No evidence for modulation of endothelial nitric oxide synthase by the olive oil polyphenol hydroxytyrosol in human endothelial cells

Conjugated Metabolites of Hydroxytyrosol and Tyrosol Contribute to the Maintenance of Nitric Oxide Balance in Human Aortic Endothelial Cells at Physiologically Relevant Concentrations

Nitric oxide (NO) is an important signaling molecule involved in many pathophysiological processes. NO mediates vasodilation and blood flow in the arteries, and its action contributes to maintaining vascular homeostasis by inhibiting vascular smooth muscle contraction and growth, platelet aggregation, and leukocyte adhesion to the endothelium. Dietary antioxidants and their metabolites have been found to be directly and/or indirectly involved in the modulation of the intracellular signals that lead to the production of NO. The purpose of this study was to investigate the contribution of conjugated metabolites of hydroxytyrosol (HT) and tyrosol (TYR) to the release of NO at the vascular level, and the related mechanism of action, in comparison to their parental forms. Experiments were performed in human aortic endothelial cells (HAEC) to evaluate the superoxide production, the release of NO and production of cyclic guanosine monophosphate (cGMP), the activation of serine/threonine-protein kinase 1 (Akt1), and the activation state of endothelial nitric oxide synthase (eNOS). It was observed that the tested phenolic compounds enhanced NO and cGMP concentration, inhibiting its depletion caused by superoxide overproduction. Moreover, some of them enhanced the activation of Akt (TYR, HT metabolites) and eNOS (HT, HVA, TYR-S, HT-3S). Overall, the obtained data showed that these compounds promote NO production and availability, suggesting that HT and TYR conjugated metabolites may contribute to the effects of parental extra virgin olive oil (EVOO) phenolics in the prevention of cardiovascular diseases.

Supplementation Effect of a Combination of Olive (Olea europea L.) Leaf and Fruit Extracts in the Clinical Management of Hypertension and Metabolic Syndrome

BACKGROUND

The role of herbal products in the prevention of cardiovascular disease requires supporting evidence. This open pilot study assessed the effect of 2-month supplementation of a combination of olive leaf and fruit extracts (Tensiofytol^®, Tilman SA, Baillonville, Belgium) in the clinical management of hypertension and metabolic syndrome (MetS).

METHODS

A total of 663 (pre)-hypertensive patients were enrolled by general practitioners and supplemented for two months with Tensiofytol^®, two capsules per day (100 mg/d of oleuropein and 20 mg/d of hydroxytyrosol). Systolic and diastolic blood pressures (SBP/DBP) were measured before and after treatment. Markers of MetS, high-density lipoprotein cholesterol (HDL-C), triglycerides (TG), fasting blood glucose (FG) and waist circumference (WC), were also examined.

RESULTS

Significant reductions (p < 0.0001) in SBP/DBP (13 ± 10/7.1 ± 6.6 mmHg) were observed and similarly in pre-diabetic and diabetic patients. Improvements in SBP/DPB were independent of age and gender but greater for elevated baseline SBP/DBP. Tensiofytol^® supplementation also significantly improved markers of MetS, with a decrease of TG (11%), WC (1.4%) and FG (4.8%) and an increase of HDL-C (5.3%). Minor side effects were reported in 3.2% patients.

CONCLUSIONS

This real-life, observational, non-controlled, non-randomized pilot study shows that supplementation of a combination of olive leaf and fruit extracts may be used efficiently and safely in reducing hypertension and MetS markers.

Wide Biological Role of Hydroxytyrosol: Possible Therapeutic and Preventive Properties in Cardiovascular Diseases

The growing incidence of cardiovascular disease (CVD) has promoted investigations of natural molecules that could prevent and treat CVD. Among these, hydroxytyrosol, a polyphenolic compound of olive oil, is well known for its antioxidant, anti-inflammatory, and anti-atherogenic effects. Its strong antioxidant properties are due to the scavenging of radicals and the stimulation of synthesis and activity of antioxidant enzymes (SOD, CAT, HO-1, NOS, COX-2, GSH), which also limit the lipid peroxidation of low-density lipoprotein (LDL) cholesterol, a hallmark of atherosclerosis. Lowered inflammation and oxidative stress and an improved lipid profile were also demonstrated in healthy subjects as well as in metabolic syndrome patients after hydroxytyrosol (HT) supplementation. These results might open a new therapeutic scenario through personalized supplementation of HT in CVDs. This review is the first attempt to collect together scientific literature on HT in both in vitro and in vivo models, as well as in human clinical studies, describing its potential biological effects for cardiovascular health.

