Seasonal Variability of Genistein and 6-Hydroxykynurenic Acid Contents in Ginkgo biloba Leaves from Different Areas of China

Abstract

Refined extracts of Ginkgo biloba L. leaves can protect brain tissue from diverse types of tissue damage. Preliminary experiments identified 6-hydroxykynurenic acid (6-HKA) as a central contributor to this effect, and thus as a potential active marker for drug quality analysis. In contrast, genistein is a negative quality marker for this drug, as high contents of this compound in G. biloba leaves samples are in most cases caused by adulteration with Sophora flavescens Aiton, which is added to the extract by unlawful producers in order to boost its content in flavones, which serve as a quality marker. Some publications even dispute the natural occurrence of genistein in G. biloba leaves altogether, thus claiming that its presence even in trace amounts would prove adulteration. The present study aims to resolve the influence of harvesting time and location on the contents of genistein and 6-HKA-HPLC: Agilent SB-C18 column (5 µm, 4.6x250 mm); phosphoric acid pH2.5, acetonitrile, methanol, gradient; 1 mL/min; 25°C; UV 350 nm-in G. biloba leaves. The lowest contents of 6-HKA were observed in July and August, whereas the maximum was reached in May and October. In the case of genistein-its natural occurrence in G. biloba leaves could be demonstrated under controlled conditions for the first time-the lowest contents were found in May and June, whereas the highest were detected in September and October. These results show that harvesting of G. biloba leaves for pharmaceutical use should be avoided in July and August because of the reduced 6-HKA content, as well as in September and October, the season of highest genistein production. Due to both favorable 6-HKA production and a relative lack of genistein, May was identified as the ideal harvesting month for G. biloba leaves.

HPLC-UV/HRMS methods for the unambiguous detection of adulterations of Ginkgo biloba leaves with Sophora japonica fruits on an extract level

“…Also, Wohlmuth et al (2014) stated that the presence of genistein in ginkgo leaf extract products is considered as evidence of adulteration. However, so far, it was not clear why other authors described genistein as a native constituent in ginkgo leaf extracts (Yao et al 2017), why some even claimed to have isolated and identified genistein from ginkgo leaf extract (Wang et al 2007). The lack of data such as the fragmentation patterns or considerations of coeluting isomers could be the reason for the misidentification of apigenin as genistein.…”

“…However, other authors have reported genistein to be a genuine constituent in ginkgo leaf extract, although in very small amounts (Wang et al 2007). It has also been reported, that the amount of genistein in the leaves was dependent on the season (Yao et al 2017), or only in leaves, stems, and fruits of male ginkgo trees and not of female trees (Pandey et al 2014). Moreover, in 2015, a limit of 1% sophoricoside (genistein-4 0 -O-glucoside) in ginkgo extracts was set by the China Food and Drug Administration (China Food and Drug Administration 2015).…”

Assessment of components of Gingko biloba leaves collected from different regions of China that contribute to its antioxidant effects for improved quality monitoring

“…The levels of these components were the highest in the materials collected from Xinjiang province, Xuzhou, and Hebei province, which indicates that these regions should be prioritized for obtaining G. biloba leaf materials with superior quality. and altitude, in different cultivation regions of China lead to variations in the active components of G. biloba leaves, which ultimately affect the quality (Lin et al, 2019;Yao et al, 2017). This uncontrolled distribution creates a considerable challenge to conventional quality control strategies that currently depend on morphological characteristics, making the qualitative or quantitative determination of one or several bioactive marker components important (Xie et al, 2010).…”

A nontargeted approach to determine the authenticity of Ginkgo biloba L. plant materials and dried leaf extracts by liquid chromatography-high-resolution mass spectrometry (LC-HRMS) and chemometrics

“…In another publication, quantification of flavonoids using ginkgo plant parts such as leaf, stem, and fruit from three authentic ginkgo trees in India was detailed and the authors noted that genistein was absent in female ginkgo tree leaves but, was identified in the leaf and stem of male ginkgo trees [25]. The reported genistein by Yao et al [26] had concentrations between 5-28 μg/g dry leaf using a validated HPLC-UV method with detection at 350 nm.…”