Structure-activity relationship in the ability of flavonols to inhibit chemiluminescence

The inhibitory effect of flavonoids on interleukin-8 release by human gastric adenocarcinoma (AGS) cells infected with cag PAI (+) Helicobacter pylori

Introduction

It is well known that the presence of Helicobacter pylori in the stomach induces gastritis and causes an immune response. Exposure of gastric epithelial cell lines to this germ induces the secretion of interleukin-8 (IL-8), which is a potent PMN-activating chemotactic cytokine. Interleukin-8 is usually elevated in gastric biopsy samples of patients with H. pylori-associated gastritis and significantly increases in the supernatant of in vitro cultivated biopsy samples of gastric mucosa with active H. pylori gastritis. Interleukin-8 is an activating factor for leucocytes and other pro-inflammatory factors, free radicals, and proteolytic enzymes. That is why natural compounds potentially useful in therapy are still investigated – among them flavonoids. They reveal anti-oxidative and anti-inflammatory activities and significantly inhibit the gastric mucosa damage.

The aim of the study

Was the estimation of the anti-inflammatory effects of flavonoids on H. pylori-induced activation of human gastric adenocarcinoma cells (AGS). After infection of AGS cells by cag PAI (+) H. pylori in vitro, secretion of IL-8, effects of flavonoids on viability of AGS cells, and effects of flavonoids on increase of H. pylori were determined. Such flavones as chrysin, quercetin, kaemferide, flavanone, galangin, and kaempferol were examined.

Results

This study has shown an inhibitory effect of flavonoids on the release of IL-8 through infected AGS cells (except chrysin), and no toxic effects to AGS cells were observed. Galangin revealed antibacterial effects against H. pylori. Flavonoids limit the inflammatory process through the inhibition of IL-8 release in infected AGS cells with H. pylori. The strongest inhibitor of IL-8 was galangin.

Effects of Flavonoids from Food and Dietary Supplements on Glial and Glioblastoma Multiforme Cells

Quercetin, catechins and proanthocyanidins are flavonoids that are prominently featured in foodstuffs and dietary supplements, and may possess anti-carcinogenic activity. Glioblastoma multiforme is the most dangerous form of glioma, a malignancy of the brain connective tissue. This review assesses molecular structures of these flavonoids, their importance as components of diet and dietary supplements, their bioavailability and ability to cross the blood-brain barrier, their reported beneficial health effects, and their effects on non-malignant glial as well as glioblastoma tumor cells. The reviewed flavonoids appear to protect glial cells via reduction of oxidative stress, while some also attenuate glutamate-induced excitotoxicity and reduce neuroinflammation. Most of the reviewed flavonoids inhibit proliferation of glioblastoma cells and induce their death. Moreover, some of them inhibit pro-oncogene signaling pathways and intensify the effect of conventional anti-cancer therapies. However, most of these anti-glioblastoma effects have only been observed in vitro or in animal models. Due to limited ability of the reviewed flavonoids to access the brain, their normal dietary intake is likely insufficient to produce significant anti-cancer effects in this organ, and supplementation is needed.

Modulation of human neutrophils' oxidative burst by flavonoids

Inflammation is a normal response towards tissue injury, but may become deleterious to the organism if uncontrolled. The overproduction of reactive species during the inflammatory process may cause or magnify the damage at inflammatory sites. Flavonoids have been suggested as therapeutic agents to avoid such damage, as these compounds exhibit anti-inflammatory activity, through the modulation of oxidative stress and signalling pathways. Both effects may attenuate neutrophils' activities at inflammatory sites. In this study, we investigated the structure/activity relationship of a series of flavonoids on the oxidative burst of human neutrophils in vitro, as a measure of its anti-inflammatory potential. Neutrophils were stimulated with phorbol-12-myristate-13-acetate, and fluorescence and chemiluminescence techniques were used to evaluate the generation of reactive oxygen species. All the tested flavonoids revealed the ability to modulate the neutrophil's oxidative burst. From the obtained results, the pivotal role of the catechol group in the B-ring was evidenced as well as the minor importance of the hydroxylations in the A-ring, which did not appear to be determinant for the activity, although clearly influencing the lipophilicity of the tested flavonoids. It is also clarified the importance of the methylation in the OH group at the B-ring catechol moiety. In conclusion, the obtained results uncover new possible strategies for the resolution of inflammatory processes, using flavonoids to modulate neutrophil's oxidative burst.

