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Description of key information

Key value for chemical safety assessment

Bioaccumulation potential:
no bioaccumulation potential

Additional information

Experimental data on toxicokinetics and metabolism are available from in vivo (rat and rabbit) and in vitro experiments with p-methoxybenzaldehyde.Its physico-chemical properties, i. e. water solubility (2 g/l at 20°C), log Pow (1.56 at 25°C) and molecular weight (136.15 g/mol), anisaldehyde favour bioavailablility via the dermal and oral route. However, on the basis of the low vapour pressure at room temperature (vapour pressure approx. 3 Pa), it can be assumed that exposure via inhalation of p-methoxybenzaldehyde as a vapour is low.

In a comparative in vitro metabolism study, p-methoxybenzaldehyde was incubated with cryopreserved hepatocytes from mouse, rat, rabbit and human at concentrations of 1, 10 and 100 µM and incubation times of 0, 1 and 4 h (RIFM, 2011). Cell suspension samples were analysed afterwards by LC-MS to elucidate species dependent metabolite profiles formed. Seven metabolites were identified:

·        Anisic acid

·        Anisic acid - glycine conjugate

·        Anisic alcohol - glucuronide conjugate

·        demethylated Anisic alcohol - glucuronide conjugate

·        three hydroxylated Anisaldehyde - glucuronide conjugates

After direct application of the test substance (0h timepoint), the metabolite anisic acid was the only detectable metabolite in the respective samples. For later incubation timepoints (1h, 4h), the glycine conjugate of anisic acid generally represented the largest fraction. For rat hepatocytes, the second largest fraction was the glucuronide conjugate of anisic alcohol, whilst for other species this was typically anisic acid for these timepoints. The remaining metabolites were typically observed at low levels and/or in a limited number of incubations. Unchanged anisaldehyde was not detectable.

Overall, an immediate formation of anisic acid was observed followed by the formation of conjugates of the respective alcohol, acid, hydroxylated and demethylated forms of p-methoxybenzaldehyde. Besides the predominant formation of anisic alcohol - glucuronide conjugate in rats and to a lesser extent in the mouse, interspecies differences in the metabolite profiles were generally small. 

In a 14-day percutaneous and oral repeated dose study in rats, p-methoxybenzaldehyde was applied at doses of 0, 100, 250, 500 and 1000 mg/kg bw/day in corn oil (dermal, daily for 6 hours under occlusive conditions) or at doses of 0, 20, 100 and 500 mg/kg bw/d in corn oil (oral, gavage), and blood plasma samples were obtained on the first day of dosage administration, i.e. prior to dosage administration and at approximately 1 hour, 2 hours, 8 hours, 12 hours and 24 hours postdosage (RIFM, 2011). Samples were also collected from rats in the vehicle control groups at approximately 1 hour postdosage and from all animals prior to scheduled euthanasia on day 15.  Key metabolites, as identified in the comparative in vitro metabolism study, i.e. anisic acid, anisic acid glycine conjugate and the glucuronide of anisic alcohol as well as the parent compound were quantified via GC/LC-MS-MS.

No p-methoxybenzaldehyde but anisic acid, anisic acid glycine conjugate and the glucuronide of anisic alcohol was detectable in blood plasma after oral or dermal application of 4-methoxybenzaldehyde.

Plasma levels of anisic acid at comparable doses were found to be 10-100 fold lower after dermal application compared to oral application of 4-methoxybenzaldehyde, whereas levels of anisic acid glycine conjugate were comparable.

After oral administration high levels of anisic acid remained for min. 12 hours at 500 mg/kg bw/d, whereas a evident decline was observed within 2 hours at lower doses. An overproportionate increase of the AUD to the applied dose became evident (approx. 15 fold for the mid dose group and approx. 150 fold for the high dose group). In contrast, AUDs for anisic acid glycine conjugate were found to be increased only approx. 5 fold between the high and the low dose group. 

Dermal administration of 4-methoxybenzaldehyde also resulted in an overproportionate increase of the AUD for anisic acid (approx. 40 fold and 90 fold for the 500 and 1000 mg/kg bw/d dose group). In line, respective estimated AUDs for anisic acid glycine conjugate were found to be increased only approx. 5 fold between the high and the low dose group. 

Overall, oral or dermal application of 4-methoxybenzaldehyde starting at 500 mg/ kg bw/d leads to an evident disproportionate increase of anisic acid plasma concentrations. Furthermore oral application led to an elongation of high anisic acid plasma levels. At these dose levels, a saturation of the formation of the respective glycine conjugate as detoxifying mechanism has been observed. 

Taken together the kinetic data of the test substance / its metabolites demonstrate that the internal dose (as indicated by calculated AUDs) is overproportional with the administered dose, especially at high dose levels. Consequently saturation processes in metabolism and / or excretion are evident and should be taken carefully into account for the assessment of the toxicity profile of 4-methoxybenzaldehyde. Such saturation processes have been described for other organic acids such as 2,4-dichlorophenoxyacetic acid, where differences in active renal transport mechanisms between species or body burden overwhelming renal clearance mechanisms are consistent with increased sensitivity to 2,4-D toxicity (Ravenzwaay et al., 2003).

 

Data from literature further confirm the metabolites identified. Anisoylglucuronide was detected in the 24-hour urine of p-methoxybenzaldehyde fed rabbits (Sammons 1945). The formation of anisyl alcohol and anisic acid has been detected in rat caecal extracts, incubated with p-methoxybenzaldehyde under anaerobic conditions for 46 hours (Scheline 1972) . Incubation of p-methoxybenzaldehyde in nasal and liver microsomes in vitro resulted in trace amounts only or no formation of formaldehyde, respectively (Dahl 1983). In the fragrance raw materials monograph on anisic aldehyde, it is reported that anisic aldehyde undergoes a very slight degree of demethylation with oxidation of its aldehyde group to an acid group, the major excreted metabolite being anisic acid (Opdyke 1974).

Based on the available data, a bioaccumulative potential of anisaldehyde is not to be expected.

 

·        B. VAN RAVENZWAAY, T. D. HARDWICK, D. NEEDHAM, S. PETHEN and G. J. LAPPIN. Comparative metabolism of 2,4-dichlorophenoxyacetic acid (2,4-D) in rat and dog. Xenobiotica, 2003, vol. 33, no. 8, 805–821.