Flavonoids are plant polyphenolic compounds present in the daily diet. Latest epidemiological studies point to a crucial role of the flavonol quercetin in the prevention of cardiovascular diseases. It is assumed that this protective effect derives from the antioxidative capacity which quercetin shows in in vitro experiments. The antiproliferative and antimutagenic activities in vitro have made it a candidate for clinical trials in cancer therapy. Quercetin is also regarded as a putative active compound in various phytopharmaceuticals. However, in vivo data on the disposition, absorption, bioavailability, and metabolism of quercetin after intravenous and oral administration in humans are scarce and contradictory. The pharmacokinetic parameters following intravenous injection were determined in two studies. The elimination half-life was reported to be 2.4 h and 0.7 h, the volume of distribution at steady-state was 92.6 l and 6.2 l, and total body clearance was 34.6 lxh(-1) and 28.1 lxh(-1), respectively. Absorption after oral administration ranged from 0 to over 50% of the dose. These inconsistencies can partly be attributed to a lack of highly sensitive and specific assay methodology. The data available so far are insufficient to clarify whether or not quercetin can be held responsible for any protective or curative effect observed after oral intake.
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"Since oral quercetin had some obvious effect on blood vessels compared to the control animals (Fig. 7), it is apparent that quercetin or its metabolites reached the systemic circulation, and this was confirmed in this study (Fig. 9). We did not concentrate on detailed pharmacokinetic analysis owing to the complex metabolism of quercetin by human/rat intestinal and liver enzymes and by bacteria in the colon (Cermak et al. 2003; Graefe et al. 1999), but on the evidence for quercetin absorption. We selected two metabolites, quercetin-3- glucuronide and 3-hydroxyphenylacetic acid, as representatives of quercetin metabolites by rat/human and bacterial enzymes, respectively. "
[Show abstract][Hide abstract] ABSTRACT: Catecholamines are endogenous amines that participate in the maintenance of cardiovascular system homeostasis. However, excessive release or exogenous administration of catecholamines is cardiotoxic. The synthetic catecholamine, isoprenaline (isoproterenol, ISO), with non-selective β-agonistic activity has been used as a viable model of acute myocardial toxicity for many years. Since the pathophysiology of ISO-cardiotoxicity is complex, the aim of this study was to elucidate the effect of oral quercetin pretreatment on myocardial ISO toxicity. Wistar-Han rats were randomly divided into four groups: solvent or quercetin administered orally by gavage in a dose of 10 mg kg(-1) daily for 7 days were followed by s.c. water for injection or ISO in a dose of 100 mg kg(-1). Haemodynamic, ECG and biochemical parameters were measured; effects on blood vessels and myocardial histology were assessed, and accompanying pharmacokinetic analysis was performed. Quercetin was unable to protect the cardiovascular system against acute ISO cardiotoxicity (stroke volume decrease, cardiac troponin T release, QRS-T junction elevation and histological impairment). The sole positive effect of quercetin on catecholamine-induced cardiotoxicity was the normalization of increased left ventricular end-diastolic pressure caused by ISO. Quercetin did not reverse the increased responsiveness of rat aorta to vasoconstriction in ISO-treated animals, but it decreased the same parameter in the control animals. Accompanying pharmacokinetic analysis showed absorption of quercetin and its metabolite 3-hydroxyphenylacetic acid formed by bacterial microflora. In conclusion, a daily oral dose of 10 mg kg(-1) of quercetin for 7 days did not ameliorate acute ISO-cardiovascular toxicity in rats despite minor positive cardiovascular effects.
Full-text · Article · Jun 2014 · Archiv für Experimentelle Pathologie und Pharmakologie
"Most of flavonoids are found as glycoside-conjugates in raw food, in which the aglycone molecule, which can be mainly a flavone or a 3-hydroxyflavone backbone (flavonols ), may be associated with either glucose (for example astragalin for kaempferol), rutinose (for example rutin for quercetin), rhamnose (for example myricitrin for myricetin), galactose (for example hypersode for quercetin), robinose and rhamnose (for example robinin for kaempferol), and so forth. Bioavailability research is often limited to domestic [67-70] or laboratory animals [71-74] and few papers regarding humans should throw a light on the comprehension of polyphenols activity in medicine         . Furthermore, a standpoint of any debate about polyphenol activity in preventing allergy must take into account the interaction with gut microflora, i.e. the possibility that polyphenols can substantially modify human intestinal microbiota . "
[Show abstract][Hide abstract] ABSTRACT: Recent evidence has brought to the spotlight plant-derived polyphenols as a promising tool to prevent allergy. The worldwide increase of allergic disease, probably relying on many factors including immune response to stressors and its loss in complexity, environmental pressure by pollutants and chemical allergens, changes in lifestyle and lifespan, failure of conventional treatments to prevent and treat allergy, has strongly suggested people to refer to healthy promising nature-derived compounds, most of which contained in fruits and vegetables, e.g. in daily diet. Phenolic acids and polyphenols, such as flavonoids, are the best studied natural substances known to possess an anti-inflammatory and anti-allergic potential. Used as nutraceuticals, these compounds are thought to dampen the onset of allergic inflammation, by acting on several immune cells, but concerns still remain about their real employment by the organism who assumes polyphenols through diet, because of their bioavailability, gut transformation and pharmacokinetics. Other issues deals with the wide panoply of actions played by these compounds within cells, which has hampered a clear comprehension of their action on cell molecular signaling and function. In this review, special emphasis is placed on the effects of dietary polyphenols on allergy prevention, the possible mechanism of action of polyphenols-containing food and future perspectives for pharmacology design.
Full-text · Article · May 2013 · Current pharmaceutical design
"Studies have been performed to evaluate the physiological functions and biological activities of quercetin in humans and animals [1,13]. However, there is limited information available on the effect of quercetin on oocyte maturation and embryonic development in pigs. "
[Show abstract][Hide abstract] ABSTRACT: Quercetin is a plant-derived flavonoid found in fruits or vegetables that has antioxidant properties and acts as a free radical scavenger. We investigated the effects of quercetin on porcine oocyte nuclear maturation and embryonic development after parthenogenetic activation. We then evaluated the antioxidant activities of quercetin by measuring reactive oxygen species (ROS) levels during oocyte maturation. Immature oocytes were untreated or treated with 1, 10, and 50 μg/mL quercetin during in vitro maturation (IVM). Quercetin treatment did not improve oocyte nuclear maturation, but significantly higher blastocyst rates (p < 0.05) of parthenogenetically activated oocytes were achieved when the IVM medium was supplemented with an adequate concentration of quercetin (1 μg/mL). However, cleavage rates and blastocyst cell numbers were not affected. Oocytes treated with 1 or 10 μg/mL quercetin had significantly lower (p < 0.05) levels of ROS than the control and group treated with the highest concentration of queretin (50 μg/mL). Moreover, this highest concentration was detrimental to oocyte nuclear maturation and blastocyst formation. Based on our findings, we concluded that exogenous quercetin reduces ROS levels during oocyte maturation and is beneficial for subsequent embryo development.
Full-text · Article · Feb 2013 · Journal of veterinary science (Suwŏn-si, Korea)