Adenovirus-mediated gene transfer as an in vivo probe of lipoprotein metabolism

Somatic gene therapy for dyslipidemias

Somatic gene transfer is a valuable tool for the in vivo evaluation of lipoprotein metabolism. It has been used to dissect metabolic pathways, to establish structure-function relationships of various gene products, and to evaluate conventional lipid-lowering and novel therapeutic genes for the treatment of lipoprotein disorders. In this article we review some general aspects of somatic gene therapy and the different vehicles used for the delivery of therapeutic genes. We highlight some recent advances in adenoviral vector development that make this vector an attractive system for clinical trials.

Gene therapy for dyslipidemia: clinical prospects

Current approaches to the treatment of lipid disorders are inadequate for a substantial number of patients with severe hyperlipoproteinemia, isolated low high-density lipoprotein (HDL) cholesterol levels, or other molecular disorders of lipoprotein metabolism. Therefore, dyslipidemias remain important targets for the development of novel therapies. Gene therapy is a logical therapeutic approach to monogenic lipoprotein disorders, such as homozygous familial hypercholesterolemia, familial lipoprotein lipase deficiency, familial lecithin-cholesterol acyltransferase deficiency, and abetalipoproteinemia, for which current therapies are inadequate. Gene therapy could also be used to increase expression of certain proteins, such as apolipoprotein A-I as a strategy to raise HDL cholesterol levels or apoE as a strategy for severe combined hyperlipidemia. With further progress in the development of vectors, gene therapy for severe dyslipidemia is likely to become a clinical reality.

Liver-directed gene transfer and prolonged expression of three major human ApoE isoforms in ApoE-deficient mice

Apolipoprotein E (apoE) plays a key role in lipoprotein metabolism and may have other important biological functions. In humans, there are three common, naturally occurring isoforms of apoE that are associated with differences in lipid levels and atherosclerosis. However, the direct in vivo effects of the apoE isoforms on lipoprotein metabolism and atherosclerosis are not yet fully understood. To investigate the effect of the apoE isoforms in vivo, we constructed second-generation recombinant adenoviruses encoding each of the apoE isoforms. These recombinant adenoviruses were injected intravenously into apoE-deficient mice fed a Western diet (mean baseline cholesterol level 1401 mg/dl) in order to study their effects in the absence of endogenous mouse apoE. Hepatic expression of apoE3 and apoE4 completely normalized the lipoprotein profile; 3 d after injection, mean plasma cholesterol levels were 194 and 217 mg/ dl, respectively, and this effect was maintained for at least 6 wk. Expression of apoE2 had much less effect on lipoprotein levels (mean cholesterol level 752 mg/dl 3 d after injection), despite much higher plasma levels of apoE2 compared with apoE3 and apoE4; by 6 wk after injection the cholesterol levels had returned to baseline levels in the apoE2-expressing mice. Expression of all three isoforms significantly increased HDL cholesterol levels by approximately threefold and was independent of the cholesterol-lowering effect. ApoE transgene expression was substantially prolonged compared with that achieved using a first generation adenovirus and apoE was readily detected in plasma 3 mo after virus injection. These studies demonstrate: (a) prolonged in vivo expression of human apoE isoforms in apoE deficient mice after second-generation recombinant adenovirus-mediated somatic gene transfer; and (b) significantly impaired ability of apoE2 in vivo to mediate clearance of remnant lipoproteins in apoE-deficient mice fed a Western diet compared with apoE3 and apoE4.