The biological activity of propolis-containing toothpaste on oral health environment in patients who underwent implant-supported prosthodontic rehabilitation

The soft and periodontal tissues surrounding dental implants are particularly susceptible to bacteria invasion and inflammatory reactions due to complex histological structures. This study was carried out to investigate the influence of a propolis-containing hygienic agent on selected oral health parameters, oral microflora, and the condition of periodontal health. Sixteen subjects who underwent an oral rehabilitation with dental implants were selected and randomly assigned into two groups, which received a newly formulated propolis-containing toothpaste (3% (CA)) or a negative control without an active ingredient (CC). Approximal plaque index (API), oral hygiene index (OHI, debris component), and sulcus bleeding index (SBI) were assessed in three subsequent stages. During the first and last examinations, the swabs were employed for microbiological inoculation. Propolis-containing toothpaste was found to be distinctively effective in improving oral health and the occurrence of gingivitis triggered by dental plaque. The qualitative and quantitative changes in oral bacteria spectrum were observed. Antibacterial measures containing propolis might be used as a natural adjuvant to other active substances in individuals with a high risk of periodontal problems against pathogenic oral microflora.

The antibacterial effect of ethanol extract of polish propolis on mutans streptococci and lactobacilli isolated from saliva

Dental caries occurrence is caused by the colonization of oral microorganisms and accumulation of extracellular polysaccharides synthesized by Streptococcus mutans with the synergistic influence of Lactobacillus spp. bacteria. The aim of this study was to determine ex vivo the antibacterial properties of ethanol extract of propolis (EEP), collected in Poland, against the main cariogenic bacteria: salivary mutans streptococci and lactobacilli. The isolation of mutans streptococci group bacteria (MS) and Lactobacillus spp. (LB) from stimulated saliva was performed by in-office CRT bacteria dip slide test. The broth diffusion method and AlamarBlue assay were used to evaluate the antimicrobial activity of EEP, with the estimation of its minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC). The biochemical composition of propolis components was assessed. The mean MIC and MBC values of EEP, in concentrations ranging from 25 mg/mL to 0.025 mg/mL, for the MS and LB were found to be 1.10 mg/mL versus 0.7 mg/mL and 9.01 mg/mL versus 5.91 mg/mL, respectively. The exposure to an extract of Polish propolis affected mutans streptococci and Lactobacillus spp. viability, exhibiting an antibacterial efficacy on mutans streptococci group bacteria and lactobacilli saliva residents, while lactobacilli were more susceptible to EEP. Antibacterial measures containing propolis could be the local agents acting against cariogenic bacteria.

In vitro evaluation of the antioxidant activity of liposomal flavonols by the HRP-H2O2-luminol system

Considering that antioxidant flavonols have been reported to be beneficial to human health, but that their low water solubility and bioavailability limit their administration through systemic route, the development of suitable flavonol-carriers is of great importance for clinical therapeutics. The aim of this study was to prepare liposomes containing flavonols or not and evaluate their antioxidant activity. Vesicles were obtained by ethanol injection method and characterized in terms of entrapment efficiency, size and zeta potential. Inhibitory activity of liposomal flavonols on reactive oxygen species generation was assessed in vitro using luminol-H(2)O(2)-horseradish peroxidase technique. Antioxidant activity of liposomal flavonols is dependent on concentration and chemical structure of active compound. Quercetin and myricetin are the most active flavonols (IC(50) = 0.6-0.9 µmol/L), followed by kaempferol (IC(50) = 3.0-4.5 µmol/L) and galangin (IC(50) = 4.0-7.0 µmol/L). Our results suggest that antioxidant-loaded liposomes may be promising tools for therapy of diseases where oxidative stress is involved.

Inhibition of inflammatory mediators by neobavaisoflavone in activated RAW264.7 macrophages

Flavonoids and coumarins are the major bioactive constituents identified in Psoralea corylifolia. The active fraction isolated from fruits, seeds and roots possesses antibacterial, antioxidative and immunomodulatory properties. Neobavaisoflavone is one of the flavonoids found in Psoralea corylifolia. In the present study we investigated in vitro the anti-inflammatory activity of neobavaisoflavone. Macrophages play an important role in inflammation through the release of inflammatory mediators involved in the immune response. Inappropriate and prolonged macrophage activation is largely responsible for the pathology of acute and chronic inflammatory conditions. Neobavaisoflavone significantly inhibited the production of reactive oxygen species (ROS), reactive nitrogen species (RNS) and cytokines: IL-1β, IL-6, IL-12p40, IL-12p70, TNF-α in LPS+IFN-γ– or PMA– stimulated RAW264.7 macrophages.

DPPH-Scavenging Activities and Structure-Activity Relationships of Phenolic Compounds

Thirty-eight phenolic compounds (including 31 flavonoids) were examined for their DPPH radical-scavenging activities, and structure-activity relationships were evaluated. Specifically, the presence of an Ortho-dihydroxyl structure in phenolics is largely responsible for their excellent antiradical activity. 3-Hydroxyl was also essential to generate a high radical-scavenging activity. An increasing number of hydroxyls on flavones with a 3′,4′-dihydroxyl basic structure, the presence of a third hydroxyl group at C-5′, a phloroglucinol structure, glycosylation and methylation of the hydroxyls, and some other hydroxyls, for example 5-, and 7-hydroxyl in ring A, decreased the radical-scavenging activities of flavonoids and other phenolics.

