Metabolism and action of alpha- and beta-thujones

H. Schmandke, Nuthetal

The neurotoxic alpha- and beta-thujones found in the essential oils of e. g. wormwood, sage, clary, tansy, juniper, cedar, thyme and rosemary are contained in absinthe, vermouth and spices. They block the gamma-aminobutyric acid type A receptor in dorsal root ganglion neurons resulting in epileptiform convulsions.

By cytochrome P450 system hydroxylation, orally administered thujones are mainly metabolized to 7-hydoxy-thujones, but also to 2- and 4-hydroxy-thujones. 3-Hydroxy-thujans and dehydrothujones are also formed. The hydroxy-products, after glucuronidation, are excreted via urine. These metabolites are less toxic than the initial thujones. After i.p. injection of a-thujone in mice, the brains of mice have shown higher concentrations of 7-hydroxy-a-thujone than of alpha-thujone. The relevance of this result for the mode of neurotoxic action is unclear.

A NOEL of 5 mg thujone/kg bw is only based on subchronic studies in female rats. Therefore an ADI has not been not established so far.

In Europe, maximum admissible thujone concentrations are 0.5 mg/kg in food and beverages, 5–35 mg/kg in alcoholic drinks, and 25 mg/kg in food products containing sage.

Key words: alpha-thujone / beta-thujone / metabolism

Sie finden den Artikel in deutscher Sprache in Ernährungs-Umschau 10/05 ab Seite 404.