Abstract
Polyethylene glycol (PEG)-phospholipids in long-circulating liposomes cause non-specific immune reactions; mainly attributable to negatively-charged phosphoryl s at the interface of PEG and phospholipid. We investigated a novel lipopolymer, by which a superhydrophilic polymer (SHP) is conjugated to a non-phospholipid N1-(2-aminoethyl)-N4-hexadecyl-2-tetradecylsuccinamide (HDAS). The modification of preformed liposomes HDAS-SHP, HDAS-PEG2000, and DSPE-PEG2000 were performed by post-insertion techniques. The efficiency of post-insertion and desorption rates, from the liposome surface, were determined. HDAS-SHP micelles showed highly positive zeta potential (+28.4 mV); zeta potentials of DSPE-PEG2000 and HDAS-PEG2000 micelles were -34.4 mV, and -3.7 mV, respectively. Critical micelle concentration predicted amphiphilicity of HDAS-SHP (CMC 2.58 µM) as close to that of DSPE-PEG2000 (CMC 2.44 µM). Both HDAS-SHP and HDAS-PEG2000 post-inserted with comparable efficiency (79%, and 73%, respectively), but noticeably lower than DSPE-PEG2000 (90%). The desorption rate of HDAS-SHP was close to that of DSPE-PEG2000 (0.53%/h, and 0.45%/h, respectively); the desorption rate for HDAS-PEG2000 was slightly more at 0.67%/h. Compared to plain liposomes, both HDAS-SHP- and DSPE-PEG2000-liposomes showed significant leakage of encapsulated Na-fluorescein isothiocyanate (FITC) upon incubation with serum. At the same time, both modified liposomes were found to suppress serum levels of the complement proteins, Bb and C4d. We infer that HDAS-SHP is a viable alternative to commonly-used PEG-phospholipid derivatives for stealth purposes.