Antioxidant activity of herbal medicine Pyrrosia lingua evaluated by electron paramagnetic resonance spectroscopy

The hydroxyl radical (˙OH) is one of the most reactive and harmful reactive oxygen species in living organisms. In this study, we used electron paramagnetic resonance (EPR) spectroscopy to evaluate the antioxidant activity of herbal medicine Pyrrosia lingua (PL) by measuring its scavenging activity against ˙OH radicals. Using the 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical as a scavenging model, the PL extract (0.6 mg mL^-1) was able to scavenge 95.1% of 0.5 mmol L^-1 DPPH radicals, showing a quantitative linear relationship between the DPPH radical concentration and the double integral area under the characteristic peaks of the EPR spectra, with a coefficient of determination R² = 0.9986. Additionally, we also studied the scavenging activity of the PL extract towards hyperactive ˙OH radicals through the reduction of the intensity of the DMPO-OH˙ adducts. The PL extract (0.5 mg mL^-1) showed a high scavenging ability against extremely short-lived ˙OH radicals, with a scavenging rate of 93.6% for ˙OH radicals generated by continuous ultraviolet-irradiation of a 5 mM H₂O₂ aqueous solution for 30 minutes. This study developed a method based on EPR spectroscopy measurements to detect ˙OH radicals captured by herbal medicine, providing a reference for the application of PL in antioxidant and clinical disease therapies.