Abstract
The hepatotropism and intrahepatic distribution of adenoviral vectors may be species dependent. Hepatocyte transduction was evaluated in three rabbit strains after transfer with E1E3E4-deleted adenoviral vectors containing a hepatocyte specific α1 -antitrypsin promoter driven expression cassette (AdAT4). Intravenous administration of 4 × 1012 particles/kg of AdAT4 induced human apo A-I levels above 40 mg/dl in Dutch Belt, but below 1 mg/dl in New Zealand White and Fauve de Bourgogne rabbits. Human apo A-I levels did not correlate with transgene DNA levels, but with human apo A-I mRNA/DNA ratio in the liver. This human apo A-I mRNA/DNA ratio in the liver was 1.6 ± 0.37 at day 14 in Dutch Belt rabbits and was 77-fold (p<0.01) and 69-fold (p<0.01) higher than in New Zealand White and Fauve de Bourgogne rabbits, respectively, indicating strain differences of intrahepatic transgene DNA distribution. Diameters of sinusoidal fenestrae determined by transmission electron microscopy were significantly (p=0.0014) larger in Dutch Belt (124 ± 3.4 nm) than in New Zealand White (108 ± 1.3 nm) and Fauve de Bourgogne (105 ± 2.6 nm) rabbits. Since the diameter of adenoviral particles determined by cryo-electon microscopy is 110 nm, the observed differences in diameters of sinusoidal fenestrae are a critical determinant of hepatocyte transduction by adenoviral vectors.The number of fenestrae per μm2 determined by scanning electron microscopy was not significantly different between New Zealand White rabbits (19 ± 0.66) and Dutch Belt rabbits (19 ± 0.60) and was not determined in Fauve de Bourgogne rabbits. Consitent with the presence of an anatomical barrier for the passage of adenoviral vectors at the level of the sinusoidal endothelium, intraportal transfer preceded by injection of sodium decanoate, which enhances endothelial permeability, increased human apo A-I levels 32- and 120-fold in New Zealand White and Fauve de Bourgogne rabbits, respectively, but did not affect expression in Dutch Belt rabbits. In conclusion, size of sinusoidal fenestrae appears to be a critical determinant of hepatocyte transduction after adenoviral transfer. The existence of several pathophysiological conditions in humans in which the anatomy of the sinusoidal endothelium is altered, underscores the relevance of these observations for the development of hepatocyte directed gene transfer. Since the diameter of lentiviral vectors is higher than adenoviral vectors and since genetic variation in the diameters of sinusoidal fenestrae in humans with a healthy liver is unknown, this determinant of parenchymal liver cell transduction should be taken into account for the development of cllinical gene transfer.
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