Evaluation of the Potential of Brazilian Propolis against UV-Induced Oxidative Stress

This study investigated the potential use of topically and orally administered propolis extracts to prevent UV irradiation-induced oxidative stress in skin. The results illustrated that green propolis extract (GPE) contained greater amounts of polyphenols, coumaric acid, drupanin, baccharin and artepillin C than did brown propolis extract (BPE). GPE showed higher antioxidant activity than BPE when the IC₅₀ (concentration that caused 50% inhibition) values were compared. Interesting, the oral treatment of hairless mice demonstrated a recovery of 30.0% for GPE and 22.8% for BPE with respect to UV irradiation-induced GSH depletion. The topical pretreatment of animals with both propolis extract solutions recovered around 14.0% of the depleted GSH. However, the employed treatments did not inhibit the increase of cutaneous proteinase secretion/activity caused by irradiation. These findings indicate that despite differences in composition and antioxidant properties, GPE and BPE both successfully prevent UV-induced GSH depletion in vivo and are both promising antioxidant systems against oxidative stress in skin. Based on these findings, complementary studies should be performed to enhance our understanding of the protective effects of propolis extracts in skin.

Antioxidant potential of peels and fleshes of peaches from different cultivars

Increasing recent interest in nutraceuticals and functional foods has led researchers to investigate the antioxidant potential of several fruits. This article evaluates the antioxidant potential and reactivity based on luminol-enhanced chemiluminescence capacity of peach extracts (peels and fleshes) and the contribution of a major compound present in these extracts to antioxidant potential and reactivity. The results obtained showed that the extracts of peels and fleshes of Maciel, Leonense, and Eldorado peach cultivars present free radical scavenging activity in all concentrations tested, with a concentration-dependent action. The immediate inhibition of chemiluminescence and the duration of this inhibition were significantly higher with the extracts than with the major compound (chlorogenic acid) alone, and it can be due to a synergistic or additive effect of other antioxidants present in the extracts. The 50% inhibitory concentration (IC(50)) values for peach extract and chlorogenic acid were 1.19 microg/mL and 8.43 microg/mL, respectively, when total radical-trapping antioxidant potential was evaluated, whereas IC(50) values of 0.41 microg/mL and 1.89 microg/mL was found when total antioxidant reactivity was evaluated in peach extract and chlorogenic acid, respectively. Chlorogenic acid presented a good contribution to antioxidant reactivity and potential, but the fruit extracts provide better antioxidant action. Peach could be of great interest as an important antioxidant source including chlorogenic acid, and it may provide health-promoting advantages to consumers by intake of this fruit or by utilization of its peels as antioxidant sources in industry.

Sesquiterpene lactones from Lychnophora pohlii: neutrophil chemiluminescence inhibition and free radical scavenger activity

Excessive production of reactive oxygen species (ROS) by polymorphonuclear leucocytes (PMNLs) is thought to contribute to the pathology of many inflammatory diseases. Sesquiterpene lactones (STLs) seem to be important contributors to the anti-inflammatory activity of many species of Lychnophora (Asteraceae), which have been widely used in Brazilian folk medicine because of this pharmacological property. In this study, the inhibitory effects of three STLs isolated from Lychnophora pohlii (lychnopholide, centratherin and goyazensolide) on rabbit PMNL oxidative burst were evaluated by the luminol-enhanced chemiluminescence (CL-lum) assay. All STLs tested showed concentration-dependent inhibitory activity on CL-lum but were not cytotoxic to PMNLs (evaluated by lactate dehydrogenase release) under the assessed conditions. Moreover, goyazensolide, the most active STL, had no free radical scavenger property, as assessed by 1,1-diphenyl-2-picrylhydrazyl radical assay, and had no inhibitory effect on the luminol-horseradish peroxidase-hydrogen peroxide chemiluminescence. Taken together, the results of this investigation suggest that the concomitant presence of methacrylate ester and hydroxyl groups contributes to a high inhibitory effect on PMNL oxidative metabolism. This effect was not mediated by free radical scavenger or cytotoxic effects, but probably by inhibition of enzymes involved in the signal transduction pathways of the ROS generation process.

Neutrophil effector functions triggered by Fc-gamma and/or complement receptors are dependent on B-ring hydroxylation pattern and physicochemical properties of flavonols

Tissue damage in autoimmune diseases involves excessive production of reactive oxygen species (ROS) triggered by immune complexes (IC) and neutrophil (PMN) interactions via receptors for the Fc portion of IgG (FcgammaR) and complement receptors (CR). Modulation of both the effector potential of these receptors and ROS generation may be relevant to the maintenance of body homeostasis. In the present study, the modulatory effect of four flavonols (myricetin, quercetin, kaempferol, galangin) on rabbit PMN oxidative metabolism, specifically stimulated via FcgammaR, CR or both classes of receptors, was evaluated by luminol- and lucigenin-dependent chemiluminescence assays. Results showed that flavonol inhibitory effect was not dependent on the cell membrane receptor class stimulated but related to the lipophilicity of the compounds (their apparent partition coefficient values were obtained by high-performance liquid chromatography), and was also inversely related to the number of hydroxyl groups in the flavonol B ring and the ROS-scavenger activity (assessed by the luminol--H2O2--horseradish peroxidase reaction). Under the experimental conditions the flavonols tested were not toxic to PMNs (evaluated by lactate dehydrogenase release and trypan blue exclusion) and did not interfere with IC-induced phagocytosis (evaluated by transmission electron microscopy). Our results suggested that inhibition of IC-stimulated PMNs effector functions by the flavonols tested herein was the result of cooperation of different cellular mechanisms.

