Hypoxanthine

The herb of P. capitatum was collected from Qianxi county, Guizhou province, China and was identified by Qingde Long (Guizhou Medical University) as the whole plant of Polygonum capitatum Buch.-Ham. ex D. Don. The voucher specimen of P. capitatum (No.: PC20201103) was deposited in the Herbarium of Guizhou Medical University.
The reference standards of gallic acid, protocatechuic acid, (+)-catechin, rutin, quercitrin, quercetin and emodin were purchased from Chengdu Chroma-Biotechnology Co., Ltd. (Chengdu, China). The pure materials of myricitrin, quercetin-3-O-(2″-O-galloyl)-β-d-glucopyranoside, quercetin-3-O-β-d-glucopyranoside, cis-N-caffeoyltyramine and 3″-O-galloylquercitrin were obtained in our laboratory. The purities of the reference standards were determined to be more than 98% by HPLC (-DAD. Hypoxanthine and potassium oxonate were purchased from the Beijing Solarbio Science and Technology Co., Ltd. (Beijing, China). Urate assay kits were purchased from Nanjing Jiancheng Bioengineering Institute (Nanjing, China).
HPLC-grade methanol and acetonitrile were acquired from Honeywell Burdick & Jackson Company (Morristown, NJ, USA). Formic acid (MS grade) was obtained from Fisher Scientific (Madrid, Spain). Deionized water for HPLC analysis was prepared using a Milli-Q water purification system (Millipore, Milford, MA, USA). All other reagents were of analytical grade.

ESR paramagnetic spectrometer (JEOL-FA200, Japan) was utilized to assess the ability of PDA-PEG NPs to scavenge ROS in an acellular environment. Scavenging of O2·⁻ was evaluated by mixing PDA-PEG NPs (100 µg/ml) with 100 mM 5,5-dimethylpyrroline N-oxide (DMPO; Dojindo, Japan), 0.5 mM hypoxanthine (Solarbio Life Science, China), and 0.05 U/ml xanthine oxidase (Solarbio Life Science, China), then incubated in 100% ethanol solution for 1 min. Then, the content of O2·⁻ was determined using ESR according to the manufacturer’s instructions.