BACKGROUND: Current studies related to the effects of proanthocyanidins on Alzheimer's disease have focused primarily on the signal transduction pathway of cellular apoptosis. However, the influence of p53 gene expression on cell cycle regulation, with regard to the protective mechanisms of proanthocyanidins, has not been reported.OBJECTIVE: To observe the effect of proanthocyanidins on cell cycle distribution, cellular apoptosis, and p53 gene expression in β-amyloid peptide (25-35) (Aβ_(25-35))-induced PC12 cells cultured in serum-free media, and to investigate the molecular neuroprotective mechanisms of proanthocyanidins with regard to cell cycle regulation.DESIGN, TIME AND SETTING: A parallel, controlled, cellular, and molecular study was performed at the Institute of Biochemistry and Molecular Biology, Guangdong Medical College from July 2006 to July 2008. MATERIALS: Proanthocyanidins were provided by Nanjing Xuezi Medical and Chemical Research Center, China; Aβ_(25-35) was provided by Sigma, USA; PC12 cells were provided by the Institute of Basic Medical Science, Academy of Military Medical Sciences; and rabbit anti-p53 polyclonal antibody was provided by Santa Cruz Biotechnology, USA.METHODS: PC12 cells were cultured in serum-free media for 24 hours. Cells from the model group were treated with 25 μmol/L Aβ_(25-35) for 24 hours. Cells in the drug protection group were pre-treated with 30 mg/L proanthocyanidins for 1 hour and then treated with 25 μmol/L Aβ_(25-35) for 24 hours. The control group was not treated.MAIN OUTCOME MEASURES: Flow cytometry was used to detect cell cycle distribution and rate of apoptosis; reverse-transcriptase polymerase chain reaction was used to detect p53 mRNA expression; and Western blot was used to detect p53 protein expression.RESULTS: After treating with 25 μmol/L Aβ_(25-35) for 24 hours, the rate of apoptosis and the percentage of cells in S phase were significantly increased (P < 0.01), and p53 mRNA and protein expressions were decreased. Pretreatment with proanthocyanidins for 1 hour blocked the increase in apoptosis and the percentage of cells in S phase in Aβ_(25-35)-induced PC12 cells (P < 0.01) and increased p53 mRNA and protein expressions. CONCLUSION: Proanthocyanidins blocked apoptosis and S-phase arrest in Aβ_(25-35)-induced PC12 cells cultured in serum-free media. The protective mechanism could be related to increased p53 mRNA and protein expressions.