Dietary quercetin supplements: Assessment of online product informations and quantitation of quercetin in the products by high-performance liquid chromatography

Benefits of Quercetin on Glycated Hemoglobin, Blood Pressure, PiKo-6 Readings, Night-Time Sleep, Anxiety, and Quality of Life in Patients with Type 2 Diabetes Mellitus: A Randomized Controlled Trial

Background: Diabetes is a rapidly growing global morbidity issue with high prevalence, and the associated dysglycemia leads to complications. Patients with type 2 diabetes mellitus (T2DM) often experience elevated anxiety levels, affecting their quality of life and diabetes management. This study investigated quercetin, a nutraceutical and potential senolytic with antioxidant activity, to detect its possible positive effect on the bio-clinical measurements and routine health of patients with T2DM. Methods: This prospective randomized controlled trial (RCT) investigated the clinical usefulness of quercetin in patients with T2DM receiving non-insulin medications. One hundred participants were stratified by age and sex (1:1) and randomized to control (n = 50) or intervention (n = 50) groups. The control received standard care only, while the intervention received 500 mg quercetin daily for 12 weeks, followed by an 8-week washout and a final consecutive 12-week supplementation period (total: 32 weeks), as adjunct to their usual care. Comprehensive health assessments, including blood analyses, were conducted at baseline and study termination. Quality of life and anxiety were assessed using the 36-item Short Form Health Survey (SF-36) and Short Anxiety Screening Test (SAST-10). Results: Eighty-eight patients with T2DM concluded the trial. Compared with the control, glycated hemoglobin (HbA1c) levels showed a significant decrease (Δ%-change: -4.0% vs. 0.1%, p = 0.011). Quercetin also significantly improved PiKo-6 readings (FEV1: 5.6% vs. -1.5%, p = 0.002), systolic blood pressure (-5.0% vs. -0.2%, p = 0.029), night-time sleep (11.6% vs. -7.3%, p < 0.001), anxiety levels (SAST-10) (-26.2% vs. 3.3%, p < 0.001), and quality of life (SF-36) (both physical and mental components, p < 0.001). Conclusions: Based on the current open-label study, quercetin appears to be a promising supplement for T2DM, providing lifestyle and care support. Further research is warranted to shift this potential from clinical usefulness and feasibility to multidisciplinary evidence.

The Impact of Three-Month Quercetin Intake on Quality of Life and Anxiety in Patients With Type II Diabetes Mellitus: An Early Data Analysis From a Randomized Controlled Trial

BACKGROUND

Diabetes is a high-prevalence, major chronic metabolic disease demanding effective interventions. Quercetin, a phytochemical with potential health benefits, has garnered interest for its therapeutic properties.

AIM

This study was designed to capture the early efficacy and clinical safety aspects following quercetin administration in patients with type II diabetes mellitus (T2DM).

METHODS

The main study involved a randomized allocation procedure to assign non-insulin-treated patients attending the 4th Health Unit of Heraklion to intervention and control groups based on age and sex. The intervention group (n=50) received 500 mg of quercetin daily for 12 + (8 free intervals) + 12 weeks, alongside their usual treatment, while the control group (n=50) did not. After randomization, for the intermediary 12-week follow-up, data from 38 patients (intervention: 20; control: 18) were analyzed in this report. All subjects provided informed consent for the collection of anthropometric measurements, vital signs, daily habits data, and PiKo-6 spirometric readings. Additionally, participants responded to the Short Anxiety Screening Test (SAST) and the 36-Item Short Form Health Survey (SF-36) questionnaires.

RESULTS

Thirty-eight participants were included (60% men and 40% women in the intervention group; 38.9% men and 61.1% women in the control group). In the treatment arm, Forced Expiratory Volume in the first second (FEV1) measured with PiKo-6 showed a Δ%- change for the intervention arm: +6.8%, control: -0.2% (p=0.059), systolic blood pressure; intervention: -7.4%, control: -3.7% (p=0.117), waist circumference; intervention: -1.5% control: -0.7% (p=0.455) and night-time sleep; intervention: +5.3%, control: +1.4% (p=0.926) were favourably influenced. The treatment group exhibited significant enhancements in both anxiety levels assessed by the anxiety symptoms scale (SAST-10, p=0.026) and quality of life evaluated by the SF-36 (p<0.001).

