Epicatechin protects endothelial cells against oxidized LDL and maintains NO synthase

Epicatechin promotes oocyte quality in mice during repeated superovulation

The negative impacts of repeated superovulation on mitochondrial function and oocyte quality remain unresolved. Epicatechin (EC), a polyphenolic compound found in the human diet with strong antioxidant activity, was investigated for its effects and underlying mechanism on embryonic development after repeated superovulation. The results showed that as the number of superovulation cycles increased, the number of 2-cell embryos decreased, the development of embryos in subsequent in vitro culture was delayed, the apoptosis rate of blastocyst cells increased and the number of blastocyst cells decreased. However, intraperitoneal injection of EC (10 mg/kg body-weight) for two consecutive days during repeated superovulation increased mitochondrial DNA copies in 2-cell embryos of mice. It also promoted the expression of antioxidant enzyme genes in ovaries, increased the content of glutathione (GSH) content and improved the antioxidant capacity of ovaries. Altogether, these results revealed that intraperitoneal injection of EC could increase the embryonic mitochondrial DNA copy number (mtDNA-CN) and enhance the ovary's antioxidant capacity and GSH content, ultimately promoting the quality of mouse embryos in the process of repeated superovulation.

( -)-Epicatechin and cardiometabolic risk factors: a focus on potential mechanisms of action

This review summarizes experimental evidence on the beneficial effects of ( -)-epicatechin (EC) attenuating major cardiometabolic risk factors, i.e., dyslipidemias, obesity (adipose tissue dysfunction), hyperglycemia (insulin resistance), and hypertension (endothelial dysfunction). Studies in humans are revised and complemented with experiments in animal models, and cultured cells, aiming to understand the molecular mechanisms involved in EC-mediated effects. Firstly, an assessment of EC metabolism gives relevance to both conjugated-EC metabolites product of host metabolism and microbiota-derived species. Integration and analysis of results stress the maintenance of redox homeostasis and mitigation of inflammation as relevant processes associated with cardiometabolic diseases. In these processes, EC appears having significant effects regulating NADPH oxidase (NOX)-dependent oxidant production, nitric oxide (NO) production, and energy homeostasis (mitochondrial biogenesis and function). The potential participation of cell membranes and membrane-bound receptors is also discussed in terms of direct molecular action of EC and EC metabolites reaching cells and tissues.

Memantine, Simvastatin, and Epicatechin Inhibit 7-Ketocholesterol-induced Apoptosis in Retinal Pigment Epithelial Cells But Not Neurosensory Retinal Cells In Vitro

Purpose

7-ketocholesterol (7kCh), a natural byproduct of oxidation in lipoprotein deposits is implicated in the pathogenesis of diabetic retinopathy and age-related macular degeneration (AMD). This study was performed to investigate whether several clinical drugs can inhibit 7kCh-induced caspase activation and mitigate its apoptotic effects on retinal cells in vitro.

Methods

Two populations of retinal cells, human retinal pigment epithelial cells (ARPE-19) and rat neuroretinal cells (R28) were exposed to 7kCh in the presence of the following inhibitors: Z-VAD-FMK (pan-caspase inhibitor), simvastatin, memantine, epicatechin, and Z-IETD-FMK (caspase-8 inhibitor) or Z-ATAD-FMK (caspase-12 inhibitor). Caspase-3/7, -8, and -12 activity levels were measured by fluorochrome caspase assays to quantify cell death. IncuCyte live-cell microscopic images were obtained to quantify cell counts.

Results

Exposure to 7kCh for 24 hours significantly increased caspase activities for both ARPE-19 and R28 cells (P< 0.05). In ARPE cells, pretreatment with various drugs had significantly lower caspase-3/7, -8, and -12 activities, reported in % change in mean signal intensity (msi): Z-VAD-FMK (48% decrease, P< 0.01), memantine (decreased 47.8% at 1 µM, P = 0.0039 and 81.9% at 1 mM, P< 0.001), simvastatin (decreased 85.3% at 0.01 µM, P< 0.001 and 84.8% at 0.05 µM, P< 0.001) or epicatechin (83.6% decrease, P< 0.05), Z-IETD-FMK (68.1% decrease, P< 0.01), and Z-ATAD-FMK (47.7% decrease, P = 0.0017). In contrast, R28 cells exposed to 7kCh continued to have elevated caspase-3/7, -8, and -12 activities (between 25.7% decrease and 17.5% increase in msi, P> 0.05) regardless of the pretreatment.

Conclusion

Several current drugs protect ARPE-19 cells but not R28 cells from 7kCh-induced apoptosis, suggesting that a multiple-drug approach is needed to protect both cells types in various retinal diseases.

Myeloperoxidase: a potential therapeutic target for coronary artery disease

INTRODUCTION

Coronary artery disease (CAD) poses significant morbidity and mortality globally. Despite significant advances in treatment interventions, residual cardiovascular risks remain unchecked. Recent clinical trials have shed light on the potential therapeutic benefits of targeting anti-inflammatory pathways. Myeloperoxidase (MPO) plays an important role in atherosclerotic plaque formation and destabilization of the fibrous cap; both increase the risk of atherosclerotic cardiovascular disease and especially CAD.

