Quercetin pharmacokinetics in humans

Metabolic interactions between acetaminophen (paracetamol) and two flavonoids, luteolin and quercetin, through in-vitro inhibition studies

OBJECTIVES

Excessive exposure to acetaminophen (APAP, paracetamol) can cause liver injury through formation of a reactive metabolite that depletes hepatic glutathione and causes hepatocellular oxidative stress and damage. Generation of this metabolite is mediated by Cytochrome-P450 (CYP) isoforms, mainly CYP2E1. A number of naturally occurring flavonoids can mitigate APAP-induced hepatotoxicity in experimental animal models. Our objective was to determine the mechanism of these protective effects and to evaluate possible human applicability.

METHODS

Two flavonoids, luteolin and quercetin, were evaluated as potential inhibitors of eight human CYP isoforms, of six UDP-glucuronosyltransferase (UGT) isoforms and of APAP glucuronidation and sulfation. The experimental model was based on in-vitro metabolism by human liver microsomes, using isoform-specific substrates.

KEY FINDINGS

Luteolin and quercetin inhibited human CYP isoforms to varying degrees, with greatest potency towards CYP1A2 and CYP2C8. However, 50% inhibitory concentrations (IC₅₀ values) were generally in the micromolar range. UGT isoforms were minimally inhibited. Both luteolin and quercetin inhibited APAP sulfation but not glucuronidation.

CONCLUSIONS

Inhibition of human CYP activity by luteolin and quercetin occurred with IC₅₀ values exceeding customary in-vivo human exposure with tolerable supplemental doses of these compounds. The findings indicate that luteolin and quercetin are not likely to be of clinical value for preventing or treating APAP-induced hepatotoxicity.

Exploiting Tyrosinase Expression and Activity in Melanocytic Tumors

Melanoma is an aggressive tumor that expresses the pigmentation enzyme tyrosinase. Tyrosinase expression increases during tumorigenesis, which could allow for selective treatment of this tumor type by strategies that use tyrosinase activity. Approaches targeting tyrosinase would involve gene transcription or signal transduction pathways mediated by p53 in a direct or indirect manner. Two pathways are proposed for exploiting tyrosinase expression: ( a) a p53-dependent pathway leading to apoptosis or arrest and ( b) a reactive oxygen species–mediated induction of endoplasmic reticulum stress in p53 mutant tumors. Both strategies could use tyrosinase-mediated activation of quercetin, a dietary polyphenol that induces the expression of p53 and modulates reactive oxygen species. In addition to antitumor signaling properties, activation of quercetin could complement conventional cancer therapy by the induction of phase II detoxification enzymes resulting in p53 stabilization and transduction of its downstream targets. In conclusion, recent advances in tyrosinase enzymology, prodrug chemistry, and modern chemotherapeutics present an intriguing and selective multitherapy targeting system where dietary bioflavonoids could be used to complement conventional cancer treatments.

Physicochemical properties of dietary phytochemicals can predict their passive absorption in the human small intestine

A diet high in phytochemical-rich plant foods is associated with reducing the risk of chronic diseases such as cardiovascular and neurodegenerative diseases, obesity, diabetes and cancer. Oxidative stress and inflammation (OSI) is the common component underlying these chronic diseases. Whilst the positive health effects of phytochemicals and their metabolites have been demonstrated to regulate OSI, the timing and absorption for best effect is not well understood. We developed a model to predict the time to achieve maximal plasma concentration (Tmax) of phytochemicals in fruits and vegetables. We used a training dataset containing 67 dietary phytochemicals from 31 clinical studies to develop the model and validated the model using three independent datasets comprising a total of 108 dietary phytochemicals and 98 pharmaceutical compounds. The developed model based on dietary intake forms and the physicochemical properties lipophilicity and molecular mass accurately predicts Tmax of dietary phytochemicals and pharmaceutical compounds over a broad range of chemical classes. This is the first direct model to predict Tmax of dietary phytochemicals in the human body. The model informs the clinical dosing frequency for optimising uptake and sustained presence of dietary phytochemicals in circulation, to maximise their bio-efficacy for positively affect human health and managing OSI in chronic diseases.

Human Stem Cell-Derived Endothelial-Hepatic Platform for Efficacy Testing of Vascular-Protective Metabolites from Nutraceuticals

Atherosclerosis underlies many cardiovascular and cerebrovascular diseases. Nutraceuticals are emerging as a therapeutic moiety for restoring vascular health. Unlike small-molecule drugs, the complexity of ingredients in nutraceuticals often confounds evaluation of their efficacy in preclinical evaluation. It is recognized that the liver is a vital organ in processing complex compounds into bioactive metabolites. In this work, we developed a coculture system of human pluripotent stem cell-derived endothelial cells (hPSC-ECs) and human pluripotent stem cell-derived hepatocytes (hPSC-HEPs) for predicting vascular-protective effects of nutraceuticals. To validate our model, two compounds (quercetin and genistein), known to have anti-inflammatory effects on vasculatures, were selected. We found that both quercetin and genistein were ineffective at suppressing inflammatory activation by interleukin-1β owing to limited metabolic activity of hPSC-ECs. Conversely, hPSC-HEPs demonstrated metabolic capacity to break down both nutraceuticals into primary and secondary metabolites. When hPSC-HEPs were cocultured with hPSC-ECs to permit paracrine interactions, the continuous turnover of metabolites mitigated interleukin-1β stimulation on hPSC-ECs. We observed significant reductions in inflammatory gene expressions, nuclear translocation of nuclear factor κB, and interleukin-8 production. Thus, integration of hPSC-HEPs could accurately reproduce systemic effects involved in drug metabolism in vivo to unravel beneficial constituents in nutraceuticals. This physiologically relevant endothelial-hepatic platform would be a great resource in predicting the efficacy of complex nutraceuticals and mechanistic interrogation of vascular-targeting candidate compounds. Stem Cells Translational Medicine 2017;6:851-863.

