Toxic essential oils. Part V: Behaviour modulating and toxic properties of thujones and thujone-containing essential oils of Salvia officinalis L., Artemisia absinthium L., Thuja occidentalis L. and Tanacetum vulgare L.

Neurotoxic thujones (α- and ß-diastereoisomers) are common constituents of plant essential oils. In this study, we employed a statistical approach to determine the contribution of thujones to the overall observed behaviour-modulating and toxic effects of essential oils (Salvia officinalis L., Artemisia absinthium L., Thuja occidentalis L. and Tanacetum vulgare L.) containing these monoterpene ketones. The data from three in vivo neuropharmacological tests on rats (open field, light-dark, and diazepam-induced sleep), and toxicity assays (brine shrimp, and antimicrobial activity against a panel of microorganisms), together with the data from detailed chemical analyses, were subjected to a multivariate statistical treatment to reveal the possible correlation(s) between the content of essential-oil constituents and the observed effects. The results strongly imply that the toxic and behaviour-modulating activity of the oils (hundreds of constituents) should not be associated exclusively with thujones. The statistical analyses pinpointed to a number of essential-oil constituents other than thujones that demonstrated a clear correlation with either the toxicity, antimicrobial effect or the activity on CNS. Thus, in addition to the thujone content, the amount and toxicity of other constituents should be taken into consideration when making risk assessment and determining the regulatory status of plants in food and medicines.

Risk assessment of thujone in foods and medicines containing sage and wormwood--evidence for a need of regulatory changes?

Thujone is a natural substance found in plants commonly used in foods and beverages, such as wormwood and sage, as well as in herbal medicines. The current limits for thujone in food products are based on short-term animal studies from the 1960s, which provided evidence for a threshold-based mechanism, yet only allowed for the derivation of preliminary values for acceptable daily intakes (ADI) based on the no-observed effect level (NOEL). While the 2008 European Union Regulation on flavourings deregulated the food use of thujone, the European Medicines Agency introduced limits for the substance in 2009. The present study re-evaluates the available evidence using the benchmark dose (BMD) approach instead of NOEL, and for the first time includes data from a long-term chronic toxicity study of the National Toxicology Program (NTP). The NTP data provide similar results to the previous short-term studies. Using dose-response modelling, a BMD lower confidence limit for a benchmark response of 10% (BMDL10) was calculated as being 11 mg/kg bw/day for clonic seizures in male rats. Based on this, we propose an ADI of 0.11 mg/kg bw/day, which would not be reachable even for consumers of high-levels of thujone-containing foods (including absinthe). While fewer data are available concerning thujone exposure from medicines, we estimate that between 2 and 20 cups of wormwood or sage tea would be required to reach this ADI, and view that the short-term medicinal use of these herbs can also be regarded as safe. In conclusion, the evidence does not point to any need for changes in regulations but confirms the current limits as sufficiently protective for consumers.

Oral dose-ranging developmental toxicity study of an herbal supplement (NT) and gallic acid in rats.

OBJECTIVE: To evaluate the combination of rhubarb, astragalus, red sage, ginger, and turmeric (mixture referred to as "NT") together with gallic acid for evidence of reproductive toxicity in rats. METHODS: Fifty virgin female rats were cohabited with male rats. Day 0 of potential pregnancy was evidence of spermatozoa on vaginal smear. The presumably pregnant rats were randomized to five groups of 10 individuals and were fed by daily gavage on days 6-20 of presumed gestation with one of the following: deionized water placebo, 21.6 mg/kg per day, 215 mg/kg per day, 430 mg/kg per day, or 860 mg/kg per day of a mixture of NT (20%) and gallic acid (80%). Cesarean section was performed on day 21. RESULTS: All 50 rats had one or more live fetuses and survived until they were killed. Body weight was reduced in the 860 mg/kg per day group compared with placebo: mean (SD), 406.8 (23.0) vs. 430.1 (27.7) g, P<0.05. There were no dose-related adverse events or differences between groups in uterine size, food intake, corpora lutea, implantations, litter size, number of live fetuses, and gender distribution of fetuses or fetal resorptions. There were no dead fetuses, and all placentae appeared normal. All rats and tissues were normal at necropsy. Fetal weights did not differ between groups, and there were no fetal abnormalities. CONCLUSION: The combination of NT and gallic acid gave no evidence of reproductive toxicity at 430 mg/kg per day or below, which is reassuring should this combination be used in the future as a dietary herbal supplement for the treatment of obesity.