Development of topical functionalized formulations added with propolis extract: stability, cutaneous absorption and in vivo studies

Propolis, which is a natural product widely consumed in the folk medicine, is a serious candidate to be applied topically due to its outstanding antioxidant properties. So, the purpose of this study was to develop stable topical formulations added with propolis extract in an attempt to prevent and/or treat the diseases occurring in skin caused by UV radiation. The antioxidant activity using a chemiluminescent method was used to evaluate the functional stability and the permeation/retention in skin of these formulations. In the long-term stability study, the formulations were stored at 25+/-2 degrees C/AH and at 40+/-2 degrees C/70% RH for 360 days. It was found in this study, that the formulations prepared with Polawax showed functional and physical stability in the period of study. In addition, this formulation presented good results in the percutaneous study, allowing the antioxidant compounds present in the propolis extract to reach lower layers in pig ear skin and in the whole hairless mice skin (retention=0.12 and 0.13 microL of propolis/g of skin, respectively). In the in vivo study, it was also suggested that this formulation may be effective in protecting skin from UVB photodamage, nevertheless other assays need to be done in order to have a complete understanding of the protective effect of formulations added with propolis extract.

In Vitro Antioxidant and In Vivo Photoprotective Effects of an Association of Bioflavonoids with Liposoluble Vitamins

A new tendency in cosmetic formulations is the association of botanical extracts and vitamins to improve skin conditions by synergic effects. The objective of this study was to determine the antioxidant activity of associated bioflavonoids, retinyl palmitate (RP), tocopheryl acetate (TA) and ascorbyl tetraisopalmitate (ATIP), as well as their photoprotective effects in preventing increased erythema, transepidermal water loss (TEWL) and sunburn cell formation in hairless mouse skin. The antioxidant activity of solutions containing the association or each substance separately was evaluated in vitro by a chemiluminescence assay. The photoprotective effect was evaluated by means of in vivo tests. Dorsal skin of hairless mice was treated daily by topical applications for 5 days with formulations containing or not containing (vehicle) the flavonoid-vitamins association (5%). The skin was irradiated (UVA/B) 15 minutes after the last application. The results showed that bioflavonoids had in vitro antioxidant properties and also that when they were associated with vitamins their antioxidant activity was more pronounced. On the other hand, erythema and UV damage to the permeability barrier function (TEWL) was not significantly reduced by previous treatment with the flavonoid-vitamin-association formulations, when compared to the irradiated vehicle-treated area. However, the treatment protected the skin from UV damage because it reduced the number of sunburn cells, when compared to the vehicle-treated area. Finally, the association of vitamins and bioflavonoids added to a dermocosmetic formulation showed a relevant biological activity in terms of photoprotection, because the association of bioflavonoids and vitamins acted by different mechanisms, such as antioxidation and absorption of UV radiation, which suggests its use in antiaging and photoprotective products.

Assessment of the antioxidant activities of Brazilian extracts of propolis alone and in topical pharmaceutical formulations

The antioxidant activity of extracts of propolis and of formulations added with these extracts were measured by scavenging different radicals in different systems. For the ethanolic extract of propolis (EEP) and the glycolic extract of propolis (GEP) the IC50 observed were respectively of 0.024 and 0.035 microL/mL in scavenging hydroxyl radical, 0.016 and 0.012 microL/mL in inhibiting lipid peroxidation, 0.22 and 0.24 microL/mL in inhibiting chemiluminescence produced in the H2O2/luminol/horseradish peroxide (HRP) system and about 0.005 microL/mL for both extracts in inhibiting chemiluminescence produced in the xanthine/luminol/xanthine oxidase (XOD) system. The antioxidant activity of extracts of propolis in the formulations was not able to be assessed neither using the deoxyribose assay, since the formulation components interfered in the assay measurements, nor using chemiluminescence in the H2O2/luminol/HRP system, since this method did not show to be sensitive for the extract of propolis evaluation. However, the antioxidant activity of extracts of propolis could be successfully evaluated in the formulations using both lipid peroxidation and chemiluminescence generated in the xanthine/luminol/XOD system inhibitions.