CONCLUSIONS

Positive evidence is emerging for a pleiotropic effect of quercetin intake in patients with T2DM, specifically in terms of anxiety reduction and amelioration of life quality, in just 12 weeks of administration and without adverse effects, indicating clinical safety and underscoring its potential for integration in T2DM supportive care.

Quercetin mitigates doxorubicin-induced neurodegenerative changes in the cerebral cortex and hippocampus of rats; insights to DNA damage, inflammation, synaptic plasticity

BACKGROUND

Doxorubicin (Dox) is one of the most effective anti-neoplastic agents. Quercetin (QE) exhibits antioxidant and anti-inflammatory properties.

AIM

To detect neuroprotective properties of quercetin in rats exposed to doxorubicin-induced brain injury.

MATERIAL AND METHODS

48 rats were allocated equally into four groups: control group: (given normal saline), QE group: (given 80 mg/kg of QE orally daily for 2 weeks), Dox group: (received 2.5 mg/kg of Dox every other day for a total of seven intraperitoneal injections), and Dox+QE group: (received 2.5 mg/kg of Dox every other day for a total of seven intraperitoneal injections and 80 mg/kg of QE orally daily for 2 weeks). Subsequently, biochemical analyses were carried out along with histopathological (light and electron microscopic) and immunohistochemical examinations of the cerebral cortex and hippocampus.

RESULTS

The Dox group revealed a decline in the activities of superoxide dismutase, catalase, and glutathione peroxidase, along with an increase in malondialdehyde and an increase in DNA damage. Furthermore, sections of the cerebral cortex and hippocampus revealed neurodegenerative changes, decreased synaptophysin, and increased Interleukin-1 beta expressions. Biochemical and histopathological results were markedly improved by QE administration.

CONCLUSIONS

It can be concluded that QE induces protective effects against Dox-induced neurotoxicity.

Towards safer and efficient formulations: Machine learning approaches to predict drug-excipient compatibility

Predicting drug-excipient compatibility is a critical aspect of pharmaceutical formulation design. In this study, we introduced an innovative approach that leverages machine learning techniques to improve the accuracy of drug-excipient compatibility predictions. Mol2vec and 2D molecular descriptors combined with the stacking technique were used to improve the performance of the model. This approach achieved a significant advancement in the predictive capacity as demonstrated by the accuracy, precision, recall, AUC, and MCC of 0.98, 0.87, 0.88, 0.93 and 0.86, respectively. Using the DE-INTERACT model as the benchmark, our stacking model could remarkably detect drug-excipient incompatibility in 10/12 tested cases, while DE-INTERACT managed to recognize only 3 out of 12 incompatibility cases in the validation experiments. To ensure user accessibility, the trained model was deployed to a user-friendly web platform (URL: https://decompatibility.streamlit.app/). This interactive interface accommodated inputs through various types, including names, PubChem CID, or SMILES strings. It promptly generated compatibility predictions alongside corresponding probability scores. However, the continual refinement of model performance is crucial before applying this model in practice.

Safety and risks of CBD oils purchased online: unveiling uncertain quality and vague health claims

Introduction: The unmet need for highly effective, naturally derived products with minimal side effects results in the over-popularity of ever-newer medicinal plants. In the middle of 2010, products containing cannabidiol (CBD), one of the special metabolites of Cannabis sativa, started to gain popularity. For consumers and healthcare providers alike, the legal context surrounding the marketing of CBD products is not entirely clear, and the safety of using some products is in doubt. Companies in the online medicinal product market profit from the confusion around CBD oils. Methods: In our study, we employed a complex method known as risk-based safety mapping of the online pharmaceutical market, which included health claim content analysis of online stores, test purchases, and labeling and quantitative analysis of the CBD content. Results: There were discovered 16 online retailers selling an average of 2-7 goods and CBD oils with a concentration of 3%-5% (30-50 mg/mL) CBD. The majority (n/N = 10/16, 62.5%) displayed potential health-related benefits indirectly on their website, and in the case of one web shop (n/N = 1/16, 6.3%), we detected COVID-19-related use. Altogether, 30 types of purported "indications" were collected. A total of 12 CBD oil products were test-purchased from online retailers in December 2020. Upon evaluating the packaging and product information, we noticed that three products (n/N = 3/12, 25%) lacked instructions on use, hence increasing the risk of inappropriate application and dosing. The cannabidiol content was quantified using UHPLC. The measured CBD concentrations of the products ranged from 19.58 mg/mL to 54.09 mg/mL (mean 35.51 mg/mL, median 30.63 mg/mL, and SD ± 12.57 mg/mL). One (8.33%) product was underlabeled, five (41.67%) were over-labeled, and only every second product (50%) was appropriately labeled based on the quantitative assessment of CBD concentration. Discussion: Further research and quality control are necessary to establish the regulatory context of the usage and classification of CBD and other cannabinoids in nonmedicinal products (e.g., food supplements), as authorities and policymakers worldwide struggle with the uncertainties surrounding CBD products.