Engineering of cell microenvironment-responsive polypeptide nanovehicle co-encapsulating a synergistic combination of small molecules for effective chemotherapy in solid tumors

In this study, we report a facile method to construct a bioactive (poly(phenylalanine)-b-poly(l-histidine)-b-poly(ethylene glycol) polypeptide nanoconstruct to co-load doxorubicin (DOX) and quercetin (QUR) (DQ-NV). The smart pH-sensitive nanovehicle was fabricated with precisely tailored drug-to-carrier ratio that resulted in accelerated, sequential drug release. As a result of ratiometric loading, QUR could significantly enhance the cytotoxic potential of DOX, induced marked cell apoptosis; change cell cycle patterns, inhibit the migratory capacity of sensitive and resistant cancer cells. In particular, pro-oxidant QUR from DQ-NV remarkably reduced the GSH/GSSG ratio, indicating high oxidative stress and damage to cellular components. DQ-NV induced tumor shrinkage more effectively than the single drugs in mice carrying subcutaneous SCC-7 xenografts. DQ-NV consistently induced high expression of caspase-3 and PARP and low expression of Ki67 and CD31 immunomarkers. In summary, we demonstrate the development of a robust polypeptide-based intracellular nanovehicle for synergistic delivery of DOX/QUR in cancer chemotherapy.

STATEMENT OF SIGNIFICANCE

In this study, we report a facile method to construct bioactive and biodegradable polypeptide nanovehicles as an advanced platform technology for application in cancer therapy. We designed a robust (poly(phenylalanine)-b-poly(l-histidine)-b-poly(ethylene glycol) nanoconstruct to co-load doxorubicin (DOX) and quercetin (QUR) (DQ-NV). The conformational changes of the histidine block at tumor pH resulted in accelerated, sequential drug release. QUR could significantly enhance the cytotoxic potential of DOX, induce marked cell apoptosis, change cell cycle patterns, and inhibit the migratory capacity of sensitive and resistant cancer cells. DQ-NV induced tumor shrinkage more effectively than the single drugs and the 2-drug cocktail in tumor xenografts. In summary, we demonstrate the development of an intracellular nanovehicle for synergistic delivery of DOX/QUR in cancer chemotherapy.

Quercetin as an Emerging Anti-Melanoma Agent: A Four-Focus Area Therapeutic Development Strategy

Replacing current refractory treatments for melanoma with new prevention and therapeutic approaches is crucial in order to successfully treat this aggressive cancer form. Melanoma develops from neural crest cells, which express tyrosinase – a key enzyme in the pigmentation pathway. The tyrosinase enzyme is highly active in melanoma cells and metabolizes polyphenolic compounds; tyrosinase expression thus makes feasible a target for polyphenol-based therapies. For example, quercetin (3,3′,4′,5,7-pentahydroxyflavone) is a highly ubiquitous and well-classified dietary polyphenol found in various fruits, vegetables, and other plant products including onions, broccoli, kale, oranges, blueberries, apples, and tea. Quercetin has demonstrated antiproliferative and proapoptotic activity in various cancer cell types. Quercetin is readily metabolized by tyrosinase into various compounds that promote anticancer activity; additionally, given that tyrosinase expression increases during tumorigenesis, and its activity is associated with pigmentation changes in both early- and late-stage melanocytic lesions, it suggests that quercetin can be used to target melanoma. In this review, we explore the potential of quercetin as an anti-melanoma agent utilizing and extrapolating on evidence from previous in vitro studies in various human malignant cell lines and propose a “four-focus area strategy” to develop quercetin as a targeted anti-melanoma compound for use as either a preventative or therapeutic agent. The four areas of focus include utilizing quercetin to (i) modulate cellular bioreduction potential and associated signaling cascades, (ii) affect transcription of relevant genes, (iii) regulate epigenetic processes, and (iv) develop effective combination therapies and delivery modalities/protocols. In general, quercetin could be used to exploit tyrosinase activity to prevent, and/or treat, melanoma with minimal additional side effects.

Comparison of the ligand binding site of CYP2C8 with CYP26A1 and CYP26B1: a structural basis for the identification of new inhibitors of the retinoic acid hydroxylases

The CYP26s are responsible for metabolizing retinoic acid and play an important role in maintaining homeostatic levels of retinoic acid. Given the ability of CYP2C8 to metabolize retinoic acid, we evaluated the potential for CYP2C8 inhibitors to also inhibit CYP26. In vitro assays were used to evaluate the inhibition potencies of CYP2C8 inhibitors against CYP26A1 and CYP26B1. Using tazarotenic acid as a substrate for CYP26, IC₅₀ values for 17 inhibitors of CYP2C8 were determined for CYP26A1 and CYP26B1, ranging from ∼20 nM to 100 μM, with a positive correlation observed between IC₅₀s for CYP2C8 and CYP26A1. An evaluation of IC₅₀'s versus in vivo C_max values suggests that inhibitors such as clotrimazole or fluconazole may interact with CYP26 at clinically relevant concentrations and may alter levels of retinoic acid. These findings provide insight into drug interactions resulting in elevated retinoic acid concentrations and expand upon the pharmacophore of CYP26 inhibition.

Quercetin, Inflammation and Immunity

In vitro and some animal models have shown that quercetin, a polyphenol derived from plants, has a wide range of biological actions including anti-carcinogenic, anti-inflammatory and antiviral activities; as well as attenuating lipid peroxidation, platelet aggregation and capillary permeability. This review focuses on the physicochemical properties, dietary sources, absorption, bioavailability and metabolism of quercetin, especially main effects of quercetin on inflammation and immune function. According to the results obtained both in vitro and in vivo, good perspectives have been opened for quercetin. Nevertheless, further studies are needed to better characterize the mechanisms of action underlying the beneficial effects of quercetin on inflammation and immunity.

Effects of dietary components on cancer of the digestive system

Cancer is the second leading cause of death in developed countries and poor diet and physical inactivity are major risk factors in cancer-related deaths. Therefore, interventions to reduce levels of smoking, improve diet, and increase physical activity must become much higher priorities in the general population's health and health care systems. The consumption of fruit and vegetables exerts a preventive effect towards cancer and in recent years natural dietary agents have attracted great attention in the scientific community and among the general public. Foods, such as tomatoes, olive oil, broccoli, garlic, onions, berries, soy bean, honey, tea, aloe vera, grapes, rosemary, basil, chili peppers, carrots, pomegranate, and curcuma contain active components that can influence the initiation and the progression of carcinogenesis, acting on pathways implied in cell proliferation, apoptosis and metastasis. The present review illustrates the main foods and their active components, including their antioxidant, cytotoxic, and pro-apoptotic properties, with a particular focus on the evidence related to cancers of the digestive system.

