Cytotoxicity mechanisms in melanoma cells and UPLC-QTOF/MS2 chemical characterization of two Brazilian stingless bee propolis: Uncommon presence of piperidinic alkaloids

The present study characterized propolis extracts produced by Scaptotrigona bipunctata (Tubuna) and Melipona quadrifasciata (Mandacaia) by LC-MS/MS; their cytotoxicity as well as the mechanism of action in a melanoma cellular model were also assessed. The chemical characterization performed by UPLC-ESIQTOF/MS2 analysis revealed uncommon presence of piperidinic alkaloids in Tubuna's propolis extract together with C-glycopyranoside flavonoids. Mandagaia's propolis collected in the same area rather presented terpenoids and flavonoids. Regarding the mechanism of cytotoxicity, propolis extracts increased the accumulation of reactive oxygen species (ROS), reduced the potential of mitochondria! membrane, induced a decrease in the proteins Bcl-2 and AKT-3 levels, and decreased melanoma cells' migration and invasion. Both propolis extracts induced apoptosis while only Mandacaia's propolis extract induced cell cycle arrest in G2/M. (C) 2017 Elsevier B.V. All rights reserved.