Modification of phospholipid structure results in greater stability of liposomes in Serum

Abstract

prevous studies have revealed that the replacement of the C-2 ester group in phoshatidylcholine by the carbamyloxy function renders the resulting lipids, without affecting the properties of the liposomes, resistant to hydrolysis by phospholipase A2 (Gupta, C.M. and Bali,A.(1981)biochim. Biophys.Acta 663 ,506-515). As an extension ofthis work, the effect of serum on the stability of liposoomes,prepared from 1-palmitoy1-2 heptadec10-ci enylacarbamyloxy phosphatidylcholine(carbamylphosphatidylcholine), has been examined. The stabililty has beenmeasured in terms of (a) bilayer permeability to solutes, and (b) the lipid transfer to serum proteins. Replacement of egg phosphatidylcholine inliposomes by the carbamyl analog prevented serum-induced leaakage of hte entrapped solutes and alsoinhibited the lipid (phospholipid and cholesterol) transfer. manipulation of the cholesterol content of the liposomes had no effect on the stability. These observations indicate that the interaction of serum proteins with lipsomes probably involves a highly specific binding of the proteins to the liposome surface.