Ethnopharmacology, phytochemistry, and biological activities of Cymbopogon citratus (DC.) Stapf extracts

Cymbopogon citratus is a widely distributed perennial herb belonging to the Poaceae family and has been extensively consumed for its medicinal, cosmetic, and nutritional effects for centuries. A large number of reports have been published describing the pharmacological, biological, and therapeutic actions of this herb. In this review, we summarized the literatures on related studies (up to January, 2014) that highlighted the pharmacologic and biological effects of the major phytochemicals isolated from C. citratus extracts and its essential oil. The components of the essential oils found in C. citratus have a similar pharmacokinetic properties, including absorption, distribution, metabolism, and excretion. They are quickly absorbed following oral, pulmonary, and dermal administration. Based on the published reports, it can also be inferred that, after absorption from the small intestine, some phytochemicals in C. citratus can undergo oxidation, glucuronidation, sulfation, and/or O-methylation. Excretion is through urine, feces and/or expired volatiles. The biotransformation reactions of C. citratus bioactive constituents are essential for its relatively safe consumption and therapeutic applications. The data available so far warrant further studies evaluating C. citratus pharmacokinetics. Reliable pharmacokinetic data in humans would be critical for a better understanding of the the systemic handling of C. citratus.

Higher plasma quercetin levels following oral administration of an onion skin extract compared with pure quercetin dihydrate in humans

PURPOSE

To investigate the plasma kinetics of quercetin derived from hard capsules filled with onion skin extract powder or quercetin dihydrate in humans.

METHODS

In a randomized, single-blind, diet-controlled crossover study, 12 healthy subjects (six men and six women) aged 21-33 years were administered a single oral supra-nutritional dose of approximately 163 mg quercetin derived from onion skin extract powder (containing 95.3 % of total flavonoids as quercetin aglycone) or quercetin dihydrate (134 mg quercetin aglycone equivalent). Blood samples were collected before and during a 24-h period after quercetin administration. The concentrations of quercetin and its two monomethylated derivatives, isorhamnetin (3'-O-methyl quercetin), and tamarixetin (4'-O-methyl quercetin), were measured using HPLC with fluorescence detection after plasma enzymatic treatment.

RESULTS

The systemic availability, determined by comparing the plasma concentration-time curves of quercetin, was 4.8 times higher, and the maximum plasma concentration (C _max) was 5.4 times higher after ingestion of the onion skin extract than after ingestion of pure quercetin dihydrate. By contrast, t _max did not differ significantly between the two formulations. The C _max values for isorhamnetin and tamarixetin were 3.8 and 4.4 times higher, respectively, after administration of onion skin extract than after pure quercetin dihydrate. The plasma kinetics of quercetin were not significantly different in men and women.

CONCLUSION

Quercetin aglycone derived from onion skin extract powder is significantly more bioavailable than that from quercetin dihydrate powder filled hard capsules.

Population Pharmacokinetic Modeling of the Enterohepatic Recirculation of Fimasartan in Rats, Dogs, and Humans

Enterohepatic recirculation (EHC) can greatly enhance plasma drug exposures and therapeutic effects. This study aimed to develop a population pharmacokinetic model that can simultaneously characterize the extent and time-course of EHC in three species using fimasartan, a novel angiotensin II receptor blocker, as a model drug. All fimasartan plasma concentration profiles in 32 rats (intravenous doses, 0.3-3 mg/kg; oral doses, 1-10 mg/kg), 34 dogs (intravenous doses, 0.3-1 mg/kg; oral doses, 1-10 mg/kg), and 42 healthy volunteers (single or multiple oral doses, 20-480 mg) were determined via liquid chromatography-tandem mass spectrometry (LC-MS/MS) and simultaneously modeled in S-ADAPT. The proposed model quantitatively characterized EHC in three species after oral and intravenous dosing. The median (range) fraction of drug undergoing recirculation was 76.3% (64.9-88.7%) in rats, 33.3% (24.0-45.9%) in dogs, and 65.6% (56.5-72.0%) in humans. In the presence compared with the absence of EHC, the area under the curve in plasma was predicted to be 4.22-fold (2.85-8.85) as high in rats, 1.50-fold (1.32-1.85) in dogs, and 2.91-fold (2.30-3.57) in humans. The modeled oral bioavailability in rats (median (range), 38.7% (20.0-59.8%)) and dogs (median, 7.13% to 15.4%, depending on the formulation) matched the non-compartmental estimates well. In humans, the predicted oral bioavailability was 25.1% (15.1-43.9%) under fasting and 18.2% (12.2-31.0%) under fed conditions. The allometrically scaled area under the curve predicted from rats was 420 ng·h/mL for 60 mg fimasartan compared with 424 ± 63 ng·h/mL observed in humans. The developed population pharmacokinetic model can be utilized to characterize the impact of EHC on plasma drug exposure in animals and humans.

Inhibitory effect of plant phenolics on fMLP-induced intracellular calcium rise and chemiluminescence of human polymorphonuclear leukocytes and their chemotactic activity in vitro

CONTEXT

Polymorphonuclear leukocytes (PMNs) produce oxidants, contributing to systemic oxidative stress. Diets rich in plant polyphenols seem to decrease the risk of oxidative stress-induced disorders including cardiovascular disease.

OBJECTIVE

The objective of this study was to examine the in vitro effect of each of the 14 polyphenols on PMNs chemotaxis, intracellular calcium response, oxidants production.

MATERIALS AND METHODS

Blood samples and PMNs suspensions were obtained from 60 healthy non-smoking donors and incubated with a selected polyphenol (0.5-10 µM) or a control solvent. We assessed resting and fMLP-dependent changes of intracellular calcium concentration ([Ca(2+)]i) in PMNs with the Fura-2AM method and measured fMLP-induced luminol enhanced whole blood chemiluminescence (fMLP-LBCL). Polyphenol chemoattractant activity for PMNs was tested with Boyden chambers.

RESULTS

Polyphenols had no effect on resting [Ca(2+)]i. Unaffected by other compounds, fMLP-dependent increase of [Ca(2+)]i was inhibited by quercetin and catechol (5 µM) by 32 ± 14 and 12 ± 10% (p < 0.04), respectively. Seven of the 14 tested substances (5 µM) influenced fMLP-LBCL by decreasing it. Catechol, quercetin, and gallic acid acted most potently reducing fMLP-LBCL by 49 ± 5, 42 ± 15, and 28 ± 18% (p < 0.05), respectively. 3,4-Dihydroxyhydrocinnamic, 3,4-dihydroxyphenylacetic, 4-hydroxybenzoic acid, and catechin (5 µM) revealed distinct (p < 0.02) chemoattractant activity with a chemotactic index of 1.9 ± 0.8, 1.8 ± 0.7, 1.6 ± 0.6, 1.4 ± 0.2, respectively.