Quality of dorzolamide hydrochloride and timolol maleate containing eye drops distributed online

Patient safety risks associated with the online purchase of medications, especially in case of ophthalmic preparations, are significant. Our study aimed to carry out quality assessment of dorzolamide hydrochloride (DZA) and timolol maleate (TIM) eye drops preserved with benzalkonium chloride (BAC) via online test purchases. Three samples were purchased online, while control preparations were acquired through authorized national drug supply chain. Our method was based on the International Pharmaceutical Federation (FIP) Inspection Checklist and integrated the evaluation of packaging and labelling. Sterility was established according to the European Pharmacopoeia (Ph. Eur.), while qualitative and quantitative quality was assessed with high-performance liquid chromatographic (HPLC) analysis. Several signs of falsification were recognized upon visual inspection of the online samples. All the products were clear, colourless, slightly viscous solutions. They were free from visible contaminants. The samples were sterile as no evidence of microbial growth was found. A quick and inexpensive HPLC analysis, optimized by the authors showed that active ingredients and the preservative deviated significantly (p < 0,05) with more than 10% from the values stated on the labels for at least one component (DZA: 99.3-113.1%, TIM: 112.8-139.2%, BAC: 82.4-97.7%). Development of comprehensive and reliable quality assessment methods are vital to increase public safety of pharmaceutical products sold online. A complex approach, integrating visual inspection, labelling assessment, microbiological analysis coupled with qualitative and quantitative methods provide a most reliable method. Due to its limited feasibility and cost-effectiveness, raising public awareness and limiting illegal online sellers should be the primary approaches to protect patients from substandard and falsified medicinal products sold via the internet. Particularly important for health professionals to understand this market and its public health concern, and to raise patient awareness of the risks associated with uncontrolled online purchase of medication.

Enhanced electrochemical determination of quercetin in a choline chloride-based ionic liquid

Electrochemical techniques have been applied to determine quercetin and to evaluate its antioxidant effect. Deep eutectic solvents as a new generation of green solvents are promising electrolyte catalytically active additives for electrochemical oxidation of quercetin. Herein, in this work, Au was directly electrodeposited on the surface of graphene-modified glassy carbon electrodes, and AuNPs/GR/GC electrodes were fabricated. Choline chloride-based ionic liquids as deep eutectic solvents were readily prepared and applied to detect quercetin in buffer solutions, allowing a detection enhancement. X-ray diffraction and scanning electron microscopy were carried out to characterize the morphology of AuNPs/GR/GCE. Fourier transform infrared spectroscopy was carried out to interpret the H-bond interactions between the DES and quercetin. This electrochemical sensor exhibited good analytical performance. The low detection limit was reduced to 0.5 μM in a 15% DES solution, which was 300% higher than the signal without DES. It proved to be fast and environmentally friendly for the determination of quercetin and the DES had no effect on antioxidant effects of quercetin. In addition, it has been successfully applied in real sample analysis.

