With the aim of developing effective anti-inflammatory drugs, we have been investigating the biochemical effects of shikonin of “Shikon” roots, which is a naphthoquinone with anti-inflammatory and antioxidative properties. Shikonin scavenged reactive oxygen species (ROS) like hydroxyl radical, superoxide anion (O2-) and singlet oxygen in previous studies, but its reactivity with ROS is not completely understood, and comparison with standard antioxidants is lacking. This study aimed elucidation of the reactivity of shikonin with nitric oxide radical (NO) and ROS such as alkyl-oxy radical and O2-. By using electron paramagnetic resonance (EPR) spectrometry, shikonin was found unable of reacting with NO in a competition assay with oxyhemoglobin. However, shikonin scavenged alkyl-oxy radical from 2,2’-azobis(2-aminopropane) dihydrochloride with oxygen radical absorbance capacity, ORAC of 0.25 relative to Trolox, and showed a strong O2—scavenging ability (42-fold of Trolox; estimated reaction rate constant: 1.66 x 105 M-1s-1) in EPR assays with CYPMPO as spin trap. Concerning another source of O2-, the phagocyte NADPH oxidase (Nox2), shikonin inhibited the Nox2 activity by impairing catalysis when added before enzyme activation(IC50: 1.1 M; NADPH oxidation assay). However, shikonin did not affect the preactivated Nox2 activity, although having potential to scavenge produced O2-.
Vol.55 No.2 p p90~96(共同研究につき本人担当部分の抽出不可能)
