Proanthocyanidines from EGb 761® improve impaired short term memory

EGb 761®, a dry extract from Ginkgo biloba leaves, is used for the treatment of declining cognitive performance. The extract is adjusted to contain 22.0–27.0% ginkgo flavonoids, 5.4–6.6% terpene lactones and less than 5ppm ginkgolic acids. Further, EGb 761® contains about 7% proanthocyanidines (PAC) [1] with a yet unknown contribution to the efficacy of EGb 761®. In the present work we aimed to assess the relevance of PAC constituents for the pharmacological activity of EGb 761®. One hour before testing spontaneous alternation in the T-maze, NMRI mice received perorally either vehicle, donepezil (0.3mg/kg), EGb 761® (10-300mg/kg), isolated PACs (3-300mg/kg), or two finished products with different Ginkgo extracts that showed eight-fold differences in PAC content but comparable levels of terpene lactones and ginkgo flavonoids (50mg/kg). 20 minutes prior to the session, mice were injected i.p. with 1mg/kg scopolamine to impair short term memory. Mice were observed for 20 trials and spontaneous alteration was documented. Both, EGb 761® (ED50=89mg/kg, Emax 90%, n=6) and its isolated PAC fraction (ED50=43mg/kg, Emax 71%, n=7-14) dose-dependently attenuated the scopolamine-mediated impairment. Interestingly, treatment with a Ginkgo product with a high PAC content extract (EGb 761®) showed better activity in reversing the scopolamine effect than a product with a low PAC content (63% vs. 34% inhibition).