Dietary lysophosphatidylcholine-EPA enriches both EPA and DHA in the brain: potential treatment for depression

Abstract

EPA and DHA protect against multiple metabolic and neurologic disorders. Although DHA appears more effective for neuroinflammatory conditions, EPA is more beneficial for depression. However, the brain contains negligible amounts of EPA, and dietary supplements fail to increase it appreciably. We tested the hypothesis that this failure is due to absorption of EPA as triacylglycerol, whereas the transporter at the blood-brain barrier requires EPA as lysophosphatidylcholine (LPC). We compared tissue uptake in normal mice gavaged with equal amounts (3.3 μmol/day) of either LPC-EPA or free EPA (surrogate for current supplements) for 15 days and also measured target gene expression. Compared with the no-EPA control, LPC-EPA increased brain EPA >100-fold (from 0.03 to 4 μmol/g); free EPA had little effect. Furthermore, LPC-EPA, but not free EPA, increased brain DHA 2-fold. Free EPA increased EPA in adipose tissue, and both supplements increased EPA and DHA in the liver and heart. Only LPC-EPA increased EPA and DHA in the retina, and expression of brain-derived neurotrophic factor, cyclic AMP response element binding protein, and 5-hydroxy tryptamine (serotonin) receptor 1A in the brain. These novel results show that brain EPA can be increased through diet. Because LPC-EPA increased both EPA and DHA in the brain, it may help in the treatment of depression as well as neuroinflammatory diseases, such as Alzheimer's disease.

Keywords: Alzheimer’s disease; blood-brain barrier; brain lipids; brain-derived neurotrophic factor; docosahexaenoic acid; eicosapentaenoic acid; fish oil; inflammation; lysophospholipid; nutrition/lipids; omega 3 fatty acids; retina.

Fig. 1.

Effect of oral free EPA and LPC-EPA on plasma lipids. A: FA composition. The FA analysis was carried out by GC/MS, as described in the text. Only the omega 3 FAs are shown here. The total FA composition of plasma is shown in supplemental Table S1. The values shown are mean ± SD, n = 6 for each group. Statistical significance was determined by one-way ANOVA with post hoc Tukey multiple comparison test. *P < 0.05, **P < 0.01; ***P < 0.001; ****P < 0.0001 compared with control (ANOVA). #P < 0.05; ##P < 0.01; ###P < 0.001; ####P < 0.0001, LPC-EPA compared with free EPA (ANOVA). B: LPC species in plasma (nanomoles per milliliter). The composition of LPC species containing omega 3 FA was analyzed by LC/MS/MS in the MRM mode, as described in the text. The values shown are mean ± SD, n = 6 per group. Statistical significance was determined by one-way ANOVA with post hoc Tukey multiple comparison test. P value symbols are as in A. C: Incorporation of omega 3 FA in plasma lipids. Molecular species of PC, PE, and TAG containing 20:5, 22:5, and 22:6 were analyzed by LC/MS/MS in the MRM mode, as described in the text. The values shown are nanomoles of each omega 3 FA associated with the indicated plasma lipid, and are mean ± SD (n = 6 per group). The individual values were calculated by adding all the molecular species of each lipid containing the indicated omega 3 FA. The values were corrected for the number of molecules of omega 3 FA expected in each molecular species (for example: for 16:0-20:5 PC, the nanomoles of 20:5 are the same as the nanomoles of PC, whereas for 20:5-20:5 PC, the nanomoles of 20:5 are double the nanomoles of PC, and for 20:5-20:5-20:5 TAG, there are three times the nanomoles of TAG). Bars with different letters are significantly different from each other (one-way ANOVA).

Fig. 2.

Omega 3 FA incorporation into brain lipids. A: Percent of total FAs. Total FA analysis of brain lipids was carried out by GC/MS. Only the values for the three long-chain omega 3 FAs are shown. The composition of all the FAs are shown in supplemental Table S2. The values shown are mean ± SD (n = 6 per group). Statistical significance was determined by one-way ANOVA with post hoc Tukey test. B: Nanomoles per gram of tissue. The concentration of the three long-chain omega 3 FAs in total brain lipids is expressed as nanomoles per gram. The statistical symbols are the same as in Fig. 1.

