Agnes W. Boots

Health effects of quercetin : from antioxidant to nutraceutical

Quercetin, a member of the flavonoids family, is one of the most prominent dietary antioxidants. It is ubiquitously present in foods including vegetables, fruit, tea and wine as well as countless food supplements and is claimed to exert beneficial health effects. This includes protection against various diseases such as osteoporosis, certain forms of cancer, pulmonary and cardiovascular diseases but also against aging. Especially the ability of quercetin to scavenge highly reactive species such as peroxynitrite and the hydroxyl radical is suggested to be involved in these possible beneficial health effects. Consequently, numerous studies have been performed to gather scientific evidence for these beneficial health claims as well as data regarding the exact mechanism of action and possible toxicological aspects of this flavonoid. The purpose of this review is to evaluate these studies in order to elucidate the possible health-beneficial effects of the antioxidant quercetin. Firstly, the definitions as well as the most important aspects regarding free radicals, antioxidants and oxidative stress will be discussed as background information. Subsequently, the mechanism by which quercetin may operate as an antioxidant (tested in vitro) as well as the potential use of this antioxidant as a nutraceutical (tested both ex vivo and in vivo) will be discussed.

Cytotoxicity and oxidative DNA damage by nanoparticles in human intestinal Caco-2 cells

Abstract The use of engineered nanoparticles in the food sector is anticipated to increase dramatically, whereas their potential hazards for the gastrointestinal tract are still largely unknown. We investigated the cytotoxic and DNA-damaging effects of several types of nanoparticles and fine particles relevant as food additives (TiO2 and SiO2) or for food packaging (ZnO and MgO) as well as carbon black on human intestinal Caco-2 cells. All particles, except for MgO, were cytotoxic (LDH and WST-1 assay). ZnO, and to lesser extent SiO2, induced significant DNA damage (Fpg-comet), while SiO2 and carbon black were the most potent in causing glutathione depletion. DNA damage by TiO2 was found to depend on sample processing conditions. Interestingly, application of different TiO2 and ZnO particles revealed no relation between particle surface area and DNA damage. Our results indicate a potential hazard of several food-related nanoparticles which necessitate investigations on the actual exposure in humans.

In vitro and ex vivo anti-inflammatory activity of quercetin in healthy volunteers

OBJECTIVE Quercetin, a commonly occurring flavonoid and well known antioxidant, has been suggested to possess other beneficial activities. The present study investigated the possible anti-inflammatory effects of physiologically attainable quercetin concentrations. METHODS The effects of quercetin were tested in vitro, i.e., added to blood in the test tube, and ex vivo and in vivo, i.e., in blood taken after 4 wk of administration of quercetin in an intervention study. RESULTS Quercetin dose-dependently inhibited in vitro lipopolysaccharide-induced tumor necrosis factor-alpha production in the blood of healthy volunteers. At a concentration of 1 muM, quercetin caused a 23% reduction. The in vitro lipopolysaccharide-induced interleukin-10 production remained unaffected by quercetin. A 4-wk quercetin intervention resulted in a significant increase in plasma quercetin concentration. The supplementation also increased total plasma antioxidant status but did not affect glutathione, vitamin C, and uric acid plasma concentrations. Basal and ex vivo lipopolysaccharide-induced tumor necrosis factor-alpha levels were not altered by the intervention. CONCLUSION The present study shows that quercetin increases antioxidant capacity in vivo and displays anti-inflammatory effects in vitro, but not in vivo or ex vivo, in the blood of healthy volunteers. This lack of effect is probably due to their low cytokine and high antioxidant levels at baseline, indicating that neither inflammation nor oxidative stress is present. Only in people with increased levels of inflammation and oxidative stress, e.g., patients with a disease of which the pathology is associated with these two processes, might antioxidant supplementation be fruitful.

