Conjugated linoleic acid (CLA) is shown to have chemoprotective properties in various experimental cancer models. CLA is easily oxidised and it has been suggested that an increased lipid oxidation may contribute to the antitumorigenic effects. This report investigates the urinary levels of 8-iso-PGF2α, a major isoprostane and 15-keto-dihydro-PGF2α, a major metabolite of PGF2α, as indicators of non-enzymatic and enzymatic lipid peroxidation after dietary supplementation of CLA in healthy human subjects for 3 months. A significant increase of both 8-iso-PGF2α and 15-keto-dihydro-PGF2α in urine was observed after 3 months of daily CLA intake (4.2 g/day) as compared to the control group (P<0.0001). Conjugated linoleic acid had no effect on the serum α-tocopherol levels. However, γ-tocopherol levels in the serum increased significantly (P=0.015) in the CLA-treated group. Thus, CLA may induce both non-enzymatic and enzymatic lipid peroxidation in vivo. Further studies of the mechanism behind, and the possible consequences of, the increased lipid peroxidation after CLA supplementation are urgently needed.
