Abstract
Although clinical studies have demonstrated that EGb 761, a standard extract of Ginkgo biloba, was effective in mild-to-moderate dementia of the Alzheimer's disease patients, the mechanism underlying its neuroprotective effect remains unclear. In this study, effects of bilobalide, the main constituent of the nonflavone fraction of EGb 761, on reactive oxygen species (ROS)-induced apoptosis in PC12 cells was studied. Exposure of cells to xanthine (100 μM)/xanthine oxidase (150 mU/ml) (ROS producer) resulted in a characteristic DNA fragmentation and an increase in the apoptosis rate. When p53, c-Myc, Bcl-2, Bcl-xL, and Bax were measured by flow cytometry and the activities of caspase-1- and caspase-3-like protease determined with Ac-YVAD-AMC or Ac-DEVD-AMC as substrates, the profile of ROS-induced changes in these apoptosis regulatory and effector proteins suggests that elevation of c-Myc, p53, and Bax and activation of caspase-3 play an important role in the apoptosis. When cells were treated with ROS and bilobalide (25–100 μM) simultaneously, a dose-dependent reduction in the apoptotic rate was found. The percentage of cells with positive staining for c-Myc and p53 decreased from 27.8 and 50.1% to 16.7 and 23.2%, respectively, when bilobalide (25 μM) was present. Bilobalide also reduced ROS-induced elevation of Bax and activation of caspase-3 effectively. Our results provide the first direct evidence that bilobalide can protect neurons against oxidative stress. Bilobalide may block the apoptosis in the early stage and then attenuate the elevation of c-Myc, p53, and Bax and activation of caspase-3 in cells.
Footnotes
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Send reprint requests to: Xing-Zu Zhu, Ph.D., Department of Pharmacology, Shanghai Institute of Materia Medica, Chinese Academy of Sciences, 294 Tai-Yuan Rd., Shanghai 200031, China. E-mail:xzzhu{at}mail.shcnc.ac.cn
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↵1 This study was supported by Grant KY95-SI-310 from the Chinese Academy of Sciences and Grant G (1998) 051108 from the Ministry of Science and Technology of China.
- Abbreviations:
- EGb
- extract of Ginkgo biloba
- ROS
- reactive oxygen species
- TUNEL
- terminal deoxynucleotidyl transferase-mediated dUTP-digoxigenin nick end-labeling
- RT-PCR
- reverse transcription-polymerase chain reaction
- bp
- base pair
- Received November 15, 1999.
- Accepted January 23, 2000.
- The American Society for Pharmacology and Experimental Therapeutics
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