Improvement of Therapeutic Value of Quercetin with Chitosan Nanoparticle Delivery Systems and Potential Applications

This paper reviews recent studies investigating chitosan nanoparticles as drug delivery systems for quercetin. The therapeutic properties of quercetin include antioxidant, antibacterial and anti-cancer potential, but its therapeutic value is limited by its hydrophobic nature, low bioavailability and fast metabolism. Quercetin may also act synergistically with other stronger drugs for specific disease states. The encapsulation of quercetin in nanoparticles may increase its therapeutic value. Chitosan nanoparticles are a popular candidate in preliminary research, but the complex nature of chitosan makes standardisation difficult. Recent studies have used in-vitro, and in-vivo experiments to study the delivery of quercetin alone or in combination with another active pharmaceutical ingredient encapsulated in chitosan nanoparticles. These studies were compared with the administration of non-encapsulated quercetin formulation. Results suggest that encapsulated nanoparticle formulations are better. In-vivo or animal models simulated the type of disease required to be treated. The types of diseases were breast, lung, liver and colon cancers, mechanical and UVB-induced skin damage, cataracts and general oxidative stress. The reviewed studies included various routes of administration: oral, intravenous and transdermal routes. Although toxicity tests were often included, it is believed that the toxicity of loaded nanoparticles needs to be further researched, especially when not orally administered.

Interaction of luteolin, naringenin, and their sulfate and glucuronide conjugates with human serum albumin, cytochrome P450 (CYP2C9, CYP2C19, and CYP3A4) enzymes and organic anion transporting polypeptide (OATP1B1 and OATP2B1) transporters

Luteolin and naringenin are flavonoids found in various foods/beverages and present in certain dietary supplements. After a high intake of these flavonoids, their sulfate and glucuronide conjugates reach micromolar concentrations in the bloodstream. Some pharmacokinetic interactions of luteolin and naringenin have been investigated in previous studies; however, only limited data are available in regard to their metabolites. In this study, we aimed to investigate the interactions of the sulfate and glucuronic acid conjugates of luteolin and naringenin with human serum albumin, cytochrome P450 (CYP2C9, 2C19, and 3A4) enzymes, and organic anion transporting polypeptide (OATP1B1 and OATP2B1) transporters. Our main findings are as follows: (1) Sulfate conjugates formed more stable complexes with albumin than the parent flavonoids. (2) Luteolin and naringenin conjugates showed no or only weak inhibitory action on the CYP enzymes examined. (3) Certain conjugates of luteolin and naringenin are potent inhibitors of OATP1B1 and/or OATP2B1 enzymes. (4) Conjugated metabolites of luteolin and naringenin may play an important role in the pharmacokinetic interactions of these flavonoids.

The effect of flavonoids on the reduction of cupric ions, the copper-driven Fenton reaction and copper-triggered haemolysis

Flavonoids are considered beneficial, but they may exhibit pro-oxidative effects likely due to metal reducing properties. For the first time, 24 structurally related flavonoids were compared for copper reduction, and modulation of the copper-triggered Fenton reaction and lysis of erythrocytes. The vast majority of flavonoids reduced cupric ions; their behaviour ranged from progressive gradual reduction through bell-shaped, neutral, to a blockade of spontaneous reduction. Similarly, different behaviours were observed with the Fenton reaction. Flavone was the only flavonoid that potentiated copper-triggered haemolysis (155 ± 81 % at twice the amount of Cu²⁺), while 18 flavonoids were at least partly protective in some concentrations. Only 5-hydroxyflavone did not reduce Cu²⁺ and behaved as an antioxidant in both assays (reduction of 60 ± 10 % and 88 ± 1%, respectively, at an equimolar ratio with Cu²⁺). In conclusion, relatively subtle structural differences resulted in very different anti/prooxidant behaviour depending on the model.

Identification and Quantification of Flavonoids in Okra (Abelmoschus esculentus L. Moench) and Antiproliferative Activity In Vitro of Four Main Components Identified

Okra is a kind of flavonoid-rich food which was reported to have a variety of health functions. Flavonoids are the major polyphenolic compounds in okra and are thought to play a role in reducing the risk of disease. The aim of this study was to isolate and identify the flavonoids composition in okra pods and explore the activity of the main flavonoids components identified on inhibiting tumor cell proliferation in vitro. Six individual flavonoids were identified by HPLC-MS/MS: quercetin-3-gentiobioside (Q3G), quercetin-3-sambubioside (Q3S), rutin, quercetin-7-glucoside (Q7G), isoquercitrin (ISO) and quercetin-3-malonylglucoside (Q3M), which were all separated well within 30 min. The analytical method was validated by the recovery of spiked samples and so on. Moreover, four main flavonoids components, namely Q3G, Q3S, ISO and Q3M, exhibited significant (p < 0.05) inhibition of NCI-N87, A375, A549 cells proliferation (25−100 μmol/L) and of HFLS-RA (200−300 μmol/L) in different levels, according to MTT method, respectively. It is demonstrated that the flavonoids components of okra exhibited a noteworthy development prospect as a possible nutraceutical dietary supplement.

