Xanthine Oxidase Inhibition and Metabolite Profiling of Aquilaria malaccensis Lam Leaves Extract and Fraction Using FTIR-LCMS

Clinically, hyperuricaemia is caused by increased uric acid synthesis catalysed by the enzyme xanthine oxidoreductase. This enzyme exists in two forms: xanthine dehydrogenase, which oxidises hypoxanthine to xanthine, and xanthine oxidase, which oxidises xanthine to uric acid. Agarwood leaves (Aquilaria malaccensis Lam.) possess antihyperuricemic activity. The flavonoid compounds contained in agarwood leaves are thought to inhibit the production of this enzyme. This study aimed to assess the inhibitory activity of agarwood leaf extracts and fractions against xanthine oxidase and to identify the active compounds in the extracts and fractions. Agarwood leaves were macerated with 96% ethanol and fractionated by liquid-liquid extraction with n-hexane, ethyl acetate, and water. The ethanol extract and fractions obtained were tested for their inhibitory activity against xanthine oxidase in vitro using a spectrophotometer at 295 nm. To determine the functional groups and active compounds, the extracts were analysed by Fourier transform infrared spectroscopy (FTIR), and the ethyl acetate fractions were analysed by liquid chromatography-mass spectrometry (LC-MS) and FTIR. The results showed that the percentage of xanthine oxidase inhibition was 92.05%, 47.88%, 91.17%, and 57.60% for the ethanol extract, n-hexane fraction, ethyl acetate fraction, and aqueous fraction, respectively. FTIR analysis showed the presence of O–H functional groups, while LC-MS analysis showed flavonoids as the main constituents. It can be concluded that the ethyl acetate fraction contains flavonoids that can inhibit the xanthine oxidase enzyme.