Assays of physical stability and antioxidant activity of a topical formulation added with different plant extracts

In the present investigation the changes on physical stability (pH, viscosity, flow index and tixotropy) of topical formulations were evaluated following inclusion of different plant extracts containing flavonoids. Also, the antioxidant effect of these plant extracts alone and after addition in the formulation was evaluated using chemiluminescence and the stable free radical 1,1-diphenyl-2-picrylhydrazyl (DPPH(.-)) assays, as well as the inhibition of lipid peroxidation. Formulation added with dl-alpha-tocopherol was used to compare the physical stability and antioxidant activity. Formulations with plant extracts showed pseudoplastic behavior with decreasing on viscosity and tixotropy. The Glycyrrhiza glabra (GG) and Ginkgo biloba (GB) extracts alone and the formulations containing these extracts showed great antioxidant and free radical scavenging activities while the other extracts studied (mixture of Glycyrrhiza glabra, Symphytum officinale L and Arctium majus root, Nelumbium speciosum and soybean) showed lower activity. The results suggest that GG and GB extracts may be used in topical formulations in order to protect skin against damage caused by free radical and reactive oxygen species.

Structure-antioxidant activity relationships of flavonoids isolated from the resinous exudate of Heliotropium sinuatum

Relationships between the structural characteristics of flavonoids isolated from the resinous exudate of Heliotropium sinuatum and their antioxidant activity were studied. Radical formation energies, DeltaH of dehydrogenation and spin densities were calculated using DFT methods (B3LYP/6-31G*). Results show that studied flavonoids can be divided into two sets according to their activity. It has been found that antioxidant activity depends both on substitution pattern of hydroxyl groups of the flavonoid skeleton and the presence of an unsaturation at the C2-C3 bond. A good tendency between DeltaH of dehydrogenation and antioxidant activity was established.

Evaluation of hesperetin 7-O-lauryl ether as lipid-lowering agent in high-cholesterol-fed rats

The lipid-lowering efficacy of hesperetin was revealed in preliminary studies on experimental animals. As such, the current study compared the effect of hesperetin 7-O-lauryl ether, with that of hesperetin and lovastatin on the lipid profile and cholesterol-regulating mechanism in high-cholesterol-fed rats. Male rats were fed a high-cholesterol diet (1%, wt/wt) or high-cholesterol diet supplemented with lovastatin (1, 0.02%, wt/wt), hesperetin (2, 0.02%, wt/wt), or hesperetin 7-O-lauryl ether (3, 0.031%, wt/wt) for six weeks. The supplemental amount of 3 was 0.066mmol/100g diet as an equivalent to the supplemental amount of 2. The plasma total cholesterol and triglyceride levels were significantly lowered by the 2 and 3 supplements compared with the control or 1-supplemented group. The hepatic HMG-CoA reductase activities were also significantly lower in all the supplemented groups compared with the control group, and the hepatic ACAT activity was significantly lower in the 2- and 3-supplemented groups. The supplementation of 3 resulted in a higher excretion of total neutral sterol and total fecal sterol compared with the control or 1-supplemented group. Accordingly, overall, compound 3, exhibited a more potent plasma lipid-lowering effect than compound 1 based on inhibiting cholesterol biosynthesis and esterification, while also increasing the fecal sterol excretion.

Effects of ethanol extract of propolis (EEP) and its flavones on inducible gene expression in J774A.1 macrophages

Propolis, a bee-hive product, has been used in folk medicine for centuries, and recently in modern medicine as an anti-inflammatory and immunomodulatory agent. These activities would be mainly due to phenolic compounds such as flavonoids, especially flavone derivatives. The present study examined the effect of ethanol extract of propolis (EEP) and selected flavone derivatives (chrysin, galangin, kaempferol and quercetin) on interleukin-1beta (IL-1beta) and inducible nitric oxide synthase (iNOS) gene expression in lipopolysaccharide (LPS)-induced J774A.1 macrophages. Treatment of cells with EEP significantly suppressed both IL-1beta mRNA (P<0.02) and iNOS mRNA (P<0.001) expression. The concentrations of cytokine in cell culture supernatants and cell lysates and nitric oxide (NO) generation were reduced in a dose-dependent manner. The tested phenolic compounds significantly decreased the IL-1beta mRNA level and IL-1beta protein concentration (P<0.05) (excluding galangin), iNOS mRNA level and NO production (P<0.001). The most potent inhibitor of the IL-1beta synthesis and NO generation was chrysin. These results indicate that EEP exerts its inhibitory effect on the IL-1beta and iNOS gene expression in J774A.1 macrophages at the transcriptional level. Tested flavone derivatives contribute to the anti-inflammatory activity of propolis.

