Effect of dietary fish oil and corn oil on lipid metabolism and apolipoprotein gene expression by rat liver.
A 3-week fish oil diet induced in weanling rats a decrease in plasma lipids and liver triacylglycerol, and an increase in insulinemia, compared to a corn oil diet. At the same time, plasma apolipoprotein (apo) A-I was slightly lower and plasma heavy apo B/light apo B ratio was higher in fish-oil-fed than in corn-oil-fed rats. Hepatocytes obtained from fish-oil-fed and corn-oil-fed rats were used to examine how fish oil affects lipid and apolipoprotein synthesis and secretion. Primary culture of hepatocytes from fish-oil-fed rats displayed a lower ability to synthesize and secrete triacylglycerol than hepatocytes from corn-fed rats, as measured by mass determination or [U-14C]glycerol incorporation. Hepatocytes from fish-oil-fed rats exhibited a lower synthesis of cholesterol, measured by [14C]acetate incorporation, than hepatocytes from corn-oil-fed rats. This impairment was associated with an increase in beta-oxidation, a higher channeling of oleic acid into phospholipids, and a lower triacylglycerol/diacylglycerol ratio in hepatocytes from fish-oil-fed rats than in hepatocytes from corn-oil-fed rats. Incorporation of [35S]methionine into secreted apoB was reduced in hepatocytes from fish-oil-fed rats, but was not paralleled by a decrease in apo B mRNA. The appearance of degradative forms of apo B suggest an increase in apo B degradation in hepatocytes from fish-oil-fed rats. Incorporation of [35S]methionine into cellular and secreted apo A-I was lower in hepatocytes from fish-oil-fed rats than in hepatocytes from corn-oil-fed rats, and was not paralleled by any difference in the apo A-I mRNA level. Finally, [35S]methionine incorporation into cellular and secreted forms of apo E and apo A-I mRNA were reduced in hepatocytes from fish-oil-fed rats, compared with hepatocytes from corn-oil-fed rats. These combined data show that fish oil diet reduces triacylglycerol synthesis and secretion and affects apo B synthesis at a post-transcriptional level, and reduces cholesterol synthesis and affects apo E and apo A-I synthesis at a transcriptional and a post-transcriptional level.
Ribeiro
A
A
Unité de Recherche Associée 1283, Départment de Biochimie, Faculté de Médecine Saint-Antoine, Université Pierre et Marie Curie, Paris, France.
Mangeney
M
M
Cardot
P
P
Loriette
C
C
Rayssiguier
Y
Y
Chambaz
J
J
Bereziat
G
G
D000818:Animals; D001053:Apolipoproteins / Q000235:genetics / Q000378:metabolism*; D002478:Cells, Cultured; D002784:Cholesterol / Q000378:metabolism; D003314:Corn Oil / Q000008:administration & dosage; D004042:Dietary Fats, Unsaturated / Q000494:pharmacology*; D004591:Electrophoresis, Polyacrylamide Gel; D005227:Fatty Acids / Q000378:metabolism; D005395:Fish Oils / Q000008:administration & dosage; D015870:Gene Expression; D050356:Lipid Metabolism; D008099:Liver / Q000378:metabolism*; D008297:Male; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D011919:Rats, Inbred Strains; D014280:Triglycerides / Q000378:metabolism
D001053:Apolipoproteins; D004042:Dietary Fats, Unsaturated; D005227:Fatty Acids; D005395:Fish Oils; D012333:RNA, Messenger; D014280:Triglycerides; D003314:Corn Oil; D002784:Cholesterol