Abstract
Many prospective studies have shown that a diet enriched in omega-3 polyunsaturated fatty acids (n-3 PUFAs) can improve cognitive function during normal aging and prevent the development of neurocognitive diseases. However, researchers have not elucidated how n-3 PUFAs are transferred from the blood to the brain or how they relate to cognitive scores. Transport into and out of the central nervous system depends on two main sets of barriers: the blood-brain barrier (BBB) between peripheral blood and brain tissue and the blood-cerebrospinal fluid (CSF) barrier (BCSFB) between the blood and the CSF. In this review, the current knowledge of how lipids cross these barriers to reach the CNS is presented and discussed. Implications of these processes in health and disease, particularly during aging and neurodegenerative diseases, are also addressed. An assessment provided here is that the current knowledge of how lipids cross these barriers in humans is limited, which hence potentially restrains our capacity to intervene in and prevent neurodegenerative diseases.
Highlights
The brain is rich in lipids since it contains 24% phospholipids (PLs) and 22% cholesterol by dry matter (Svennerholm et al, 1997)
Because lipids are a major component of brain membranes, it is important to understand how they are transported from the blood to the central nervous system (CNS) and how modifications in the blood-brain barrier (BBB) and blood-cerebrospinal fluid (CSF) barrier (BCSFB) fatty acid profiles might change their permeability to lipids
Unlike polyunsaturated fatty acid (PUFA), cholesterol in the CNS is almost entirely synthesized within the brain since the BBB prevents any direct transfer of sterols from the blood to the brain, especially when they are contained in lipoprotein particles (Dietschy and Turley, 2001; Björkhem et al, 2004)
Summary
The brain is rich in lipids since it contains 24% phospholipids (PLs) and 22% cholesterol by dry matter (Svennerholm et al, 1997). Long-chain PUFAs must be supplied by the peripheral blood circulation and cross the barriers protecting against the entrance of toxic molecules into the central nervous system (CNS) (Igarashi et al, 2007; Lacombe et al, 2018). CP epithelial cells (CPECs) surrounding fenestrated capillaries filter water and other substances from the blood and transport them through the epithelial layer into brain ventricles (Lun et al, 2015b) This clear fluid produced by the CP is the cerebrospinal fluid (CSF), which fills the ventricles, cisterns and sulci of the brain as well as the central canal of the spinal cord. Because lipids are a major component of brain membranes, it is important to understand how they are transported from the blood to the CNS and how modifications in the BBB and BCSFB fatty acid profiles might change their permeability to lipids.
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