Factors affecting the metabolism of cinnamyl anthranilate in the rat and mouse

The biological actions of cinnamyl anthranilate are dependent on both dose size and animal species. The present study aimed to examine metabolism as a possible source of explanation for these differences. [3-14C]Cinnamyl anthranilate was synthesized, injected ip into male Fischer 344 (F344) rats and CD-1 mice and urine and faeces collected for 3 days. The pattern of elimination of 14C was the same in both species, with the bulk of the administered material recovered in urine over the first 24 hr. Urinary metabolic profiles were compared by radioHPLC, which showed that the major radioactive excretion product in the rat was hippuric acid accompanied by smaller amounts of benzoic acid. In contrast, mouse urine contained relatively less hippuric acid, more benzoic acid and small amounts (approx. 3% of dose) of unchanged cinnamyl anthranilate. The effect of dose size on urinary metabolites produced by mice was examined using both 3-14C-labelled and unlabelled cinnamyl anthranilate, detected by fluorescence HPLC. Over a dose range of 5 to 250 mg/kg body weight administered ip it was found that at 5 mg/kg body weight no intact ester was excreted in urine whereas at 20 mg/kg body weight or above, the proportion present as the intact ester remained constant. Dietary administration to male and female B6C3F1 mice for 21 days over a dose range of 0 to 30,000 ppm revealed the same qualitative picture with no intact cinnamyl anthranilate detected in urine at or below 1000 ppm (equivalent to 100 mg/kg body weight). A study in human volunteers using a single oral dose of 250 mg failed to reveal any intact cinnamyl anthranilate in 0-24-hr urine. These data support the hypothesis that the peroxisome proliferating action of cinnamyl anthranilate, which is mediated by the intact ester, is manifest only at high doses in species in which its metabolism by hydrolysis is saturated, as a consequence of which the intact ester 'overflows' into urine.