Cyclic fatty acids found in frying oils are detoxified via classical drug metabolic pathway but also by β-oxidation and eliminated as conjugates in rats.

Cyclic fatty acid monomers (CFAM) are mainly formed during heat treatments, such as frying, of edible oils. These fatty acids are mixtures of disubstituted five- or six-carbon-membered ring structures. Some earlier studies have suggested that some of these molecules could be metabolized and detoxified, but so far, neither the detoxification mechanisms nor the metabolite identifications have been elucidated. The objective of the present study was to identify the metabolites resulting from the metabolism and detoxification of CFAM. A deuterium-labeled CFAM, [9-(2)H]-10-(6-propyl-2-cyclohexenyl)-dodecenoic acid, was synthesized and fed to rats for 3 days, along with a standard chow diet while the control group was fed the same chow diet which did not contain any CFAM. Biological fluids (urine, blood) were collected for both groups of rats and analyzed using an untargeted metabolomic approach by ultra-performance liquid chromatography coupled with mass spectrometry. Two discriminant metabolites and 18 molecules derived from CFAM were identified or tentatively identified in plasma and urine samples, respectively. The structures of the metabolites suggest that CFAM having a six-carbon-membered ring could be detoxified by the classical drug metabolic pathway (phase I and phase II reactions), but our study also indicates that these are substrates for the β-oxidation pathway and eliminated as glucuronide, sulphate, and/or nitrate conjugates. Urine metabolomics investigations without diet effects have indicated a higher excretion of medium-chain acylcarnitines in the D-CFAM diet group, which may indicate an incomplete β-oxidation.