were measured, and animal's hearts with ischemia/reperfusion injuries were used using Langendorff technique.

Results:

Blood pressure, blood glucose, serum malondialdehyde, infarct size, coronary effluent creatine kinase-MB, and coronary resistance of diabetic-hypertensive group were significantly higher than those of the control group, while those of the oleuropein-receiving groups were significantly lower than those of the diabetic hypertensive group receiving the vehicle. Erythrocyte superoxide dismutase, left ventricular developed pressure, and rate of rise and rate of decrease of ventricular pressure of diabetic-hypertensive group were significantly lower than those of the control group. These parameters as well as heart rate of oleuropein-receiving groups were significantly higher than those of the diabetic-hypertensive group.

Conclusion:

The findings indicate that oleuropein offered cardioprotection, which might be partly mediated by its antioxidant properties.

Effects of oleuropein in rats with simultaneous type 2 diabetes and renal hypertension: a study of antihypertensive mechanisms

The mechanism of oleuropein's antihypertensive effects was examined in rat model of simultaneous type 2 diabetes and renal hypertension (diabetic hypertensive). Five groups of male Sprague-Dawley rats including a control, a diabetic-hypertensive group receiving vehicle, and three diabetic-hypertensive groups receiving oleuropein at 20, 40, or 60 mg/kg/day were used. The duration of diabetes was 10 weeks; during the last 4 weeks of which, animals were hypertensive and received vehicle or oleuropein. Systolic blood pressure, glucose and malondialdehyde, heart rate, and maximal response to phenylephrine (PE) in the absence of nitro-L-arginine methyl ester (L-NAME) of oleuropein-treated groups were significantly lower than those of vehicle-treated group. Erythrocyte superoxide dismutase, maximal response to PE in the presence of L-NAME, and maximal response to acetylcholine (Ach) of oleuropein-treated groups were significantly higher than those of vehicle-treated group. The findings indicate that antihypertensive effects of oleuropein might be partly mediated by improving the release of nitric oxide, and antioxidant and sympathoplegic activities.

One-step semisynthesis of oleacein and the determination as a 5-lipoxygenase inhibitor

The dialdehydes oleacein (2) and oleocanthal (4) are closely related to oleuropein (1) and ligstroside (3), the two latter compounds being abundant iridoids of Olea europaea. By exploiting oleuropein isolated from the plant leaf extract, an efficient procedure has been developed for a one-step semisynthesis of oleacein under Krapcho decarbomethoxylation conditions. Highlighted is the fact that 5-lipoxygenase is a direct target for oleacein with an inhibitory potential (IC50: 2 μM) more potent than oleocanthal (4) and oleuropein (1). This enzyme catalyzes the initial steps in the biosynthesis of pro-inflammatory leukotrienes. Taken together, the methodology presented here offers an alternative solution to isolation or total synthesis for the procurement of oleacein, thus facilitating the further development as a potential anti-inflammatory agent.

Components of a standardised olive leaf dry extract (Ph. Eur.) promote hypothiocyanite production by lactoperoxidase

We investigated in vitro the ability of a standardised olive leaf dry extract (Ph. Eur.) (OLE) as well as of its single components to circumvent the hydrogen peroxide-induced inhibition of the hypothiocyanite-producing activity of lactoperoxidase (LPO). The rate of hypothiocyanite (⁻OSCN) formation by LPO was quantified by spectrophotometric detection of the oxidation of 5-thio-2-nitrobenzoic acid (TNB). By using excess hydrogen peroxide, we forced the accumulation of inactive enzymatic intermediates which are unable to promote the two-electronic oxidation of thiocyanate. Both OLE and certain extract components showed a strong LPO-reactivating effect. Thereby an o-hydroxyphenolic moiety emerged to be essential for a good reactivity with the inactive LPO redox states. This basic moiety is found in the main OLE components oleuropein, oleacein, hydroxytyrosol, caffeic acid as well as in different other constituents including the OLE flavone luteolin. As LPO is a key player in the humoral immune response, these results propose a new mode of action regarding the well-known bacteriostatic and anti-inflammatory properties of the leaf extract of Olea europaea L.

