Insights into the inhibition of the p90 ribosomal S6 kinase (RSK) by the flavonol glycoside SL0101 from the 1.5 A crystal structure of the N-terminal domain of RSK2 with bound inhibitor.
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Separation of the antioxidant compound quercitrin from Lindera obtusiloba Blume and its antimelanogenic effect on B16F10 melanoma cells.
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Considering the growing evidence of the presence of antioxidant compounds in plant extracts, the objectives of this study were to identify antioxidant compounds in Lindera obtusiloba Blume (Lauraceae) and to evaluate their antimelanogenic activities on B16F10 melanoma cells. Organic solvent fractions were separated from L. obtusiloba extracts (LOE). The ethyl acetate fraction (LOE-E) was significantly active against oxidative damage induced by tert-butyl hydroperoxide in primary rat hepatocytes. Two single purified compounds, quercitrin (quercetin-3-O-alpha-L-rhamnopyranoside) and afzelin (kaempferol-3-O-alpha-L-rhamnoside), were identified by HPLC and NMR. These compounds were evaluated for antioxidant activities by 1,1-diphenyl 2-picrylhydrazyl (DPPH) radical scavenging assay and ferric reducing antioxidant power (FRAP) assay, and for their antimelanogenic activities by tyrosinase inhibitory assay melanin formation inhibition assay and Western bolt analysis for the signaling pathway. The significant effects of quercitrin on antioxidant and antimelanogenic activities, and signal modulation of ERK and MITF in B16F10 melanoma cells were observed. This is the first report to identify quercitrin in L. obtusiloba and its whitening effect. (+info)