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Adenoviral-mediated gene transfer of the human lipoprotein lipase gene Ashbourne Excoffon, Katherine J. D.

Abstract

Lipoprotein lipase is a pivotal enzyme involved in the metabolism of circulating lipoproteins. Through the hydrolysis of the triglycerides (TG) in TG-rich particles, free fatty acids and glycerol are available for uptake by muscle, for energy, or adipose for storage. Patients with complete and partial LPL deficiency exhibit marked hypertriglyceridemia and altered lipoprotein metabolism. Gene therapy to deliver functional LPL to the circulation has been proposed in order to reduce the clinical morbidity and atherogenic risk due to this metabolic disorder. In vitro analysis of first generation recombinant adenoviral (Ad) vectors expressing the human LPL gene from an RSV promoter or a CMV promoter (Ad-LPL) revealed efficient infection and subsequent LPL expression in several cell lines. Delivery of Ad-LPL (RSV or CMV driven) to the liver of either normal mice or mice heterozygous for LPL deficiency results in an improved lipoprotein profile for at least 42 days and the correction of impaired fat load tolerance. Similarly, an Ad incorporating a common polymorphism that deletes the last two amino acids of LPL (Ser447Ter) results in an improved profile. Despite minimal hepatoxicity in these animals, the augmentation of LPL expression from natural sites, including muscle and adipose, was investigated using the CMV-driven Ad-LPL vector. After intra-adipose or intra-muscular Ad-LPL treatment via direct injection, expression within the adipose and muscle tissue compartments was significantly elevated until D14. Regardless of this over expression, no change in plasma LPL activity or TG levels was evident. Due to the neo-natal lethality associated with complete LPL deficiency in mice, a larger feline model of complete deficiency was explored. Complete correction in a cohort of homozygous LPL deficient cats was observed for 14 days before expression was extinguished, likely due to a vigorous immune response to both the adenovirus and the human LPL gene. In summary, the outcome effected by transferring the LPL gene to animal models, as well as somatic cells in tissue culture, have been defined for the first time. Evaluation of the systemic and tissue-specific efficiency, stability, potential toxicity and immunogenicty of adenoviral-mediated LPL gene expression has been delineated over the duration of these studies providing proof-of-principle towards LPL gene therapy. Although adenovirus is an efficient vector for gene delivery, future studies will evaluate alternative vector systems that display longer term expression and less immunogenicity, such as the adeno-associated virus.

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