Abstract
Toona sinensis leaf is used as a seasonal vegetable in Korea. A 70% ethanol extract of these leaves exhibited potent xanthine oxidase (XO) inhibition, with a 50% inhibitory concentration (IC50) of 78.4 µM. To investigate the compounds responsible for this effect, bioassay-guided purification led to the isolation of five constituents, identified as quercetin-3-O-rutinoside, quercetin-3-O-β-d-glucopyranoside, 1,2,3,4,6-penta-O-galloyl-β-d-glucopyranose (compound 3), quercetin-3-O-α-l-rhamnopyranoside, and kaempferol-3-O-α-l-rhamnopyranoside. Compound 3 showed the most potent inhibition of XO, with an IC50 of 2.8 µM. This was similar to that of allopurinol (IC50 = 2.3 µM), which is used clinically to treat hyperuricemia. Kinetic analyses found that compound 3 was a reversible noncompetitive XO inhibitor. In vivo, the T. sinensis leaf extract (300 mg/kg), or compound 3 (40 mg/kg), significantly decreased serum uric acid levels in rats with potassium oxonate-induced hyperuricemia. Furthermore, ultraperformance liquid chromatography-quadrupole time-of-flight mass spectrometry analysis identified a high level of compound 3 in the leaf extract. These findings suggest that T. sinensis leaves could be developed to produce nutraceutical preparations.
Highlights
Hyperuricemia results from overproduction or underexcretion of uric acid [1,2] and is characterized by high serum uric acid levels (>7 mg/dL in humans)
Xanthine oxidase (XO) is an important enzyme that catalyzes the oxidation of hypoxanthine to xanthine and the subsequent oxidation of xanthine to uric acid in humans [6]
We investigated which active compounds were responsible for this effect
Summary
Hyperuricemia results from overproduction or underexcretion of uric acid [1,2] and is characterized by high serum uric acid levels (>7 mg/dL in humans) This increases the precipitation of urate crystals in the joints and kidneys, causing gout and gouty arthritis [3]. XO inhibitors such as allopurinol and febuxostat reduce uric acid synthesis and act as useful clinical treatments for hyperuricemia and gout [7,8]. These synthetic drugs produce side effects such as skin rash, renal failure, renal toxicity, and allergic
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