Fatty acids are rapidly delivered to and extracted from membranes by methyl- -cyclodextrin

Abstract

A frequently used approach for adding FA at higher concentration is to complex the FA with albumin, which allows preparation of FA that is solubilized at millimolar concentrations. Although albumin is a physiologically relevant carrier of FA, careful consideration must be given to the facts that albumin can deliver impurities to cells and can extract FA and other nutrients from cells, which could alter their metabolic state ( 3 ). In addition, there is continuing disagreement about the rates of FA dissociation from albumin and whether this affects biophysical measurements of FA transport ( 4, 5 ). Furthermore, the binding properties of albumin are complex: different FA binding sites have different relative affi nities, and the kinetics of desorption are dependent on acyl chain length ( 6 ). The high affi nity of albumin for FA may result in very little delivery to membranes ( 7 ).A promising new vehicle for solubilization of FA is the family of cyclodextrins (CDs), which are cyclic oligosaccharides formed by bacterial degradation of starch. These molecules typically contain six ( ␣ ), seven ( ␤ ), or eight ( ␥ ) glucose residues linked by (1 → 4) glycosidic bonds. They have a polar surface and a hydrophobic cylindrical cavity that can bind and solubilize a wide variety of hydrophobic molecules, such as cholesterol and FA, while remaining soluble in water ( 8 ). The number of CD molecules required to solubilize one FA molecule increases with an increase in the hydrocarbon chain length of FA ( 9 ), although the exact stoichiometry is diffi cult to determine.In pharmaceutical applications, CD is widely used to solubilize hydrophobic drugs and enhance drug absorption in the gastrointestinal tract ( 8 ). It is used as a lipidbinding agent in the culture media of bacteria and animal cells ( 10, 11 ) and as a substitute for albumin for intrave- The very low aqueous solubility of long-chain fatty acids (FAs) is one of the major limitations in studies of FA transport in vitro and in vivo. A common misconception is that FA can form micelles at physiological pH because the pk a values for monomeric FA are typically 4.8. Instead, they form insoluble structures similar to phospholipid bilayers, in which ‫ف‬ 50% of the FA is ionized ( 1 ). The aqueous solubilities of the monomeric forms of the common 16-and 18-carbon dietary FA are <10 µM ( 2 ).

Genetic Ablation of CD36 Does not Alter Mouse Brain Polyunsaturated Fatty Acid Concentrations

“…Consistent with the Hamilton Model [27][28][29], Ouellet et al [30] demonstrated that the brain transport coefficient (Clup, ll g -1 s -1 ) of [ 14 C]-DHA and [ 14 C]-eicosapentaenoic acid (EPA) was not saturable at super-physiological concentrations, up to 100 lM, suggesting that DHA and EPA cross the BBB by simple diffusion. It was also reported that, upon crossing the BBB, EPA is rapidly b-oxidized possibly explaining its low concentration within the brain [31].…”

Delineating the role of alterations in lipid metabolism to the pathogenesis of inherited skeletal and cardiac muscle disorders

“…A proposed mechanism for fatty acid uptake is an insulin-or muscle contraction-induced translocation of fatty acid transport proteins to the plasma membrane, resulting in a net uptake of circulating fatty acids ( 26 ). However, the precise mechanism of long-chain fatty acid uptake into myocytes is still rather uncertain and is split between two prevailing hypotheses: passive diffusion-and protein-specifi c-mediated transport ( 22,(26)(27)(28)(29)(30)(31) ( Fig. 2 ).…”

In situ assay of fatty acid β-oxidation by metabolite profiling following permeabilization of cell membranes

“…Although albumin is frequently used, methyl-␤ -cyclodextrin (MBCD) is an alternative vehicle for the solubilization of FAs ( 25,26 ). We found that MBCD applied as described previously ( 25 ) led to an improved reconstitution of defi ned acylcarnitine standards in solution compared with albumin.…”