Docosahexaenoic acid synthesis from α-linolenic acid by rat brain is unaffected by dietary n-3 PUFA deprivation

Igarashi Miki,James C Demar,Ma Kaizong,Chang Lisa,Jane M Bell,Stanley I Rapoport

doi:10.1194/jlr.m600549-jlr200

Igarashi Miki, James C Demar + Show 4 more

Open Access

https://doi.org/10.1194/jlr.m600549-jlr200

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Abstract

Rates of conversion of alpha-linolenic acid (alpha-LNA, 18:3n-3) to docosahexaenoic acid (DHA, 22:6n-3) by the mammalian brain and the brain's ability to upregulate these rates during dietary deprivation of n-3 polyunsaturated fatty acids (PUFAs) are unknown. To answer these questions, we measured conversion coefficients and rates in post-weaning rats fed an n-3 PUFA deficient (0.2% alpha-LNA of total fatty acids, no DHA) or adequate (4.6% alpha-LNA, no DHA) diet for 15 weeks. Unanesthetized rats in each group were infused intravenously with [1-(14)C]alpha-LNA, and their arterial plasma and microwaved brains collected at 5 minutes were analyzed. The deficient compared with adequate diet reduced brain DHA by 37% and increased brain arachidonic (20:4n-6) and docosapentaenoic (22:5n-6) acids. Only 1% of plasma [1-(14)C]alpha-LNA entering brain was converted to DHA with the adequate diet, and conversion coefficients of alpha-LNA to DHA were unchanged by the deficient diet. In summary, the brain's ability to synthesize DHA from alpha-LNA is very low and is not altered by n-3 PUFA deprivation. Because the liver's reported ability is much higher, and can be upregulated by the deficient diet, DHA converted by the liver from circulating alphaLNA is the source of the brain's DHA when DHA is not in the diet.

Highlights

Rates of conversion of a-linolenic acid (a-LNA, 18:3n-3) to docosahexaenoic acid (DHA, 22:6n-3) by the mammalian brain and the brain’s ability to upregulate these rates during dietary deprivation of n-3 polyunsaturated fatty acids (PUFAs) are unknown
We reported that k*i(a2LNAYDHA) was increased 6.6, 8.4, and 2.3-fold in i 5 liver triacylglycerol, phospholipid, and cholesteryl ester, respectively, in male rats fed, for 15 weeks after weaning, an n-3 PUFA-adequate diet without DHA (4.6% a-LNA of fatty acids, no DHA) compared with an n-3 PUFA-deficient diet (0.2% a-LNA, no DHA) [10, 16]
In the deficient compared with adequate group, the brain DHA concentration was reduced significantly by 37%, and a-LNA, EPAn-3 (20:5n-3), and DPAn-3 (22:5n-3) were not detected

Summary

Introduction

Rates of conversion of a-linolenic acid (a-LNA, 18:3n-3) to docosahexaenoic acid (DHA, 22:6n-3) by the mammalian brain and the brain’s ability to upregulate these rates during dietary deprivation of n-3 polyunsaturated fatty acids (PUFAs) are unknown. To answer these questions, we measured conversion coefficients and rates in post-weaning rats fed an n-3 PUFA deficient (0.2% a-LNA of total fatty acids, no DHA) or adequate (4.6% a-LNA, no DHA) diet for 15 weeks. 1% of plasma [1-14C]a-LNA entering brain was converted to DHA with the adequate diet, and conversion coefficients of a-LNA to DHA were unchanged by the deficient diet.

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