Effect of bilobalide B on cholinergic hippocampal neurons exposed to cholesterol and apolipoprotein E4

BACKGROUND: Extracts of ginkgo biloba leaves have been reported to improve nerve function and activity in Alzheimer's disease, which is associated with reduced secretion of cholinergic neurotransmitter in hippocampal neurons. OBJECTIVE: To validate the protective effect of bilobalide B against in vitro injury of cholinergic neurons of the hippocampus induced by combined cholesterol and apoE4 DESIGN, TIME AND SETTING: This randomized, controlled animal experiment was performed in the Pathology Laboratory, Tianjin University of Traditional Chinese Medicine from July 2003 to July 2006. MATERIALS: Neonatal Wistar rats, I-day-old, both male and female, and mean body mass of 5 g were selected for this study. Cholesterol and apolipoprotein E4 (apoE4) were purchased from Sigma Company (USA), bilobalide B was purchased from Tianjin Zhongyi Pharmaceutical Factory, batch number 20050312. METHODS: Hippocampal neurons we're divided into three groups: a normal control group (routinely added media), a model group (exposed to media containing 40 mg/L cholesterol and 30 mg/L apoE4 for 24 hours) and a bilobalide B group (exposed to media containing 160 mg/L bilobalide B for 16 hours, and then with addition of 40 mg/L cholesterol and 30 mg/L apoE4 for an additional 24 hours). MAIN OUTCOME MEASURES: Levels of acetylcholine (ACh) and activity of acetylcholinesterase (AChE) and choline acetyltransferase (ChAT) in hippocampal neurons were determined by microdosage hydroxylamine colorimetry, hydroxylamine colorimetry and radiological chemistry, respectively. RESULTS: The ACh level was significantly lower in the model group than that in the normal control group (P < 0.01), while it was markedly higher in the bilobalide B group than in the model group (P < 0.05). Activity of AChE was significantly decreased in the model group compared with the normal control group (P < 0.05). However, there was no significant difference between the model group and the bilobalide B group (P > 0.05). Activity of ChAT was significantly lower in the model group than in the normal control group (P < 0.01), while the activity was significantly higher in the bilobalide B group than in the model group (P < 0.05). CONCLUSION: Bilobalide B can enhance the ACh level of hippocampal neurons damaged by combined cholesterol and apoE4, by promoting the synthesis, but not the degradation, of ACh.