The versatile use of exhaled volatile organic compounds in human health and disease

Exhaled breath contains thousands of volatile organic compounds (VOCs) of which the composition varies depending on health status. Various metabolic processes within the body produce volatile products that are released into the blood and will be passed on to the airway once the blood reaches the lungs. Moreover, the occurrence of chronic inflammation and/or oxidative stress can result in the excretion of volatile compounds that generate unique VOC patterns. Consequently, measuring the total amount of VOCs in exhaled air, a kind of metabolomics also referred to as breathomics, for clinical diagnosis and monitoring purposes gained increased interest over the last years. This paper describes the currently available methodologies regarding sampling, sample analysis and data processing as well as their advantages and potential drawbacks. Additionally, different application possibilities of VOC profiling are discussed. Until now, breathomics has merely been applied for diagnostic purposes. Exhaled air analysis can, however, also be applied as an analytical or monitoring tool. Within the analytic perspective, the use of VOCs as biomarkers of oxidative stress, inflammation or carcinogenesis is described. As monitoring tool, breathomics can be applied to elucidate the heterogeneity observed in chronic diseases, to study the pathogen(s) responsible for occurring infections and to monitor treatment efficacy.

Oxidized quercetin reacts with thiols rather than with ascorbate: implication for quercetin supplementation

When an antioxidant scavenges a reactive species, i.e., when it exerts its antioxidant activity, the antioxidant is converted into potentially harmful oxidation products. In this way, the antioxidant quercetin might yield an ortho-quinone, denoted as QQ, which has four tautomeric forms, i.e., the ortho-quinone and three quinonmethides. We evaluated the interaction of QQ with ascorbate or glutathione (GSH). Ascorbate recycles QQ to the parent compound quercetin, while GSH forms two adducts with QQ, i.e., 6-GSQ and 8-GSQ. When both GSH and ascorbate are present, QQ is converted exclusively into GSQ. In the absence of GSH, protein thiols will be arylated by QQ. This protein arylation is not prevented by ascorbate. Thiol arylation by quinones and quinonmethides can impair several vital enzymes. This implies that the product formed when quercetin displays its antioxidant scavenging effect is toxic in the absence of GSH. Therefore, an adequate GSH level should be maintained when quercetin is supplemented.

Oxidant metabolism in chronic obstructive pulmonary disease

The development and progression of chronic obstructive pulmonary disease (COPD) have been associated with increased oxidative stress or reduced antioxidant resources. Several indicators of oxidative stress, such as hydrogen peroxide exhalation, lipid peroxidation products and degraded proteins, are indeed elevated in COPD patients. As a result, the antioxidant capacity decreases in COPD patients. The fall in antioxidant capacity of blood from COPD patients should not only be regarded as a reflection of the occurrence of oxidative stress but also as evidence that oxidative stress spreads out to the circulation and can therefore generate a systemic effect. COPD is linked to weight loss and in particular to loss in fatfree mass by skeletal muscle wasting. This systemic effect can be mediated by both oxidative stress and oxidative stressmediated processes like apoptosis and inflammation. Furthermore, COPD is a predisposition for lung cancer through several mechanisms including oxidative stress and oxidative stressmediated processes such as inflammation and disruption of genomic integrity. Current therapeutic interventions against the farreaching consequences of the systemic oxidative stress in chronic obstructive pulmonary disease are not yet optimised. A diet designed to reduce chronic metabolic stress might form an effective therapeutic strategy in chronic obstructive pulmonary disease.

Distinctive Toxicity of TiO2 Rutile/Anatase Mixed Phase Nanoparticles on Caco-2 Cells

Titanium dioxide has a long-standing use as a food additive. Micrometric powders are, e.g., applied as whiteners in confectionary or dairy products. Possible hazards of ingested nanometric TiO(2) particles for humans and the potential influence of varying specific surface area (SSA) are currently under discussion. Five TiO(2)-samples were analyzed for purity, crystallinity, primary particle size, SSA, ζ potential, and aggregation/agglomeration. Their potential to induce cytotoxicity, oxidative stress, and DNA damage was evaluated in human intestinal Caco-2 cells. Only anatase-rutile containing samples, in contrast to the pure anatase samples, induced significant LDH leakage or mild DNA damage (Fpg-comet assay). Evaluation of the metabolic competence of the cells (WST-1 assay) revealed a highly significant correlation between the SSA of the anatase samples and cytotoxicity. The anatase/rutile samples showed higher toxicity per unit surface area than the pure anatase powders. However, none of the samples affected cellular markers of oxidative stress. Our findings suggest that both SSA and crystallinity are critical determinants of TiO(2)-toxicity toward intestinal cells.