AREAS COVERED

This article examines the role of MPO in the pathogenesis of atherosclerotic CAD and the mechanistic data from several key therapeutic drug targets. There have been numerous interesting studies on prototype compounds that directly or indirectly attenuate the enzymatic activities of MPO, and subsequently exhibit atheroprotective effects; these include aminobenzoic acid hydrazide, ferulic acid derivative (INV-315), thiouracil derivatives (PF-1355 and PF-06282999), 2-thioxanthines derivative (AZM198), triazolopyrimidines, acetaminophen, N-acetyl lysyltyrosylcysteine (KYC), flavonoids, and alternative substrates such as thiocyanate and nitroxide radical.

EXPERT OPINION

Future investigations must determine if the cardiovascular benefits of direct systemic inhibition of MPO outweigh the risk of immune dysfunction, which may be less likely to arise with alternative substrates or MPO inhibitors that selectively attenuate atherogenic effects of MPO.

Effect of myeloperoxidase modified LDL on bovine and human aortic endothelial cells

Cardiovascular disease associated with atherosclerosis is a leading cause of death worldwide. Atherosclerosis is primarily caused by the dysfunction of vascular endothelial cells and the subendothelial accumulation of oxidized forms of low-density lipoproteins (LDL). Early observations have associated fibrin deposition with atheroma plaque formation, which has led to the proposition that a decrease in endothelial cell fibrinolysis may negatively influence atherogenesis. It has been recently demonstrated that myeloperoxidase modified LDL (MoxLDL) decreases endothelial cell profibrinolytic capacity in real-time. The present study investigated the role of MoxLDL in endothelial cell dysfunction by determining the molecules that may be involved in decreasing the fibrinolysis of human aortic endothelial cells (HAEC). Accordingly, reverse transcription-quantitative PCR was performed to screen for the differential expression of major genes that are implicated in the fibrinolytic process. In addition, the response of the latter cell type to MoxLDL was compared with bovine aortic endothelial (BAE) cells. Furthermore, the effect of the treatment on the generation of reactive oxygen species (ROS) was also determined. Although the current study did not demonstrate an association between MoxLDL treatment and a change in the expression of any major fibrinolytic factor in HAEC, a discrepancy between HAEC and BAE cells with respect to their response to modified LDL treatment was observed. The result have also demonstrated that MoxLDL does not increase ROS generation in HAEC as opposed to the other major type of modified LDL, cupper oxidized LDL (CuoxLDL) that was reported to exhibit a positive effect at this level. The present study provided important insight into the different effects of MoxLDL and CuoxLDL in endothelial cells, which may aid future studies to determine the various signaling pathways that are promoted by these molecules. The results of the present study may be utilized to identify potential molecular drug targets for the treatment of atherosclerosis.

Cocoa Flavanols: Natural Agents with Attenuating Effects on Metabolic Syndrome Risk Factors

The interest in cacao flavanols is still growing, as bioactive compounds with potential benefits in the prevention of chronic diseases associated with inflammation, oxidative stress and metabolic disorders. Several analytical methodologies support that the flavanols in cacao-derived products can be absorbed, have bioactive properties, and thus can be responsible for their beneficial effects on human health. However, it must be considered that their biological actions and underlying molecular mechanisms will depend on the concentrations achieved in their target tissues. Based on the antioxidant properties of cacao flavanols, this review focuses on recent advances in research regarding their potential to improve metabolic syndrome risk factors. Additionally, it has included other secondary plant metabolites that have been investigated for their protective effects against metabolic syndrome. Studies using laboratory animals or human subjects represent strong available evidence for biological effects of cacao flavanols. Nevertheless, in vitro studies are also included to provide an overview of these phytochemical mechanisms of action. Further studies are needed to determine if the main cacao flavanols or their metabolites are responsible for the observed health benefits and which are their precise molecular mechanisms.

Pure flavonoid epicatechin and whole genome gene expression profiles in circulating immune cells in adults with elevated blood pressure: A randomised double-blind, placebo-controlled, crossover trial

Cocoa consumption has beneficial cardiometabolic effects, but underlying mechanisms remain unclear. Epicatechin, the cocoa major monomeric flavan-3-ol, is considered to contribute to these cardio-protective effects. We investigated effects of pure epicatechin supplementation on gene expression profiles of immune cells in humans. In a double blind, placebo-controlled cross-over trial, 32 (pre)hypertensive subjects aged 30 to 80, received two 4-week interventions, i.e. epicatechin (100mg/day) or placebo with a 4-week wash-out between interventions. Gene expression profiles of peripheral blood mononuclear cells were determined before and after both interventions. Epicatechin regulated 1180 genes, of which 234 differed from placebo. Epicatechin upregulated gene sets involved in transcription and tubulin folding and downregulated gene sets involved in inflammation, PPAR signalling and adipogenesis. Several negatively enriched genes within these gene sets were involved in insulin signalling. Most inhibited upstream regulators within the epicatechin intervention were cytokines or involved in inflammation. No upstream regulators were identified compared to placebo. Epicatechin, a cocoa flavan-3-ol, reduces gene expression involved in inflammation, PPAR-signalling and adipogenesis in immune cells. Effects were mild but our findings increase our understanding and provide new leads on how epicatechin rich products like cocoa may affect immune cells and exert cardiometabolic protective effects.

