Antioxidant and anti-inflammatory activities of N-acetyldopamine dimers from Periostracum Cicadae

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A known N-acetyldopamine dimer, (2R,3S)-2-(3′,4′-dihydroxyphenyl)-3-acetylamino-7-(N-acetyl-2″-aminoethyl)-1,4-benzodioxane (1) and a new N-acetyldopamine dimer, (2R,3S)-2-(3′,4′-dihydroxyphenyl)-3-acetylamino-7-(N-acetyl-2″-aminoethylene)-1,4-benzodioxane (2) were isolated from the methanolic extracts of Periostracum Cicadae. Compounds 1 and 2 inhibited the Cu2+-mediated, 2,2′-azobis(2-amidinopropane) hydrochloride (AAPH)-mediated, and 3-morpholinosydnonimine (SIN)-1-mediated LDL oxidation in the thiobarbituric acid-reactive substances (TBARS) assay. The antioxidant activities of 1 and 2 were tested with respect to other parameters, such as lag time of conjugated diene formation, relative electrophoretic mobility (REM), and apoB-100 fragmentation on copper-mediated LDL-oxidation. Compounds 1 and 2 also showed 1,1-diphenyl-2-picrylhydrasyl (DPPH) radical scavenging activity. Compound 2 was more efficient than compound 1 at inhibiting the reactive oxygen species (ROS) generation, nitric oxide (NO) production, and nuclear factor-κB (NF-κB) activity as well as the expression of pro-inflammatory molecules such as inducible nitric oxide synthase (iNOS), interleukin (IL)-6, tumor necrosis factor (TNF)-α, and cyclooxygenase (COX)-2 in LPS-induced RAW264.7 cells.