METABOLIC FATE AND EFFECT OF DIETARY TRANS FATTY ACIDS (OCTADECENOATES, MEMBRANE FLUIDITY)

Various aspects of the metabolic fate and effects of dietary trans fatty acids have been investigated. C57Bl/6J mice were fed a semi-synthetic control or experimental diet containing 10% fat. These diets were identical in all respects with the exception that 18:1-trans isomers present in the experimental diet (25% trans) were absent in the control diet and were replaced by corresponding cis isomer, oleic acid.;Alterations in membrane structure and function by dietary trans fatty acids were studied in the erythrocyte ghost membranes. Lipids extracted from experimental erythrocyte ghosts contained up to 6% trans fatty acids, and the 18:2/20:4 ratio was significantly elevated compared to controls. From Arrhenius plots, the activation energy for acetylcholinesterase (AChE) was similar for both groups; however, the specific activities for AChE were significantly higher for the experimental erythrocyte ghosts. Based on the membrane microviscosity-temperature plots, the flow activation energy was similar in both groups studied, but the higher fluorescence anisotropy in the experimental erythrocyte ghosts is indicative of a more rigidly structured hydrophobic environment. Similar studies performed with mitochondria demonstrated insignificant alterations in the membrane structural order parameter and the specific activity of an ATPase-catalyzed ATP/(('32)P)P(,i) exchange reaction. Results of mitochondrial lipid analyses were suggestive of a homeostatic mechanism for the control of membrane structure and function.;In vitro reconstitution studies utilizing purified microsomal cytochrome P-450, NADPH-cytochrome P-450 and control or experimental phospholipids elucidated the influence of membrane fluidity on a membrane-associated enzyme activity.;Initial studies investigated the levels of trans fatty acids incorporated into liver lipids at various ages. Lowest levels of trans isomers were detected at birth (2.4%) followed by a rapid increase to peak incorporation at 7 days (6.6%). Thereafter, the levels of trans fatty acids in liver lipids remained relatively constant (5.0%) over the ages studied (1-18 months). During development, the 18:2/20:4 ratio in liver lipids of mice fed the experimental diet increased from 0.7 to 1.6 and this ratio was always higher in animals fed the experimental diet, suggesting inhibition of linoleic acid metabolism particularly at the D6-desaturase step.