Protective effects of 2,3-diaryl-substituted indole-based cyclooxygenase-2 inhibitors on oxidative modification of human low density lipoproteins in vitro

It has been suggested that 2,3-diaryl-substituted indole-based cyclooxygenase-2 (COX-2) inhibitors (2,3-diaryl-indole coxibs) do not only appear as potent anti-inflammatory agents but also show the ability to scavenge reactive oxygen species (ROS). This led to the hypothesis that 2,3-diaryl-indole coxibs also may act as potent inhibitors of oxidative modification of low-density lipoprotein (LDL), which is considered a key factor in atherogenesis. The aim of this study was to explore i) the reactivity of a series of new synthesized 2,3-diaryl-indoles with several well characterized LDL oxidation systems and ii) subsequent effects on an inflammatory/atherogenic microenvironment. The results demonstrate that under the present experimental conditions 2,3-diaryl-indoles showed potent ROS scavenging activity and were able to markedly inhibit LDL oxidation. Subsequently, this led to a substantial decrease of modified LDL uptake by scavenger receptors in THP-1 macrophages in vitro and in rats in vivo. Moreover, modified LDL-mediated monocyte/neutrophil adhesion to endothelial cells, macrophage NFκB activation, as well as macrophage and endothelial cell cytokine release was diminished in vitro. The reduction of modified LDL-induced atherogenic effects by antioxidant 2,3-diaryl-indole coxibs may widen the therapeutic window of COX-2 targeted treatment.

Monitoring seasonal variation of epicatechin and gallic acid in the bark of Saraca asoca using reverse phase high performance liquid chromatography (RP-HPLC) method

Background:

Saraca asoca (Roxb.) Wilde (Fabaceae) is a high valued but vulnerable medicinal plant of Western Ghats region. This plant is mainly known for its use in various gynecological disorders.

Objective:

The objective of the present study was to investigate seasonal variation of the polyphenolic compounds viz., epicatechin and gallic acid in the bark of S. asoca by using Reverse Phase High Performance Liquid Chromatography-Diode Array Detector (RP-HPLC-DAD) method.

Materials and Methods:

The bark was collected in six different Ritu (season) viz. Varsha (monsoon), Sharad (autumn), hemant (early winter), Shishir (winter), Vasanta (spring), and Grishma (summer) mentioned in Ayurveda.

Results:

The RP-HPLC-DAD analysis indicated that levels of epicatechin and gallic acid in the bark of S. asoca vary seasonally. The highest concentration of epicatechin was observed in Shishir Ritu (3315.19 ± 165.76 mg/100g) and gallic acid during Hemant Ritu (211.90 ± 10.60 mg/100 g).

Conclusions:

In present study, the ability to synthesize and accumulate both the compounds in bark of S. asoca varied greatly throughout the seasons. It was also observed that the compound epicatechin was present abundantly as compared to gallic acid throughout the seasons.

Dietary supplementation of chardonnay grape seed flour reduces plasma cholesterol concentration, hepatic steatosis, and abdominal fat content in high-fat diet-induced obese hamsters

The mechanisms for the hypocholesterolemic and antiobesity effects of grape seed flours derived from white and red winemaking processing were investigated using male Golden Syrian hamsters fed high-fat (HF) diets supplemented with 10% partially defatted grape seed flours from Chardonnay (ChrSd), Cabernet Sauvignon (CabSd), or Syrah (SyrSd) pomace as compared to a HF control diet for 3 weeks. Hamsters fed the ChrSd diet had significantly lowered plasma total-, VLDL-, and LDL-cholesterol concentrations compared to the CabSd, SyrSd, and control diets. The improved plasma cholesterol after ChrSd was correlated with the up-regulation of hepatic genes related to cholesterol (CYP51) and bile acid (CYP7A1) synthesis as well as LDL-cholesterol uptake (LDLR). A reduction of hepatic lipid content was associated with altered expression of the genes related to lipid metabolism. However, fecal total lipid content was not changed. Expression of ileal apical sodium bile acid transporter (ASBT) was not affected by ChrSd, indicating unchanged ileal bile acid reabsorption. The antiobesity effect of the ChrSd diet appears to be related to expression of adipogenesis- and inflammation-related genes in adipose tissue. These findings suggest that flavonoid-rich Chardonnay grape seed flour induced cholesterol-lowering, antiobesity, and anti-inflammatory health benefits and attenuation of hepatic steatosis via regulation of gene expression related to cholesterol, bile acid, and lipid metabolism in liver and adipose tissue.

