The influence of chemical composition of potent inhibitors in the hydrolyzed extracts of anti-hyperuricemic plants to their xanthine oxidase activities

Anti-hyperuricemic plant parts that were selected for this study, are traditionally used to treat gout in Malaysia. Caffeic acid (a hydroxycinnamic acid), apigenin (a flavone), myricetin, quercetin and kaempferol (flavonols), were reported to act as potent xanthine oxidase inhibitors. These compounds can be found in some of the selected ethnomedicinal plants. However, there is still lack of published research works on the quantification of these inhibitors from these urate-lowering phytotherapies. The compounds were quantified from 21 hydrolyzed extracts of the phytotherapies for gout. The activity-content contributions of the compounds to the potent extracts were determined. The anti-hyperuricemic activities of the extracts and the compounds were determined using a xanthine oxidase inhibitory assay. Ultra-Performance Liquid Chromatography (UPLC) coupled with Photodiode Array Detector (PDA) was used to quantify the compounds in the extracts. The results revealed higher activity of the hydrolyzed extracts. The hydrolyzed extract of the flower bud of Syzygium aromaticum Merr. & L.M.Perry exhibited the highest activity (EC50 = 39.58 ± 0.10 μg/mL) due to the highest content of myricetin (42,297.55 ± 159.47 μg/g). The activity-content contribution of myricetin was 7.69%. Due to the highest activity of apigenin (EC50 = 3.27 ± 0.09 μg/mL), the highest contribution of this flavone (29.96%) to the hydrolyzed extract of Orthosiphon aristatus (Blume) Miq. was observed. The results revealed different contents and activities of xanthine oxidase inhibitors in the hydrolyzed extracts of anti-hyperuricemic plants can play a major role to influence the activity. [Display omitted] •Not all antigout plants are potent xanthine oxidase inhibitors.•Hydrolyzed extracts show higher activity than crude extracts.•Syzygium aromaticum shows the highest xanthine oxidase inhibitory activity.•Apigenin is the most potent xanthine oxidase inhibitor.•Apigenin contributes 29.96% to the activity of Orthosiphon aristatus.