In Vitro Xanthine Oxidase Inhibitory Activity of Morinda citrifolia L. (Noni) Leaf and Identification of Its Xanthine Oxidase Inhibitors

Abstract

Hyperuricemia causes an excessive level of uric acid in the body, which leads to the formation of gouty arthritis and high uric acid-related diseases. To cure this condition, xanthine oxidase (XO), a key enzyme in uric acid production, was targeted. A routinely used XO inhibitor drug, allopurinol, has side effects. Therefore, an alternative XO inhibitor with a high activity and fewer side effects is strongly desired. In this research, we evaluated the XO inhibitory activity of Morinda citrifolia L. (noni) leaves extracted using 2 solvents, 95 % ethanol and water. The total phenolic and flavonoid content was analyzed. Moreover, the phenolic profile was investigated using liquid column chromatography-mass spectrometry (LC-MS). The results showed that at a concentration of 100 µg mL−1, the ethanolic (McE) and water (McW) extracts could exhibit XO inhibitory activity above 90 %, and the IC50 values predicted using dose-response logarithmic function curves were 2.24 ± 0.2 and 7.2 ± 0.1 µg mL−1, respectively, while the IC50 of allopurinol was 1.02 ± 0.1 µg mL−1. The total phenolic and flavonoid content in McE was higher than that in McW. LC-MS analysis revealed that all extracts contained several phenolic compounds. Interestingly, known potent XO inhibitors were found in both extracts. Kaempferol, esculetin, saponarin, physcion and γ-aminobutyric acid were found in McE, while McW contained esculetin, saponarin and rutin. Taken together, M. citrifolia L. leaves could be used as an effective alternative XO inhibitor for curing hyperuricemia and high uric acid-related diseases caused by XO activity.