Negligible Effect of Quercetin in the Pharmacokinetics of Sulfasalazine in Rats and Beagles: Metabolic Inactivation of the Interaction Potential of Quercetin with BCRP

Breast cancer resistance protein (BCRP) mediates pharmacokinetic drug interactions. This study evaluated the potential of quercetin to inhibit and induce BCRP in vitro and in vivo. The inhibition of BCRP was investigated for quercetin and its metabolites using BCRP/mBcrp1-overexpressing MDCKII cells by flow cytometry. The induction of BCRP was investigated in LS174T cells using quantitative PCR. The expression of rat BCRP in rat small intestine, liver, and kidney was also measured after multiple administrations of quercetin in rats (50, 100, and 250 mg/kg, seven days). The in vivo pharmacokinetic changes of sulfasalazine following single or multiple administration of quercetin in rats and beagles were investigated. Although the induction effect of quercetin on BCRP was observed in vitro, the in vivo expression of rat BCRP was not changed by multiple quercetin administrations. Oral administration of quercetin did not affect the plasma concentration or pharmacokinetic parameters of sulfasalazine, regardless of dose and dosing period in either rats or beagles. In addition, the inhibitory effect of quercetin metabolites on BCRP/mBcrp1 was not observed. These results suggest that the in vivo drug interaction caused by quercetin via BCRP was negligible, and it may be related to the metabolic inactivation of quercetin for the inhibition of BCRP.

Redesigning Nature: Ruthenium Flavonoid Complexes with Antitumour, Antimicrobial and Cardioprotective Activities

Flavonoids are a class of natural polyphenolic compounds sharing a common 2-phenyl-3,4-dihydro-2H-1-benzopyran (flavan) backbone. Typically known for their antioxidant activity, flavonoids are also being investigated regarding antitumour and antimicrobial properties. In this review, we report on the complexation of both natural and synthetic flavonoids with ruthenium as a strategy to modulate the biological activity. The ruthenoflavonoid complexes are divided into three subclasses, according to their most prominent bioactivity: antitumour, antimicrobial, and protection of the cardiovascular system. Whenever possible the activity of the ruthenoflavonoids is compared with that of commercial drugs for a critical assessment of the feasibility of using them in future clinical applications.

Immunopharmacological perspective on zinc in SARS-CoV-2 infection

The novel SARS-CoV-2 which was first reported in China is the cause of infection known as COVID-19. In comparison with other coronaviruses such as SARS-CoV and MERS, the mortality rate of SARS-CoV-2 is lower but the transmissibility is higher. Immune dysregulation is the most common feature of the immunopathogenesis of COVID-19 that leads to hyperinflammation. Micronutrients such as zinc are essential for normal immune function. According to the assessment of WHO, approximately one-third of the world's society suffer from zinc deficiency. Low plasma levels of zinc are associated with abnormal immune system functions such as impaired chemotaxis of polymorphonuclear cells (PMNs) and phagocytosis, dysregulated intracellular killing, overexpression of the inflammatory cytokines, lymphopenia, decreased antibody production, and sensitivity to microbes especially viral respiratory infections. Zinc exerts numerous direct and indirect effects against a wide variety of viral species particularly RNA viruses. The use of zinc and a combination of zinc-pyrithione at low concentrations impede SARS-CoV replication in vitro. Accordingly, zinc can inhibit the elongation step of RNA transcription. Furthermore, zinc might improve antiviral immunity by up-regulation of IFNα through JAK/STAT1 signaling pathway in leukocytes. On the other hand, zinc supplementation might ameliorate tissue damage caused by mechanical ventilation in critical COVID-19 patients. Finally, zinc might be used in combination with antiviral medications for the management of COVID-19 patients. In the current review article, we review and discuss the immunobiological roles and antiviral properties as well as the therapeutic application of zinc in SARS-CoV-2 and related coronaviruses infections.

