Apolipoprotein Ad (apo A-I), the major protein component of hi.-h density lipoprotein (HDL), plays a key role in reverse cholesterol transport from peripheral tissues to liver or steroidogenic organs. Class 13, type 1 scavenger receptor (SR-BI) is abundantly expressed in these target tissues and recognizes apo A-I of HDL for selective cholesteryl ester uptake. Recently, we reported the liver-targeting potential of plasma-derived apo Ad and the efficient delivery of therapeutic small interfering RNAs (siRNA) assembled with cationic liposome and apo A-I. In this study, we expressed and purified recombinant human apo Ad (rhapo Ad), low endotoxin grace, from an Escherichia coli expression system. The liver-targeting property of rhapo A-I was compared to that of plasma-derived apo A-L Using a hepatitis C virus mouse model, intravenous administration of virus-specific siRNA with liposome and rhapo A-I significantly inhibited viral protein expression, demonstrating,g great promise for its use in clinical applications. (C) 2008 Elsevier Inc. All rights reserved.