Fish oil and krill oil differentially modify the liver and brain lipidome when fed to mice

Abstract

Background: Marine food is an important source of omega-3 fatty acids with beneficial health effects. Oils from marine organisms have different fatty acid composition and differ in their molecular composition. Fish oil (FO) has a high content of eicosapentaenoic and docosahexaenoic acids mainly esterified to triacylglycerols, while in krill oil (KO) these fatty acids are mainly esterified to phospholipids. The aim was to study the effects of these oils on the lipid content and fatty acid distribution in the various lipid classes in liver and brain of mice.

Methods: Mice were fed either a high-fat diet (HF), a HF diet supplemented with FO or with KO (n = 6). After six weeks of feeding, liver and brain lipid extracts were analysed using a shotgun and TAG lipidomics approach. Student t-test was performed after log-transformation to compare differences between study groups.

Results: Six weeks of feeding resulted in significant changes in the relative abundance of many lipid classes compared to control mice. In both FO and KO fed mice, the triacylglycerol content in the liver was more than doubled. The fatty acid distribution was affected by the oils in both liver and brain with a decrease in the abundance of 18:2 and 20:4, and an increase in 20:5 and 22:6 in both study groups. 18:2 decreased in all lipid classes in the FO group but with only minor changes in the KO group. Differences between the feeding groups were particularly evident in some of the minor lipid classes that are associated with inflammation and insulin resistance. Ceramides and diacylglycerols were decreased and cholesteryl esters increased in the liver of the KO group, while plasmalogens were decreased in the FO group. In the brain, diacylglycerols were decreased, more by KO than FO, while ceramides and lactosylceramides were increased, more by FO than KO.

Conclusion: The changes in the hepatic sphingolipids and 20:4 fatty acid levels were greater in the KO compared to the FO fed mice, and are consistent with a hypothesis that krill oil will have a stronger anti-inflammatory action and enhances insulin sensitivity more potently than fish oil.

Fig. 1

Relative differences in liver and brain lipid classes. Differences between FO, KO and control mice based on a concentration in liver, b mole percentage in liver and c concentration in brain. *** p < 0.001, ** p < 0.01, * p < 0.05

Fig. 2

Relative differences in liver concentrations of polyunsaturated fatty acids. Differences in liver lipid classes between FO, KO and control mice for the following fatty acids 20:5 (a), 22:6, (b), 18:2, 18:3 and 20:4 (c). *** p < 0.001, ** p < 0.01, * p < 0.05

Fig. 3

Relative differences in liver lipids which show a statistically significant change. a Lipids with a statistically significant relative difference > 250 in either FO or KO group as compared to the control group. b Lipids that had p-value < 0.01 between the FO and KO groups. *** p < 0.001, ** p < 0.01, * p < 0.05

Fig. 4

Relative differences in liver concentrations of saturated (SFA) and monounsaturated (MUFA) fatty acids. Differences in liver lipid classes between FO, KO and control mice. *** p < 0.001, ** p < 0.01, * p < 0.05

Fig. 5

Relative differences in concentrations of brain lipids. Lipids that showed statistically significanct changes in any of the comparisons between FO, KO and control mice are shown. ** p < 0.01, * p < 0.05

Fig. 6

Comparison of relative differences in liver and brain lipids. Differences in a cholesteryl esters and b ceramides between FO, KO and control mice. ** p < 0.01, * p < 0.05