The Metabolism and Distribution of Docosapentaenoic Acid (n-6) in the Liver and Testis of Growing Rats

Bioconversion of Docosapentaenoic Acid in Human Cell Lines, Caco-2, HepG2, and THP-1

Docosapentaenoic acids (DPAs) are long chain polyunsaturated fatty acids that exist as two major structural isomers: n-3 DPA and n-6 DPA. n-3 DPA is found in seal meat, salmon and abalone, and n-6 DPA is found in several marine microbial oil. We investigated the bioconversion of n-3 and n-6 DPAs in three different human cell lines, Caco-2, HepG2, and THP-1. n-3 DPA was converted to docosahexaenoic acid only in HepG2 cells. In contrast, retro-conversion to eicosapentaenoic acid (EPA) was observed in all three cell lines. n-6 DPA was also retro-converted to arachidonic acid (AA) in Caco-2 and HepG2 cells. EPA and AA were particularly elevated in Caco-2 cells, compared to HepG2 cells. Further, the retro-conversion of n-3 DPA led to a greater increase of EPA in the phospholipid fraction than in the neutral lipid fraction.

Metabolic fate of docosahexaenoic acid (DHA; 22:6n-3) in human cells: direct retroconversion of DHA to eicosapentaenoic acid (20:5n-3) dominates over elongation to tetracosahexaenoic acid (24:6n-3)

Docosahexaenoic acid (22:6n-3) supplementation in humans causes eicosapentaenoic acid (20:5n-3) levels to rise in plasma, but not in neural tissue where 22:6n-3 is the major omega-3 in phospholipids. We determined whether neuronal cells (Y79 and SK-N-SH) metabolize 22:6n-3 differently from non-neuronal cells (MCF7 and HepG2). We observed that (13) C-labeled 22:6n-3 was primarily esterified into cell lipids. We also observed that retroconversion of 22:6n-3 to 20:5n-3 was 5- to 6-fold greater in non-neural compared to neural cells and that retroconversion predominated over elongation to tetracosahexaenoic acid (24:6n-3) by 2-5-fold. The putative metabolic intermediates, (13) C-labeled 22:5n-3 and (13) C-labeled 24:5n-3, were not detected in our assays. Analysis of the expression of enzymes involved in fatty acid beta-oxidation revealed that MCF7 cells abundantly expressed the mitochondrial enzymes CPT1A, ECI1, and DECR1, whereas the peroxisomal enzyme ACOX1 was abundant in HepG2 cells, thus suggesting that the initial site of 22:6n-3 oxidation depends on the cell type. Our data reveal that non-neural cells more actively metabolize 22:6n-3 to 20:5n-3 via channeled retroconversion, while neural cells retain 22:6n-3.

Effects of graded levels of arachidonic acid on the reproductive physiology of Senegalese sole (Solea senegalensis): Fatty acid composition, prostaglandins and steroid levels in the blood of broodstock bred in captivity

Previous studies on Senegalese sole (Solea senegalensis) indicated that cultured broodstock (first generation, G1) have lower tissue levels of arachidonic acid (20:4n-6, ARA) than wild counterparts. ARA is metabolized to form prostaglandins (PGs) that are involved in steroid production and follicle maturation in fish. In the present study the effects of different dietary levels of ARA on blood lipid and fatty acid composition, prostaglandin (PGF2α, PGF3α, PGE2 and PGE3) levels and plasmatic steroid levels (11-ketotestosterone, 11-KT, testosterone, T and estradiol, E2) in G1 Senegalese sole were studied. For this purpose, 12 groups of ten fish (1:1 male and female), were fed six diets (each diets was fed to two groups) with different dietary ARA levels over nine months (diets A=0.7, B=1.6, C=2.3, D=3.2, E=5.0, F=6.0% ARA). ARA and CHOL levels in blood showed a significant increase in an ARA dose related manner (P<0.05) whereas EPA and EPA/ARA ratio were reduced. In males, steroid (11-KT and T) levels increased significantly with increasing dietary ARA in a dose dependent manner, whereas in females E2 did not show any change related to dietary ARA content. Plasma concentration of 3-series PGs (i.e., PGE3 and PGF3α) were reduced in parallel to increased ARA levels in blood (P<0.05) and levels of PGs 3-series were always higher than 2-series PGs (PGE2 and PGF2α). In conclusion there is an effect of dietary ARA on steroid production of Senegalese sole males, which might have important consequences in the reproduction of cultured fish.

Orally administered [¹⁴C]DPA and [¹⁴C]DHA are metabolised differently to [¹⁴C]EPA in rats

Previous studies have revealed that C20 PUFA are significantly less oxidised to CO₂ in whole-body studies compared with SFA, MUFA and C18 PUFA. The present study determined the extent to which three long-chain PUFA, namely 20:5n-3 EPA, 22:5n-3 docosapentaenoic acid (DPA) and 22:6n-3 DHA, were catabolised to CO₂ or, conversely, incorporated into tissue lipids. Rats were administered a single oral dose of 2·5 μCi [1-¹⁴C]DPA, [1-¹⁴C]EPA, [1-¹⁴C]DHA or [1-¹⁴C]oleic acid (18:1n-9; OA), and were placed in a metabolism chamber for 6 h where exhaled ¹⁴CO₂ was trapped and counted for radioactivity. Rats were euthanised after 24 h and tissues were removed for analysis of radioactivity in tissue lipids. The results showed that DPA and DHA were catabolised to CO₂ significantly less compared with EPA and OA (P<0·05). The phospholipid (PL) fraction was the most labelled for all three n-3 PUFA compared with OA in all tissues, and there was no difference between C20 and C22 n-3 PUFA in the proportion of label in the PL fraction. The DHA and DPA groups showed significantly more label than the EPA group in both skeletal muscle and heart. In the brain and heart tissue, there was significantly less label in the cholesterol fraction from the C22 n-3 PUFA group compared with the C20 n-3 PUFA group. The higher incorporation of DHA and DPA into the heart and skeletal muscle, compared with EPA, suggests that these C22 n-3 PUFA might play an important role in these tissues.