Two cinnamate derivatives produce similar alteration in mRNA expression and activity of antioxidant enzymes in rats

Cinnamate is a widespread secondary metabolite of phenolic compound synthesized by plants for defensive purposes. The current study was designed to investigate the effect of two structurally related cinnamate derivatives, 4-hydroxycinnamate and 3-(4-hydroxyphenyl)propionic acid (HPP), on the mRNA expression and activity of antioxidant enzymes in high-cholesterol-fed rats. Male rats were fed a 1 g/100 g high-cholesterol diet with supplements of either 4-hydroxycinnamate or HPP (0.135 mmol/100 g diet) for 6 weeks. The plasma paraoxonase activity was found to be higher in the cinnamate-derivative-supplemented groups than in the control group. The erythrocyte superoxide dismutase (SOD) and catalase (CAT) activities, plus glutathione (GSH) level, were all significantly higher in the 4-hydroxycinnamate- and HPP-supplemented groups than in the control group. However, both 4-hydroxycinnamate and HPP supplementation significantly lowered the hepatic activities and mRNA expression of CAT and glutathione peroxidase (GSH-Px) compared to the control group. The hepatic mRNA expression and activity of SOD did not differ between the groups. The hepatic thiobarbituric acid reactive substances (TBARS) level was significantly lowered by the 4-hydroxycinnamate and HPP supplementation. Accordingly, these results indicate that supplementation by 4-hydroxycinnamate and HPP would seem to enhance the antioxidative defense of erythrocyte. Both HPP and 4-hydroxycinnamate would appear to be beneficial in improving the function of antioxidative enzymes on a molecular level in high-cholesterol-fed rats.

Comparison of antioxidant activities of tocopherols alone and in pharmaceutical formulations

The objective of the present investigation was to compare the antioxidant effect of different forms of Vitamin E (DL-alpha-tocopherol, Mixed Tocopherols, Ronoxan MAP and alpha-tocopherol acetate) and of topical formulations containing these active pharmaceutical ingredients, using chemiluminescence and the stable free radical 1,1-diphenyl-2-picrylhydrazyl (DPPH) assays. Inhibition of the intensity of chemiluminescence, using the H2O2-luminol-horseradish peroxidase (HRP) enzyme system, was measured for 10 min at room temperature in 10 microl samples of each vitamin at different concentrations, and of formulations containing these vitamins. H-donor ability in the DPPH assay, was measured in 10 microl samples at different concentrations of each vitamin, as well as in formulation in ethanol solution; the decrease of absorbency was read at 517 nm. DL-alpha-tocopherol, Mixed Tocopherols and Ronoxan MAP alone or in formulations, markedly inhibited chemiluminescence intensity and decreased absorbency in the DPPH assay in a concentration-dependent manner. Alpha-tocopherol acetate and formulations containing this vitamin did not show antioxidant activity in either assay. Other components of the formulations did not interfere with the measurements, indicating that the methods employed can be used to evaluate antioxidant activity in topical formulations.

Naringenin 7-O-cetyl ether as inhibitor of HMG-CoA reductase and modulator of plasma and hepatic lipids in high cholesterol-fed rats

Numerous studies in vitro have shown a close relationship between the chemical structure and biologic activity of flavonoids, whereby their basic structure is modified to increase or decrease their biologic activity. The effects of naringenin (1) and its synthetic derivative, naringenin 7-O-cetyl ether (2), on the lipid profile, the cholesterol-regulating enzyme activity and the excretion of sterol were compared in rats fed a high-cholesterol (1% wt/wt) diet. Either 1 or 2 was supplemented with a high-cholesterol diet for 6 weeks at a dose of 0.073 mmol/100g diet. The supplementation of 1 or 2 significantly lowered the levels (mean+/-SE) of the plasma total cholesterol (4.93+/-0.19 and 4.75+/-0.16 mmol/L vs 5.87+/-0.36 mmol/L, p<0.05) and hepatic triglyceride (0.12+/-0.01 and 0.11+/-0.01 mmol/g vs 0.18+/-0.01 mmol/g, p<0.05) and cholesterol (0.23+/-0.01 and 0.21+/-0.01 mmol/g vs 0.31+/-0.01 mmol/g, p<0.05) compared to those of the control. The compound 1 or 2 supplementation appeared to decrease the excretion of neutral sterols. The plasma HDL-cholesterol concentration and ratio of HDL to total cholesterol were significantly higher in 1 and 2 groups than in control group. Although the biological effect of 2 on inhibiting hepatic HMG-CoA reductase and ACAT activities was only significant compared to the control group, both compounds exhibited a significant hypocholesterolemic effect in rats fed a high-cholesterol diet. The results suggest that cholesterol biosynthesis and esterification were concomitantly reduced by 2, as indicated by the decreased HMG-CoA reductase and ACAT activities.