CONCLUSION AND DISCUSSION

Catechol, quercetin, and gallic acid at concentrations commensurate in human plasma strongly suppressed the oxidative response of PMNs. Regarding quercetin and catechol, this could result from an inhibition of [Ca(2+)]i response.

Comparing the metabolism of quercetin in rats, mice and gerbils

PURPOSE

Several species of rodents are used to investigate the metabolism of quercetin in vivo. However, it is unclear whether they are a proper animal model. Thus, we compared the metabolism of quercetin in Wistar rats (rats), Balb/c mice (mice) and Mongolian gerbils (gerbils).

METHODS

We determined the levels of quercetin metabolites, quercetin-3-glucuronide (Q3G), quercetin-3'-sulfate (Q3'S) and methyl-quercetin isorhamnetin (IH), in the plasma, lungs and livers of three species of animals by high-performance liquid chromatography after acute and/or chronic quercetin administration. The metabolic enzyme activities in the intestinal mucosal membrane and liver were also investigated.

RESULTS

First, we found that after acute quercetin administration, the Q3'S level was the highest in gerbils. However, after long-term supplementation (20 weeks), Q3G was the dominant metabolite in the plasma, lungs and livers followed by IH and Q3'S in all animals, although the gerbils still had a higher Q3'S conversion ratio. The average concentrations of total quercetin concentration in the plasma of gerbils were the highest in both short- and long-term studies. The activities of uridine 5'-diphosphate-glucuronosyltransferase, phenolsulfotransferase and catechol-O-methyltransferase were induced by quercetin in a dose- and tissue-dependent manner in all animals.

CONCLUSIONS

Taken together, in general, after long-term supplementation the metabolism of quercetin is similar in all animals and is comparable to that of humans. However, the accumulation of quercetin and Q3'S conversion ratio in gerbils are higher than those in the other animals.

Using in vitro and in vivo models to evaluate the oral bioavailability of nutraceuticals

Nutraceuticals are the bioactive compounds found in many dietary sources. Numerous publications have reported their ability to prevent the development of degenerative diseases through modulation of physiological and physiochemical processes in living systems. Having sufficient concentration at the target site of action is the most critical factor for nutraceuticals to deliver the health benefits. For consumers, it is commonly accepted to ingest these bioactive components through oral delivery route because it is convenient and cost-efficient and allows flexible dosing schedule. Thus, it is important to understand the oral bioavailability of nutraceuticals to evaluate their qualifications as disease preventive agents and to calculate the required ingestion dosages. To predict the oral bioavailability of nutraceuticals, many in vitro and in vivo models have been developed to reduce the need for frequent human pharmacokinetic studies, which are costly and time-consuming and involve ethical complications. These models evaluate one or more of the influential factors that contribute to the oral bioavailability and are efficient screening techniques with the potential of predicting the pharmacokinetic process in humans. To accurately predict human oral bioavailability, further research is required to develop not only a better correlation between the in vitro and in vivo models but also an accurate scaling factor that takes into account interspecies variations.

Effect of carnosic acid, quercetin and α-tocopherol on lipid and protein oxidation in an in vitro simulated gastric digestion model

Carnosic acid, quercetin and α-tocopherol are well-known antioxidants in many biological systems. However, their antioxidative effect during food digestion against lipid and protein oxidation is not well known. Therefore, in this study, an in vitro simulated gastric digestion model was used to investigate their stability during gastrointestinal conditions and their antioxidative properties during low pH digestion. In general, the stability of the antioxidants in the different steps of digestion was in the order of α-tocopherol > quercetin > carnosic acid. Salivary components, as well as the acidity of the gastric juice, were responsible for the reduction in antioxidants. Both α-tocopherol and quercetin were able to lower lipid oxidation during digestion, while the effect on protein oxidation was not clear. In contrast, carnosic acid did not have any effect on lipid oxidation and tended to stimulate protein oxidation. This study clearly demonstrated that the environmental conditions are of major importance to the properties of antioxidant compounds.

Electrospun acid–base pair solid dispersions of quercetin

An electrospun acid–base pair solid dispersion in the form of core–shell nanofibers was developed for improving the dissolution of quercetin.

Effects of red wine on established markers of arterial structure and function in human studies: current knowledge and future research directions

Evidence from observational studies suggests that mild-to-moderate consumption of red wine is associated with reduced cardiovascular morbidity and mortality. Various individual chemical components of red wine also show salutary effects on vascular homeostasis, that is, enhanced endothelial function and arterial distensibility, both in vitro and in animal studies. However, testing the beneficial potential of red wine in primary and secondary cardiovascular prevention on established surrogate cardiovascular markers requires further study with longer term intervention trials. This report reviews and critically appraises the published evidence for the effects of red wine on endothelium-dependent vasodilation, arterial stiffness and arterial wave reflections in healthy subjects and in patients with cardiovascular disease. Suggestions for future research directions are also provided.

Prediction of the wine polyphenol metabolic space: an application of the Phenol-Explorer database

SCOPE

Knowledge of in vivo polyphenol metabolites derived from the consumption of red wine could be key to understanding its health benefits. This work aimed to predict the wine polyphenol metabolic space in biofluids by using all available data compiled in the Phenol-Explorer database.

METHODS AND RESULTS

A search strategy was developed for Phenol-Explorer to obtain the widest range of metabolites related to wine consumption. A total of 97 metabolites have been described in intervention studies with wine and related products (n = 37), and after consumption of pure compounds known to be wine constituents (n = 90). These 97 metabolites, derived from host and microbial metabolism of several classes of polyphenols, were found in plasma and urine samples and some of them have demonstrated higher or lower biological activities than the parent compound in in vitro studies. The metabolites have been linked to generate, for the first time, a global pathway map of wine in vivo polyphenol metabolism.

CONCLUSION

The retrieval of the widest range of metabolites so far described and their assembly as a metabolic pathway map could aid the identification of possible biomarkers of wine consumption and improve current understanding of the health effects of wine consumption.

Exposure of breastfed infants to quercetin after consumption of a single meal rich in quercetin by their mothers

SCOPE

The exposure to quercetin (Q) has not been studied in breastfed infants whose mothers were consuming a Q-rich diet. The objective of the study was to determine whether plant-origin antioxidant-Q passes from the mother's diet to her milk and to calculate the pharmacokinetic parameters of this phenomenon.

