[Effect of shikonin and alkannin on hydroxyl radical generation system concerned with iron ion]

The effects of shikonnin (SK) and its optical isomer alkannin (AK) on the hydroxyl radical (HO.) generation system including iron ions were evaluated using the spin trap method by ESR spectroscopy. 5,5-Dimethyl-1-pyrroline-1-oxide (DMPO) was used as a spin trap agent and HO. was generated by a reaction between an iron ion and hydrogen peroxide, which is called Fenton reaction system. SK inhibited the HO. spin adduct (DMPO-OH) yielded in a dose-dependent manner. In this effect no difference was observed between SK and AK. When different concentrations of DMPO were used for the confirmation of its competitive reaction, no difference was also observed in the concentration of SK required to reduce the amount of the DMPO-OH by 50% (ID50). These findings suggested that the inhibitory effect of SK against the thus yielded DMPO-OH was not generated by the scavenging for HO., but by the inhibition on the Fenton reaction system. The mechanism of the inhibition on this system may be based on the formation of a complex between SK and the iron ion. The molar ratio of SK to the iron ion in the complex was considered 2 to 1 (2:1), because the concentrations of the observed ID50 and the used iron ion exhibited the same value. In addition, the same result was also obtained from the study using spectroscopic analysis.