Abstract
Catechins and procyanidins, together with flavonoid glycosides and terpene trilactones, are three important categories of components in the standard extract of Ginkgo biloba leaves (EGb761). In this research, catechins and proanthocyanidins were found to exist in both the extract of Ginkgo leaves and Ginkgo products. By comparing with reference compounds, six of them were identified as (+)-catechin, (−)-epicatechin, (−)-gallocatechin, (−)-epigallocatechin and procyanidins B1 and B3. The activities of these polyphenols in the inhibition of Aβ42 aggregation and the destabilization of preformed fibrils were evaluated using biochemical assays, which showed that all six of the polyphenols, as well as a fraction of the extract of Ginkgo biloba leaves (EGb) containing catechins and procyanidins, exerted potent inhibitory activities towards Aβ42 aggregation and could also destabilize the performed fibrils. Catechins and procyanidins can therefore be regarded as the potent active constituents of EGb761 in terms of their inhibition of Aβ42 aggregation and destabilization of the fibrils. Although quantitative mass spectroscopic analysis revealed that the catechins and procyanidins are only present in low concentrations in EGb761, these components should be studied in greater detail because of their potent inhibitory effects towards Aβ42 aggregation and their ability to destabilize preformed fibrils, especially during the quality control of Ginkgo leaves and the manufacture of Ginkgo products.
Highlights
The standard extract of the leaves of Ginkgo biloba (EGb761) is current used clinically in Europe for the symptomatic treatment of impaired cerebral function in primary degenerative dementia syndromes such as Alzheimer’s disease (AD) dementia and vascular dementia
Because we have demonstrated that these potent polyphenolic compounds (i.e., C, EC, GC, EGC, procyanidins B1 (P-B1) and procyanidin B3 (P-B3)) are present in only minor concentrations in the Ginkgo extracts and Ginkgo products (Table 5), it was envisaged that a fraction enriched with catechins and procyanidins would be useful for assessing the inhibitory activities of these compounds towards Aβ42 aggregation
In an attempt to investigate the roles of catechins and procyanidins in the anti- aggregation effect of the Ginkgo extract, we isolated fractions enriched in these compounds from extract of Ginkgo biloba leaves (EGb) and subjected to a biochemical assays in vitro
Summary
The standard extract of the leaves of Ginkgo biloba (EGb761) is current used clinically in Europe for the symptomatic treatment of impaired cerebral function in primary degenerative dementia syndromes such as Alzheimer’s disease (AD) dementia and vascular dementia. FGs and a range of terpene trilactones (TTLs) (i.e., bilobalide and ginkgolides A, B and C) showed very little activity towards the same target [2] Taken together, these results indicated that some other compounds may be responsible for the effect of the total extract. Catechins and proanthocyanidins have been reported to be important to the beneficial properties of EGb761, and compounds belonging to these structural classes make up 2% and 7% of the total extract content, respectively [3] With this in mind, we became interested in identifying catechins and procyanidins of EGb761 and evaluating their activities towards the inhibition of Aβ42 aggregation and the destabilization of fibrils
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