The FEMA GRAS assessment of trans-anethole used as a flavouring substance

This publication is the fourth in a series of safety evaluations performed by the Expert Panel of the Flavour and Extract Manufacturers' Association ( FEMA). In 1993, the Panel initiated a comprehensive program to re-evaluate the safety of more than 1700 GRAS flavouring substances under conditions of intended use. In this review, scientific data rc:levant to the safety eval uation of trans-anethole (i.e. 4-methoxypropenylbenzene) as a flavouring su bstance is critically evaluated by the FEMA Expert Panel. The evaluation us es a mechanism-based approach in which production of the hepatotoxic metabo lite anethole epoxide (AE) is used to interpret the pathological changes ob served in different species and sexes of laboratory rodents in chronic and subchronic dietary studies. Female Sprague-Dawley rats metabolize more tran s-anethole to AE than mice or humans and, therefore, are the most conservat ive model for evaluating the potential for AE-induced hepatotoxicity in hum ans exposed to trans-anethole from use as a flavouring substance. At low le vels of exposure, trans-anethole is efficiently detoxicated in rodents and humans primarily by O-demethylation and omega-oxidation, respectively, whil e epoxidation is only a minor pathway. At high dose levels in rats, particu larly females, a metabolic shift occurs resulting in increased epoxidation and formation of AE. Lower activity of the "fast" acting detoxication enzym e epoxide hydrolase in the female is associated with more pronounced hepato toxicity compared to that in the male. The continuous intake of high dose l evels of il ans-anethole (i.e. cumulative exposure) has been shown in dieta ry studies to induce a continuum of cytotoxicity, cell necrosis and cell pr oliferation. In chronic dietary studies in rats, hepatotoxicity was observe d when the estimated daily hepatic production of AE exceeded 30 mg AE/kg bo dy weight. In female rats, chronic hepatotoxicity and a low incidence of li ver tumours were reported at a dietary intake of 550 mg trans-anethole/kg b ody weight/day. Under these conditions, daily hepatic production of AE exce eded 120 mg/kg body weight. Additionally, neither ti ans-anethole nor AE sh ow any evidence of genotoxicity. Therefore, the weight of evidence supports the conclusion that hepatocarcinogenic effects in the female rat occur via a non-genotoxic mechanism and are secondary to hepatotoxicity caused by co ntinuous exposure to high hepatocellular concentrations of AE. trans-Anetho le was reaffirmed as GRAS (GRASr) based on (1) its low level of flavour int ake (54 mu g/kg body weight/day); (2) its metabolic detoxication pathway in humans at levels of exposure from use as a flavouring substance; (3) the l ack of mutagenic or genotoxic potential; (4) the NOAEL of 120 mg trans-anet hole/kg body weight/day in the female rat reported in a 2+-year study which produces a lever of AE (i.e. 22 mg AE/kg body weight/day) at least 10,000 times the level (0.002 mg AE/kg body weight/day) produced from the intake o f trans-anethole from use as a flavouring substance; and (5) the conclusion that a slight increase in the incidence of hepatocellular tumours in the h igh dose group (550 mg trans-anethole/kg body weight/day) of female rats wa s the only significant neoplastic finding in a 2+-year dietary study. This finding is concluded to be secondary to hepatotoxicity induced by high hepa tocellular concentrations of AE generated under conditions of the study. Be cause trans-anethole undergoes efficient metabolic detoxication in humans a t low levels of exposure, the neoplastic effects in rats associated with do se-dependent hepatotoxicity are not indicative of any significant risk to h uman health from the use of Irans-anethole as a flavouring substance. (C) 1999 Elsevier Science Ltd. All rights reserved.