In vitro Anti-inflammatory Activity of Ligustrum vulgare Extracts and Their Analytical Characterization

Interest in the anti-inflammatory effects of Ligustrum vulgare L., which has been used traditionally in China and Japan prompted us to determine anti-inflammatory effects of the plant's compounds in leukocytes. The leaves of L. vulgare were used to prepare a decoction which was successively extracted with organic solvents (dichloromethane (DCM), n-butanol, ethyl acetate) using liquid-liquid partition. Extracts were tested for inhibition of LTB4, resp. PGE2 biosynthesis. Each extract was evaluated for its in vitro cyclooxygenase-1/2 (COX-1/2) inhibitory activity using assays with purified COX-1 and COX-2 enzymes, as well as for their LTB4 formation inhibitory activity using an assay with activated human neutrophil granulocytes. All extracts reported inhibitory actions against COXs in comparison with the synthetic inhibitors NS-398 (IC50 = 2.6 μM) and indomethacin (IC50 = 0.9 μM). The dichloromethane extract of privet leaves showed a considerable inhibitory effect against COX-1 and COX-2 enzyme activity. The DCM extract revealed 2.7 times higher inhibitory activity against LTB4 formation in comparison with the known specific LT inhibitor zileuton (IC50 = 5.0 μM). Additionally, oleuropein and echinacoside were detected by HPLC-DAD and LC-MS in the Ligustrum vulgare leaves. Both compounds exhibited weak inhibitory activity on cyclooxygenases and leukotriene formation.

Oleuropein and oleacein may restore biological functions of endothelial progenitor cells impaired by angiotensin II via activation of Nrf2/heme oxygenase-1 pathway

Endothelial progenitor cells (EPCs) are responsible for neovascularization of ischaemic tissue and may participate in re-endothelization of an injured arterial wall. There is evidence that angiotensin II, by an increase of gp91phox expression and induction of ROS generation, accelerates cell senescence and impairs functions of EPCs. Oleacein is a main phenolic compound from olive oil, whereas oleuropein is present in olive leaves. Both compounds possess antioxidative, hypotensive and anti-inflammatory properties and show beneficial activity on the cardiovascular system. In this study, we examined whether oleoeuropein and oleacein could protect EPCs against impairment of their functions due to angiotensin-induced cell senescence. CD31(+)/VEGFR-2(+) cells were isolated from young healthy volunteers blood samples and cultured on fibronectin-coated plates with angiotensin (1.0μM) in presence or absence of increasing concentrations (from 1.0 to 10.0 μM) of oleoeuropein or oleacein. As compared to angiotensin II-treated cells, EPCs exposed to oleacein or oleuropein prior to angiotensin II showed a significant increase of proliferation and telomerase activity, and a decrease in the percentage of senescent cells and intracellular ROS formation. Oleacein and oleuropein restored migration, adhesion and tube formation of EPCs diminished by angiotensin II in a concentration-dependent manner. This effect was related to NF-E2-related factor 2 (Nrf2) transcription factor activation and the increase of heme oxygenase-1 (HO-1) expression.

HPLC determination of antilipoxygenase activity of a water infusion of Ligustrum vulgare L. leaves and some of its constituents

The aim of the study was a HPLC evaluation of the lipoxygenase activity inhibiting activity of a water infusion of Ligustrum vulgare L. leaves and selected isolates from it. The antiradical activity of the water infusion was determined using DPPH, ABTS and FRAP tests. Oleuropein and echinacoside concentrations in the water infusion were determined by HPLC. Water infusion, echinacoside and oleuropein were used for an antilipoxygenase activity assay using lipoxygenase isolated from rat lung cytosol fraction. Activity of 8-LOX, 12-LOX and 15-LOX were monitored through formation of 8-HETE, 12-HETE and 15-HETE, respectively. The water infusion exhibited the highest activity against all lipoxygenases, followed by oleuropein. Echinacoside was ineffective against LOXs in lower concentrations, while higher concentration showed similar inhibition on 8-LOX and 12-LOX. 15-LOX was affected more and the presence of echinacoside remarkably decreased its activity.

Secoiridoid glucosides and unusual recyclized secoiridoid aglycones from Ligustrum vulgare

Phytochemical investigation of the dried leaves and twigs of Ligustrum vulgare has led to the isolation of the secoiridoid glucosides, (2''R)- and (2''S)-10-hydroxy-2''-methoxyoleuropeins (1 and 2), and the secoiridoid aglycones, ligustrohemiacetals A (3) and B (4). Their structures were elucidated by spectroscopic and chemical means. Enzymatic hydrolysis of 10-hydroxyoleuropein to the analog of ligustrohemiacetals A and B led to the structural revision of jasmolactones.