Human plasma albumin transports [13C]docosahexaenoic acid in two lipid forms to blood cells.

ABSTRACT

Docosahexaenoic acid (226) 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) uptake, nonesterified FA (NEFA) bound to albumin are assumed to be the delivery route of FA to these cells. The supply of 13C-labeled 226 to blood cells by plasma albumin was studied in humans after a single ingestion of this FA esterified in a triglyceride (TG). The 226 13C/12C ratio, measured by gas chromatography 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 [13C]226 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 226, lyso-phosphatidylcholines (lyso-PC), in which [13C]226 accumulated while the nonesterified [13C]226 reached its minimal plasma concentrations. Computation of the relative contribution of NEFA and lyso-PC for the [13C]226 delivery to platelets and erythrocytes showed that the [13C]226 supply to platelets occurred uniquely through NEFA, whereas this pool was weakly involved in the delivery to erythrocytes. In contrast, lyso-PC was uniquely concerned with the 226 delivery to erythrocytes and represented the major part of this supply. We conclude that plasma albumin carries 226 in two lipid forms that are involved differently in the delivery of this FA to target cells.