METHODS AND RESULTS

Eleven breastfeeding women were included in this controlled case study. Volunteers followed a Q-restricted diet for 5 consecutive days with the exception of the 3rd day when they received a single meal providing 1 mg of Q per kg of body weight. Urine analysis showed the presence of Q already in the first collected samples after the test (1.5-4 h), which indicated its rapid absorption from the meal. The Cmax = 68 ± 8.44 nmol/L concentration of Q in the milk was calculated for Tmax = 11.89 ± 3.37 h. It was significantly different (p = 0.007) from 40 nmol/L and (p = 0.016) from 42 nmol/L of Q concentration before and 48 h after the test, respectively.

CONCLUSIONS

Q was shown to be a component of human milk at the nmol/L level. Infants breastfed by mothers consuming a diet rich in Q are exposed to a dose of approximately 0.01 mg of Q daily.

Quercetin solid lipid microparticles: a flavonoid for inhalation lung delivery

Purpose

The aim of the present work was to develop solid lipid microparticles (SLMs), as dry powders containing quercetin for direct administration to the lung.

Methods

Quercetin microparticles were prepared by o/w emulsification via a phase inversion technique, using tristearin as the lipid component and phosphatidylcholine as an emulsifier. The quercetin SLMs were characterised for morphology, drug loading (15.5% ± 0.6, which corresponded to an encapsulation efficiency of 71.4%), particle size distribution, response to humidity, crystallinity, thermal behaviour and in vitro respirable fraction. Furthermore, the toxicity and the in vitro transport of the SLMs on an air liquid interface model of the Calu-3 cell line were also investigated using a modified twin-stage impinger apparatus.

Results

Results showed that quercetin SLMs could be formulated as dry powder suitable for inhalation drug delivery (20.5 ± 3.3% fine particle fraction ⩽4.46 μm) that was absorbed, via a linear kinetic model across the Calu-3 monolayer (22.32 ± 1.51% over 4 h). In addition, quercetin SLMs were shown to be non-toxic at the concentrations investigated. Interestingly, no apical to basolateral transport of the micronised quercetin was observed over the period of study.

Conclusions

These observations suggest quercetin diffusion was enhanced by the presence of the lipid/emulsifying excipients in the SLMs; however further studies are necessary to elucidate the exact mechanisms.

Dietary fat increases quercetin bioavailability in overweight adults

SCOPE

Epidemiologic evidence supports that dietary quercetin reduces cardiovascular disease (CVD) risk, but its oral bioavailability is paradoxically low. The aim of this study was to determine whether dietary fat would improve quercetin bioavailability in adults at high risk for CVD and to assess lipid-mediated micellarization of quercetin in vitro.

METHODS AND RESULTS

In a randomized, cross-over study, overweight/obese men and postmenopausal women (n = 4 M/5 F; 55.9 ± 2.1 years; 30.8 ± 1.4 kg/m(2) ) ingested 1095 mg of quercetin aglycone with a standardized breakfast that was fat-free (<0.5 g), low-fat (4.0 g), or high-fat (15.4 g). Plasma was obtained at timed intervals for 24 h to measure quercetin and its methylated metabolites isorhamnetin and tamarixetin. Compared to the fat-free trial, plasma quercetin maximum concentration (Cmax ), and area under curve (AUC0-24 h ) increased (p < 0.05) by 45 and 32%, respectively, during the high-fat trial. During the high-fat trial, isorhamnetin Cmax and AUC0-24 h also increased by 40 and 19%, respectively, whereas Cmax and AUC0-24 h of tamarixetin increased by 46 and 43%, respectively. Dietary fat dose-dependently increased micellarization efficiency of quercetin aglycone in vitro.

CONCLUSION

Dietary fat improves quercetin bioavailability by increasing its absorption, likely by enhancing its micellarization at the small intestine.

Beneficial effects of natural phenolics on levodopa methylation and oxidative neurodegeneration

Levodopa (L-DOPA) is widely used for symptomatic management in Parkinson's disease. We recently showed that (-)-epigallocatechin-3-gallate, a tea polyphenol, not only inhibits L-DOPA methylation, but also protects against oxidative hippocampal neurodegeneration. In the present study, we sought to determine several other common dietary phenolics, namely, tea catechins [(+)-catechin and (-)-epicatechin] and a representative flavonoid (quercetin), for their ability to modulate L-DOPA methylation and to protect against oxidative hippocampal injury. A combination of in vitro biochemical assays, cell culture-based mechanistic analyses, and in vivo animal models was used. While both tea catechins and quercetin strongly inhibit human liver catechol-O-methyltransferase (COMT)-mediated O-methylation of L-DOPA in vitro, only (+)-catechin exerts a significant inhibition of L-DOPA methylation in both peripheral compartment and striatum in rats. The stronger in vivo effect of (+)-catechin on L-DOPA methylation compared to the other dietary compounds is due to its better bioavailability in vivo. In addition, (+)-catechin strongly reduces glutamate-induced oxidative cytotoxicity in HT22 mouse hippocampal neurons in vitro through inactivation of the nuclear factor-κB signaling pathway. Administration of (+)-catechin also exerts a strong neuroprotective effect in the kainic acid-induced oxidative hippocampal neurodegeneration model in rats. In conclusion, (+)-catechin is a dietary polyphenolic that may have beneficial effects in L-DOPA-based treatment of Parkinson patients by inhibiting L-DOPA methylation plus reducing oxidative neurodegeneration.

Phytochemicals and their impact on adipose tissue inflammation and diabetes

Type 2 diabetes mellitus is an inflammatory disease and the mechanisms that underlie this disease, although still incompletely understood, take place in the adipose tissue of obese subjects. Concurrently, the prevalence of obesity caused by Western diet's excessive energy intake and the lack of exercise escalates, and is believed to be causative for the chronic inflammatory state in adipose tissue. Overnutrition itself as an overload of energy may induce the adipocytes to secrete chemokines activating and attracting immune cells to adipose tissue. But also inflammation-mediating food ingredients like saturated fatty acids are believed to directly initiate the inflammatory cascade. In addition, hypoxia in adipose tissue as a direct consequence of obesity, and its effect on gene expression in adipocytes and surrounding cells in fat tissue of obese subjects appears to play a central role in this inflammatory response too. In contrast, revisiting diet all over the world, there are also some natural food products and beverages which are associated with curative effects on human health. Several natural compounds known as spices such as curcumin, capsaicin, and gingerol, or secondary plant metabolites catechin, resveratrol, genistein, and quercetin have been reported to provide an improved health status to their consumers, especially with regard to diabetes, and therefore have been investigated for their anti-inflammatory effect. In this review, we will give an overview about these phytochemicals and their role to interfere with inflammatory cascades in adipose tissue and their potential for fighting against inflammatory diseases like diabetes as investigated in vivo.

