Binding of ethyl oleate to low density lipoprotein, phospholipid vesicles, and albumin: a 13C NMR study.

Fatty acid ethyl esters (FAEE), esterification products of ethanol and fatty acids, have been implicated as mediators of ethanol-induced organ damage. After ethanol ingestion in humans, FAEE circulate in blood, bound to lipoproteins and albumin. We have analyzed the binding of ethyl (1-13C, 99%) oleate (EO) to small unilamellar phospholipid vesicles (SUV), human low density lipoprotein (LDL), and bovine serum albumin (BSA) by 13C-NMR spectroscopy. Binding of < or = 25 mol% EO to SUV yielded a single EO carbonyl peak (172.6-172.9 ppm) downfield from that of EO oil (171.9 ppm). Thus, the carbonyl forms hydrogen bonds with water in the SUV aqueous interface. At 30 mol% EO in SUV, a second EO carbonyl peak appeared, indicating a limit in FAEE solubility in SUV. Addition of EO to isolated human LDL yielded a peak at 171.9 ppm, suggesting that the EO exists in an unhydrated environment, most likely the core of the lipoprotein. This binding was also observed using high levels of EO added to human serum. The addition of EO dissolved in ethanol or as an oil to a solution of BSA yielded no visible EO peak, whereas addition of (1-13C, 99%) oleic acid resulted in several narrow peaks, demonstrating a much greater affinity of BSA for oleic acid than for EO. Bidirectional transfer of EO between LDL and SUV was observed and was 85% complete within 30 min. There was no measurable transfer of EO from LDL or SUV to albumin. The weak binding of EO to albumin will result in increased transport of EO by lipoproteins as plasma levels of EO increase.