Transport of Endocrine Disruptors in Phospholipid Bilayer Membranes

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Transport process of endocrine disruptors (ED) solubilized in phospholipid bilayer membranes was analyzed for the first time by NMR. The self-diffusion rates of ED, bisphenol A (BPA) and 4-octylphenol (OP), were directly determined and compared with those in water. Dynamics of the lipid matrices in membranes was simultaneously monitored without labeled nuclei. It owes its success to a specially designed high-power, high-sensitivity probe. The new probe can apply a large magnetic field-gradient sufficiently enough to monitor dynamic events in highly-viscous lipid membranes. Combining this probe to a high-resolution 600 MHz NMR apparatus, we showed how fast BPA, OP, and lipids moved in membrane and how the ED mobility was related to the membrane lipid dynamics. Attention was also paid to the relation of the ED mobility to the location in membrane.The ED transport in membrane was not rapid but more than one order of magnitude as slow as that in solution. ED had a high affinity for the membrane interface between the lipid headgroup and the hydrophobic core. The ED motion was slowed down by the site-specific, strong binding to membrane lipids and synchronized with that of the membrane lipid matrices.The slowdown of ED and lipid motions was leveled off in sufficiently large lipid bilayer vesicles, although the hydrodynamic continuum model gives the lipid aggregate motion slowed inversely to the spherical size. The limited motion is related to the intra-aggregate fluidity of the lipid bilayer membrane, the membrane not rigid but soft, fluctuating confined geometries. The method opens the possibility to give insight into the wide range of molecular dynamics within such confined but fluid intact cell membranes; neither labeling nor the invasive probing is required.