Fig. 3.

Increase in omega 3 FAs of brain phospholipids (nanomoles per gram). The molecular species of phospholipids containing the three omega 3 FAs were analyzed by LC/MS/MS, as described in the text. The increase in each species above the average of the control value was then calculated for the free EPA- and LPC-EPA-treated mice. The values shown are the sum of the increases in all molecular species containing the indicated FA (mean ± SD, n = 6 per group). *P < 0.0001, all differences between free EPA and LPC-EPA were significantly different by the unpaired t-test with Welch’s correction (GraphPad Prism). The increases in individual molecular species are shown in supplemental Figs. S1–S4.

Fig. 4.

Omega 3 FA incorporation into tissue lipids: liver (A); heart (B); adipose tissue (C); and erythrocytes (D). The total FA composition was analyzed by GC/MS, as described in the text. Only the values for the omega 3 FAs are shown here. The total FA composition of the tissues is shown in supplemental Tables S3–S6. The values shown are mean ± SD (n = 6 per group). Statistical significance was determined by one-way ANOVA with post hoc Tukey test. The symbols for the P values are the same as in Fig. 1.

Fig. 5.

Effect of free EPA and LPC-EPA on ARA levels in tissues. The ARA values for each tissue are shown for comparison. The symbols are as described in Fig. 1.

Fig. 6.

Effect of free EPA and LPC-EPA on the omega 3 FA composition of the retina. The total FA composition is shown in supplemental Table S7. Statistical significance was determined by one-way ANOVA with post hoc Tukey test. The symbols for the P values are the same as in Fig. 1.

Fig. 7.

Effect of free EPA and LPC-EPA on gene expression and CREB phosphorylation in the brain. A–D: Gene expression: BDNF (A); CREB (B); 5-HT1A (C); TNFα (D). Quantitative PCR was carried out as described in the text. The values shown are the mean ± SD of six animals per group. E: BDNF protein levels were measured by ELISA. The values shown are the mean ± SD of six samples for each group. The free EPA value was not significantly different from the control. However, the BDNF level in in LPC-EPA-treated animals was significantly higher than the control or free EPA-treated animals, both at P < 0.0001 (ANOVA with post hoc Tukey multiple comparison test). F: Phosphorylated CREB was measured by Western blot as described in the text. Values shown are expressed as relative to control mean (n = 3 per group). *P < 0.05, **P < 0.01, ***P < 0.001, and ****P < 0.0001 compared with control. ##P < 0.01, ###P < 0.001, and #### P < 0.0001 compared with free EPA (one-way ANOVA with post hoc Tukey multiple comparison test).

Fig. 8.

Proposed mechanisms for the differential effects of free EPA and LPC-EPA. Whereas free EPA (as well as EPA from fish oil and krill oil) is absorbed as TAG, LPC-EPA is absorbed as PC or LPC. The liver secretes more LPC-EPA and LPC-DHA after the uptake of phospholipid-EPA than after the uptake of TAG-EPA. The sodium-dependent symporter at the blood-brain barrier (Mfsd2a) facilitates the uptake of LPC-EPA and LPC-DHA by the brain. Part of the EPA taken up by the brain through this pathway is converted to DHA, and both EPA and DHA are incorporated into membrane lipids. LPC-EPA (and LPC-DHA) may also take part in transesterification reactions with endogenous ARA-containing phospholipids, resulting in the displacement of ARA and its subsequent oxidation of the latter by the β-oxidation pathway. This accounts for the loss of ARA after feeding EPA. In contrast to LPC-EPA, the free EPA generated in the plasma is taken up by diffusion and enters a different metabolic pool where it is preferentially oxidized by the β-oxidation pathway (10, 11) and, therefore, does not accumulate in the brain membranes.