Effects of (-)-epicatechin and derivatives on nitric oxide mediated induction of mitochondrial proteins

Impaired mitochondrial function represents an early manifestation of endothelial dysfunction and likely contributes to the development of cardiovascular diseases (CVD). The stimulation of mitochondrial function and/or biogenesis is seen as a means to improve the bioenergetic and metabolic status of cells and thus, reduce CVD. In this study we examined the capacity of the flavanol (-)-epicatechin and two novel derivatives to enhance mitochondrial function and protein levels in cultured bovine coronary artery endothelial cells. As nitric oxide production by endothelial cells is suspected in mediating mitochondria effects (including biogenesis), we also examined the dependence of responses on this molecule using an inhibitor of nitric oxide synthase. Results indicate that the flavanol (-)-epicatechin and derivatives are capable of stimulating mitochondrial function as assessed by citrate synthase activity as well as induction of structural (porin, mitofilin) and oxidative phosporylation protein levels (complex I and II). Effects were blocked by the use of the chemical inhibitor of the synthase thus, evidencing a role for nitric oxide in mediating these effects. The results observed indicate that the three agents are effective in enhancing mitochondria function and protein content. The effects noted for (-)-epicatechin may serve to explain the healthy effects on cardiometabolic risk ascribed to the consumption of cocoa products.

Aspirin inhibits the production of reactive oxygen species by downregulating Nox4 and inducible nitric oxide synthase in human endothelial cells exposed to oxidized low-density lipoprotein

Aspirin has antithrombotic activity and is commonly used to protect patients from cardiovascular disease attacks. The present study investigated whether aspirin reduces reactive oxygen species and proinflammatory proteins in oxidized low-density lipoprotein (ox-LDL)-stimulated human umbilical vein endothelial cells. The results showed that aspirin attenuated reactive oxygen species generation induced by ox-LDL and downregulated Nox4 and inducible nitric oxide synthase expression. Redox-sensitive transcription factor nuclear factor kappa B was inactivated by aspirin, significantly preventing nuclear factor kappa B p65 subunit translocation into the nucleus. The expression of the monocyte/macrophage chemotactic protein 1 also decreased, but endothelial nitric oxide synthase expression increased in aspirin-treated cells. Aspirin ameliorated oxidative stress by downregulating Nox4 and inducible nitric oxide synthase and improved endothelial cell function by increasing endothelial nitric oxide synthase expression. Thus, aspirin may possess protective effects against ox-LDL-induced endothelial cell injury.

Protective effects of (-)-epicatechin against nitrative modifications of fibrinogen

Fibrinogen appears to be particularly sensitive to toxic action of peroxynitrite; a potent oxidizing and nitrating species. An increased nitration of fibrinogen has been reported in cardiovascular diseases. The defense mechanisms against PN are crucial for complex hemostasis process. Flavonoids have antioxidative properties and could protect biomolecules against action of peroxynitrite. The aim of our studies was to establish, if (-)-epicatechin may in vitro protect fibrinogen molecule against peroxynitrite-induced nitration of tyrosines and change its thrombin-catalyzed polymerization. The exposure of purified fibrinogen (6 μM) to peroxynitrite (1-100 μM) resulted in both structural modifications and clotting ability of this glycoprotein. Peroxynitrite at the concentration of 1 μM increased maximum velocity of Fg polymerization, whereas exposure to 100 μM PN resulted in a significant decrease of Vmax. (-)-Epicatechin (1-100 μM) caused a dose-dependent inhibition of 3-nitrotyrosine formation in fibrinogen treated with peroxynitrite (100 μM) in both Western blot assays and C-ELISA assays. At the highest concentration of (-)-epicatechin (100 μM) the level of 3-NT in fibrinogen reached the control values. At lower doses (-)-epicatechin reduced tyrosine nitration by approx. 23% and 40% at the concentration of 1 μM and 10 μM, respectively. (-)-Epicatechin also abolished the pro-thrombotic effect of peroxynitrite on fibrinogen clotting. The presented in vitro results demonstrated for the first time that (-)-epicatechin might have protective effects against the impairment of structure and properties of Fg, caused by action of the strong biologic oxidant/nitration and inflammatory mediators.

Cholesterol-lowering activity of the major polyphenols in grape seed

The major polyphenols in grape seed have been shown to have beneficial health effects in the prevention of dyslipidemia and cardiovascular diseases. In this present study, we investigated the cholesterol-lowering activity of three major polyphenolic compounds found in grape seed. The results showed that gallic acid, catechin, and epicatechin significantly inhibited pancreatic cholesterol esterase in a concentration-dependent manner. Moreover, they bound to taurocholic acid, taurodeoxycholic acid, and glycodeoxycholic acid at levels ranging from 38.6% to 28.2%. At the concentration of 0.2 mg/mL, gallic acid, catechin, and epicatechin reduced the formation of cholesterol micelles 27.26 ± 2.17%, 11.88 ± 0.75%, and 19.49 ± 3.71%, respectively. These findings clearly demonstrate that three major polyphenolic compounds present in a particular grape seed have cholesterol-lowering activity by inhibiting pancreatic cholesterol esterase, binding of bile acids, and reducing solubility of cholesterol in micelles which may result in delayed cholesterol absorption.

