Brazilian green propolis induced apoptosis in human lung cancer A549 cells through mitochondrial-mediated pathway

ObjectivesPropolis effect on the growth and apoptosis of human lung adenocarcinoma (A549 cells) was investigated as well as its mechanisms. MethodsCells were incubated with propolis for 72h, and 3-(4,5- dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide and lactate dehydrogenase assays were employed to assess cell viability and the inhibitory concentration (IC). Apoptosis was detected by Acridine Orange/Ethidium Bromide and 4,6-diamidino-2-phenylindole staining after 24 and 48h of incubation with 1/4 IC50 of propolis by testing the mitochondrial membrane potential (m) and the expression of apoptosis-related genes (p53, Caspase-3, Bax, Bcl-2, Bcl-X-L, Noxa, Puma and p21) by reverse transcription polymerase chain reaction. Key findingsPropolis displayed antiproliferative and cytotoxic effects on A549 cells in a dose- and time-dependent manner, but it did not suppress the growth of normal Vero cells. An enhanced apoptosis was seen in A549 propolis-treated cells after 48h compared with the control cells. Propolis decreased mitochondrial membrane potential by overexpression of pro-apoptotic genes (Bax and Noxa) and reduction of the antiapoptotic gene Bcl-X-L. The expression level of other genes remained unchanged (p53, Caspse-3 and Bax), whereas p21 expression was increased. Propolis induced caspase-independent apoptosis through a p53-independent mitochondrial pathway, and cell cycle arrest by upregulation of p21. ConclusionsAlthough propolis induces apoptosis mainly by p53-independent manner, it may be induced by another pathway, and new insights may arise for preventing or treating lung cancer.