Incorporation Of Docosahexaenoic Acid Research Articles

Docosahexaenoic acid metabolism and effect on prostacyclin production in endothelial cells

Bovine aortic endothelial cultures readily take up docosahexaenoic acid (DHA). Most of the DHA was incorporated into phospholipids, primarily in ethanolamine and choline phosphoglycerides, and plasmalogens accounted for 34% of the DHA contained in the ethanolamine fraction after a 24-h incubation. The retention of DHA in endothelial phospholipids was not greater than other polyunsaturated fatty acids and unlike arachidonic and eicosapentaenoic acids, DHA did not continue to accumulate in the ethanolamine phosphoglycerides after the initial incorporation. About 15% of the [ 14C(U)]DHA uptake was retroconverted to docosapentaenoic and eicosapentaenoic acids in 24 h. Some of the newly incorporated [ 14C(U)]DHA was released when the cells were incubated subsequently in a medium containing serum and albumin. The released radioactivity was in the form of free fatty acid and phospholipids and after 24 h, 11% was retroconverted to docosapentaenoic and eicosapentaenoic acids. Total DHA uptake was decreased only 10% by the presence of a 100 μ m mixture of physiologic fatty acids, but as little as 10 μ m docosatetraenoic acid reduced DHA incorporation into phospholipids by 25%. DHA was not converted to prostaglandins or lipoxygenase products by the endothelial cultures. When DHA was available, however, less arachidonic acid was incorporated into endothelial phospholipids, and less was converted to prostacyclin (PGI 2). Enrichment of the endothelial cells with DHA also reduced their capacity to subsequently produce PGI 2. These findings indicate that endothelial cells can play a role in DHA metabolism and like eicosapentaenoic acid, DHA can inhibit endothelial PGI 2 production when it is available in elevated amounts.

Docosahexaenoate metabolism and fatty-acid composition in developing retinas of normal and rd mutant mice

The fatty-acid composition of retinal lipids in developing control and rd mice (C57BL/6J) was determined. In addition, fatty-acid composition in brain and retina of normal and rd adult animals was compared. At 11 days of postnatal age, rd retinas contained proportionally less docosahexaenoate than controls, whereas the reverse relationship held for oleate at 20 days of age. In contrast, no differences in the fatty-acid composition of brain lipids were observed between rd and control animals. We also examined docosahexaenoate metabolism in rd and control retinas of different postnatal ages in vitro. These studies of [1-14C]docosahexaenoic-acid incorporation into retinal phospholipids and neutral lipids demonstrated significantly higher incorporation into triacylglycerols of the rd retina, beginning at 14-15 days of postnatal age. Incorporation into diacylglycerols and phospholipids was also higher in rd retinas than in controls at 14 days of age and older. Moreover, the concentration of ganglioside (a glycolipid class probably enriched within inner retinal layers) was higher in adult rd retinas. Degeneration of the rd retina can be detected histologically as early as 8-9 days. Therefore, the alterations of fatty-acid composition and docosahexaenoate metabolism described here are probably an effect, rather than a cause, of retinal degeneration in the rd mouse.

Incorporation of polyunsaturated fatty acids into bis(monoacylglycero) phosphate and other lipids of macrophages and of fibroblasts from control and Niemann-Pick patients

