Ferulic acid (FA), a naturally occurring polyphenol abundant in vegetables and rice bran, is known to possess a potent antioxidant activity, thereby protecting cells from oxidative stress. In the present study, we show that in addition to its known anti-oxidant activity, ferulic acid exerts substantial inhibitory activity on cellular mammalian target of rapamycin (mTor)-signaling pathways. In HeLa cells and mouse primary hepatocytes cultured with conventional nutrient-rich media, ferulic acid (1 mm) elicited dephosphorylation of S6 kinase and its substrate ribosomal S6. The dephosphorylating activity of ferulic acid was almost comparable to that of rapamycin, an established mTor inhibitor (TORC1). We next investigated the effect of ferulic acid on autophagy, a major cellular degradative process, which significantly contributes to the maintenance of cell homeostasis. Using a conventional green fluorescent protein-microtubule-associated protein IA/IB light chain 3 (GFP-LC3) dot assay to evaluate autophagy flux, we showed that ferulic acid caused a significant increase in GFP-LC3 dots under serum-rich conditions in HeLa cells. The enhancement of autophagic flux by ferulic acid was almost equivalent to that of rapamycin. Furthermore, ferulic acid significantly enhanced autophagic degradation of 14 C-leucine-labeled long-lived proteins of cultured mouse hepatocytes under nutrient-rich conditions, but not nutrient-deprived conditions. These results indicate that ferulic acid is almost the equivalent of rapamycin in the ability to inhibit mTor (TORC1), which makes it a potent activator of basal autophagy.Key words ferulic acid; ribosomal S6; S6 kinase; mammalian target of rapamycin; autophagy; microtubuleassociated protein IA/IB light chain 3Ferulic acid [(E)-3-(4-hydroxy-3-methoxy-phenyl) prop-2-enoic acid] (FA) is a polyphenolic compound abundant in vegetables, and in particular, artichokes, eggplant, and rice bran. 1) Because polyphenols are known to possess potent antioxidant activity, they have been widely used for the prevention of reactive oxygen species (ROS)-related diseases such as cancer, neurodegenerative and inflammatory diseases. As is the case with other polyphenols, FA significantly reduces lipid peroxidation and protein oxidation.2,3) Stimulation of phosphatidylinositol 3-kinase (PI3-kinase) and extracellular signal-regulated kinase by FA has been proposed as an underlying mechanism, which eventually causes nuclear factor erythroid 2-related factor 2 nuclear translocation. Through this effect, FA enhances the expression of anti-oxidant enzymes and elevates reduced glutathione levels.
4)Recently, the neuroprotective effect of FA has attracted more attention. Oral pre-administration of FA (ca. 17 mg/ kg per day for 4 weeks) has ameliorated memory deficits in mice caused by intracerebroventicular injection of amyloid beta (Aβ 42 ).5) Effective suppression of interleukin (IL)-β expression in the hippocampus by FA is thought to exert an anti-inflammatory effect on learning and memory deficits of Aβ 42 -admi...