Grifolic acid induces GH3 adenoma cell death by inhibiting ATP production through a GPR120-independent mechanism

Background: Grifolic acid is a derivative of grifolin, an antitumor natural compound, and it was reported as an agonist of free fatty acid receptor GPR120. Little is known about its antitumor effects and the involvement of GPR120. Methods: GH3 cells, the rat anterior pituitary adenoma cells, were cultured and the cell death was measured by MTT assay and Annexin V/PI staining. The mitochondrial membrane potential (MMP) of GH3 cells was measured by JC-1 staining. Cellular ATP levels and the intracellular NAD/NADH ratio were measured. GPR120 expression in GH3 cells was observed by RT-PCR and Western Blot, and siRNA was used to inhibit GPR120 expression in GH3 cells. Results: Grifolic acid dose- and time-dependently induced the necrosis of GH3 cells. Grifolic acid significantly reduced the mitochondrial membrane potential (MMP) and decreased cellular ATP levels in GH3 cells. In contrast, the MMP of isolated mitochondria was not decreased by grifolic acid. The intracellular NAD/NADH ratio was significantly increased by grifolic acid. GPR120 is expressed in GH3 cells, but GPR120 agonists such as EPA, GW9508 and TUG891 did not affect the viability of GH3 cells. Moreover, GPR120 siRNA knockdown showed no significant influence on grifolic acid-induced GH3 cell death. Conclusion: Grifolic acid induces GH3 cell death by decreasing MMP and inhibiting ATP production, which may be due to the inhibition of NADH production through a GPR120-independent mechanism.