Evaluation of Apricot, Bilberry, and Elderberry Pomace Constituents and Their Potential To Enhance the Endothelial Nitric Oxide Synthase (eNOS) Activity

Pomace, the press residue from different fruits accumulating as waste product in food industry, contains high amounts of secondary metabolites that could be utilized for health-related applications. This study aims at evaluating the potential of pomaces of apricot, bilberry, and elderberry to serve as a source for endothelial nitric oxide synthase (eNOS)-activating compounds. Five extracts obtained from the lyophilized pomace of apricot and elderberry with solvents of different polarity were found to enhance A23187-stimulated eNOS activity when tested at 50 μg/mL in an [¹⁴C]-l-arginine to [¹⁴C]-l-citrulline conversion assay in the human endothelium-derived cell line EA.hy926 (p < 0.05). The bioassay-guided fractionation of the extracts obtained with methanol/water (70:30) led to several active fractions from apricot pomace (p < 0.05) and elderberry pomace (p < 0.01). Liquid chromatography-mass spectrometry-based chemical analysis of the extracts and active fractions pointed mainly to triterpenoic acids as active compounds. One particular dihydroxytriterpenoic acid, characteristic for elderberry, was enriched as the main compound in the two most active fractions and might serve as a promising lead structure for further studies.

Chia Oil-Enriched Restructured Pork Effects on Oxidative and Inflammatory Status of Aged Rats Fed High Cholesterol/High Fat Diets

Chia oil has the highest recognized α-linolenic acid (ALA) content. ALA is associated with beneficial changes in plasma lipids and the prevention of cardiovascular diseases. Present article aims to analyze the effect of Chia oil-enriched restructured pork (RP) on aged rats in a nonalcoholic steatohepatitis (NASH) model. Groups of six male Wistar rats (1-year old) were fed the experimental diets: control RP diet (C) noncholesterol high saturated; cholesterol-enriched high-saturated fat/high-cholesterol control RP diet (HC) with added cholesterol and cholic acid; and Chia oil- or Hydroxytyrosol RP cholesterol-enriched high-saturated fat/high cholesterol (CHIA and HxT). Total cholesterol, hepatosomatic index, Nrf2, antioxidant, and inflammation markers were determined. CHIA reduced the hypercholesterolemic effect by lowering levels similar to C; also, ameliorated redox index. CHIA, despite high polyunsaturated fatty acids (PUFA) content, reduced thiobarbituric acid reactive substances (TBARS) and induced the lowest SOD protein synthesis but not a reduction on its activity. Chia oil activated the Nrf2 to arrest the pro-oxidative response to cholesterol and aging. Endothelial nitric oxide synthase (eNOS) system was lower in HxT than in CHIA, suggesting its antiatherogenic activity and related protective effect against high PUFA. Increase in tumor necrosis factor alpha (TNFα) was partially blocked by CHIA. Chia oil has the ability to prevent oxidative damage and modify the inflammatory response, suggesting adequate regulation of the antioxidant system. Results stress the importance of incorporating ALA into the diet.