Developing a framework regarding a complex risk based methodology in the evaluation of hazards associated with medicinal products sourced via the internet

Today, the increasing number of illicit internet pharmacies is a global phenomenon, however, the size of the online pharmaceutical market is still relatively unknown and the dubious quality of products is questionable and warrants investigation. Descriptive data from this black market channel are derived from studies analyzing the online availability of different medications procured over the internet and their methodology is quite heterogeneous. Our aim was to develop a comprehensive and specific risk assessment for selecting high patient safety risk medications from the online pharmaceutical market. A rapid tool was developed based upon the two quality and safety standard resolutions in pharmaceutical practice, published by the European Directorate for the Quality of Medicines, and was illustrated on eye drops. We developed five dimensions in support of the risk assessment including intrinsic, extrinsic and potential risks of counterfeiting. The five criteria were integrated in a comprehensively weighted risk-scoring format. The probability of procuring the product from the internet was also assessed based on the number of relevant links within the first twenty search engine results and the cost of the products. With the application of the tool a dorzolamide & timolol combination eye drop represented the highest overall patient safety risk score. In consideration of our literature review of the past 20 years, there is no current, standardized methodology to effectively identify pharmaceutical products associated with high patient safety risks. Notably, the fully comprehensive analysis of the internet pharmaceutical market and the test purchase of all online available medicines is unrealistic. Therefore, we developed a method to aid online surveillance researches and targeted international organizational led joint actions against the uncontrolled sale of falsified and substandard medications (e.g.: Operation Pangea).

Inhibitory effects of polyphenols and their colonic metabolites on CYP2D6 enzyme using two different substrates

Polyphenolic compounds (including flavonoids, chalcones, phenolic acids, and furanocoumarins) represent a common part of our diet, but are also the active ingredients of several dietary supplements and/or medications. These compounds undergo extensive metabolism by human biotransformation enzymes and the microbial flora of the colon. CYP2D6 enzyme metabolizes approximately 25% of the drugs, some of which has narrow therapeutic window. Therefore, its inhibition can lead to the development of pharmacokinetic interactions and the disruption of drug therapy. In this study, the inhibitory effects of 17 plant-derived compounds and 19 colonic flavonoid metabolites on CYP2D6 were examined, employing two assays with different test substrates. The O-demethylation of dextromethorphan was tested employing CypExpress 2D6 kit coupled to HPLC analysis; while the O-demethylation of another CYP2D6 specific substrate (AMMC) was investigated in a plate reader assay with BioVision Fluorometric CYP2D6 kit. Interestingly, some compounds (e.g., bergamottin) inhibited both dextromethorphan and AMMC demethylation; however, certain substances proved to be inhibitors only in one of the assays applied. Our results demonstrate that some polyphenols and colonic metabolites are inhibitors of CYP2D6-catalyzed reactions. Nevertheless, the inhibitory effects showed strong substrate dependence.

Inhibitory Effects of Quercetin and Its Main Methyl, Sulfate, and Glucuronic Acid Conjugates on Cytochrome P450 Enzymes, and on OATP, BCRP and MRP2 Transporters

Quercetin is a flavonoid, its glycosides and aglycone are found in significant amounts in several plants and dietary supplements. Because of the high presystemic biotransformation of quercetin, mainly its conjugates appear in circulation. As has been reported in previous studies, quercetin can interact with several proteins of pharmacokinetic importance. However, the interactions of its metabolites with biotransformation enzymes and drug transporters have barely been examined. In this study, the inhibitory effects of quercetin and its most relevant methyl, sulfate, and glucuronide metabolites were tested on cytochrome P450 (CYP) (2C19, 3A4, and 2D6) enzymes as well as on organic anion-transporting polypeptides (OATPs) (OATP1A2, OATP1B1, OATP1B3, and OATP2B1) and ATP (adenosine triphosphate) Binding Cassette (ABC) (BCRP and MRP2) transporters. Quercetin and its metabolites (quercetin-3'-sulfate, quercetin-3-glucuronide, isorhamnetin, and isorhamnetin-3-glucuronide) showed weak inhibitory effects on CYP2C19 and 3A4, while they did not affect CYP2D6 activity. Some of the flavonoids caused weak inhibition of OATP1A2 and MRP2. However, most of the compounds tested proved to be strong inhibitors of OATP1B1, OATP1B3, OATP2B1, and BCRP. Our data demonstrate that not only quercetin but some of its conjugates, can also interact with CYP enzymes and drug transporters. Therefore, high intake of quercetin may interfere with the pharmacokinetics of drugs.