On the basis of earlier studies of rabbit pulmonary alveolar macrophages, the incorporation of 14C-labelled polyunsaturated fatty acids into the lipids of human fibroblasts from patients with various phenotypes of Niemann-Pick disease was examined in order to define further the disturbance in metabolism of bis(monoacylglycero)phosphate occurring in these disorders. Docosahexaenoic acid, which had not been studied previously, was found to be incorporated by macrophages into bis(monoacylglycero)phosphate in a highly selective fashion and was therefore used along with arachidonic acid for studies of fibroblasts. Following incubation of fibroblasts in serum-free medium for 60 min, the distribution of arachidonic acid label in lipids was: phosphatidylcholine, 51%; phosphatidylethanolamine, 12%; phosphatidylinositol, 9.5%; and bis(monoacylglycero)phosphate, 2.3%; and of docosahexaenoic acid label was 36, 20, 2.6 and 10.3% respectively. Phosphatidylinositol had the highest specific activity of arachidonic acid label and bis(monoacylglycero)phosphate of docosahexaenoic acid label. Prolongation of incubation to 21 h, with or without removal of label remaining in the medium at 1 h, resulted in proportional redistributions with phosphatidylcholine decreasing and phosphatidylethanolamine increasing. In bis(monoacylglycero)phosphate and phosphatidylinositol, the proportions of arachidonic acid label decreased and increased respectively, whereas the proportions of docosahexaenoic acid label in these lipids were unchanged. As virtually all label taken up by cells was esterified, these redistributions are taken to reflect transacylations. In Niemann-Pick cells, the expected redistribution of arachidonic acid label in bis(monoacylglycero)phosphate failed to occur with cell types A and B which are deficient in sphingomyelinase-phospholipase C, and excess label accumulated after a 21-h incubation. Excess docosahexaenoic acid label also accumulated in the bis(monoacylglycero)phosphate of these cells. The highly selective incorporation of docosahexaenoic acid in two cell types suggests a special role for bis(nionoacylglycero)phosphate in the metabolism of n-3 polyunsaturated fatty acids. A high specific activity found early in incubations of macrophages suggests that polyunsaturated fatty acids may be incorporated into phospholipids during de novo synthesis of phosphatidic acid.

In Vitro Incorporation and Metabolism of Icosapentaenoic and Docosahexaenoic Acids in Human Platelets - Effect on Aggregation

Washed human platelets were pre-loaded with icosapentaenoic acid (EPA), docosahexaenoic acid (DHA) or EPA + DHA and tested for their aggregation response in comparison with control platelets. In fatty acid-rich platelets, an inhibition of the aggregation could be observed when induced by thrombin, collagen or U-46619. The strongest inhibition was observed with DHA-rich platelets and it was reduced when DHA was incorporated in the presence of EPA. Study of fatty acid distribution in cell lipids after loading showed that around 90% of EPA or DHA taken up was acylated into phospholipids and a very small amount (less than 2%) remained in their free and hydroxylated forms. DHA was more efficiently acylated into phosphatidylethanolamine (PE) than into phosphatidylinositol (PI) in contrast to what observed with EPA, and both acids were preferentially incorporated into phosphatidylcholine (PC). EPA inhibited total incorporation of DHA and increased its relative acylation into PE at the expense of PC. In contrast, DHA did not affect the acylation of EPA. Upon stimulation with thrombin, EPA was liberated from phospholipids and oxygenated (as judged by the formation of its monohydroxy derivative) whereas DHA was much less metabolized, although consistently transferred into PE. It is concluded that EPA and DHA might affect platelet aggregation via different mechanisms when pre-loaded in phospholipids. Whereas EPA is known to alter thromboxane A2 metabolism from endogenous arachidonic acid, by competing with it, DHA might act directly at the membrane level for inhibiting aggregation.

Selective incorporation of docosahexaenoic acid in rat brain

The incorporation of [ 14C]docosahexaenoic acid (22:6) into various lipid classes was compared with that of [ 3H]arachidonic acid (20:4) in developing rat brains in order to characterize the retention of 22:6. The percentage distribution of 20:4 in neutral glycerides was similar to the mass distribution and, of the phospholipids, 20:4 was incorporated into choline glycerophospholipids and inositol glycerophospholipids in relatively higher amounts. The incorporation of labeled 22:6 differed from that of 20:4, as it was incorporated into ethanolamine glycerophospholipids and triacylglycerols in greater amounts in comparison with its mass distribution. Further division of ethanolamine glycerophospholipids into diacyi, alkylacyl and alkenylacyl types revealed that the high incorporation of radioactive 22:6 in ethanolamine glycerophospholipids was predominantly due to its rapid incorporation into diacyi and alkylacyl compounds. The distributions of both radioactively labeled 20:4 and 22:6 among the three types of ethanolamine glycerophospholipids were compared with those of radioactively labeled glycerol. The value of [ 3H]20:4 [ 3H] glycerol was much higher in alkenylacyl-GPE than in alkylacyl-GPE, and this indicates that 20:4 is incorporated into alkenylacyl-GPE by a deacylation-reacylation mechanism. In addition, [ 14C]22:6 was incorporated into ether-linked ethanolamine phospholipids in a similar manner to 20:4. This observation suggests that 22:6 may be incorporated into alkenylacyl-GPE by the same rearranging system, while another possibility is that preferential synthesis of hexaene species may occur in the desaturation of alkylacyl-GPE.