25 - Fatty acid and lipid intermediate transport

Summary

Introduction

Palmitate, docosahexaenoate and arachidonate

The knowledge about the fatty acid (FA) transport through microcapillary barriers is increasing nowadays. The basis upon which studies are built is the assumption that FAs enter the brain across blood–brain barrier (BBB) from blood circulation (Pardridge and Mietus, 1980; Spector, 1992). They are also distributed to the posterior segment tissues through the blood–retina barrier (BRB) via the retinal or choroidal vessels and pigment epithelium (RPE) (Li et al., 1992). In the plasma, there are many vehicles that deliver FAs to cells. Endocytosed lipoproteins are the major source, and free fatty acids (FFA) bound to albumin constitute a much smaller pool. At first sight, the process of cellular FA uptake and sorting from this pool should include release from albumin complexes at the luminal endothelial surface and transport to intracellular organelles or abluminal membrane. The last step might be facilitated by cytosolic fatty acidbinding proteins (Schoentgen et al., 1989). However, we are still lacking strong evidence for or against the idea that one integral protein might serve either as receptor for FA–albumin complexes or carrier for unbound fatty acids at BRB and BBB level. More controversial is whether or not there is a saturable, energy-independent endothelial transporter or simply transendothelial passive exchange (Kimes et al., 1985).