Prenylated Flavonoids as Antioxidant and Melanin Inhibitors From Stingless Bee (Wallacetrigona incisa) Propolis

Propolis from 4 stingless bees Homotrigona apicalis, Wallacetrigona incisa, Tetragonula fuscobalteata, and Tetragonula fuscibasis) was investigated in the search for medicinal and cosmetic materials from tropical rainforest resources. Methanol extracts of the propolis were screened using antioxidant and antimelanogenesis assays (tyrosinase enzyme activity and melanin inhibitor in B16 melanoma). The extract of H. apicalis showed the strongest antioxidant activity, both in the 2,2-diphenyl-1-picrylhydrazyl and 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) assays, with half-maximal inhibitory concentration values of 0.72 +/- 0.01 (mg/mL) and 0.26 +/- 0.00 (mg/mL), respectively. The H. apicalis extract also displayed the strongest inhibition of tyrosinase (53% at 100 mu g/mL). In the B16 melanoma cell assay, the W. incisa extract showed the strongest inhibition of melanin (21%) and was less cytotoxic. The W. incisa extract was fractioned to isolate the compounds with biological activities. Two prenylated flavonoids were obtained, named broussoflavonol F and glyasperin A. Both showed potent antioxidant activities, as well as inhibiting melanin in B16 melanoma, but not tyrosinase activity. These results indicated the potential of methanol extract of W. incisa to be developed for cosmetic material, but further experiments are needed to verify the function.