Grifolic acid induces mitochondrial membrane potential loss and cell death of RAW264.7 macrophages

Grifolic acid is a phenolic compound that was first extracted from the mushroom Albatrellus confluens; it acts as an agonist of the free fatty acid receptor (FFAR4). FFAR4 is expressed in macrophages and mediates the anti-inflammatory effects of n-3 unsaturated free fatty acids. In the present study, the effects of grifolic acid on macrophages were observed in mouse RAW264.7 cells. It was demonstrated that grifolic acid (2.5-20 mu mol/l) treatment reduced RAW264.7 cell viability in a dose- and time-dependent manner. The number of apoptotic cells significantly increased following grifolic acid treatment compared with the untreated control cells. Grifolic acid treatment resulted in a significant decrease in cellular adenosine 5'-triphosphate (ATP) content in RAW264.7 cells. Mitochondrial membrane potential (MMP), as measured by JC-1 staining, was significantly diminished by grifolic acid treatment in a dose- and time-dependent manner. Treatment with cyclosporine A, a protector of MMP, attenuated grifolic acid-induced reduction of MMP and viability in RAW264.7 cells. FFAR4 knockdown did not significantly influence grifolic acid-induced reduction of cell viability, ATP levels or MMP. In conclusion, grifolic acid may induce macrophage cell death by reducing MMP and by inhibiting ATP production probably in an FFAR4-independent manner.