Publicação
Oleanolic acid but not ursolic acid induces cell death in HepG2 cells under starvation-induced autophagy
| Resumo: | Cancer incidence is increasing worldwide mainly due to changes in diet, life style and increased lifespan. In particular, liver cancer is the fifth most common cancer in the world and the third most common cause of cancer mortality. Plant phytochemicals are a good and promising source of anticancer compounds. In a previous study, we reported the potential of ursolic acid (UA) to induce cell death and to inhibit proliferation in colorectal cancer cells. This natural triterpenoid, UA, was also shown to activate JNK and to modulate molecular markers of autophagy. In the present study, the ability of two isomer triterpenoids, UA and oleanolic acid (OA), to induce cell death and modulate autophagy in the human hepatocellular carcinoma cell line (HepG2 cells) was tested. For that, the effect of these phytochemicals on cell death was evaluated by MTT assay and propidium iodide staining, in complete and starvation medium. Autophagy markers were evaluated by western blot and fluorescence microscopy. Contrary to our previous data with other cell lines, HepG2 cells were less susceptible to UA and, unexpectedly, OA was a more potent inducer of cell death than UA. Interestingly, starvation-induced autophagy sensitized HepG2 cells to cell death caused by OA, but not by UA. The IC50 of OA decreased from about 50 μM in complete medium to 3.5 μM in starvation medium. Although UA and OA increased the levels of autophagy markers LC3 and p62, as well as the number of acidic vacuoles (as assessed by MDC staining), the cell death induced by OA was not prevented by inhibitors of autophagy and of lysosome proteases. Overall, the results seem to indicate that autophagy is not directly involved in cell death induced by OA. Interestingly, methyl- -cyclodextrin (a polymer able to decrease membrane cholesterol content) prevented OA-induced cell death, which indicates that disruption of cholesterol homeostasis, and in particular in lipid rafts, may be involved in OA effects under starvation conditions. The present results suggest the application of OA as a specific drug for cancer treatment in particular cell physiological conditions, such as under metabolic stress. |
|---|---|
| Autores principais: | Duarte, Cecília Carlos Leite |
| Ano: | 2012 |
| País: | Portugal |
| Tipo de documento: | dissertação de mestrado |
| Tipo de acesso: | acesso aberto |
| Instituição associada: | Universidade do Minho |
| Idioma: | inglês |
| Origem: | RepositóriUM - Universidade do Minho |
| Resumo: | Cancer incidence is increasing worldwide mainly due to changes in diet, life style and increased lifespan. In particular, liver cancer is the fifth most common cancer in the world and the third most common cause of cancer mortality. Plant phytochemicals are a good and promising source of anticancer compounds. In a previous study, we reported the potential of ursolic acid (UA) to induce cell death and to inhibit proliferation in colorectal cancer cells. This natural triterpenoid, UA, was also shown to activate JNK and to modulate molecular markers of autophagy. In the present study, the ability of two isomer triterpenoids, UA and oleanolic acid (OA), to induce cell death and modulate autophagy in the human hepatocellular carcinoma cell line (HepG2 cells) was tested. For that, the effect of these phytochemicals on cell death was evaluated by MTT assay and propidium iodide staining, in complete and starvation medium. Autophagy markers were evaluated by western blot and fluorescence microscopy. Contrary to our previous data with other cell lines, HepG2 cells were less susceptible to UA and, unexpectedly, OA was a more potent inducer of cell death than UA. Interestingly, starvation-induced autophagy sensitized HepG2 cells to cell death caused by OA, but not by UA. The IC50 of OA decreased from about 50 μM in complete medium to 3.5 μM in starvation medium. Although UA and OA increased the levels of autophagy markers LC3 and p62, as well as the number of acidic vacuoles (as assessed by MDC staining), the cell death induced by OA was not prevented by inhibitors of autophagy and of lysosome proteases. Overall, the results seem to indicate that autophagy is not directly involved in cell death induced by OA. Interestingly, methyl- -cyclodextrin (a polymer able to decrease membrane cholesterol content) prevented OA-induced cell death, which indicates that disruption of cholesterol homeostasis, and in particular in lipid rafts, may be involved in OA effects under starvation conditions. The present results suggest the application of OA as a specific drug for cancer treatment in particular cell physiological conditions, such as under metabolic stress. |
|---|