Focus on Ginkgo biloba Adulteration

Part II: A Validated GC-MS Method to Characterize Ginkgolic Acids in Ginkgo biloba Plant Material and Dietary Supplements

Reviewed: Wang M, Zhao J, Avula B, Wang YH, Avonto C, Chittiboyina AG, Wylie PL, Parcher JF, Khan IA. High-resolution gas chromatography/mass spectrometry method for characterization and quantitative analysis of ginkgolic acids in Ginkgo biloba plants, extracts, and dietary supplements. J Agric Food Chem. 2014;62(50):12103-12111.

The ginkgolic acids are a group of compounds that, together with cardanols and cardols, represent the alkylphenols found in Ginkgo biloba leaves and seed coats. These alkylphenols are considered to be a safety concern due to their structural similarity with urushiols, the allergenic compounds in poison ivy (Toxicodendron radicans, Anacardiaceae) and poison sumac (T. vernix), and due to cytotoxic effects found in in vitro studies and immunotoxic effects in a mouse model.^1-4 The American Herbal Products Association’s Botanical Safety Handbook notes that “contact with ginkgo fruit pulp has been associated with contact dermatitis in a number of individuals.”⁵ However, to date there is only one case report of a serious allergic skin reaction (a measles-like eruption covering most of the patient’s body and pinpoint red spots caused by intradermal bleeding developing on the legs) that may be due to ingestion of alkylphenols from a ginkgo leaf product.⁶ The patient had taken a ginkgo product, of which batches were found to contain elevated levels of ginkgolic acids based on subsequent analytical work by Dr. Willmar Schwabe GmbH & Co. KG (Karlsruhe, Germany). Consequently, many countries have limited the contents of ginkgolic acids in ginkgo extracts to a maximum of 5 ppm.

A high-resolution gas chromatography-mass spectrometry (GC-MS) method was used to evaluate the contents of ginkgolic acids in ginkgo leaves (n=8), seeds (n=6), seed coat (n=1), commercial leaf extracts (n=2), standard reference leaf extracts (n=2), and commercial dietary supplements (n=21). Ginkgolic acid contents varied among leaves (42-534 ppm), seeds (4-39 ppm), and seed coat (143 ppm). In the dietary supplement samples, ginkgolic acids were not detected, or the content of ginkgolic acids was found to be between below 0.2 ppm and 56 ppm. Six dietary supplement samples (29%) contained levels of ginkgolic acid above 5 ppm. The presence of ginkgo was confirmed in all 21 dietary supplements based on identification of five ginkgo terpene lactones and three flavonols by ultra-high-performance liquid chromatography (UHPLC)-MS.

Comment: There are no regulatory requirements in the United States that limit the contents of alkylphenols in ginkgo supplements. Therefore, all the analyzed products comply with current US regulations with regard to ginkgolic acid levels. However, the presence of ginkgolic acids at levels above 5 ppm raises the question about the phytoequivalency of these products to the clinically tested EGb 761 extract. The higher concentration of ginkgolic acids suggests that some of the products were manufactured differently and therefore the chemistry and subsequent therapeutic efficacy is expected to be different from EGb 761.

The paper also confirmed the findings of Little (2014, per above) that most of the products on the market contain G. biloba.⁷ The ginkgo terpene lactones (ginkgolides A, B, C, J, and bilobalide) are compounds that are unique to G. biloba, and therefore these terpene lactones can be used as marker compounds for identity confirmation of the material. On the other hand, the presence of ginkgolides and bilobalide alone is not sufficient proof for absence of adulteration with flavonols or flavonol-rich extracts from other plant species (see comments on the study by Little, above).

References

1.  Ahlemeyer B, Selke D, Schaper C, Klumpp S, Krieglstein J. Ginkgolic acids induce neuronal death and activate protein phosphatase type-2C. Eur J Pharmacol. 2001;430(1):1-7.

2.  Hecker H, Johannisson R, Koch E, Siegers CP. In vitro evaluation of the cytotoxic potential of alkylphenols from Ginkgo biloba L. Toxicology. 2002;177(2-3):167-177.

3.  Koch E, Jaggy H, Chatterjee SS. Evidence for immunotoxic effects of crude Ginkgo biloba L. leaf extracts using the popliteal lymph node assay in the mouse. Int J Immunopharmacol. 2000;22(3):229-236.

4.   Baron-Ruppert G, Luepke NP. Evidence for toxic effects of alkylphenols from Ginkgo biloba in the hen’s egg test (HET). Phytomedicine. 2001;8(2):133-138.

5.  Gardner Z, McGuffin M, eds. American Herbal Products Association’s Botanical Safety Handbook, 2^nd ed. Boca Raton, FL: CRC Press; 2013.

6.  Chiu AE, Lane AT, Kimball AB. Diffuse morbilliform eruption after consumption of Ginkgo biloba supplement. J Am Acad Dermatol. 2002;46(1):145-146.

7.  Little DP. Authentication of Ginkgo biloba herbal dietary supplements using DNA barcoding. Genome. 2014;57(9):513-516.