Antimelanogenic Effect of Isoquinoline Alkaloids from Plumula Nelumbinis

Plumula Nelumbinis, the green embryo of a lotus seed, is widely consumed in China as a well-known food with medicinal effects. In this study, 14 alkaloids, including 4 new and 10 known alkaloids, were isolated from it, which were elucidated by comprehensive spectroscopic analysis, and were investigated for their antimelanogenic effects in vitro and in vivo. As a result, melanogenesis in α-MSH-stimulated B16F10 cells was reduced significantly by a new compound 4 and known compound 12 at a concentration of 0.5 μg/mL, and the tyrosinase (TYR) activities were inhibited by 78.7 and 82.0% at 4 μg/mL, prior to α-arbutin (41.3%). Additionally, compounds 4 and 12 also exhibited superior antimelanogenic effects compared to α-arbutin on a zebrafish assay model at equivalent concentrations. Mechanistically, our preliminary findings suggested that compounds 4 and 12 exerted antimelanogenesis effect probably by inhibiting key proteins involved in melanin production such as microphthalmia-associated transcription factor, TYR, TRP-1, and TRP-2. The findings highlight the potential use of Plumula Nelumbinis containing compounds 4 and 12 as functional foods for treating hyperpigmentation.