Modification of liposomes with N-substituted polyacrylamides: identification of proteins adsorbed from plasma

Liposomes prepared from DMPC (80%) and cholesterol (20%) were modified with a series of hydrophobically modified N-substituted polyacrylamides, namely , poly[N-isopropylacrylamide] (PNIPAM), poly[N,N-bis(2-methoxyethyl) acryla mide] (PMEAM), and poly[(3-methoxypropyl)acrylamide] (PMPAM). The hydrophob ic group, N-[4-(1-pyrenylbutyl)-N-n-octadecylamine was attached to one end of the polymer chains to serve as an anchor for incorporation into the lipo some bilayer. Liposome-polymer interactions were confirmed using fluorescen ce spectroscopy and chemical analysis. Microscopy revealed differences in a ggregation tendency between unmodified and polymer-modified liposomes. Prot eins adsorbed to liposome surfaces during exposure to human plasma were ide ntified by immunoblot analysis. It was found that both unmodified and polym er-modified liposomes adsorb a wide variety of plasma proteins. Contact pha se coagulation proteins, complement proteins, cell-adhesive proteins, serin e protease inhibitors, plasminogen, antithrombin III, prothrombin, transfer rin, alpha(2)-microglobulin, hemoglobin, haptoglobin and beta-lipoprotein a s well as the major plasma proteins were all detected. Some differences wer e found between the unmodified and polymer-modified liposomes. The unmodifi ed liposomes adsorbed plasminogen mainly as the intact protein, whereas on the modified liposomes plasminogen was present in degraded form. Also, the liposomes modified with PNIPAM in its extended conformation (below the lowe r critical solution temperature) appeared to adsorb less protein than those containing the 'collapsed' form of PNIPAM (above the LCST). (C) 1999 Elsev ier Science B.V. All rights reserved.