Hydroxytyrosol in the Prevention of the Metabolic Syndrome and Related Disorders

Virgin olive oil (VOO) constitutes the main source of fat in the Mediterranean diet. VOO is rich in oleic acid, displaying health-promoting properties, but also contains minor bioactive components, especially phenolic compounds. Hydroxytyrosol (HT), the main polyphenol of olive oil, has been reported to be the most bioactive component. This review aims to compile the results of clinical, animal and cell culture studies evaluating the effects of HT on the features of Metabolic Syndrome (MetS) (body weight/adiposity, dyslipidemia, hypertension, and hyperglycemia/insulin resistance) and associated complications (oxidative stress and inflammation). HT was able to improve the lipid profile, glycaemia, and insulin sensitivity, and counteract oxidative and inflammatory processes. Experimental studies identified multiple molecular targets for HT conferring its beneficial effect on health in spite of its low bioavailability. However, rodent experiments and clinical trials with pure HT at biologically relevant concentrations are still lacking. Moreover, the roles of intestine and its gut microbiota have not been elucidated.

An extra-virgin olive oil rich in polyphenolic compounds has antioxidant effects in meat-type broiler chickens

The aim of this study was to extend the knowledge on the antioxidant effect of extra-virgin olive oil (EVOO) in the liver of broiler chickens not subjected to any form of insult. A total of 120 male broiler chickens (Hubbard strain) were divided into three groups and fed ad libitum with three isoenergetic diets from hatching until slaughter age (49 days) on a completely randomized design. The dietary treatments consisted of 2.5% added oil or fat from three sources as follows: diet containing sunflower oil (SFO); diet containing lard (LRD), and diet containing extra-virgin olive oil (EVOO). The activity of the main antioxidative enzymes, superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GS-Px) and glutathione S-transferase (GST), and lipid peroxidation as thiobarbituric acid-reactive substances (TBARS) content, was measured in the liver of chickens. The susceptibility to undergo lipid peroxidation was assessed by exposing liver homogenate to 30 °C or to an ascorbate/iron mixture as pro-oxidant system. Dietary oil or fat type improved significantly (P < 0.05) the body weight and gain as well as feed efficiency in birds fed EVOO compared to those fed with the other treatments. Supplementing EVOO in the diet significantly (P < 0.05) reduced lipid peroxidation by increasing antioxidant defense system. These findings, besides adding more results on the antioxidant effect of extra-virgin olive oil on liver of other experimental model other than rats and humans, could be significant for animal welfare, with consequent benefits for both producers and consumers.

Triterpenoic Acids from Apple Pomace Enhance the Activity of the Endothelial Nitric Oxide Synthase (eNOS)

Pomace is an easy-accessible raw material for the isolation of fruit-derived compounds. Fruit consumption is associated with health-promoting effects, such as the prevention of cardiovascular disease. Increased vascular nitric oxide (NO) bioavailability, for example, due to an enhanced endothelial nitric oxide synthase (eNOS) activity, could be one molecular mechanism mediating this effect. To identify compounds from apple (Malus domestica Borkh.) pomace that have the potential to amplify NO bioavailability via eNOS activation, a bioassay-guided fractionation of the methanol/water (70:30) extract has been performed using the (14)C-L-arginine to (14)C-L-citrulline conversion assay (ACCA) in the human endothelium-derived cell line EA.hy926. Phytochemical characterization of the active fractions was performed using the spectrophotometric assessment of the total phenolic content, as well as TLC, HPLC-DAD-ELSD, and HPLC-MS analyses. Eleven triterpenoic acids, of which one is a newly discovered compound, were identified as the main constituents in the most active fraction, accompanied by only minor contents of phenolic compounds. When tested individually, none of the tested compounds exhibited significant eNOS activation. Nevertheless, cell stimulation with the reconstituted compound mixture restored eNOS activation, validating the potential of apple pomace as a source of bioactive components.

Impact of trans-resveratrol-sulfates and -glucuronides on endothelial nitric oxide synthase activity, nitric oxide release and intracellular reactive oxygen species

Resveratrol (3,5,4'-trihydroxy-trans-stilbene) is a polyphenolic natural product mainly present in grape skin, berries and peanuts. In the vasculature resveratrol is thought to boost endothelial function by increasing endothelial nitric oxide synthase (eNOS) expression, by enhancing eNOS activity, and by reduction of reactive oxygen species (ROS) levels. Recent studies show that dietary resveratrol is metabolized in the liver and intestine into resveratrol-sulfate and -glucuronide derivatives questioning the relevance of multiple reported mechanistic in vitro data on resveratrol. In this study, we compare side by side different physiologically relevant resveratrol metabolites (resveratrol sulfates- and -glucuronides) and their parent compound in their influence on eNOS enzyme activity, endothelial NO release, and intracellular ROS levels. In contrast to resveratrol, none of the tested resveratrol metabolites elevated eNOS enzyme activity and endothelial NO release or affected intracellular ROS levels, leaving the possibility that not tested metabolites are active and able to explain in vivo findings.

