Purple sweet potato color repairs d-galactose-induced spatial learning and memory impairment by regulating the expression of synaptic proteins

Purple sweet potato color (PSPC), a class of naturally occurring anthocyanins used to color food (E163), has been reported to possess a variety of biological activities, including anti-oxidant, anti-tumor, and anti-inflammatory. The effect of PSPC on the spatial learning and memory of mice treated with d-galactose (d-gal) was evaluated by the Morris water maze; d-gal-treated mice had decreased performance compared with mice in the vehicle and PSPC groups, while the PSPC + d-gal group showed significantly shortened escape latency to platform, increased swimming speed, more target quadrant search time and more platform crossings as compared with the d-gal group. Brain functions, such as memory formation and recovery of function after injury, depend on proper regulation of the expression levels of the pre- and post-synaptic proteins. We investigated the expression of four pre-synaptic proteins (growth-associated protein-43, synapsin-I, synaptophysin, and synaptotagmin) and two post-synaptic proteins (post-synaptic density protein-95 and Ca²⁺/calmodulin-dependent protein kinase II) in the hippocampus and cerebral cortex, respectively, in response to different treatments. Western blotting analysis showed that there were significant decreases in the expression of these representative synaptic proteins in the hippocampus and cerebral cortex of d-gal-treated mice. Interestingly, these decreased expression levels of synaptic proteins could be reversed by PSPC. The levels of expression of these representative synaptic proteins in mice treated with PSPC alone were not significantly different from those in untreated mice. The results of this study suggested that memory impairment and synaptic protein loss in d-gal-treated mice may be improved by treatment with PSPC.