Control of in vitro cytotoxicity of positively charged liposomes

The parameters which influence the in vitro cytotoxicity of positively charged liposomes for L 1210 cells were analyzed. The cytotoxicity was liposome/cell ratio-dependent. It also depended upon the mole fractions of stearylamine (SA) to phosphatidylcholine (PC). There was no difference between the cytotoxicity of unilamellar and multilamellar vesicles but the cytotoxic effect of free SA was about 4 times greater than that of liposome incorporated SA at a molar ratio of 1:4, SA:PC, respectively. The process which resulted in cell death was irreversible after 60 min of cell-liposome contact. The simultaneous presence of neutral liposomes or of positively charged liposomes with a lesser charge density decreased the cytotoxic effect of liposomes with a higher SA content. The cytotoxicity could be decreased by trypsinization of cells following exposure to liposomes while treatment of cells with trypsin prior to the exposure to positively charged liposomes had no effect on the subsequent cytotoxicity. The cytotoxicity was also decreased if cells were incubated in the presence of sodium azide. The usual concentration of serum (10%) present in the growth medium had no effect on the cytotoxicity while preincubation of cells with liposomes in 80% serum resulted in full protection. The protective effect of serum could be replaced by the albumin fraction.