Myeloperoxidase-mediated LDL oxidation and endothelial cell toxicity of oxidized LDL: attenuation by (−)-epicatechin

Recent data suggest an inverse epidemiological association between intake of flavanol-rich cocoa products and cardiac mortality. Potential beneficial effect of cocoa may be attributed to flavanol-mediated improvement of endothelial function, as well as to enhancement of bioavailability and bioactivity of nitric oxide in vivo. ( - )-Epicatechin is one bioactive flavanol found in cocoa. This review deals with protective actions of ( - )-epicatechin on two key processes in atherogenesis, oxidation of LDL and damage to endothelial cell by oxidized LDL (oxLDL), with emphasis on data from this laboratory. ( - )-Epicatechin not only abrogates or attenuates LDL oxidation but also counteracts deleterious actions of oxLDL on vascular endothelial cells. These protective actions are only partially shared by other vasoprotective agents such as vitamins C and E or aspirin. Thus, ( - )-epicatechin appears to be a pleiotropic protectant for both LDL and endothelial cells.

Sulfation of dietary flavonoids by human sulfotransferases

Dietary flavonoids catechin, epicatechin, eriodictyol, and hesperetin were investigated as substrates and inhibitors of human sulfotransferases (hSULTs). Purified recombinant proteins and human intestine cytosol were used as enzyme sources. hSULT1A1 and hSULT1A3 as well as human intestine cytosol can catalyse the sulfation of the investigated flavonoids. Sulfation of catechin, epicatechin, eriodictyol, and hesperetin by recombinant hSULTs showed substrate inhibition at high flavonoid concentrations. Hesperetin and eriodictyol are potent inhibitors of purified hSULT1A1, hSULT1A3, hSULT1E1, and hSULT2A1. Catechin and epicatechin inhibited hSULT1A1 and hSULT1A3, but not hSULT1E1 and hSULT2A1. The sulfation efficacy and potency of inhibition is related to the C-ring structure of flavonoids. These results suggest that dietary flavonoids may regulate human SULT activity and, therefore, affect the regulation of hormones and neurotransmitters, detoxification of drugs, and the bioactivation of pro- carcinogens and pro-mutagens.

In vitro effects of tea polyphenols on redox metabolism, oxidative stress, and apoptosis in PC12 cells

Tea polyphenols, especially catechins, have been reported to be potent antioxidants and beneficial in oxidative stress-related diseases including cancer. Numerous animal and cell culture models demonstrate anticancer effects of tea catechins. Experimental and epidemiological evidence suggests the use of black tea polyphenols (BTP), green tea catechins (especially epigallocatechin gallate [EGCG]), and other polyphenols in preventing the progression of cancer both in animal and human populations. In the present study, we have demonstrated alterations in oxidative stress and redox metabolism using an isolated cell-free system and also in PC12 cancer cells after treatment with EGCG and BTP. We have demonstrated that tea catechins, alter the production of reactive oxygen species, glutathione metabolism, lipid peroxidation, and protein oxidation under in vitro conditions. We have also demonstrated that EGCG and BTP affect redox metabolism under cell culture conditions. Induction of apoptosis was observed, after the treatment with tea polyphenols, as shown by increased DNA breakdown and activation of the apoptotic markers, cytochrome c, caspase 3, and poly-(ADP-ribose) polymerase. These results may have implications in determining the chemopreventive and therapeutic use of tea catechins in vivo.

Microcirculation and oxidative stress

The microcirculation is a complex and integrated system, transporting oxygen and nutrients to the cells. The key component of this system is the endothelium, contributing to the local balance between pro and anti-inflammatory mediators, hemostatic balance, as well as vascular permeability and cell proliferation. A constant shear stress maintains vascular endothelium homeostasis while perturbed shear stress leads to changes in secretion of vasodilator and vasoconstrictor agents. Increased oxidative stress is a major pathogenetic mechanism of endothelial dysfunction by decreasing NO bioavailability, promoting inflammation and participating in activation of intracellular signals cascade, so influencing ion channels activation, signal transduction pathways, cytoskeleton remodelling, intercellular communication and ultimately gene expression. Targeting the microvascular inflammation and oxidative stress is a fascinating approach for novel therapies in order to decrease morbidity and mortality of chronic and acute diseases.