UHPLC-(ESI)QTOF MS/MS profiling of quercetin metabolites in human plasma postconsumption of applesauce enriched with apple peel and onion

An ultrahigh pressure liquid chromatography accurate mass quadrupole time-of-flight mass spectrometry with electrospray ionization (UHPLC-(ESI)QTOF MS/MS) method was developed for measuring individual quercetin metabolites in human plasma with high sensitivity and high selectivity. Quercetin (3,3',4',5,7-pentahydroxyflavone) occurs as glycosides in foods. The composition of glycosides is species and cultivar specific. In humans, quercetin undergoes extensive biotransformation, resulting in a range of metabolites. The bioactivity of quercetin metabolites will depend on the type and position of the conjugates. Herein, individual quercetin metabolites (i.e., sulfate, glucuronide or methyl conjugates) were identified by accurate mass MS in human plasma (females = 8 and males = 8) over 24 h after consumption of applesauce enriched with either micronized apple peel (AP) or onion powder (OP). The AP and OP contained ~180 μmol of quercetin glycosides. The relative amounts of quercetin metabolites were quantified in plasma. The complement of identified quercetin metabolites was similar after consumption of AP and OP. Primary metabolites included the following: quercetin sulfate, quercetin glucuronide, and quercetin diglucuronide. A quercetin glutathione adduct was identified in negative ion mode but not apparent in positive ion mode. The pharmacokinetic parameters for AUC0-24 h and Cmax were significantly different for AP and OP. For example, consumption of the AP resulted in Cmax of quercetin sulfate, 4.6 ng/mL; quercetin glucuronide, 15.5 ng/mL; quercetin diglucuronide, 9.3 ng/mL; quercetin glucuronide sulfate, 1.3 ng/mL; methyl quercetin glucuronide, 7.5 ng/mL; and methyl quercetin diglucuronide, 3.6 ng/mL, whereas the OP resulted in Cmax of quercetin sulfate, 37.3 ng/mL; quercetin glucuronide, 212.8 ng/mL; quercetin diglucuronide, 168.8 ng/mL; quercetin glucuronide sulfate, 43.0 ng/mL; methyl quercetin glucuronide, 90.1 ng/mL; methyl quercetin diglucuronide, 65.4 ng/mL. Gender-related differences in the AUC0-24 h for quercetin sulfate and quercetin sulfate glucuronide metabolites were also observed.

Inhibition of cytochrome P450 2C8-mediated drug metabolism by the flavonoid diosmetin

The aim of this study was to assess the effects of diosmetin and hesperetin, two flavonoids present in various medicinal products, on CYP2C8 activity of human liver microsomes using paclitaxel oxidation to 6α-hydroxy-paclitaxel as a probe reaction. Diosmetin and hesperetin inhibited 6α-hydroxy-paclitaxel production in a concentration-dependent manner, diosmetin being about 16-fold more potent than hesperetin (mean IC(50) values 4.25 ± 0.02 and 68.5 ± 3.3 µM for diosmetin and hesperetin, respectively). Due to the low inhibitory potency of hesperetin, we characterized the mechanism of diosmetin-induced inhibition only. This flavonoid proved to be a reversible, dead-end, full inhibitor of CYP2C8, its mean inhibition constant (K(i)) being 3.13 ± 0.11 µM. Kinetic analysis showed that diosmetin caused mixed-type inhibition, since it significantly decreased the V(max) (maximum velocity) and increased the K(m) value (substrate concentration yielding 50% of V(max)) of the reaction. The results of kinetic analyses were consistent with those of molecular docking simulation, which showed that the putative binding site of diosmetin coincided with the CYP2C8 substrate binding site. The demonstration that diosmetin inhibits CYP2C8 at concentrations similar to those observed after in vivo administration (in the low micromolar range) is of potential clinical relevance, since it may cause pharmacokinetic interactions with co-administered drugs metabolized by this CYP.

Quercetin-imprinted nanospheres as novel drug delivery devices

In this work, molecularly imprinted nanospheres for controlled/sustained release of quercetin were synthesized employing methacrylic acid and ethylene glycoldymethacrylate as functional monomer and crosslinking agent, respectively. One pot precipitation polymerization was chosen as polymerization technique to obtain nanosized materials with spherical shape. Morphological and hydrophilic properties by scanning electron microscopy and water content measurements were determined, and recognition and selectivity properties of the imprinted materials were tested using the template quercetin and its structural analogue, the flavonoid catechin. Finally, the applicability of the obtained materials as drug delivery devices was evaluated by performing in vitro release studies in plasma simulating fluids and cytotoxicity testson HeLa cells.

Effect of phytochemicals on phase II enzyme expression in infant human primary skin fibroblast cells

Phase II metabolising enzymes enable the metabolism and excretion of potentially harmful substances in adults, but to date it is unclear whether dietary phytochemicals can induce phase II enzymes differently between adults and infants. We investigated the expression of phase II enzymes in an in vitro model of primary skin fibroblasts at three different developmental stages, 1 month, 2 years and adult, to examine potential differences in age-related phase II enzymes in response to different phytochemicals (5-20 μm) including sulphoraphane, quercetin and catechin. Following phytochemical treatment, a significant increase in mRNA of glutathione S-transferase A1 (GSTA1) and NAD(P)H:quinone oxidoreductase 1 (NQO1) was observed, with the most marked increases seen in response to sulphoraphane (3-10-fold for GSTA1, P = 0·001, and 6-35-fold for NQO1, P = 0·001-0·017). Catechin also induced 3-5-fold changes in NQO1 transcription, whereas quercetin had less effect on NQO1 mRNA induction in infant cells. Moreover, NQO1 protein levels were significantly increased in 2-year-old and adult cell models in response to sulphoraphane treatment. These results suggest that metabolic plasticity and response to xenobiotics may be different in infants and adults; and therefore the inclusion of phytochemicals in the infant diet may modulate their induction of phase II metabolism, thereby providing increased protection from potentially harmful xenobiotics in later life.