ATP-mediated Activation of the NADPH Oxidase DUOX1 Mediates Airway Epithelial Responses to Bacterial Stimuli

Activation of the NADPH oxidase homolog dual oxidase 1 (DUOX1) within the airway epithelium represents a key mechanism of innate airway host defense, through enhanced production of H2O2, which mediates cellular signaling pathways that regulate the production of various inflammatory mediators. Production of the CXC chemokine interleukin (IL)-8/CXCL8 forms a common epithelial response to many diverse stimuli, including bacterial and viral triggers, environmental oxidants, and other biological mediators, suggesting the potential involvement of a common signaling pathway that may involve DUOX1-dependent H2O2 production. Following previous reports showing that DUOX1 is activated by extracellular ATP and purinergic receptor stimulation, this study demonstrates that airway epithelial IL-8 production in response to several bacterial stimuli involves ATP release and DUOX1 activation. ATP-mediated DUOX1 activation resulted in the activation of ERK1/2 and NF-κB pathways, which was associated with epidermal growth factor receptor (EGFR) ligand shedding by ADAM17 (a disintegrin and metalloproteinase-17). Although ATP-mediated ADAM17 activation and IL-8 release were not prevented by extracellular H2O2 scavenging by catalase, these responses were attenuated by intracellular scavengers of H2O2 or related oxidants, suggesting an intracellular redox signaling mechanism. Both ADAM17 activation and IL-8 release were suppressed by inhibitors of EGFR/ERK1/2 signaling, which can regulate ADAM17 activity by serine/threonine phosphorylation. Collectively, our results indicate that ATP-mediated DUOX1 activation represents a common response mechanism to several environmental stimuli, involving H2O2-dependent EGFR/ERK activation, ADAM17 activation, and EGFR ligand shedding, leading to amplified epithelial EGFR activation and IL-8 production.

Influence of simulated gastrointestinal conditions on particle-induced cytotoxicity and interleukin-8 regulation in differentiated and undifferentiated Caco-2 cells

Abstract Novel aspects of engineered nanoparticles offer many advantages for optimising food products and packaging. However, their potential hazards in the gastrointestinal tract require further investigation. We evaluated the toxic and inflammatory potential of two types of particles that might become increasingly relevant to the food industry, namely SiO2 and ZnO. The materials were characterised for their morphology, oxidant generation and hydrodynamic behaviour. Cytotoxicity and interleukin-8 mRNA and protein expression were evaluated in human intestinal Caco-2 cells. Particle pretreatment under simulated gastric and intestinal pH conditions resulted in reduced acellular ROS formation but did not influence cytotoxicity (WST-1 assay) or IL-8 expression. However, the differentiation status of the cells markedly determined the cytotoxic potency of the particles. Further research is needed to determine the in vivo relevance of our current observations regarding the role of particle aggregation and the stage of intestinal epithelial cell differentiation in determining the hazards of ingested particles.

Oxidative damage shifts from lipid peroxidation to thiol arylation by catechol-containing antioxidants

Catechol-containing antioxidants are able to protect against lipid peroxidation by nonenzymatic scavenging of free radicals with their catechol moiety. During their antioxidant activity, catechol oxidation products such as semiquinone radicals and quinones are formed. These oxidation products of 4-methylcatechol inactivate the GSH-dependent protection against lipid peroxidation and the calcium sequestration in liver microsomes. This effect is probably due to arylation by oxidation products of 4-methylcatechol of free thiol groups of the enzymes responsible for the GSH-dependent protection and calcium sequestration, i.e. the free radical reductase and calcium ATPase. It is concluded that a catechol-containing antioxidant might shift radical damage from lipid peroxidation to sulfhydryl arylation.