How do dietary flavanols improve vascular function? A position paper

Epidemiological and clinical studies revealed that high-flavanol diet or isolated (-)-epicatechin improves the function of the vascular endothelium, as assessed by flow-mediated dilation, through elevation of bioavailability and bioactivity of NO*. We have demonstrated that exposure of human endothelial cells to (-)-epicatechin elevates the cellular levels of NO* and cyclic GMP and protects against oxidative stress elicited by proinflammatory agonists. (-)-Epicatechin acts like a prodrug, since these effects involve O-methylation of the flavanol and are attributed to apocynin-like inhibition of endothelial NADPH oxidase. Thus, generation of superoxide and peroxynitrite is diminished and, consequently, the cellular NO* level is preserved or augmented. We propose therefore that endothelial NO* metabolism rather than general antioxidant activity is a major target of dietary flavanols and that NADPH oxidase activity is a crucial site of action. Moreover, flavonoid glucuronides appear to serve as plasma transport metabolites to target cells rather than solely as excretion products. Implications for the interpretation of the role of dietary polyphenols for cardiovascular health are discussed.

Protective effect of pine (Pinus morrisonicola Hay.) needle on LDL oxidation and its anti-inflammatory action by modulation of iNOS and COX-2 expression in LPS-stimulated RAW 264.7 macrophages

The protective effects of pine (Pinus morrisonicola Hay.) needle on low-density lipoprotein (LDL) oxidation and nitric oxide production in macrophages as well as its bioactive compounds were investigated. Of the four solvent extracts, the ethyl acetate extract of pine needle (EAE-PN) exhibited the strongest scavenging action on free radicals. EAE-PN significantly inhibited copper-induced LDL oxidation through prolonging the lag phase of conjugated dienes formation and decreasing the relative electrophoretic mobility of LDL. Lipid accumulation and foam cell formation were significantly reduced when EAE-PN (75 microg/mL) was added to the medium co-incubated with macrophages cells and copper-induced LDL. EAE-PN also markedly inhibited reactive oxygen species production in RAW 264.7 cells stimulated with lipopolysaccharide (LPS). As regards NO production in cells, EAE-PN showed dose-dependent inhibitory effect on nitric oxide (NO) production in LPS-stimulated RAW 264.7 cells. The inducible nitric oxide synthase (iNOS) and cyclooxygenase 2 (COX-2) protein expressions in LPS-stimulated RAW 264.7 cells were inhibited by EAE-PN. RT-PCR analysis indicated that the iNOS and COX-2 mRNA expression were suppressed by EAE-PN. The major phenolic compounds in EAE-PN were epicatechin and p-coumaric acid by HPLC analysis. The presence of epicatechin and p-coumaric acid in EAE-PN may be partially responsible for the biological action of EAE-PN. Taken together, these results suggest that EAE-PN may provide potential protective effects against LDL oxidation and attenuating excessive NO generation at inflammatory sites; consequently, this may contribute to anti-atherosclerotic and anti-inflammatory effects of EAE-PN.

(-)-Epicatechin elevates nitric oxide in endothelial cells via inhibition of NADPH oxidase

Dietary (-)-epicatechin is known to improve bioactivity of (*)NO in arterial endothelium of humans, but the mode of action is unclear. We used the fluorophore 4,5-diaminofluorescein diacetate to visualize the (*)NO level in living human umbilical vein endothelial cells (HUVEC). Untreated cells showed only a weak signal, whereas pretreatment with (-)-epicatechin (10 microM) or apocynin (100 microM) elevated the (*)NO level. The effects were more pronounced when the cells were treated with angiotensin II with or without preloading of the cells with (*)NO via PAPA-NONOate. While (-)-epicatechin scavenged O2(*-), its O-methylated metabolites prevented O2(*-) generation through inhibition of endothelial NADPH oxidase activity, even more strongly than apocynin. From the effect of 3,5-dinitrocatechol, an inhibitor of catechol-O-methyltransferase (COMT), on HUVEC it is concluded that (-)-epicatechin serves as 'prodrug' for conversion to apocynin-like NADPH oxidase inhibitors. These data indicate an (*)NO-preserving effect of (-)-epicatechin via suppression of O2(*-)-mediated loss of (*)NO.

In vitro protection of reactive oxygen species-induced degradation of lipids, proteins and 2-deoxyribose by tea catechins

Both the anti- and pro-oxidant effects of tea catechins, have been implicated in the alterations of cellular functions which determine their chemoprotective and therapeutic potentials in toxicity and diseases. Here, we have studied the protective mechanism (s) of three main green tea catechins namely, epicatechin (EC), epicatechin gallate (ECG) and epigallocatechin gallate (EGCG) on free radical induced oxidative degradation of membrane lipids and proteins under in vitro conditions using isolated cell free fractions from rat liver. In addition, we have also studied the effects of the tea catechins on 2-deoxyribose degradation in the presence of Fenton and Haber-Weiss oxidants. Glutathione S-transferase and cytochrome P450 2E1 activities and lipid peroxidation were found to be markedly inhibited by tea catechins. These catechins also inhibited the reactive oxygen species formation and oxidative carbonylation of subcellular proteins induced by a physiological oxidant, 4-hydroxynonenal. EGCG and the other catechins showed a time and concentration-dependent effects on the degradation of 2-deoxyribose in the presence of Fenton oxidants. Our results indicate that tea catechins prevent molecular degradation in oxidative stress conditions by directly altering the subcellular ROS production, glutathione metabolism and cytochrome P450 2E1 activity. These results may have implications in determining the chemotherapeutic use of tea catechins in oxidative stress related diseases.

