two lipid forms to blood cells

Docosahexaenoic acid (22 : 6) decreases blood platelet function and is highly concentrated in the brain where its depletion leads to functional impairments. Because the platelets and blood brain barrier capillary endothelium cannot hydrolyze the complex lipids for fatty acid (FA) u p take, nonesterified FA (NEFA) bound to albumin are assumed to be the delivery route of FA to these cells. The supply of "Clabeled 22: 6 to blood cells by plasma albumin was studied in humans after a single ingestion of this FA esterified in a triglyceride (TG). The 22:6 13C/'2C ratio, measured by gas chro matography combustion-isotope ratio mass spectrometry was measured in lipid classes from albumin, platelets, leukocytes, and erythrocytes (taken as a tentative index of the brain uptake). Nonesterified [ "C]22 : 6 bound to albumin was rapidly produced after ingestion, as a result of the hydrolysis of very low density lipoprotein (VLDL) plus chylomicron TG. We found that albumin carried another source of 22: 6, lyso-phosphatidylcholines (lyso-PC), in which ["C] 22: 6 accumulated while the nonesterified [ 13C]22:6 reached its minimal plasma concentrations. Computation of the relative contribution of NEFA and lyso-PC for the [ l3 C] 22 : 6 delivery to platelets and erythrocytes showed that the [ 13C]22:6 supply to platelets occurred uniquely through NEFA, whereas this pool was weakly involved in the delivery to erythrocytes. In contrast, lysoPC was uniquely concerned with the 22 : 6 delivery to erythrocytes and represented the major part of this supp1y.l We conclude that plasma albumin carries 22:6 in two lipid forms that are involved differently in the delivery of this FA to target cells.Brossard, N., M. Croset, S. Normand, J. Pousin, J. Lecerf, M. Laville, j. L. Tayof, and M. -de. Human plasma albumin transports ['3C]docosahexaenoic acid in two lipid forms to blood cells. J Lipid Res. 1997. 38: 1571-1582. Supplementary key words leukocytes erythrocytes n-3 fatty acid stable isotope platelets Docosahexaenoic acid (22 : 6), a long chain polyunsaturated fatty acid (PUFA) from the n-3 family, is present at high levels in fish that also contain eicosapentaenoic acid, the precursor fatty acid. The decreased risk of cardiovascular diseases observed in populations consuming fish has been attributed to these two PUFAs (1, 2), although their relative importance in the effects ob served and their specific properties are not fully elucidated (3). They exert antiatherogenic and antithrombotic effects through modulation of blood lipids and lipoproteins (4, 5). Given as a dietary supplement, they lower plasma triglycerides (TG) , mainly by decreasing hepatic VLDL secretion and free fatty acid biosynthesis (6). Feeding 22:Grich oil reduces the ratio of LDL to HDL, increases HDLB, and decreases the LDL particle size and their cholesterol content (3 ,7) . The incorporation of longchain n-3 PUFA in cell membranes also modifies eicosanoid production resulting in altered platelet and leukocyte reactivities (1, 8). Moreover, 22:6 is the sole n-3 PUFA that is highly concentrated in the brain (9) and retina ( lo), especiallyin neuromembranes such as brain synaptosomes and photoreceptor outer segments of the retina (11). Its depletion in these tissues during periods of growth leads to functional impairments in experimental animals (11) and infants (12), including abnormal electroretinogram, impaired visual acuity, and alterations in learning-related behavAbbreviations: BHT, butylated hydroxy toluene; GCCIRMS, gaschromatography combustion-isotope ratio mass spectrometry; CE, cholesteryl ester; 22: 6, docosahexaenoic acid; HDL, high density lipproteins; HPLC, high performance liquid chromatography; LCAT, lecithin : cholesterol acyltransferase; LDL, low density lipoproteins; Lyso-PC, lysophosphatidylcholine; NEFA, nonesterified fatty acids; PC, phosphatidylcholine; PE, phosphatidylethanolamine; PL, phospholipid; PUFA, polyunsaturated fatty acids; TLC, thin-layer chromatography; TG, triglyceride; VLDL, very low density lipoproteins; VLDL/Chyl, VLDL plus chylomicrons. 'To whom correspondence should be addressed. Journal of Lipid Research Volume 38, 1997 1571 by gest, on N ovem er 6, 2017 w w w .j.org D ow nladed fom iors. Although the biological properties of 22: 6 have been well described, it is still unclear how this fatty acid is delivered to blood cells and to the brain. During its transport by chylomicrons and VLDL TG, 22:6 is released by lipoprotein lipase from capillary endothelium and utilized by tissues for lipid synthesis, storage, and oxidation. Concomitant to this hydrolysis, some 22: 6 is made available to the blood and binds to albumin (13, 14). The fatty acid-albumin complex represents the TABLE 1. Fatty acid composition of [ ' "21 22: 6-triglycerides