Dietary cholesterol induces changes in molecular species of hepatic microsomal phosphatidylcholine |
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Authors: | Ana M Bernasconi Horacio A Garda Rodolfo R Brenner |
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Affiliation: | (1) Instituto de Investigationes Bioquímicas (INIBIOLP), CONICET-UNLP, Facultad de Ciencias Médicas, calles 60y 120, 1900 La Plata, Argentina |
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Abstract: | After 21 days on a diet containing 1g% cholesterol and 0.5g% cholic acid, rats had an increased content of cholesterol in
liver microsomal lipids. In liver, both cholesterol content and δ9 desaturase activity increased, whereas δ6 and δ5 desaturase
activities decreased. These changes correlated with increases in oleic, palmitoleic, and linoleic acids and decreases in arachidonic
and docosahexenoic acids in total microsomal lipids. Similar fatty acid changes were found in phosphatidylcholine (PC), the
principal lipid of the microsomal membrane. In PC the predominant molecular fatty acid species (67% of the total) in the control
rats were 18:0/20:4, 16:0/20:4, and 16:0/18:2; and they mainly determined the contribution of PC to the biophysical and biochemical
properties of the phospholipid bilayer. The cholesterol diet decreased specifically the 18:0/20:4 species, and to a lesser
extent, 16:0/20:4 and 18:0/22:6. The 18:1-containing species, especially 18:1/18:2 and less so 16:0/18:1 and 18:1/20:4, were
increased. A new 18:1/18:1 species appeared. The independent effects of the presence of cholesterol and change of the fatty
acid composition of the phospholipid bilayer of liver microsomes on the packing were studied by fluorescence methods using
6-lauroyl-2,4-dimethylaminonaphthalene, 1,6-diphenyl-1,3,5-hexatriene and 1-(4-trimethylammonium phenyl)-6-phenyl-1,3,5-hexatriene,
which test different parameters and depths of the bilayer. Data showed that the increase of cholesterol in the membrane, and
not the change of the fatty acid composition of phospholipids, was the main determinant of the increased bulk packing of the
bilayer. The increase of fluid oleic- and linoleic-containing species almost compensated for the drop in 20:4- and 22:6-containing
molecules. But the most important effect was that the general drop in essential n-6 and n-3 polyunsaturated fatty acids meant
that this endogenous source for the needs of the animal decreased. |
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