Liposomes as carriers of DNA

A recombinant plasmid encoding for rat preproinsulin I was encapsulated in large liposomes and injected intravenously into rats. Glycemia and blood, splenic and hepatic insulin were assayed from 6 h after inoculation. Control animals received (1) empty liposomes, (2) liposomes carrying the E. coli pBR322 plasmid, (3) the free rat insulin I gene, or (4) no injection. All controls showed unchanged glucose and insulin levels. Six hours after inoculation, the treated rats had 72 +/- 6 mg glucose per 100 ml of blood, compared with 107 +/- 2 mg for controls. Radioimmunoassay of blood insulin gave 61 +/- 8 microU/ml (43 +/- 5 microU/Ml for controls). Spleen and liver values were 242 +/- 20 and 205 +/- 22 microU/g of tissue, respectively (112 +/- 20 and 87 +/- 15 microU/g in controls). The kinetics and extent of uptake of liposomes by spleen and liver were studied by external gamma-camera imaging after injection of 111In-labeled liposomes. The results paralleled insulin synthesis in the two organs. The insulin gene was localized in liver cells after the injection of liposomes containing the plasmid encoding insulin. Livers were processed 4 h after inoculation for isolation of hepatocytes, Kupffer cells, and endothelial cells. DNA was purified and exogenous DNA detected by Southern blotting. Kupffer cells were the primary targets for gene incorporation with liposomes consisting of phospholipids and cholesterol. Targeting of liposomes to other liver cells was attempted by including lactosylceramide in the liposomes. This increased the amount of exogenous gene in hepatocytes and particularly in endothelial cells. Detailed electron microscopy and biochemical studies were performed in order to follow the liposome-encapsulated DNA from the moment of i.v. injection to its entering the nucleus of different liver cells. Interactions of liposomes taken up in vivo by the liver cells with subcellular organelles were studied as well. The mechanism of DNA transport by liposomes in vivo and its potential are discussed.