Immunomodulatory Effects of Diterpene Quinone Derivatives from the Roots of Horminum pyrenaicum in Human PBMC

Table 2

Half maximal inhibitory concentration (IC₅₀) of the isolated compounds on IDO-1 activity, as indicated by the kynurenine to tryptophan ratio in phytohemagglutinin stimulated PBMC, calculated according Chou and Talalay [28] (n.d.: concentration-dependent activity could not be determined in the tested concentration range; cursive: estimated values, only limited repetitions were possible due to sample limitations).

	IDO-1 activity; IC50 [μM]
(1) Horminone	346
(2) 7-O-Acetylhorminone	71.7
(3) Agastaqiunone	46.3
HP-r4 (1 : 1 mixture of (4) 15,16-dehydroinuroyleanol and (5) 15,16-dehydroagastol)	25.8
(6) Inuroyleanol	n.d.
(7) Agastol	165
(8) 3-Deoxyagastaquinone	79.5
1-Methyl-D-tryptophan (positive control)	9.3