Effects of Chrysin and Its Major Conjugated Metabolites Chrysin-7-Sulfate and Chrysin-7-Glucuronide on Cytochrome P450 Enzymes and on OATP, P-gp, BCRP, and MRP2 Transporters

Chrysin is an abundant flavonoid in nature, and it is also contained by several dietary supplements. Chrysin is highly biotransformed in the body, during which conjugated metabolites chrysin-7-sulfate and chrysin-7-glucuronide are formed. These conjugates appear at considerably higher concentrations in the circulation than the parent compound. Based on previous studies, chrysin can interact with biotransformation enzymes and transporters; however, the interactions of its metabolites have been barely examined. In this in vitro study, the effects of chrysin, chrysin-7-sulfate, and chrysin-7-glucuronide on cytochrome P450 enzymes (2C9, 2C19, 3A4, and 2D6) as well as on organic anion-transporting polypeptides (OATPs; 1A2, 1B1, 1B3, and 2B1) and ATP binding cassette [P-glycoprotein, multidrug resistance-associated protein 2, and breast cancer resistance protein (BCRP)] transporters were investigated. Our observations revealed that chrysin conjugates are strong inhibitors of certain biotransformation enzymes (e.g., CYP2C9) and transporters (e.g., OATP1B1, OATP1B3, OATP2B1, and BCRP) examined. Therefore, the simultaneous administration of chrysin-containing dietary supplements with medications needs to be carefully considered due to the possible development of pharmacokinetic interactions. SIGNIFICANCE STATEMENT: Chrysin-7-sulfate and chrysin-7-glucuronide are the major metabolites of flavonoid chrysin. In this study, we examined the effects of chrysin and its conjugates on cytochrome P450 enzymes and on organic anion-transporting polypeptides and ATP binding cassette transporters (P-glycoprotein, breast cancer resistance protein, and multidrug resistance-associated protein 2). Our results demonstrate that chrysin and/or its conjugates can significantly inhibit some of these proteins. Since chrysin is also contained by dietary supplements, high intake of chrysin may interrupt the transport and/or the biotransformation of drugs.

Inhibition of Xanthine Oxidase-Catalyzed Xanthine and 6-Mercaptopurine Oxidation by Flavonoid Aglycones and Some of Their Conjugates

Flavonoids are natural phenolic compounds, which are the active ingredients in several dietary supplements. It is well-known that some flavonoid aglycones are potent inhibitors of the xanthine oxidase (XO)-catalyzed uric acid formation in vitro. However, the effects of conjugated flavonoid metabolites are poorly characterized. Furthermore, the inhibition of XO-catalyzed 6-mercaptopurine oxidation is an important reaction in the pharmacokinetics of this antitumor drug. The inhibitory effects of some compounds on xanthine vs. 6-mercaptopurine oxidation showed large differences. Nevertheless, we have only limited information regarding the impact of flavonoids on 6-mercaptopurine oxidation. In this study, we examined the interactions of flavonoid aglycones and some of their conjugates with XO-catalyzed xanthine and 6-mercaptopurine oxidation in vitro. Diosmetin was the strongest inhibitor of uric acid formation, while apigenin showed the highest effect on 6-thiouric acid production. Kaempferol, fisetin, geraldol, luteolin, diosmetin, and chrysoeriol proved to be similarly strong inhibitors of xanthine and 6-mercaptopurine oxidation. While apigenin, chrysin, and chrysin-7-sulfate were more potent inhibitors of 6-mercaptopurine than xanthine oxidation. Many flavonoids showed similar or stronger (even 5- to 40-fold) inhibition of XO than the positive control allopurinol. Based on these observations, the extremely high intake of flavonoids may interfere with the elimination of 6-mercaptopurine.

