title: Evaluation of radical scavenging properties of shikonin.
abstract: 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 like hydroxyl radical, superoxide anion (O2 (•-)) and singlet oxygen in previous studies, but its reactivity with reactive oxygen species is not completely understood, and comparison with standard antioxidants is lacking. This study aimed elucidation of the reactivity of shikonin with nitric oxide radical and reactive oxygen species such as alkyl-oxy radical and O2 (•-). By using electron paramagnetic resonance spectrometry, shikonin was found unable of reacting with nitric oxide radical 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: 1.7 × 10(5) M(-1)s(-1)) in electron paramagnetic resonance 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 µM; NADPH oxidation assay). However, shikonin did not affect the preactivated Nox2 activity, although having potential to scavenge produced O2 (•-). In conclusion, shikonin scavenged O2 (•-) and alkyl-oxy radical, but not nitric oxide radical.
authors.affiliation: Research Institute of Pharmaceutical Sciences, Musashino University, 1-1-20 Shinmachi, Nishitokyo, Tokyo 202-8585, Japan.
authors.forename: Lucia S
authors.initials: LS
authors.lastname: Yoshida
authors.affiliation: Center for Medical Education, Sapporo Medical University, South-1 West-17, Chuo-ku, Sapporo, Hokkaido 060-8556, Japan.
authors.forename: Shunji
authors.initials: S
authors.lastname: Kohri
authors.affiliation: Department of Biochemistry, Showa University School of Medicine, 1-5-8 Hatanodai, Shinagawa-ku, Tokyo 142-8555, Japan.
authors.forename: Shohko
authors.initials: S
authors.lastname: Tsunawaki
authors.affiliation: Faculty of Pharmaceutical Sciences, Josai International University, 1 Gunmyo, Togane, Chiba 283-8555, Japan.
authors.forename: Tomohito
authors.initials: T
authors.lastname: Kakegawa
authors.affiliation: Faculty of Pharmaceutical Sciences, Himeji Dokkyo University, 7-2-1 Kami-Ono, Himeji, Okayama 670-8524, Japan.
authors.forename: Taizo
authors.initials: T
authors.lastname: Taniguchi
authors.affiliation: Research Institute of Pharmaceutical Sciences, Musashino University, 1-1-20 Shinmachi, Nishitokyo, Tokyo 202-8585, Japan.
authors.forename: Hiromi
authors.initials: H
authors.lastname: Takano-Ohmuro
authors.affiliation: Center for Medical Education, Sapporo Medical University, South-1 West-17, Chuo-ku, Sapporo, Hokkaido 060-8556, Japan.
authors.forename: Hirotada
authors.initials: H
authors.lastname: Fujii
keywords: ORAC; Trolox; naphthoquinone; nitric oxide; superoxide