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Hyperuricemia (HUA) is a metabolic disease caused by excessive uric acid in patients. Flavonoids have attracted extensive attention due to their safety, effectiveness, and little side effects in the treatment of HUA and inhibition of xanthine oxidase (XO) activity. In this paper, the studies on the treatment of HUA and the inhibition of XO activity by flavonoids (including flavones, flavonols, flavanones, flavanols, isoflavonoids, anthocyanins, and chalcones) were comprehensively reviewed from the aspects of structure–activity relationship and animal experiments. Results showed that hydrogen bonds and hydrophobic interactions were the two most important forces involved in the interaction between flavonoids and XO. Flavonoids could combine with the hydrophobic cavity of XO to cause changes in XO structure and influence the action of enzyme and substrate, thereby decreasing the catalytic activity of XO. Moreover, flavonoids undergo a series of metabolic reactions in the organism, which plays a role in alleviating HUA by affecting the expression of related genes and proteins (e.g., glucose transporter 9, urate transporter 1, and organic anion transporter 1) in the kidneys, liver, and intestinal tract of the organism and changing the internal environment in organs. In addition, this paper provides new perspectives on the shortcomings of the current research, to promote the in‐depth development and application of flavonoids.

Hyperuricemia, a lifestyle-related disease characterized by elevated serum urate levels, is the main risk factor for gout; therefore, the serum urate-lowering effects of human diets or dietary ingredients have attracted widespread interest. As Urate transporter 1 (URAT1) governs most urate reabsorption from primary urine into blood, URAT1 inhibition helps decrease serum urate levels by increasing the net renal urate excretion. In this study, we used a cell-based urate transport assay to investigate the URAT1-inhibitory effects of 162 extracts of plant materials consumed by humans. Among these, we focused on Aspalathus linearis, the source of rooibos tea, to explore its active ingredients. Using liquid–liquid extraction with subsequent column chromatography, as well as spectrometric analyses for chemical characterization, we identified quercetin as a URAT1 inhibitor. We also investigated the URAT1-inhibitory activities of 23 dietary ingredients including nine flavanols, two flavanonols, two flavones, two isoflavonoids, eight chalcones, and a coumarin. Among the tested authentic chemicals, fisetin and quercetin showed the strongest and second-strongest URAT1-inhibitory activities, with IC50 values of 7.5 and 12.6 μM, respectively. Although these effects of phytochemicals should be investigated further in human studies, our findings may provide new clues for using nutraceuticals to promote health.

Although flavonoid compounds exhibit various pharmacological activities, their clinical applications are restricted by low oral bioavailability owing to their poor solubility. Nanocrystals (NCs) represent an excellent strategy for enhancing the oral bioavailability of flavonoids. Hydroxyethyl starch (HES), a biomaterial compound used as a plasma expander, could be an ideal stabilizer material for preparing flavonoid NCs. HES was used to stabilize flavonoid nanocrystals (NCs), using luteolin (LUT) as a model drug. After full characterization, the freeze-drying and storage stability, solubility, intestinal absorption, pharmacokinetics, and in vivo anti-hyperuricemic effect of the optimized HES-stabilized LUT NCs (LUT-HES NCs) were investigated. Uniformed LUT-HES NCs were prepared with mean particle size of 191.1±16.8 nm, zeta potential of about -23 mV, drug encapsulation efficiency of 98.52 ± 1.01%, and drug loading of 49.26 ± 0.50%. The freeze-dried LUT-HES NCs powder showed good re-dispersibility and storage stability for 9 months. Notably, compared with the coarse drug, LUT-HES NCs exhibited improved saturation solubility (7.49 times), increased drug dissolution rate, enhanced Caco-2 cellular uptake (2.78 times) and oral bioavailability (Fr=355.7%). Pharmacodynamic studies showed that LUT-HES NCs remarkably lowered serum uric acid levels by 69.93% and ameliorated renal damage in hyperuricemic mice. HES is a potential stabilizer for poorly soluble flavonoid NCs and provides a promising strategy for the clinical application of these compounds. LUT-HES NCs may be an alternative or complementary strategy for hyperuricemia treatment.