Effect of flavone derivatives on interleukin-1beta (IL-1beta) mRNA expression and IL-1beta protein synthesis in stimulated RAW 264.7 macrophages

It is known that the redox status of cells affects gene expression. Flavones, as natural antioxidants, efficiently modulate this status and may play a role in the regulation of inducible gene expression of inflammatory mediators. This study was designed to investigate the effect of five flavone derivatives variously substituted with hydroxyl groups (chrysin, galangin, kaempferol, quercetin and myricetin) on interleukin-1beta (IL-1beta) gene expression in stimulated RAW 264.7 macrophages. The cells were incubated with tested hydroxyflavones and stimulated with lipopolysaccharide (LPS) and interferon-gamma (IFN-gamma). Then, the following were estimated: the level of IL-1beta mRNA in these cells and the concentration of IL-1beta protein in cell-culture supernatants and cell lysates. Each of the tested compounds significantly decreased IL-1beta mRNA expression. The most potent inhibitor was chrysin (hydroxyflavone with two hydroxyl groups and a weak antioxidant activity). The effects of galangin and kaempferol were similar. Myricetin (hydroxyflavone with a strong antioxidant activity) significantly decreased the level of IL-1beta mRNA, but it had no effect on the IL-1beta protein synthesis. The results indicated that hydroxyflavones could modulate the IL-1beta gene expression in activated RAW 264.7 macrophages via inhibiting gene transcription. This action seems unlikely to be the result of antioxidant properties of tested compounds.

The biochemistry and medical significance of the flavonoids

Flavonoids are plant pigments that are synthesised from phenylalanine, generally display marvelous colors known from flower petals, mostly emit brilliant fluorescence when they are excited by UV light, and are ubiquitous to green plant cells. The flavonoids are used by botanists for taxonomical classification. They regulate plant growth by inhibition of the exocytosis of the auxin indolyl acetic acid, as well as by induction of gene expression, and they influence other biological cells in numerous ways. Flavonoids inhibit or kill many bacterial strains, inhibit important viral enzymes, such as reverse transcriptase and protease, and destroy some pathogenic protozoans. Yet, their toxicity to animal cells is low. Flavonoids are major functional components of many herbal and insect preparations for medical use, e.g., propolis (bee's glue) and honey, which have been used since ancient times. The daily intake of flavonoids with normal food, especially fruit and vegetables, is 1-2 g. Modern authorised physicians are increasing their use of pure flavonoids to treat many important common diseases, due to their proven ability to inhibit specific enzymes, to simulate some hormones and neurotransmitters, and to scavenge free radicals.

Supplementation of naringenin and its synthetic derivative alters antioxidant enzyme activities of erythrocyte and liver in high cholesterol-fed rats

The antioxidative effects of naringenin (1) and its synthetic derivative, naringenin 7-O-cetyl ether (2), were tested. Male rats were fed a 1 g/100 g high-cholesterol diet for 6 weeks with supplements of either 1 or 2 (0.073 mmol/100 g diet) to study the effects on the antioxidant enzyme activities in the erythrocyte and liver. The erythrocyte catalase (CAT) and superoxide dismutase (SOD) activities were significantly higher in the compounds 1 or 2 supplemented groups than in the control group, whereas the hepatic SOD and CAT activities were significantly lower in the compound 2 supplemented group. The compounds 1 and 2 supplements to a high cholesterol diet lowered or tended to lower the plasma TBARS levels, that is, lipid peroxide products, while enhancing the plasma paraoxonase activity. These results indicate that the supplementation of 1 and 2 was effective in improving the antioxidant capacity of the erythrocyte and liver, plus the synthetic functional compound 2 appeared to be as potent as 1 in enhancing the antioxidant defense system.

Chemistry of the antioxidant effect of polyphenols

Most plant-derived polyphenols exhibit strong antioxidant potentials, established by various assay procedures. With pulse radiolysis experiments, absolute scavenging rate constants can be obtained with a variety of oxidizing radicals which allow further structure-activity correlations and, combined with EPR spectroscopy, detailed insight into the mechanisms governing these antioxidant reactions. The most striking difference occurs between regular flavonoids and both condensed and hydrolyzable tannins. The tannins are considered superior antioxidants as their eventual oxidation may lead to oligomerization via phenolic coupling and enlargement of the number of reactive sites, a reaction which has never been observed with the flavonoids themselves.

The effect of ginkgo biloba extract on free radical production in hypoxic rats

In the present study, we assayed the antioxidant properties of Ginkgo biloba (Gb) extract on rats submitted to 21 d of chronic hypoxia. Doses of 25 and 50 mg/kg were examined. Oxygenated free radical production measured by the chemiluminescence technique was significantly decreased in treated rats compared to control rats placed in similar experimental conditions, and this effect was more significant at the 50 mg/kg dose. On the other hand, no antioxidant enzyme activities of the drug were observed towards red blood cells. These results suggest that ginkgo biloba extract has a free radical scavenging action. These antioxidant properties could explain the beneficial hematological properties of Gb extract.

