Different extracts of Angelica dahuricae were available for whitening or treating vitiligo clinically. They showed inhibitory or activating effects on tyrosinase, a rate-limiting enzyme of melanogenesis. This study aimed to identify active compounds on tyrosinase in water extract of Angelica dahurica Radix. We applied spectrum-effect relationship and component knock-out methods to make it clear. HPLC was used to obtain the specific chromatograms. The effects on tyrosinase activity were examined

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... by measuring the oxidation rate of levodopa in vitro. Partial least squares method was used to examine the spectrum-effect relationships. The knocked-out samples were prepared by HPLC method, and the identification of knocked-out compounds was conducted by the high performance liquid chromatography-four stage rod-electrostatic field orbit trap high resolution mass spectrometry. Results showed that S6, S14, S18, S21, S35, S36, S37, S40, and S41 were positively correlated to inhibitory activity of Angelica dahuricae on tyrosinase whereas S9, S11, S8, S12, S22, and S30 were negatively correlated. When the concentration of each sample was 1 g·mL −1 , equal to the amount of raw medicinal herbs, oxypeucedanin hydrate, imperatorin, cnidilin, and isoimperatorin had inhibitory effects on tyrosinase activity whereas byakangelicin and bergapten had activating effects. The previous "spectrum-effect relationship" researches were based on different fields, origins, harvest time, processing method and batches of TCM etc. [18] [19] [20] [21] [22] [23] . However, there have been great changes that have taken place after a long-term regional difference on TCM. Then the types and contents of trace elements and chemical components have also been changed. These changes may lead to subtle changes in some pieces of information but may play a decisive role miss after common peaks matched from HPLC specific chromatograms [24] . Our previous studies showed that the active components were changed in the TCMs processed through the classical constant temperature method. Therefore, this study used the classical constant temperature method to carry on the processing with different methods to the same batch of AD, to eliminate the disturbance from the origin, the batch and other factors, and to screen out more accurately the material basis of AD on tyrosinase activity. The quantitative chromatographic peaks were determined by the software < Chinese traditional medicine chromatographic fingerprint similarity evaluation system 2004, 1.0 A Edition > Multi-point correction of chromatographic peak position was performed based on chromatographic peaks, which were found in each sample with good separation by reference to the chromatogram of crude AD water extract. A contrast chromatogram was generated by average method. The matching chromatograms and peak areas were shown in Figure 1 and Tables 1-4.