Effect of ingestion of thermally oxidized frying oil on desaturase activities and fluidity in rat-liver microsomes

Abstract

Fresh and thermally oxidized olive and sunflower oils were fed to rats at a practical level of concentration. Rats were fed a diet ad libitum for 10 months that contained 12% (wt/wt) of a test oil. Fatty acid composition of liver microsomes; physical state of the membrane lipids; and activities of the Δ 9, Δ 6, and Δ 5 desaturases were determined. The results demonstrate that dietary heated oils produce alterations in the desaturase activities of rat liver microsomes with concomitant changes in fatty acid composition of these membranes. Dietary heated oils accelerate the conversion of palmitic to palmitoleic acid by activating the Δ 9 desaturase activity and slow down the synthesis of arachidonic from linoleic acid by inhibiting the Δ 6 and Δ 5 desaturase activities in the rat liver microsomes. Fluorescence polarization studies, using diphenylhexatriene as a probe, showed lower membrane fluidity in olive oil groups than in sunflower oil groups. Moreover, there were significant differences between physical states of the membrane lipids from each group of the heated and non-heated oils. We concluded that thermally oxidized oils appear to produce alterations at the molecular level in the microsomes of rats, which are dependent on the composition of dietary lipids.