Acanthopanax divaricatus var. chiisanensis reduces blood pressure via the endothelial nitric oxide synthase pathway in the spontaneously hypertensive rat model

In this study, we investigated the antihypertensive effects of Acanthopanax divaricatus var. chiisanensis extract (AE) and its active compound, acanthoside D (AD), on arterial blood pressure (BP) in vivo and endothelial function in vitro. We hypothesized that AE has antihypertensive effects, which is attributed to enhancement of endothelial function via the improvement of nitric oxide synthesis or the angiotensin II (Ang II) response. Spontaneously hypertensive rats (SHRs) and Wistar-Kyoto rats (WKYs) were randomly divided into 7 groups and then fed the following diets for 14 weeks: WKY fed a normal diet (WN); SHR fed a normal diet (SN); SHR fed a high-cholesterol (HC) diet (SH); SHR fed a HC diet with AE of 150, 300, 600 mg/kg body weight (SH-L, SH-M, SH-H); and SHR fed an HC diet with AD of 600 μg/kg body weight (SH-D). Blood pressure was significantly reduced in the SH-H compared with the SH from week 10 until week 14; BP was also significantly decreased in the SHR fed a HC diet with AE of 300 at week 14. Aortic wall thickness showed a tendency to decrease by AE and AD treatment. The SH-H showed increased endothelial nitric oxide synthase (eNOS) expression in the intima and media, compared with the SH. Furthermore, a significant increase in intracellular nitric oxide production was induced by AE and AD treatment in human umbilical vein endothelial cells. A significant increase of phospho-eNOS was found with a high dose of AE in human umbilical vein endothelial cells but not with AD. These results suggest that AE can regulate BP and improve endothelial function via eNOS-dependent vasodilation.

Pharmacological potential of Populus nigra extract as antioxidant, anti-inflammatory, cardiovascular and hepatoprotective agent

OBJECTIVE

To evaluate antioxidant, anti-inflammatory, hepatoprotective and vasorelaxant activities of Populus nigra flower buds ethanolic extract.

METHODS

Antioxidant and anti-inflammatory activities of the extract were assessed using respectively the ABTS test and the animal model of carrageenan-induced paw edema. Protection from hepatic toxicity caused by aluminum was examined by histopathologic analysis of liver sections. Vasorelaxant effect was estimated in endothelium-intact and -rubbed rings of porcine coronary arteries precontracted with high concentration of U46619.

RESULTS

The results showed a moderate antioxidant activity (40%), but potent anti-inflammatory activity (49.9%) on carrageenan-induced mice paw edema, and also as revealed by histopathologic examination, complete protection against AlCl₃-induced hepatic toxicity. Relaxant effects of the same extract on vascular preparation from porcine aorta precontracted with high concentration of U46619 were considerable at 10⁻¹ g/L, and comparable (P>0.05) between endothelium-intact (67.74%, IC₅₀=0.04 mg/mL) and -rubbed (72.72%, IC₅₀=0.075 mg/mL) aortic rings.

CONCLUSIONS

The extract exerted significant anti-inflammatory, hepatoprotective and vasorelaxant activities, the latter being endothelium-independent believed to be mediated mainly by the ability of components present in the extract to exert antioxidant properties, probably related to an inhibition of Ca²⁺ influx.

