α-eleostearic acid (9Z11E13E-18:3) is quickly converted to conjugated linoleic acid (9Z11E-18:2) in rats

We previously showed that α-eleostearic acid (α-ESA; 9Z11E13E-18:3) is converted to conjugated linoleic acid (CLA; 9, 11-18:2) in the liver and plasma of rats that were given diets including 1% α-ESA for 4 wk. In this study, we investigated this phenomenon in detail. First, the chemical structure of CLA produced by α-ESA administration was determined. After α-ESA was orally administered to rats, CLA in rat liver was isolated by HPLC. The positional and geometric isomerism was determined using GC-EI/MS and ¹³C-NMR, respectively, and the CLA generated in rats after α-ESA feeding was confirmed to be 9Z11E-CLA. Next, the concentrations of α-ESA and CLA were determined 0, 3, 6, and 24 h after oral administration of α-ESA to rats. Moreover, we also investigated whether enteric bacteria are involved in the conversion of α-ESA to CLA using germ-free rats. α-ESA was orally administered to germ-free and normal rats and α-ESA and CLA were detected in the organs of both groups. In addition, to confirm that this reaction was enzyme-mediated, α-ESA was reacted with tissue homogenates (liver, kidney, and small intestine mucous) and coenzymes (NADH, NAD⁺, NADPH, and NADP⁺), and the enzyme activities were estimated from the amount of CLA produced. CLA was detected when α-ESA was reacted with liver, kidney, and small intestine mucous homogenates and a coenzyme (NADPH). These results indicated that α-ESA is converted to 9Z11E-CLA in rats by a Δ13-saturation reaction carried out by an NADPH-dependent enzyme.