Immunopharmacological properties of flavonoids

The flavonoids are a heterogeneous group of ubiquitous plant polyphenols that abound in the human diet and are endowed with several biological activities, including immunomodulating and antioxidant activities. The bioactivity of flavonoids is tightly correlated with their chemical structure and action mechanisms, mostly inhibitory, on enzymatic systems involved in cellular activation. The aim of this study was to evaluate the effects of acetonic extracts from Lunularia cruciata gametophytes and Feijoa sellowiana fruits on human phagocyte functions. A purified native flavonoid, a catechin, and two of its derivatives were also tested. The extract, and its flavonoid activity, was evaluated by analyzing luminol-dependent chemiluminescence emitted by human circulating phagocytes, at rest or activated by phorbol miristate acetate (PMA). The results demonstrate that both the raw extracts and flavonoids significantly inhibit CL emission by leukocytes, especially when these cells are activated by PMA. The antioxidant activity of flavonoids can be increased by changing the chemical structure of the native molecule.

Study on the inhibitory effect of tannins and flavonoids against the 1,1-diphenyl-2 picrylhydrazyl radical

Fifty-one tannins and forty-one flavonoids isolated from Oriental medicinal herbs were evaluated for their antioxidant ability with a 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical-generating system. The results showed that tannins and certain flavonoids are potential free-radical scavengers, and that their activity against the DPPH radical is closely associated with their chemical structure. A comparison of the two classes of compounds showed that tannins have more potential than flavonoids because almost all the tannins demonstrated significant scavenging action within a low concentration range, whereas the activity of flavonoids varied distinctively among the different compounds. An increase of galloyl groups, molecular weight, and ortho-hydroxyl structure enhanced the activity of tannins, whereas the number and position of hydroxyl groups were important features for the scavenging of free radicals by flavonoids. Moreover, it appeared that when the free hydroxyl group was methoxylated or glycosylated, the inhibitory activity was obviously decreased or even abolished.

Inhibition of N-formylmethionyl-leucyl-phenylalanine-stimulated tyrosine phosphorylation and phospholipase D activation by quercetin in rabbit neutrophils

We investigated the effect of bioflavonoid quercetin on tyrosine phosphorylation and phospholipase D (PLD, EC 3.1.4.4) activation in rabbit peritoneal neutrophils stimulated by N-formylmethionyl-leucyl-phenylalanine (fMLP). The quercetin dose-dependently inhibited degranulation and superoxide production in fMLP-stimulated neutrophils. A strong inhibitory effect of quercetin on the tyrosine phosphorylation of several proteins (40, 42, 43, 45, 46 and 75 kDa) was observed when the neutrophils were pretreated with different concentrations of quercetin. Furthermore, quercetin inhibited mitogen activated protein kinase (MAP kinase) and PLD activation induced by fMLP in a dose-dependent manner. The reduction in PLD activity was 30% at 0.1 microM and 70% at 100 microM of quercetin. These results suggest that impairment of neutrophil functions by quercetin may be due, at least in part, to inhibition of tyrosine phosphorylation and PLD activation.

Inhibition of neutrophils' chemiluminescence by ethanol extract of propolis (EEP) and its phenolic components

Ethanol extract of propolis (EEP), a natural beehive product, has been known for centuries for a variety of beneficial traditional medical properties, among which an anti-inflammatory effect is a major one. Now that most of its components have been isolated and recently identified, we tested 19 of them (all phenolic compounds) for their degree of anti-inflammatory activity. This was performed by evaluating the luminol-enhanced chemiluminescence, formed after their scavenging free radicals, generated by neutrophils that had been stimulated by phorbol myristate acetate. Caffeic-acid-phenylethyl-ester abolished the chemiluminescence completely at a concentration of 10 microM, while three flavone derivatives and three flavonols (galangin, kaempferol and kaempferid) diminished this chemiluminescence by 73-93% at the same concentration. These results indicate that some of the phenolic components of the ethanol extract of propolis are its active components in exerting its renowned anti-inflammatory activity.

Inhibition of nitric oxide (NO.) production in murine macrophages by flavones

The effect of flavone (2-phenylbenzopyran-4-one) and three amino-substituted flavones on the production of nitrite by murine activated peritoneal macrophages was studied in vitro. Activated peritoneal macrophages obtained from mice pre-treated with concanavalin A (Con A) (in vivo), after exposure in vitro to lipopolysaccharide (LPS) at a concentration of 100 ng/ml, produced nitrite (20.3 +/- 2.5 nmol/10(6) cells), as measured after 24 hr by the Griess reaction. Stimulation of production of nitrite was inhibited by NG-monomethyl-L-arginine, suggesting that nitrite was formed via nitric oxide (NO.) as a product of metabolism of arginine. Stimulation was inhibited by flavone and the aminoflavones (20-100 microM). 3'-amino-4'-hydroxyflavone was the most potent inhibitor of nitrite production. Genistein (5,7-dihydroxy- 3-(4-hydroxy-phenyl)-4H-1-benzopyran-4-one) also inhibited production of nitrite, by a mechanism that appears not to involve protein tyrosine kinases. These results suggest that the flavones can modulate the immune responses and the inflammatory reactions by controlling production of nitric oxide.