Erding granule (EDG) is a traditional Chinese medicine that has recently been identified as having anti-hypouricemic effects. However, the active components and underlying mechanism for this new indication have not been elucidated. Therefore, we compared the effects of different EDG extracts (water, 50% ethanol and 95% ethanol) on serum uric acid concentrations in the hyperuricemia model mouse. We also analyzed the constituents of different extracts by ultra-high performance liquid chromatography combined with electrospray ionization quadrupole time-of-flight mass spectrometry (UHPLC-Q-TOF-MS/MS) to observe the variation between the active and inactive products. Extract activity and target site were evaluated by assessing uric acid- and inflammation-suppressing effects along with evaluating ability to regulate the uric acid transporter. The results showed that the 50% ethanol extract (EDG-50) had an obvious serum uric acid concentration lowering effect compared with water (EDG-S) and the 95% ethanol extract (EDG-95). UHPLC-Q-TOF-MS/MS analysis showed that EDG-50 was compositionally different to EDG-S and EDG-95. EDG-50 showed dose-dependent effects on reducing uric acid, suppressing inflammation and regulating uric acid transporters. Moreover, western blot analysis showed that EDG-50 down-regulated GLUT9 and URAT1 expression, and up-regulated OAT1 expression. Therefore, our findings enable the preliminarily conclusion that EDG-50 lowers serum uric acid concentrations, mainly by down-regulating the expression of GLUT9 and URAT1 proteins and up-regulating the expression of OAT1 proteins. This provides a research basis for clinical use of EDG as an anti-hyperuricemic agent.

Background/Objectives: Hyperuricemia (HUA) is a metabolic disease with increasing incidence. Chicory (Cichorium intybus L.), a traditional medicinal and edible plant, has demonstrated anti-HUA effects. However, the metabolic profiles of its aerial parts and roots are still not fully characterized. Moreover, few studies have investigated its anti-HUA effects using cell metabolomics. Methods: The metabolomes of chicory root and aerial parts were characterized using UPLC-QTOF-MS-based untargeted metabolomics. Subsequently, the anti-HUA mechanism of chicory root was investigated by performing non-targeted metabolomics in HK-2 cells. Results: The results demonstrated that various hydroxycinnamic acids and flavonoids were more abundant in aerial parts, whereas sesquiterpenes and oligosaccharides were characteristic of the root. Both chicory root and aerial part extracts significantly reduced uric acid (UA) levels in HK-2 cells induced by adenosine with xanthine oxidase (XO). Cellular metabolomic profiling indicated a distinct separation between the root extract (CR40, 40 mg/mL) and the model group. OPLS-DA identified 165 differential metabolites, including acylcarnitines, acylamino acids, peptides, phospholipids, glycerides, and lipid-like molecules. These metabolites were associated with key metabolic pathways of sphingolipids, glycerophospholipids, phosphonate and phosphinate, linoleic acid, biotin, purine, as well as taurine and hypotaurine metabolism. Conclusions: Chicory is rich in diverse bioactive compounds and exhibits significant anti-HUA activity by modulating multiple metabolic pathways.

Although many investigations on phytochemicals in rice plant parts and root exudates have been conducted, information on the chemical profile of essential oil (EO) and potent biological activities has been limited. In this study, chemical compositions of rice leaf EO and in vitro biological activities were investigated. From 1.5 kg of fresh rice leaves, an amount of 20 mg EO was obtained by distillation and analyzed by gas chromatography-mass spectrometry (GC-MS), electrospray ionization (ESI), and atmospheric pressure chemical ionization (APCI) to reveal the presence of twelve volatile constituents, of which methyl ricinoleate (27.86%) was the principal compound, followed by palmitic acid (17.34%), and linolenic acid (11.16%), while 2-pentadecanone was the least (2.13%). Two phytoalexin momilactones A and B were first time identified in EO using ultra-performance liquid chromatography coupled with electrospray mass spectrometry (UPLC/ESI-MS) (9.80 and 4.93 ng/g fresh weight, respectively), which accounted for 7.35% and 3.70% of the EO, respectively. The assays of DPPH (IC50 = 73.1 µg/mL), ABTS (IC50 = 198.3 µg/mL), FRAP (IC50 = 700.8 µg/mL) and β-carotene oxidation (LPI = 79%) revealed that EO possessed an excellent antioxidant activity. The xanthine oxidase assay indicated that the anti-hyperuricemia potential was in a moderate level (IC50 = 526 µg/mL) as compared with the standard allopurinol. The EO exerted potent inhibition on growth of Raphanus sativus, Lactuca sativa, and two noxious weeds Echinochloa crus-galli, and Bidens pilosa, but in contrast, the growth of rice seedlings was promoted. Among the examined plants, the growth of the E. crus-galli root was the most inhibited, proposing that constituents found in EO may have potential for the control of the problematic paddy weed E. crus-galli. It was found that the EO of rice leaves contained rich phytochemicals, which were potent in antioxidants and gout treatment, as well as weed management. Findings of this study highlighted the potential value of rice leaves, which may provide extra benefits for rice farmers.