Inhibition of hepatic uptake transporters by flavonoids

Members of the human SLC superfamily such as organic anion transporting polypeptide 1B1 (OATP1B1), OATP1B3, and organic cation transporter 1 (OCT1) are drug uptake transporters that are localised on the basolateral membrane of hepatocytes mediating the uptake of drugs such as atorvastatin and metformin into hepatocytes. Ingredients of food such as flavonoids influence the effects of drugs, e.g. by inhibition of drug transporters. Therefore, we investigated the impact of the Ginkgo biloba flavonoids apigenin, kaempferol, and quercetin, and the grapefruit flavonoids naringenin, naringin, and rutin on the OATP1B1, OATP1B3, and OCT1 transport activity. Transporter expressing HEK293 cell lines were used with [3H]sulfobromophthalein ([3H]BSP) as substrate for OATP1B1 and OATP1B3, [3H]atorvastatin as substrate for OATP1B1, and [3H]1-methyl-4-phenylpyridinium ([3H]MPP(+)) as substrate for OCT1. The G. biloba flavonoids showed a competitive inhibition of the OATP1B1- and OATP1B3-mediated [3H]BSP and the OATP1B1-mediated [3H]atorvastatin uptake. Quercetin was the most potent inhibitor of the OATP1B1- and OATP1B3-mediated [3H]BSP transport with K(i)-values of 8.8±0.8μM and 7.8±1.7μM, respectively. For the inhibition of the OATP1B1-mediated [3H]atorvastatin transport, apigenin was the most potent inhibitor with a K(i) value of 0.6±0.2μM. Among the grapefruit flavonoids, naringenin was the most potent inhibitor of the OATP1B1- and OATP1B3-mediated [3H]BSP transport with IC(50)-values of 81.6±1.1μM and 101.1±1.1μM, respectively. All investigated flavonoids showed no significant inhibition of the OCT1-mediated [3H]MPP(+) uptake. Taken together, these in vitro studies showed that the investigated flavonoids inhibit the OATP1B1- and OATP1B3-mediated drug transport, which could be a mechanism for food-drug interactions in humans.

The role of nutraceuticals in chemoprevention and chemotherapy and their clinical outcomes

The genesis of cancer is often a slow process and the risk of developing cancer increases with age. Altering a diet that includes consumption of beneficial phytochemicals can influence the balance and availability of dietary chemopreventive agents. In chemopreventive approaches, foods containing chemicals that have anticancer properties can be supplemented in diets to prevent precancerous lesions from occurring. This necessitates further understanding of how phytochemicals can potently maintain healthy cells. Fortunately there is a plethora of plant-based phytochemicals although few of them are well studied in terms of their application as cancer chemopreventive and therapeutic agents. In this analysis we will examine phytochemicals that have strong chemopreventive and therapeutic properties in vitro as well as the design and modification of these bioactive compounds for preclinical and clinical applications. The increasing potential of combinational approaches using more than one bioactive dietary compound in chemoprevention or cancer therapy will also be evaluated. Many novel approaches to cancer prevention are on the horizon, several of which are showing great promise in saving lives in a cost-effective manner.

Population pharmacokinetic analysis of sorafenib in patients with solid tumours

WHAT IS ALREADY KNOWN ABOUT THIS SUBJECT

Sorafenib is a multikinase inhibitor with activity against B-raf, C-raf, VEGFR2, PDGFRβ and FGFR1. Sorafenib is clinically approved for the treatment of renal cell carcinoma (RCC) and hepatocellular carcinoma (HCC). The pharmacokinetics (PK) of sorafenib are highly variable between subjects. Sorafenib exposure increases less than dose proportionally (likely due to limited solubility). Sorafenib undergoes enterohepatic recycling (EHC).

WHAT THIS STUDY ADDS

This is the first study to characterize the PK of sorafenib using a model based on sorafenib's known disposition characteristics such as delayed/solubility-limited GI absorption and EHC. The parameterization of the EHC model used a square wave function to describe the gall bladder emptying. This study evaluated the effect of baseline bodyweight, BSA, age, gender, liver function parameters, kidney function parameters and genotype with respect to CYP3A4*1B, CYP3A5*3C, UGT1A9*3 and UGT1A9*5 on sorafenib PK. No clinically important covariates were identified. This model can be used to simulate and explore alternative dosing regimens and to develop exposure-response relationships for sorafenib.

AIMS

To characterize the pharmacokinetics (PK) of sorafenib in patients with solid tumours and to evaluate the possible effects of demographic, clinical and pharmacogenetic (CYP3A4*1B, CYP3A5*3C, UGT1A9*3 and UGT1A9*5) covariates on the disposition of sorafenib.

METHODS

PK were assessed in 111 patients enrolled in five phase I and II clinical trials, where sorafenib 200 or 400 mg was administered twice daily as a single agent or in combination therapy. All patients were genotyped for polymorphisms in metabolic enzymes for sorafenib. Population PK analysis was performed by using nonlinear mixed effects modelling (NONMEM). The final model was validated using visual predictive checks and nonparametric bootstrap analysis.

RESULTS

A one compartment model with four transit absorption compartments and enterohepatic circulation (EHC) adequately described sorafenib disposition. Baseline bodyweight was a statistically significant covariate for distributional volume, accounting for 4% of inter-individual variability (IIV). PK model parameter estimates (range) for an 80 kg patient were clearance 8.13 l h(-1) (3.6-22.3 l h(-1) ), volume 213 l (50-1000 l), mean absorption transit time 1.98 h (0.5-13 h), fraction undergoing EHC 50% and average time to gall bladder emptying 6.13 h.

CONCLUSIONS

Overall, population PK analysis was consistent with known biopharmaceutical/PK characteristics of oral sorafenib. No clinically important PK covariates were identified.

