Lipid mediated gene delivery in the adult rat brain: quantitative analysis of expression

Gene transfer into the adult brain is potentially an attractive alternative to commonly employed transgenic approaches. DNA-lipid complexes have been used to obtain brain gene transfer, but data are sparse to indicate to what extent this results in significant expression of functional protein. Here, an expression construct encoding the functional reporter, chloramphenicol-acetyl-transferase (CAT), was complexed to a novel biodegradable lipid, and delivered into the rat brain. CAT-activity was assayed in tissue extracts to allow a precise quantitation of functional enzyme protein. Following bilateral intraventricular (i.c.v.) injection, robust enzyme activity was found in all brain regions studied, peaking at 4 weeks. Other routes of administration, e.g. intra-parenchymal injection or chronic infusion of complexes, resulted in marginal or no activity. Presence of CAT mRNA and plasmid DNA in tissue extracts was confirmed at 4 weeks post i.c.v. administration. In agreement with previous studies, labelled lipid-DNA complexes were mainly found in the ventricular ependyma. Present data support the feasibility of lipid mediated brain gene transfer, and outline some of its anatomical and temporal limitations.