Polyphenols: benefits to the cardiovascular system in health and in aging

Numerous studies have demonstrated the importance of naturally occurring dietary polyphenols in promoting cardiovascular health and emphasized the significant role these compounds play in limiting the effects of cellular aging. Polyphenols such as resveratrol, epigallocatechin gallate (EGCG), and curcumin have been acknowledged for having beneficial effects on cardiovascular health, while some have also been shown to be protective in aging. This review highlights the literature surrounding this topic on the prominently studied and documented polyphenols as pertaining to cardiovascular health and aging.

Malvidin-3-glucoside protects endothelial cells up-regulating endothelial NO synthase and inhibiting peroxynitrite-induced NF-kB activation

Anthocyanins are the most abundant flavonoid constituents of fruits and vegetables and several epidemiological studies suggest that the consumption of these compounds protect against several diseases, including vascular disorders. Previously, we have reported that anthocyanins are able to counteract peroxynitrite-induced apoptotic effects in endothelial cells through inhibition of several crucial signaling cascades, upstream and downstream of mitochondria. Following these studies, here we investigated possible effects of malvidin-3-glucoside, one of the main dietary anthocyanins, on NO bioavailability and on peroxynitrite-induced NF-kB activation in the same cell model. Our results show that treatment of bovine arterial endothelial cells with malvidin-3-glucoside up-regulated eNOS mRNA, leading to the enhancement of eNOS activity and NO production, an effect even greater when cells were further stimulated with peroxynitrite. On the other hand, in these activated endothelial cells, malvidin-3-glucoside suppressed pro-inflammatory mediators, namely iNOS expression/NO biosynthesis, COX-2 expression and IL-6 production, through inhibition of NF-kB activation. These findings suggest a potential role of malvidin-3-glucoside in NO balance and in inhibition of pro-inflammatory signaling pathways, supporting its benefits in cardiovascular health and pointing to anthocyanins as a promising tool for development of functional foods and nutraceuticals to improve endothelial function.

2-(2,4-dihydroxyphenyl)-5-(E)-propenylbenzofuran promotes endothelial nitric oxide synthase activity in human endothelial cells

Endothelial nitric oxide synthase (eNOS) mediates important vaso-protective and immunomodulatory effects. Aim of this study was to examine whether lignan derivatives isolated from the roots of the anti-inflammatory medicinal plant Krameria lappacea influence eNOS activity and endothelial nitric oxide (NO) release. The study was performed using cultured human umbilical vein endothelial cells (HUVECs) and HUVEC-derived EA.hy926 cells. Among the eleven isolated compounds only 2-(2,4-dihydroxyphenyl)-5-(E)-propenylbenzofuran (DPPB) was able to increase eNOS enzyme activity.

DPPB (1–10 μM) treatment for 24 h induced a significant and dose-dependent increase in eNOS activity as determined by the [¹⁴C]l-arginine/[¹⁴C]l-citrulline conversion assay. Immunoblotting studies further revealed a time-dependent DPPB-induced increase in eNOS-Ser¹¹⁷⁷ and decrease in eNOS-Thr⁴⁹⁵ phosphorylation, as well as increased AMPK phosphorylation at Thr¹⁷², whereas Akt phosphorylation at Ser⁴⁷³ was not affected. Si-RNA-mediated knockdown of AMPK and inhibition of CaMKKβ by STO 609, as well as intracellular Ca²⁺ chelation by Bapta AM abolished the stimulating effect of DPPB on eNOS-Ser¹¹⁷⁷ and AMPK-Thr¹⁷² phosphorylation. Furthermore, we could show that DPPB increases intracellular Ca²⁺ concentrations assessed with the fluorescent dye Fluo-3-AM. DPPB enhances eNOS activity and endothelial NO release by raising intracellular Ca²⁺ levels and increases signaling through a CaMKKβ–AMPK dependent pathway.