Structure-activity relationships of flavonoid-induced cytotoxicity on human leukemia cells

The aim of this study was to identify structure elements in flavonoids that are associated with enhanced cytotoxic activity. We determined the cytotoxicity (EC(50)) of 23 different flavonoids, including O-methylated and glucuronidated metabolites, on the human leukemia cell line Jurkat E6-1 by analyzing cell death triggered after 24 and 48 h. By comparing the cytotoxicity of selected molecules that differ in only one structure element, we identified several structure-function relationships associated with enhanced cytotoxicity, including the presence of a 2-3 double bond, the presence of a 4-carbonyl group and ortho- compared to meta-hydroxylation in the B ring. Molecules with a 3-hydroxyl group exhibited significantly lower cytotoxicity than their non-hydroxylated counterparts. O-Methylation and glucuronidation were associated with a significant increase in cytotoxicity, suggesting that metabolites found in vivo are more active than unmodified flavonoids. We identified the solubility maximum of the tested flavonoids in culture medium and found a negative correlation between maximum solubility and cytotoxicity. The results of our study may help to identify novel flavonoid structures with optimized cytotoxic activity to be tested for anti-cancer treatment.

Flavonoids attenuate cardiovascular disease, inhibit phosphodiesterase, and modulate lipid homeostasis in adipose tissue and liver

Plant flavonoids are widely distributed polyphenolic compounds of the human diet. They consist of six major classes based on specific structural differences: flavonols, flavones, flavanones, catechins, anthocyanidins, and isoflavones. All of the major classes of flavonoids are comprised of three six-membered rings: an aromatic A-ring fused to a heterocyclic C-ring that is attached through a single carbon-carbon bond to an aromatic Bring. Population studies have shown that flavonoid intake is inversely correlated with mortality from cardiovascular disease, and numerous flavonoids of dietary significance have been shown to beneficially impact parameters associated with atherosclerosis, including lipoprotein oxidation, blood platelet aggregation, and vascular reactivity. Therapeutic effects of flavonoids on platelet aggregability and blood pressure have been attributed to competitive inhibition of cyclic nucleotide phosphodiesterase (PDE), an elevation in cAMP level, and subsequent activation of protein kinase A (cAMP-dependent protein kinase). In addition, flavonoids may induce neutral lipid hydrolysis from lipid stores through PDE inhibition in adipose tissue and liver. Indeed, the three-dimensional structure of many flavonoids is sterically and electrostatically compatible with the catalytic site of cAMP PDE3 and PDE4. Flavonoids have also been reported to suppress pathways of lipid biosynthesis and of very low-density lipoprotein production in cultured hepatocytes. Continued studies of the biochemical mechanisms underlying the biological effects of plant flavonoids may uncover new strategies for the treatment of cardiovascular disease, as well as associated conditions such as obesity, hepatic steatosis, and Type 2 diabetes.

Cytotoxicity of myeloperoxidase/nitrite-oxidized low-density lipoprotein toward endothelial cells is due to a high 7beta-hydroxycholesterol to 7-ketocholesterol ratio

Oxygenated cholesterols (oxysterols) formed during oxidation of low-density lipoprotein (LDL) are associated with endothelial dysfunction and atherogenesis. We compared the profile of oxysterols in modified human LDL obtained on reaction with myeloperoxidase/H2O2 plus nitrite (MPO/H2O2/nitrite-oxLDL) with that on Cu2+ -catalyzed oxidation. The 7beta-hydroxycholesterol/7-ketocholesterol ratio was markedly higher in MPO/H2O2/nitrite-oxLDL than in Cu2+ -oxidized LDL (7.9 +/- 3.0 versus 0.94 +/- 0.10). Like MPO/H2O2/nitrite-oxLDL, 7beta-hydroxycholesterol was cytotoxic toward endothelial cells through eliciting oxidative stress. Cytotoxicity was accompanied by DNA fragmentation and was prevented by the NADPH oxidase inhibitor apocynin, suggesting stimulation of NADPH oxidase-mediated O2-* formation. 7-Ketocholesterol was only cytotoxic when added alone, whereas a 1:1-mixture with 7beta-hydroxycholesterol surprisingly was noncytotoxic. We conclude from our data that (i) 7beta-hydroxycholesterol is a pivotal cytotoxic component of oxidized LDL, (ii) 7-ketocholesterol protects against 7beta-hydroxycholesterol in oxysterol mixtures or oxLDL, (iii) the 7beta-hydroxycholesterol/7-ketocholesterol ratio is a crucial determinant for cytotoxicity of oxidized LDL species and oxysterol mixtures, and (iv) the low share of 7-ketocholesterol explains the higher cytotoxicity of MPO/H2O2/nitrite-oxLDL than other forms of oxidized LDL. The dietary polyphenol (-)-epicatechin inhibited not only formation but also cytotoxic actions of both oxLDL and oxysterols.