Enriched cereal bars are more effective in increasing plasma quercetin compared with quercetin from powder-filled hard capsules

The flavonol quercetin, is one of the major flavonoids found in edible plants. The bioavailability of quercetin in humans may be influenced by the food matrix in which it is consumed as well as by its chemical and physical form. The objective of the present study was to investigate the biokinetics of quercetin from quercetin-enriched cereal bars and quercetin powder-filled hard capsules. In a randomised, single-blinded, diet-controlled cross-over study, six healthy women aged 22-28 years took a single oral dose of approximately 130 mg quercetin equivalents from either quercetin-enriched cereal bars (containing 93·3 % quercetin aglycone plus 6·7 % quercetin-4'-glucoside) or quercetin powder-filled hard capsules (100 % quercetin aglycone). Blood samples were drawn before and after quercetin administration over a 24 h period. The concentrations of quercetin and its monomethylated derivatives, isorhamnetin (3'-O-methyl quercetin) and tamarixetin (4'-O-methyl quercetin), were measured by HPLC with fluorescence detection after plasma enzymatic treatment. The systemic availability as determined by comparing the plasma concentration-time curves of quercetin was found to be five times and the cmax values six times higher after ingestion of 130 mg quercetin by quercetin-enriched cereal bars than after ingestion by quercetin capsules. In contrast, tmax did not differ significantly between the two treatments. The cmax values for isorhamnetin and tamarixetin were four and nine times higher after ingestion of quercetin by quercetin-enriched cereal bars than after ingestion by quercetin capsules. In conclusion, quercetin from quercetin-enriched cereal bars is significantly more bioavailable than from quercetin powder-filled hard capsules.

Metabolic conversion of dietary flavonoids alters their anti-inflammatory and antioxidant properties

The notion that dietary flavonoids exert beneficial health effects in humans is often based on in vitro studies using the glycoside or aglycone forms of these flavonoids. However, flavonoids are extensively metabolized in humans, resulting in the formation of glucuronide, methyl, and sulfate derivatives, which may have different properties than their parent compounds. The goal of this study was to investigate whether different chemical modifications of the same flavonoid molecule affect its biological and antioxidant activities. Hence, we studied the anti-inflammatory effects of several major human metabolites of quercetin and (-)-epigallocatechin-3-O-gallate (EGCG) by assessing their inhibitory effects on tumor necrosis factor α (TNFα)-induced protein expression of cellular adhesion molecules in human aortic endothelial cells (HAEC). HAEC were incubated with 1-30 μM quercetin, 3'- or 4'-O-methyl-quercetin, quercetin-3-O-glucuronide, and quercetin-3'-O-sulfate or 20-100 μM EGCG, 4''-O-methyl-EGCG, and 4',4''-di-O-methyl-EGCG, prior to coincubation with 100 U/ml of TNFα. 3'-O-Methyl-quercetin, 4'-O-methyl-quercetin, and their parent aglycone compound, quercetin, all effectively inhibited expression of intercellular adhesion molecule-1 (ICAM-1) with IC(50) values (concentration required for 50% inhibition) of 8.0, 5.0, and 4.4 μM, respectively; E-selectin expression was suppressed to a somewhat lesser but still significant degree by all three compounds, whereas vascular cell adhesion molecule-1 (VCAM-1) was not affected. In contrast, quercetin-3-O-glucuronide (20-100 μM), quercetin-3'-O-sulfate (10-30 μM), and phenolic acid metabolites of quercetin (20-100 μM) did not inhibit adhesion molecule expression. 4',4''-Di-O-methyl-EGCG selectively inhibited ICAM-1 expression with an IC(50) value of 94 μM, whereas EGCG (20-60 μM) and 4''-O-methyl-EGCG (20-100 μM) had no effect. The inhibitory effects of 3'-O-methyl-quercetin and 4',4''-di-O-methyl-EGCG on adhesion molecule expression were not related either to inhibition of NF-κB activation or to their antioxidant reducing capacity. Our data indicate that flavonoid metabolites have different biological and antioxidant properties than their parent compounds, and suggest that data from in vitro studies using nonmetabolites of flavonoids are of limited relevance in vivo.

Effects of flavonoids and other polyphenols on inflammation

Flavonoids are a family of polyphenolic compounds which are widespread in nature (vegetables) and are consumed as part of the human diet in significant amounts. There are other types of polyphenols, including, for example, tannins and resveratrol. Flavonoids and related polyphenolic compounds have significant antiinflammatory activity, among others. This short review summarizes the current knowledge on the effects of flavonoids and related polyphenolic compounds on inflammation, with a focus on structural requirements, the mechanisms involved, and pharmacokinetic considerations. Different molecular (cyclooxygenase, lipoxygenase) and cellular targets (macrophages, lymphocytes, epithelial cells, endothelium) have been identified. In addition, many flavonoids display significant antioxidant/radical scavenging properties. There is substantial structural variation in these compounds, which is bound to have an impact on their biological profile, and specifically on their effects on inflammatory conditions. However, in general terms there is substantial consistency in the effects of these compounds despite considerable structural variations. The mechanisms have been studied mainly in myeloid cells, where the predominant effect is an inhibition of NF-κB signaling and the downregulation of the expression of proinflammatory markers. At present there is a gap in knowledge of in vitro and in vivo effects, although the pharmacokinetics of flavonoids has advanced considerably in the last decade. Many flavonoids have been studied for their intestinal antiinflammatory activity which is only logical, since the gastrointestinal tract is naturally exposed to them. However, their potential therapeutic application in inflammation is not restricted to this organ and extends to other sites and conditions, including arthritis, asthma, encephalomyelitis, and atherosclerosis, among others.

Microsomal quercetin glucuronidation in rat small intestine depends on age and segment

UDP-glucuronosyltransferase (UGT) activity toward the flavonoid quercetin and UGT protein were characterized in three equidistant small intestine (SI) segments from 4-, 12-, 18-, and 28-month-old male Fischer 344 rats (n = 8/age) using villin to control for enterocyte content. SI microsomal intrinsic clearance of quercetin was increased 3- to 9-fold from 4 months in the proximal and distal SI at 12 and 18 months. Likewise, at 30 μM quercetin, SI microsomal glucuronidation activity was increased with age: 4.8- and 3.9-fold greater at 18 months than at 4 months. Quercetin UGT regioselectivity was not changed by age. The distal SI preferentially catalyzed glucuronidation at the 7-position, whereas the proximal SI produced the greatest proportion of 4'- and 3'-conjugates. Enterocyte UGT content in different SI segments was not consistently changed with age. In the proximal SI, UGT1A increased 64 and 150% at 12 and 18 months and UGT1A1, UGT1A7, and UGT1A8 were also increased at 12 and 18 months. However, age-related changes in expression were inconsistent in the medial and distal segments. Microsomal rates of quercetin glucuronidation and UGT expression were positively correlated with UGT1A1 content for all pooled samples (r = 0.467) and at each age (r = 0.538-0.598). UGT1A7 was positively correlated with total, 7-O- and 3-O-quercetin glucuronidation at 18 months. Thus, age-related differences in UGT quercetin glucuronidation depend on intestinal segment, are more pronounced in the proximal and distal segments and may be partially related to UGT1A1 and UGT1A7 content.