norathyriol and Hyperuricemia

Hyperuricaemia, which results from the overproduction and underexcretion of uric acid, has been linked with chronic renal dysfunction, cardiovascular diseases, diabetes and metabolic syndrome. However, available clinical drugs cannot simultaneously target the production and excretion of uric acid. Norathyriol, a natural xanthone, was expected to have the dual actions. We previously reported that norathyriol possessed potent anti-hyperuricaemic activity related to the inhibition of uric acid production. Here, we investigated the uricosuric actions in hyperuricaemic animals and explored the possible molecular mechanisms associated with renal urate transporters and xanthine oxidase (XO). The results showed that norathyriol (0.5-4.0 mg/kg) dose- and time-dependently decreased serum urate levels in uric acid-induced hyperuricaemic mice and markedly increased the fractional excretion of urate in oxonate-induced hyperuricaemic rats, demonstrating a promotion of urate excretion in the kidney. Further evidence showed that norathyriol markedly increased renal mRNA and protein expression of the secretory organic anion transporter 1 (OAT1) in hyperuricaemic mice and strengthened its transport function in vitro. Moreover, norathyriol also upregulated the mRNA expression of the secretory transporters OAT3, ATP-binding cassette transporter G2 and multidrug resistance protein 4, but not their protein expression. Changes in the expression of the reabsorptive transporters were not observed. This is the first report that norathyriol has uricosuric effects by targeting OAT1. Moreover, norathyriol significantly inhibited XO activity in an uncompetitive manner. Taken together, these findings suggest that norathyriol has the potential to be developed as a new anti-hyperuricaemic agent with dual actions that activate OAT1 and inhibit XO activity.

Topics: Animals; Enzyme Inhibitors; HEK293 Cells; Humans; Hyperuricemia; Kidney; Mice; Organic Anion Transport Protein 1; Organic Anion Transporters; Uric Acid; Xanthenes; Xanthine Oxidase

Context Mangiferin has been reported to possess a potential hypouricaemic effect. However, the pharmacokinetic studies in rats showed that its oral bioavailability was only 1.2%, suggesting that mangiferin metabolites might exert the action. Objective The hypouricaemic effect and the xanthine oxidase inhibition of mangiferin and norathyriol, a mangiferin metabolite, were investigated. Inhibition of norathyriol analogues (compounds 3-9) toward xanthine oxidase was also evaluated. Materials and methods For a dose-dependent study, mangiferin (1.5-6.0 mg/kg) and norathyriol (0.92-3.7 mg/kg) were administered intragastrically to mice twice daily for five times. For a time-course study, mice received mangiferin and norathyriol both at a single dose of 7.1 μmol/kg. In vitro, inhibition of test compounds (2.4-2.4 mM) against xanthine oxidase activity was evaluated by the spectrophotometrical method. The inhibition type was identified from Lineweaver-Burk plots. Results Norathyriol (0.92, 1.85 and 3.7 mg/kg) dose dependently decreased the serum urate levels by 27.0, 33.6 and 37.4%, respectively. The action was more potent than that of mangiferin at the low dose, but was equivalent at the higher doses. Additionally, the hypouricaemic action of them exhibited a time dependence. In vitro, norathyriol markedly inhibited the xanthine oxidase activities, with the IC50 value of 44.6 μM, but mangiferin did not. The kinetic studies showed that norathyriol was an uncompetitive inhibitor by Lineweaver-Burk plots. The structure-activity relationships exhibited that three hydroxyl groups in norathyriol at the C-1, C-3 and C-6 positions were essential for maintaining xanthine oxidase inhibition. Discussion and conclusion Norathyriol was responsible for the hypouricaemic effect of mangiferin via inhibiting xanthine oxidase activity.

Topics: Administration, Oral; Animals; Biomarkers; Biotransformation; Disease Models, Animal; Dose-Response Relationship, Drug; Drug Administration Schedule; Enzyme Inhibitors; Gout Suppressants; Hyperuricemia; Kinetics; Mice; Molecular Structure; Oxonic Acid; Structure-Activity Relationship; Uric Acid; Xanthenes; Xanthine Oxidase; Xanthones