A high-fat, high-oleic diet, but not a high-fat, saturated diet, reduces hepatic n3 fatty acid content in mice

Authors: Picklo, Matthew; MURPHY, ERIC - University Of North Dakota

Submitted to: Workshop Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: 5/1/2015
Publication Date: 5/31/2015
Citation: Picklo, M.J., Murphy, E.J. 2015. A high-fat, high-oleic diet, but not a high-fat, saturated diet, reduces hepatic n3 fatty acid content in mice [abstract]. Canadian Nutrition Society. p 6.

Interpretive Summary: While considerable research has centered upon the role of linoleic acid (LNA; 18:2n6) as a competitive inhibitor of alpha-linolenic (ALA; 18:3n3) metabolism, a growing literature indicates that the amount of fat consumed can reduce the elongation and desaturation process. However, little data exist as to the impact of saturated fatty acids (SFA) and monounsaturated fatty acids (MUFA) on ALA metabolism. In this work, we tested the hypothesis that a high SFA diet, compared to a high MUFA (oleic acid 18:1n9) diet, reduces ALA conversion to LCn3. To test this hypothesis, mice were fed for 12 wks on three diets: (1) a control, low fat energy (en) diet consisting of 5 % SFA, 6% MUFA, 2 % ALA, and 2% LNA; (2) a high MUFA energy diet, 7% SFA, 36% MUFA, 2% ALA, 3% LNA, or (3) a high SFA energy diet, 34% SFA, 8% MUFA, 2% ALA, 2% LNA. SFA was a mixture of C14 to C18. Analysis of hepatic lipids demonstrated a selective reduction (40%) in hepatic ALA but not LNA and a 35% reduction in eicosapentaenoic acid (EPA; 20:5n3) in the high MUFA mice compared to control or high SFA mice. This loss of ALA was reflected to a greater extent in the neutral lipid fraction, while decreases in phospholipid esterified EPA and docosapentaenoic acid (DPA; 22:5n3) were also evident. Interestingly, while total and phospholipid docosahexaenoic acid (DHA; 22:6n3) content was not changed by the high MUFA diet; the high SFA diet resulted in an elevation of total and phospholipid DPA and DHA vs the control diet. Both the high MUFA and high SFA diets resulted in higher levels of phospholipid arachidonic acid (20:4n6). Expression of FADS1 (delta 5 desaturase) and FADS2 (delta 6 desaturase) were elevated by the high MUFA and reduced by the high SFA diet compared to the control diet. These data indicate that a high MUFA diet, but not a high SFA diet, reduces ALA metabolism and point to selective hepatic disposition of ALA vs LNA.

Technical Abstract: While considerable research has centered upon the role of linoleic acid (LNA; 18:2n6) as a competitive inhibitor of alpha-linolenic (ALA; 18:3n3) metabolism, a growing literature indicates that the amount of fat consumed can reduce the elongation and desaturation process. However, little data exist as to the impact of saturated fatty acids (SFA) and monounsaturated fatty acids (MUFA) on ALA metabolism. In this work, we tested the hypothesis that a high SFA diet, compared to a high MUFA (oleic acid 18:1n9) diet, reduces ALA conversion to LCn3. To test this hypothesis, mice were fed for 12 wks on three diets: (1) a control, low fat energy (en) diet consisting of 5 % SFA, 6% MUFA, 2 % ALA, and 2% LNA; (2) a high MUFA energy diet, 7% SFA, 36% MUFA, 2% ALA, 3% LNA, or (3) a high SFA energy diet, 34% SFA, 8% MUFA, 2% ALA, 2% LNA. SFA was a mixture of C14 to C18. Analysis of hepatic lipids demonstrated a selective reduction (40%) in hepatic ALA but not LNA and a 35% reduction in eicosapentaenoic acid (EPA; 20:5n3) in the high MUFA mice compared to control or high SFA mice. This loss of ALA was reflected to a greater extent in the neutral lipid fraction, while decreases in phospholipid esterified EPA and docosapentaenoic acid (DPA; 22:5n3) were also evident. Interestingly, while total and phospholipid docosahexaenoic acid (DHA; 22:6n3) content was not changed by the high MUFA diet; the high SFA diet resulted in an elevation of total and phospholipid DPA and DHA vs the control diet. Both the high MUFA and high SFA diets resulted in higher levels of phospholipid arachidonic acid (20:4n6). Expression of FADS1 (delta 5 desaturase) and FADS2 (delta 6 desaturase) were elevated by the high MUFA and reduced by the high SFA diet compared to the control diet. These data indicate that a high MUFA diet, but not a high SFA diet, reduces ALA metabolism and point to selective hepatic disposition of ALA vs LNA.