Apolipoprotein E-deficient mice created by systemic administration of antisense oligodeoxynucleotides: a new model for lipoprotein metabolism studies

Atherosclerotic cardiovascular disease results from complex interactions among multiple genetic and environmental factors. Thus, it is important to elucidate the influence of each factor on cholesterol metabolism. For this purpose, transgenic/gene-targeting technology is a powerful tool for studying gene functions. However, this technology has several disadvantages such as being time consuming and expensive. Accordingly, we established new animal models using in vivo gene transfer technology. In this study, we examined the feasibility of the creation of a new animal model for the study of atherosclerosis. We hypothesized that apolipoprotein (apo) E-deficient mice can be created by systemic administration of antisense apo E oligodeoxynucleotides (ODN) coupled to the HVJ-liposome complex. Initially, we examined the localization and cellular fate of FITC-labeled antisense ODN administered intravenously. FITC-labeled ODN transfection by the HVJ-liposome method resulted in fluorescence in the liver, spleen and kidney, but not in other organs such as brain. Moreover, fluorescence with the HVJ-liposome method was sustained for up to 2 weeks after transfection, which resulted in a striking difference from transfection of ODN alone or ODN in liposomes without HVJ, which showed rapid disappearance of fluorescence (within 1 day). Given these unique characteristics of the HVJ-liposome method, we next examined transfection of antisense apo E ODN by intravenous administration. Transfection of antisense apo E ODN resulted in a marked reduction of apo E mRNA levels in the liver, but no change in apo B and beta-actin mRNA levels. In mice fed a normal diet, a transient increase in cholesterol and triglyceride levels was observed in the antisense apo E-treated group, but they returned to normal levels by 6 days after transfection. Similar findings were also found in mice fed a high cholesterol diet. Neither scrambled nor mismatched ODN resulted in any increase in cholesterol. To make chronic hypercholesterolemic mice, we therefore performed repeated injections of apo E antisense ODN. Whenever antisense apo E ODN were injected, mice showed a transient increase in cholesterol and triglyceride. Cumulative administration of antisense apo E ODN resulted in a sustained increase in cholesterol for up to 3 weeks after the last transfection. Finally, mice treated with repeated injections of antisense apo E every week developed sustained hypercholesterolemia and hypertriglyceridemia until withdrawal of injections. Apolipoprotein-deficient nice created by intravenous administration of antisense ODN are a promising new animal model to help understand the role of apolipoprotein in vivo and develop a new drug therapy targeting apolipoprotein.