Purple Sweet Potato Color Alleviates D-galactose-induced Brain Aging in Old Mice by Promoting Survival of Neurons via PI3K Pathway and Inhibiting Cytochrome C-mediated Apoptosis

Purple sweet potato color (PSPC), a class of naturally occurring anthocyanins, protects brain function against oxidative stress induced by D‐galactose (D‐gal) (Sigma‐Aldrich, St. Louis, MO, USA). Our data showed that PSPC enhanced open‐field activity, decreased step‐through latency, and improved spatial learning and memory ability in D‐gal‐treated old mice by decreasing advanced glycation end‐products' (AGEs) formation and the AGE receptor (RAGE) expression, and by elevating Cu,Zn‐superoxide dismutase (Cu,Zn‐SOD) (Sigma‐Aldrich) and catalase (CAT) expression and activity. Cleavage of caspase‐3 and increased terminal deoxynucleotidyl transferase (TdT)‐mediated deoxyuridine triphosphate (dUTP) nick‐end‐labeling (TUNEL)‐positive cells in D‐gal‐treated old mice were inhibited by PSPC, which might be attributed to its antioxidant property. PSPC also suppressed the activation of c‐Jun NH2‐terminal kinase (JNK) and the release of cytochrome c from mitochondria that counteracted the onset of neuronal apoptosis in D‐gal‐treated old mice. Furthermore, it was demonstrated that phosphoinositide 3‐kinase (PI3K) activation was required for PSPC to promote the neuronal survival accompanied with phosphorylation and activation of Akt and p44/42 mitogen‐activated protein kinase (MAPK) by using PI3K inhibitor LY294002 (Cell Signaling Technology, Inc., Beverly, MA, USA), implicating a neuronal survival mechanism. The present results suggest that neuronal survival promoted by PSPC may be a potentially effective method to enhance resistance of neurons to age‐related disease.