Sterol efflux from mammalian cells induced by human serum albumin-phospholipid complexes. Dependence on phospholipid acyl chain length, degree of saturation, and net charge.

Human serum albumin and phospholipids can interact to cause a synergistic sterol release from mammalian cells in tissue culture. In the presence of the complexes formed between albumin and saturated phosphatidylcholine, release was twice as great as that which occurred with the unsaturated phospholipid complexes. Within the saturated series, sterol release increased with chain length until the number of carbon atoms in the acyl group was 18, after which sterol release decreased. In the unsaturated series, sterol release decreased as the number of double bonds increased. Branching of the acyl chain, or analogues with the polar group in the sn-2 position reduced sterol efflux. In the presence of human serum albumin, maximal sterol efflux occurred with phospholipids having two adjacent acyl chains and zero net charge; sterol release decreased as net charge increased.