Alkaloids and flavonoids exert protective effects against UVB-induced damage in a 3D skin model using human keratinocytes

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This study isolated six carboline alkaloids, (3S,4R)-1-(β-carbolin-1-yl)-3,4,5-trihydroxy-1-pentanone (1), β-carboline (2), 1-hydroxymethyl-β-carboline (3), perlolyrine (4), (1S,3S)-1-methyl-1,2,3,4-tetrahydro-β-carboline-3-carboxylic acid (5) and (1R,3S)-1-methyl-1,2,3,4-tetrahydro-β-carboline-3-carboxylic acid (6) from the leaves of Dendrobium officinale Kimura et Migo (Orchidaceae). These alkaloids, along with 14 flavonoids, vicenin-2 (7), vicenin-1 (8), isoschaftoside (9), schaftoside (10), neoschaftoside (11), violanthin (12), isoviolanthin (13), vicenin-3 (14), apigenin 6-C-α-l-arabinopyranosyl-8-C-β-d-xylopyranoside (15), vitexin 2″-O-glucoside (16), vitexin 2″-O-rhamnoside (17), rutin (18) and quercetin (19), which were previously found in D. officinale leaves by other researchers, and apigenin (20), which is the aglycone of flavone C-glycosides 7–17, were bioassayed to determine their protective effects on UVB-induced damage in human keratinocytes. Carboline alkaloids 1 and 3 and flavonoids 8 and 20 significantly increased cell viability in human keratinocytes irradiated by UVB. In a 3D skin model, compounds 1 and 8 showed promising protective effects, maintained reasonable skin structures and increased the expression of filaggrin and claudin-1, which was inhibited by UVB irradiation. The anti-UVB activities of compounds 1, 3 and 8 were reported for the first time, and these three compounds exhibit potential for application in sunscreen cosmetics.