Ascorbate stimulates endothelial nitric oxide synthase enzyme activity by rapid modulation of its phosphorylation status

Long-term exposure to ascorbate is known to enhance endothelial nitric oxide synthase (eNOS) activity by stabilizing the eNOS cofactor tetrahydrobiopterin (BH4). We investigated acute effects of ascorbate on eNOS function in primary (HUVEC) and immortalized human endothelial cells (EA.hy926), aiming to provide a molecular explanation for the rapid vasodilatation seen in vivo upon administration of ascorbate. Enzymatic activity of eNOS and intracellular BH4 levels were assessed by means of an arginine-citrulline conversion assay and HPLC analysis, respectively. Over a period of 4h, ascorbate steadily increased eNOS activity, although endothelial BH4 levels remained unchanged compared to untreated control cells. Immunoblot analyses revealed that as early as 5 min after treatment ascorbate dose-dependently increased phosphorylation at eNOS-Ser1177 and concomitantly decreased phosphorylation at eNOS-Thr495, a phosphorylation pattern indicative of increased eNOS activity. By employing pharmacological inhibitors, siRNA-mediated knockdown approaches, and overexpression of the catalytic subunit of protein phosphatase 2A (PP2A), we show that this effect was at least partly owing to reduction of PP2A activity and subsequent activation of AMP-activated kinase. In this report, we unravel a novel mechanism for how ascorbate rapidly activates eNOS independent of its effects on BH4 stabilization.

Interleukin-8 induces the endothelial cell migration through the activation of phosphoinositide 3-kinase-Rac1/RhoA pathway

Endothelial cell migration is essential for tumor angiogenesis, and interleukin-8 (IL-8) has been shown to play an important role in tumor growth, angiogenesis, and metastasis. This study aimed to investigate the molecular mechanism of IL-8 induced endothelial cell migration. Our results indicated that IL-8 induced a rapid rearrangement of the actin cytoskeleton in EA.Hy926 cells, generating extensions resembling membrane ruffling and stress fibers. These processes required parallel upregulation of the small GTPases Rac1 and RhoA. Moreover, we demonstrated that IL-8 activated PI3K following the same kinetics observed from IL-8 induction of cytoskeletal rearrangement, suggesting the participation of PI3K in these processes. Taken together, our study demonstrates that PI3K-Rac1/RhoA signaling pathway plays a vital role in IL-8 induced endothelial cell migration, and provides new insight into the molecular mechanisms by which IL-8 contributes to tumor angiogenesis and metastasis.

Hydroxytyrosol: from laboratory investigations to future clinical trials

Mediterranean countries have lower rates of mortality from cardiovascular disease and cancer than Northern European or other Western countries. This has been attributed, at least in part, to the so-called Mediterranean diet, which is composed of specific local foods, including olive oil. Traditionally, many beneficial properties associated with this oil have been ascribed to its high oleic acid content. Today, it is clear that many of the beneficial effects of ingesting virgin olive oil are due to its minor compounds. This review summarizes the existing knowledge concerning the chemistry, pharmacokinetics, and toxicology of hydroxytyrosol, a minor compound of virgin olive oil, as well as this compound's importance for health. The main findings in terms of its beneficial effects in cardiovascular disease and cancer, including its properties against inflammation and platelet aggregation, are emphasized. New evidence and strategies regarding the use of hydroxytyrosol as a natural drug for the prevention and treatment of diseases with high incidences in Western countries are also presented.

Elevated circulating LDL phenol levels in men who consumed virgin rather than refined olive oil are associated with less oxidation of plasma LDL

In human LDL, the bioactivity of olive oil phenols is determined by the in vivo disposition of the biological metabolites of these compounds. Here, we examined how the ingestion of 2 similar olive oils affected the content of the metabolic forms of olive oil phenols in LDL in men. The oils differed in phenol concentrations as follows: high (629 mg/L) for virgin olive oil (VOO) and null (0 mg/L) for refined olive oil (ROO). The study population consisted of a subsample from the EUROLIVE study and a randomized controlled, crossover design was used. Intervention periods lasted 3 wk and were preceded by a 2-wk washout period. The levels of LDL hydroxytyrosol monosulfate and homovanillic acid sulfate, but not of tyrosol sulfate, increased after VOO ingestion (P < 0.05), whereas the concentrations of circulating oxidation markers, including oxidized LDL (oxLDL), conjugated dienes, and hydroxy fatty acids, decreased (P < 0.05). The levels of LDL phenols and oxidation markers were not affected by ROO consumption. The relative increase in the 3 LDL phenols was greater when men consumed VOO than when they consumed ROO (P < 0.05), as was the relative decrease in plasma oxLDL (P = 0.001) and hydroxy fatty acids (P < 0.001). Plasma oxLDL concentrations were negatively correlated with the LDL phenol levels (r = -0.296; P = 0.013). Phenols in LDL were not associated with other oxidation markers. In summary, the phenol concentration of olive oil modulates the phenolic metabolite content in LDL after sustained, daily consumption. The inverse relationship of these metabolites with the degree of LDL oxidation supports the in vivo antioxidant role of olive oil phenolics compounds.

