Fast diffusion of very long chain saturated fatty acids across a bilayer membrane and their rapid extraction by cyclodextrins: implications for adrenoleukodystrophy.

[adrenomyeloneuropathy]

Abnormalities in the transport of saturated very long chain fatty acids (VLCFA ; >C 18 :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-beta -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 .