Fate of DNA targeted to the liver by asialoglycoprotein receptor-mediated endocytosis in vivo. Prolonged persistence in cytoplasmic vesicles after partial hepatectomy.

Abstract

After intravenous injection, DNA complexed with asialoglycoprotein-polylysine conjugates is endocytosed by hepatocytes via asialoglycoprotein receptors and is expressed transiently. Long term persistence and expression occurs when partial hepatectomy is performed after gene delivery. To determine the intracellular location of the persisting DNA, we transferred a plasmid expressing bacterial chloramphenicol acetyltransferase into the liver of rats in vivo by asialoglycoprotein receptor-mediated endocytosis. The internalized DNA was measured by Southern blot. Twenty min after administration, 80-85% of the plasmid appeared in the liver, 80% of which was within hepatocytes (12,000-18,000 copies/hepatocyte). In sham-operated control rats, the transgene concentration decreased to 8-12 and 2-4% of the initial levels in 4 and 24 h, respectively, and became undetectable at 7 days. In rats subjected to 66% hepatectomy 20 min after DNA administration, 20, 9, and 7% of the plasmid in the residual liver persisted at 4 h, 24 h, and 7 days, respectively. Liver homogenates were fractionated by differential centrifugation and Percoll gradient centrifugation. In 66% hepatectomized rats, the plasmid persisted in an undegraded, transfection-competent form in plasma membrane/endosome-enriched fractions throughout the duration of the experiment (7 days), indicating that cytoplasmic vesicles are the main site of persistence of the endocytosed DNA.