A Maillard reaction product enhances eNOS activity in human endothelial cells

Nitric oxide (NO) produced by the endothelial nitric oxide synthase (eNOS) is an important signaling molecule in the cardiovascular system. Although dietary factors can modulate eNOS activity, putative effects of processed food are barely investigated. We aimed to examine whether the model Maillard reaction product 3-hydroxy-2-methyl-1-propyl-4(1H)-pyridone (HMPP), formed from maltol or starch and propylamine, affects the eNOS system. Incubation of EA.hy926 endothelial cells with 30-300 microM HMPP for 18 h enhanced endothelial NO release measured with the fluorescent probe diaminofluorescein-2 and eNOS activity determined by the [14C]L-arginine-[14C]L-citrulline conversion assay. HMPP increased NO production also in two different types of primary human endothelial cells. Protein levels of eNOS and inducible NO synthase remained unaltered by HMPP. HMPP inhibited eNOS activity within the first 2-4 h, whereas it potently increased eNOS activity after 12-24 h. Levels of eNOS phosphorylation, expression of heat-shock protein 90, caveolin-1 and various antioxidant enzymes were not affected. Intracellular reactive oxygen species remained unchanged by HMPP. This is the first study to demonstrate positive effects of a Maillard reaction product on eNOS activity and endothelial NO production, which is considered favourable for cardiovascular protection.

Norfuraneol dephosphorylates eNOS at threonine 495 and enhances eNOS activity in human endothelial cells

AIM

Pentoses are widely abundant in organic food. Thermal treatment of pentoses leads to the formation of norfuraneol (NF). The aim of this study was to show whether NF, which is taken up regularly, for example with cooked food, affects the human endothelial nitric oxide synthase (eNOS) system.

METHODS AND RESULTS

The study was performed using cultured human umbilical vein endothelial cells (HUVEC), HUVEC-derived EA.hy926 cells, and bovine aortic endothelial cells. Nitric oxide (NO) release and eNOS activity were measured using diaminofluorescein-2 and [14C]L-arginine/[14C]L-citrulline conversion. Levels of (phospho-)eNOS were detected by western blotting. Reactive oxygen species (ROS) production was assessed using 2',7'-dichlorodihydrofluorescein diacetate. Pharmacokinetic parameters of NF were calculated by VolSurf software. NF dose dependently increased eNOS activity and NO release (30-300 microM), but did not affect total eNOS protein or cellular ROS levels. The increase in eNOS activity coincided with specific dephosphorylation of eNOS-Thr495, known to enhance eNOS activity. Inhibition of protein phosphatase 1 (PP1) by calyculin A, tautomycetin, or siRNA against PP1 reversed NF-induced eNOS-Thr495 dephosphorylation. Phosphorylation at eNOS-Ser1177 was not significantly altered by NF. Inhibition of protein kinase C with bisindolylmaleimide I (GFX) or calphostin C mimicked the effect of NF. In contrast to GFX, however, NF had no effect on phorbol-12-myristate-13-acetate-induced endothelial ROS formation. In silico, NF is stable towards CYP3A4 metabolism, shows low protein binding, and high tissue distribution.

CONCLUSION

NF enhances endothelial NO release most likely by promoting specific dephosphorylation of eNOS-Thr495 via PP1 in vitro and may be a promising compound to enhance endothelial function in vivo.