Quercetin Is a Flavonoid Breast Cancer Resistance Protein Inhibitor with an Impact on the Oral Pharmacokinetics of Sulfasalazine in Rats

The potential inhibitory effect of quercetin, a major plant flavonol, on breast cancer resistance protein (BCRP) activity was investigated in this study. The presence of quercetin significantly increased the cellular accumulation and associated cytotoxicity of the BCRP substrate mitoxantrone in human cervical cancer cells (HeLa cells) in a concentration-dependent manner. The transcellular efflux of prazosin, a stereotypical BCRP substrate, was also significantly reduced in the presence of quercetin in a bidirectional transport assay using human BCRP-overexpressing cells; further kinetic analysis revealed IC₅₀ and Ki values of 4.22 and 3.91 μM, respectively. Moreover, pretreatment with 10 mg/kg quercetin in rats led to a 1.8-fold and 1.5-fold increase in the AUC_8h (i.e., 44.5 ± 11.8 min∙μg/mL vs. 25.7 ± 9.98 min∙μg/mL, p < 0.05) and C_max (i.e., 179 ± 23.0 ng/mL vs. 122 ± 23.2 ng/mL, p < 0.05) of orally administered sulfasalazine, respectively. Collectively, these results provide evidence that quercetin acts as an in vivo as well as in vitro inhibitor of BCRP. Considering the high dietary intake of quercetin as well as its consumption as a dietary supplement, issuing a caution regarding its food-drug interactions should be considered.

Testing the Pharmacokinetic Interactions of 24 Colonic Flavonoid Metabolites with Human Serum Albumin and Cytochrome P450 Enzymes

Flavonoids are abundant polyphenols in nature. They are extensively biotransformed in enterocytes and hepatocytes, where conjugated (methyl, sulfate, and glucuronide) metabolites are formed. However, bacterial microflora in the human intestines also metabolize flavonoids, resulting in the production of smaller phenolic fragments (e.g., hydroxybenzoic, hydroxyacetic and hydroxycinnamic acids, and hydroxybenzenes). Despite the fact that several colonic metabolites appear in the circulation at high concentrations, we have only limited information regarding their pharmacodynamic effects and pharmacokinetic interactions. Therefore, in this in vitro study, we investigated the interactions of 24 microbial flavonoid metabolites with human serum albumin and cytochrome P450 (CYP2C9, 2C19, and 3A4) enzymes. Our results demonstrated that some metabolites (e.g., 2,4-dihydroxyacetophenone, pyrogallol, O-desmethylangolensin, and 2-hydroxy-4-methoxybenzoic acid) form stable complexes with albumin. However, the compounds tested did not considerably displace Site I and II marker drugs from albumin. All CYP isoforms examined were significantly inhibited by O-desmethylangolensin; nevertheless, only its effect on CYP2C9 seems to be relevant. Furthermore, resorcinol and phloroglucinol showed strong inhibitory effects on CYP3A4. Our results demonstrate that, besides flavonoid aglycones and their conjugated derivatives, some colonic metabolites are also able to interact with proteins involved in the pharmacokinetics of drugs.

Inhibitory Effects of Quercetin and Its Human and Microbial Metabolites on Xanthine Oxidase Enzyme

Quercetin is an abundant flavonoid in nature and is used in several dietary supplements. Although quercetin is extensively metabolized by human enzymes and the colonic microflora, we have only few data regarding the pharmacokinetic interactions of its metabolites. Therefore, we investigated the interaction of human and microbial metabolites of quercetin with the xanthine oxidase enzyme. Inhibitory effects of five conjugates and 23 microbial metabolites were examined with 6-mercaptopurine and xanthine substrates (both at 5 μM), employing allopurinol as a positive control. Quercetin-3'-sulfate, isorhamnetin, tamarixetin, and pyrogallol proved to be strong inhibitors of xanthine oxidase. Sulfate and methyl conjugates were similarly strong inhibitors of both 6-mercaptopurine and xanthine oxidations (IC₅₀ = 0.2-0.7 μM); however, pyrogallol inhibited xanthine oxidation (IC₅₀ = 1.8 μM) with higher potency vs. 6-MP oxidation (IC₅₀ = 10.1 μM). Sulfate and methyl conjugates were approximately ten-fold stronger inhibitors (IC₅₀ = 0.2-0.6 μM) of 6-mercaptopurine oxidation than allopurinol (IC₅₀ = 7.0 μM), and induced more potent inhibition compared to quercetin (IC₅₀ = 1.4 μM). These observations highlight that some quercetin metabolites can exert similar or even a stronger inhibitory effect on xanthine oxidase than the parent compound, which may lead to the development of quercetin-drug interactions (e.g., with 6-mercaptopurin or azathioprine).