Flavonoids from seabuckthorn protect endothelial cells (EA.hy926) from oxidized low-density lipoprotein induced injuries via regulation of LOX-1 and eNOS expression

The present investigation was undertaken to determine the protective effects of flavonoids from seabuckthorn (FSBT), a traditional Chinese medicine, on endothelial cell line EA.hy926 injury induced by oxidized low-density lipoprotein (ox-LDL). Possible mechanisms were then explored. The effects of quercetin and isorhamnetin, 2 major components of FSBT, were examined as well. Indices such as cell viability, lactate dehydrogenase, nitric oxide (NO), superoxide dismutase, and superoxide were measured. Reverse transcription polymerase chain reaction, Western blot, and immunocytochemistry were employed to determine the endothelial constitutive NO synthase (eNOS) and lectinlike low-density lipoprotein receptor-1 (LOX-1) expression. Cell viability decreased significantly after 24 hours treatment with ox-LDL, accompanied with apparent secretion disorders such as NO reduction and lactate dehydrogenase increase. FSBT pretreatment could remarkably prevent both cell death and secretion disorders in a concentration-dependent manner. Besides, it was observed that ox-LDL triggered superoxide production and suppressed the superoxide dismutase activity, both of which could be prevented by FSBT pretreatment. Moreover, ox-LDL inhibited eNOS expression and increased LOX-1 expression, whereas FSBT pretreatment partly abolished these effects. Similar effects were obtained with quercetin and isorhamnetin, implying that they may contribute, at least in part, to the protective effects of FSBT. The data indicate that the protective effects of FSBT against ox-LDL induced endothelial cell injuries might derive from its antioxidant activity and its capability in modulating the expression of eNOS and LOX-1. And quercetin and isorhamnetin may contribute to these effects of FSBT.

Quercitrin, a glycoside form of quercetin, prevents lipid peroxidation in vitro

Reactive oxygen species have been demonstrated to be associated with a variety of diseases including neurodegenerative disorders. Flavonoid compounds have been investigated for their protective action against oxidative mechanisms in different in vivo and in vitro models, which seems to be linked to their antioxidant properties. In the present study, we examine the protective mechanism of quercitrin, a glycoside form of quercetin, against the production of TBARS induced by different agents. TBARS production was stimulated by the incubation of rat brain homogenate with Fe2+, Fe2+ plus EDTA, quinolinic acid (QA), sodium nitroprusside (SNP) and potassium ferricyanide ([Fe(CN)6]3-). Quercitrin was able to prevent the formation of TBARS induced by pro-oxidant agents tested; however, it was more effective against potassium ferricyanide ([Fe(CN)6]3-, IC50=2.5), than quinolinic acid (QA, IC50=6 microg/ml) and sodium nitroprusside (SNP, IC50=5.88 microg/ml) than Fe2+ (Fe2+, IC50=14.81 microg/ml), Fe2+ plus EDTA (Fe2+ plus EDTA, IC50=48.15 microg/ml). The effect of quercitrin on the Fenton reaction was also investigated (deoxyribose degradation). Quercitrin caused a significant decrease in deoxyribose degradation that was not dependent on the concentration. Taken together, the data presented here indicate that quercitrin exhibits a scavenger and antioxidant role, and these effects probably are mediated via different mechanisms, which may involve the negative modulation of the Fenton reaction and NMDA receptor.

The emerging role of flavonoid-rich cocoa and chocolate in cardiovascular health and disease

Cocoa and chocolate have recently been found to be rich plant-derived sources of antioxidant flavonoids with beneficial cardiovascular properties. These favorable physiological effects include: antioxidant activity, vasodilation and blood pressure reduction, inhibition of platelet activity, and decreased inflammation. Increasing evidence from experimental and clinical studies using cocoa-derived products and chocolate suggest an important role for these high-flavanol-containing foods in heart and vascular protection.

Modification of low-density lipoprotein by myeloperoxidase-derived oxidants and reagent hypochlorous acid

Substantial evidence supports the notion that oxidative processes contribute to the pathogenesis of atherosclerosis and coronary heart disease. The nature of the oxidants that give rise to the elevated levels of oxidised lipids and proteins, and decreased levels of antioxidants, detected in human atherosclerotic lesions are, however, unclear, with multiple species having been invoked. Over the last few years, considerable data have been obtained in support of the hypothesis that oxidants generated by the heme enzyme myeloperoxidase play a key role in oxidation reactions in the artery wall. In this article, the evidence for a role of myeloperoxidase, and oxidants generated therefrom, in the modification of low-density lipoprotein, the major source of lipids in atherosclerotic lesions, is reviewed. Particular emphasis is placed on the reactions of the reactive species generated by this enzyme, the mechanisms and sites of damage, the role of modification of the different components of low-density lipoprotein, and the biological consequences of such oxidation on cell types present in the artery wall and in the circulation, respectively.