In vitro and in vivo effects of an extract of Ginkgo biloba (EGb 761), ginkgolide B, and bilobalide on apoptosis in primary cultures of rat hippocampal neurons

Abstract

Primary cultures of rat hippocampal neurons were prepared and exposed to increasing concentrations of a peroxyl radical-generator, 2,2′-azobis 2 amidinopropane (AAPH). Addition of AAPH (20 or 50 mM) to the medium caused a decrease in cell viability and an increase in the number of apoptotic cells. Values for the number of nucleosomes were obtained using an ELISA technique. “Factor F,” an indicator of enrichment in nucleosomes, was found to be directly proportional to the number of neuronal apoptoses. Addition of an extract of Ginkgo biloba (Egb 761; 5–20 μg/ml) or ginkgolide B (one of its terpenoid constituents; 0.2 or 0.4 μg/ml) to the culture medium in vitro led to increases in cell viability and decreases in the number of hippocampal cells undergoing AAPH-induced apoptosis, whereas addition of bilobalide (another terpenoid constituent of Egb 761; 0.1–1.0 μg/ml) was ineffective. These in vitro results were corroborated and extended when these same substances were administered to rats in vivo. Oral administration of Egb 761 (50 mg/kg/day) for 8 days caused a significant increase in cell viability and a highly significant decrease in the numbers of both spontaneously occurring and AAPH-induced apoptoses. Similar protective effects were observed with ginkgolide B (2 mg/kg/day, p.o.), whereas bilobalide (2 mg/kg/day, p.o.) was ineffective. As AAPH enhances the production of peroxyl radicals, the protective actions of subacute in vivo treatments with Egb 761 and ginkgolide B appear to be associated with an anti-lipoperoxidative effect of these substances. Drug Dev. Res. 45:23–29, 1998. © 1998 Wiley-Liss, Inc.