Measurement of carbon clearance in mice as toxicity parameter for liposomal preparations

The measurement of carbon clearance in female BDF1 mice was used for the characterization of affinity of empty multilamellar (MLV) or small unilamellar vesicles (SUV) made from HEPC:CH:DCP 1:1:0,25 to the reticuloendothelial system (RES). Five mice each were treated i.v. with the corresponding liposomes or physiologic saline. At different times after treatment india ink was administered i.v. and its elimination over 15 minutes was determined by measuring the extinction in blood at 650 nm. MLV had a significant influence on the phagocytic function of RES, leading to a three-fold prolongation of elimination half time after 8h. At 48 hours the normal function of RES was restored. This effect was already seen with a dose of 0.05 ml MLV/mouse corresponding to 1.06 mg lipid. On the contrary, SUV caused no change of carbon clearance up to a dose of 0.8 ml/mouse. From these results we conclude that liposomes, especially MLV, can lead to a measurable but reversible impairment of RES function, while SUV are better suited for a by-pass of this tissue and a probable reaching of other targets, as, for example tumors.