Table 2.

Alkyl-oxy radical-scavenging activity of shikonin

	ORAC†
	kAOx/kCYPMPO	relative to Trolox
Shikonin	58 ± 6	0.25 ± 0.03
Alkannin	46 ± 3	0.20 ± 0.02
N-acetylcysteine		0.40‡

The scavenging of alkyl-oxy radical derived from AAPH was determined by EPR in a competition assay with CYPMPO, as described in Materials and Methods. Shikonin, alkannin or Trolox was assayed at concentrations of 50 and 100 µM. The k_AOx/k_CYPMPO values are means ± SD (n = 5). ^†ORAC: Oxygen Radical Absorbance Capacity, the scavenging activity relative to Trolox is expressed as means ± propagated error (n = 5), to reflect both the standard deviations of the antioxidant and Trolox in the calculations: i.e., division of k_AOx/k_CYPMPO of shikonin or alkannin by that of Trolox k_AOx/k_CYPMPO = 237 ± 23; means ± SD, n = 5). ^‡From Kohri et al. (ref. 18).