Curcumin improves learning and memory ability and its neuroprotective mechanism in mice

Abstract

Background: Increasing evidence suggests that many neurons may die through apoptosis in Alzheimer's disease (AD). Mitochondrial dysfunction has been implicated in this process of neuronal cell death. One promising approach for preventing AD is based upon anti-apoptosis to decrease death of nerve cells. In this study, we observed the memory improving properties of curcumin in mice and investigated the neuroprotective effect of curcumin in vitro and in vivo. Methods: The mice were given AlCl3 orally and injections of D-galactose intraperitoneally for 90 days to establish the AD animal model. From day 45, the curcumin group was treated with curcumin for 45 days. Subsequently, the step-through test, neuropathological changes in the hippocampus and the expression of Bax and Bcl-2 were carried out to evaluate the effect of curcumin on the AD model mice. In cultured PC12 cells, AlCl3 exposure induced apoptosis. The MTT assay was used to measure cell viabilities; flow cytometric analysis to survey the rate of cell apoptosis; DNA-binding fluorochrome Hoechst 33258 to observe nuclei changes in apoptotic cells and Western blot analysis of Bax, Bcl-2 to investigate the mechanisms by which curcumin protects cells from toxicity. Results: Curcumin significantly improved the memory ability of AD mice in the step-through test, as indicated by the reduced number of step-through errors (P <0.05) and prolonged step-through latency (P <0.05). Curcumin also attenuated the neuropathological changes in the hippocampus and inhibited apoptosis accompanied by an increase in Bcl-2 level (P <0.05), but the activity of Bax did not change (P >0.05). AlCl3 significantly reduced the viability of PC12 cells (P <0.01). Curcumin increased cell viability in the presence of AlCl3 (P <0.01). The rate of apoptosis decreased significantly in the curcumin group (P <0.05) when measured by flow cytometric analysis. Curcumin protected cells by increasing Bcl-2 level (P <0.05), but the level of Bax did not change (P >0.05). Conclusions: This study demonstrates that curcumin improves the memory ability of AD mice and inhibits apoptosis in cultured PC12 cells induced by AlCl3. Its mechanism may involve enhancing the level of Bcl-2.