Distribution of dietary octadecenoate isomers at the 1‐ and 2‐positions of hepatoma and liver phospholipids

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AbstractPhosphatidylcholines and phosphatidylethanolamines were isolated from hepatoma 7288CTC, normal liver, and host liver of rats fed one of the following diets: fat‐free diet; fat‐free diet supplemented with safflower oil, safflower oil fatty acids, or partially hydrogenated safflower oil fatty acids; and commercial chow. Thecis andtrans octadecenoate fatty acids were isolated from the 1‐ and 2‐positions of both phosphoglycerides and analyzed quantitatively for chain positional isomers. Octadecenoates from hepatoma and liver phosphoglycerides of animals fed fat‐free or natural fatsupplemented diets contained almost exclusively twocis isomers: oleic and vaccenic acids. Oleic acid predominated in the 2‐position octadecenoates of both phosphoglycerides from hepatoma and liver. In contrast, vaccenic acid predominated in the 1‐position of normal liver phosphatidylcholine and, to a lesser extent, phosphatidylethanolamine. Host liver and hepatoma exhibited a shift to a higher percentage of oleic acid at the 1‐position. Dietarytrans fatty acids were incorporated predominately in the 1‐position of both phosphoglycerides of hepatoma and liver. Except for thecis Δ10 octadecenoate isomer, all of the unnatural dietarycis isomers between Δ8 and Δ14 were incorporated into the 1‐position of the phospholipids, while the unnaturalcis octadecenoates at the 2‐position consisted primarily of the Δ12 isomer. Hepatoma phosphoglycerides contained higher percentages of thetrans Δ10 isomer that was nearly excluded from the 1‐position of the two liver phosphoglycerides. All the othertrans octadecenoate isomers were incorporated into the 1‐position of both phosphoglycerides, but the small amount oftrans fatty acids incorporated into the 2‐position of liver and hepatoma phosphatidylcholine consisted of four isomers, Δ9 to Δ12, including the Δ10 isomer. Phosphatidylethanolamine exhibited a similar distribution, except for the presence of the Δ13 and Δ14 isomers at the 2‐position. A combination of evidence suggests that the 1‐position fatty acids in phosphatidylcholine and phosphatidylethanolamine are of similar origin. The octadecenoates at the 2‐position of these two phosphoglycerides appear to be of the same origin in hepatoma but not in liver. It was also revealed that the 2‐position of hepatoma phosphatidylcholine contained much higher percentages of palmitate than liver.