Interactions of very long-chain saturated fatty acids with serum albumin

134

101

Background: Serum albumin is a highly abundant circulating protein and may have chaperone-like activity. Results: Serum albumin titratably inhibits aggregation and amyloid formation of client proteins and maintains chaperone-like activity under physiological conditions. Conclusion: The chaperone-like activity of serum albumin suggests it protects against protein misfolding and aggregation. Significance: This may have implications for protein misfolding disorders of the extracellular compartment.

Section: Discussionmentioning

confidence: 98%

Serum Albumin Prevents Protein Aggregation and Amyloid Formation and Retains Chaperone-like Activity in the Presence of Physiological Ligands

Finn

Nunez

Sunde

et al. 2012

134

101

“…However, we cannot rule out the possibility that CD36 directly binds long versus very long chain FAs via distinct binding sites or mechanisms and promotes their transfer to the membrane as has been previously suggested (1). Like albumin, CD36 may have unique binding sites for FAs of differing chain lengths (26).…”

Section: Discussionmentioning

confidence: 99%

CD36 Mediates Both Cellular Uptake of Very Long Chain Fatty Acids and Their Intestinal Absorption in Mice

Drover

Nguyen

Bastie

et al. 2008

143

113

The intestine has an extraordinary capacity for fatty acid (FA) absorption. Numerous candidates for a protein-mediated mechanism of dietary FA absorption have been proposed, but firm evidence for this process has remained elusive. Here we show that the scavenger receptor CD36 is required both for the uptake of very long chain FAs (VLCFAs) in cultured cells and the absorption of dietary VLCFAs in mice. We found that the fraction of CD36-dependent saturated fatty acid association/absorption in these model systems is proportional to the FA chain length and specific for fatty acids and fatty alcohols containing very long saturated acyl chains. Moreover, intestinal VLCFA absorption is completely abolished in CD36-null mice fed a high fat diet, illustrating that the predominant mechanism for VLCFA absorption is CD36-dependent. Together, these findings represent the first direct evidence for protein-facilitated FA absorption in the intestine and identify a novel therapeutic target for the treatment of diseases characterized by elevated VLCFA levels.In typical Western diets, the bulk of the calories exist in the chemical form of triacylglycerols (TAGs) 4 that consist of glycerol esterified to three fatty acid (FA) molecules. Once consumed, the FAs are liberated from TAG via pancreatic enzymes and are quantitatively absorbed by the body for energy, storage, and other cellular processes. The mechanism(s) responsible for the absorption of dietary FAs have not been well characterized. Given the extraordinary capacity of the gut for FA absorption, it seems likely that diffusion plays a major role in this process. The most common fatty acids in a typical diet are the long chain FAs palmitate (16:0) and oleate (18:1), which have relatively high rates of simple diffusion in model membrane systems (reviewed in Ref. 1).Unlike the long chain FAs, saturated very long chain FAs (VLCFAs) are much less soluble in aqueous environments, and the diffusion rates are much lower. In mixtures of vesicles and albumin (which model FA delivery to peripheral cells such as adipocytes), VLCFAs partition more favorably into phospholipid bilayers compared with long chain FAs (2). In addition, the dissociation of saturated VLCFAs from model vesicles is 10 5 -10 6 -fold slower than the dissociation of long chain FAs (3). This combination of preferential partitioning and slow dissociation suggests that protein-based mechanisms may be required for efficient absorption and utilization of VLCFAs in peripheral tissues in vivo.In contrast to peripheral absorption, VLCFA absorption in the intestine is essentially an unstudied field. The only direct experimentation to date was published in 1963 wherein Fields and Gatt (4) determined that intragastric or intraduodenal [ 14 C]lignoceric acid (24:0) was absorbed in the rat intestine and appeared in the lymph primarily in the neutral glyceride fraction (i.e. triacylglycerol). Since then, intestinal fatty acid absorption has been primarily studied using only long chain FAs and often employed indirect measures su...

“…VLCFA have very low aqueous solubility, a property that limits its transport between aqueous compartments and is a major impediment to its study even in model membrane systems. VLCFA have been shown to exhibit very slow dissociation rates from both serum albumin and membranes into the surrounding aqueous phase (several orders of magnitude slower than that of typical dietary long-chain FA) (22,23). Additionally, serum albumin has a much lower capacity for VLCFA.…”

mentioning

confidence: 99%

Fast Diffusion of Very Long Chain Saturated Fatty Acids across a Bilayer Membrane and Their Rapid Extraction by Cyclodextrins

Pillai

Jasuja

Simard

et al. 2009

Self Cite

Abnormalities in the transport of saturated very long chain fatty acids (VLCFA; >C18:0) contribute to their toxic levels in peroxisomal disorders of fatty acid metabolism, such as adrenoleukodystrophy and adrenomyeloneuropathy. We previously showed that VLCFA desorb much slower than normal dietary fatty acids from both albumin and protein-free lipid bilayers. The important step of transbilayer movement (flip-flop) was not measured directly as a consequence of this very slow desorption from donors, and the extremely low aqueous solubility of VLCFA precludes addition of unbound VLCFA to lipid membranes. We have overcome these limitations using methyl-␤-cyclodextrin to solubilize VLCFA for rapid delivery to "acceptor" phosphatidylcholine vesicles (small and large unilamellar) and to cells. VLCFA binding was monitored in real time with the fluorescent probe fluorescein-labeled phosphatidylethanolamine in the outer membrane leaflet, and entrapped pyranine was used to detect flip-flop across the membrane. The upper limit of the rate of flip-flop across the membrane was independent of temperature and media viscosity and was similar for model raft and non-raft membranes as well as living cells. We further showed that cyclodextrins can extract VLCFA rapidly (within seconds) from vesicles and cells, which have implications for the mechanism and potential alternative approaches to treat adrenoleukodystrophy. Because VLCFA diffuse through the lipid bilayer, proteins may not be required for their transport across the peroxisomal membrane.Elevated levels of saturated very long-chain saturated fatty acids (VLCFA 3 ; Ͼ18 carbons) in plasma serve as a biomarker for certain inherited neurological disorders, including ALD (1-4). Several peroxisomal biogenesis disorders (Zellweger syndrome, neonatal ALD, and infantile Refsum disease) and deficiencies of peroxisomal fatty acid (FA) degradation enzymes are also marked by abnormally high levels of VLCFA (5, 6). However, the clinical manifestations are quite different (1, 7), and it is not clear whether there is a common underlying biophysical or biochemical mechanism. It is generally presumed that VLCFA accumulate mainly because of inefficient degradation (␤-oxidation), which normally takes place in the peroxisomes (8 -11), or possibly because of the combination of impaired ␤-oxidation and enhanced FA elongation (12).ALD patients are also known to have a mutation in the abcd1 gene that encodes ALD protein (ALDP), an integral peroxisomal membrane protein and a member of the ATP-binding cassette transporter superfamily (13). abcd1 knock-out mice show VLCFA accumulation in brain tissue and have a neurological phenotype. Overexpression of ALDP in fibroblasts from both ALD patients and abcd1 knock-out mice can reverse biochemical abnormalities (14). Elucidating the function of ALDP is critical to our understanding of the biochemical abnormalities in ALD. Transfection of fibroblasts from ALD patients with ALDP results in normal expression levels and partially corrects for defective VLCFA ␤-...