Evidence for toxic effects of alkylphenols from Ginkgo biloba in the hen's egg test (HET).

Extracts from the leaves of the Gingko tree (Ginkgo biloba L.) are therapeutically used for the treatment of peripheral and cerebral vascular disorders as well as multi-infarct or Alzheimer-type dementia. As constituents with potential contact allergenic and toxic properties in crude Ginkgo extracts a group of alkylphenols (e.g., ginkgolic acids, ginkgol, bilobol) has been described. Thus, for reasons of drug safety a maximal concentration (< or = 5 ppm) of ginkgolic acids is requested by the Monograph of the Commission E of the former German Federal Health Agency (Bundesgesundheitsamt, BGA). During production of the standardized Ginkgo extract EGb 761, alkylphenols are largely eliminated as water insoluble compounds (decanter sludge) from the primary acetone extract. To further assess the adverse properties of alkylphenols, different fractions derived from the decanter sludge were evaluated for their embryotoxic effects in the hen's egg test (HET). A fraction enriched for ginkgolic acids (16%) and biflavones (6.7%) was found to induce death of 50% of the chick embryos (LD50) at a dose of 1.8 mg/egg (approximately/= 33 ppm). A similar strong lethal effect (LD50: 3.5 mg/egg; 64 ppm) was oberserved for a fraction which contained 58% ginkgolic acids but less than 0.02% biflavones. In contrast, an extreme low toxic potential (LD50: 250 mg/egg or 4540 ppm) was established for a fraction containing 16% biflavones and 1% ginkgolic acids. Thus, the present investigations confirm the high toxic potential of ginkgolic acids, although it can not be excluded that biflavones or some other constituents in the different fractions may amplify the adverse effect of these substances. Since no contribution of alkylphenols to the therapeutic efficacy of Ginkgo extracts has been confirmed and their elimination during the manufacturing process does not cause technical problems, these results further support the requirement for the completest possible removal of these compounds under toxicological considerations.

Hen's egg chorioallantoic membrane test for irritation potential.

The increasingly large number of chemicals introduced onto the market and into the environment has necessitated the monitoring of environmental materials and specimen banking, as well as the development of rapid and reliable methods for the evaluation of toxicity. The Hen's Egg Test, or Hühner-Embryonen-Test (HET) is a rapid, sensitive and inexpensive toxicity test and can give information on embryotoxicity, teratogenicity, systemic and immunopathological effects, metabolic pathways and now, in developed form, on mucous-membrane irritation potencies of chemical substances. Testing with incubated hen's eggs is a borderline case between in vivo and in vitro systems and does not conflict with ethical and legal obligations especially animal protection laws. In the special field of mucous-membrane irritation testing, a specific score and classification scheme was developed for the HET, which allows risk assessments analogous to the Draize scheme. There is a good correlation between the results for HET tests on a variety of pyrithiones, phenols and isothiazolinones, and the corresponding data based on Draize tests. HET chorioallantoic membrane testing should and could not entirely replace current irritation tests in mammals, but it can diminish the number of investigations with mammals, as well as limit or eliminate pain and injury during animal experiments and allow regulators to set priority and toxicity categories.