Differential Radiation Sensitivity of Shikonin Derivatives from Lithospermum erythrorhizon S.

Differences in radiation sensitivity and color degradation of shikonin derivatives between the extracts of Lithospermum erythrorhizon root and authentic compounds were investigated. The degradation of shikonin derivatives in both root extracts and authentic compounds were drastically increased to above 8 kGy. HPLC analysis revealed radiation sensitivities of root extracts and authentic compounds differed significantly. Both shikonin and deoxyshikonin were the most sensitive with a degradation rate of 87-91%, while other derivatives in the extracts were the most resistant with a rate of 44-67%. Mixture of shikonin and deoxyshikonin showed a degradation rate of 20-24% at 4 kGy and around 60% at 8 kGy, whereas other shikonin derivatives showed a 48-62% degradation rate at 4 kGy and an 89-94% degradation at 8 kGy. The degradation pattern of shikonin derivatives in the mixture exhibited a similar pattern to those of the extract, but showed opposite pattern in individual derivative. The order of radiation sensitivity of shikonin derivatives are as follows: shikonin, deoxyshikonin>acetylshikonin, dimethylacrylshikonin, isobutyrylshikonin, isovalerylshikonin, 2-methyl-n-butyrylshikonin>hydroxyisovalerylshikonin in authentic compounds and isobutyrylshikonin, acetylshikonin, hydroxyisovalerylshikonin, isovalerylshikonin, 2-methyln-butyrylshikonin>deoxyshikonin, dimethylacrylshikonin>shikonin in root extracts.