Recombinant adenoviruses are attractive vectors for in-vivo vascular gene therapy, although chronic inflammation and transgene loss results from host immunity to viral proteins. However, early acute effects of adenovirus may also have important implications for in vivo vascular gene transfer. We aimed to assess the mechanism and functional significance of endothelial injury after adenoviral gene transfer. We performed β-Galactosidase (β-Gal) gene transfer to rabbit carotid arteries (CA), using increasing viral titers. Arteries were either left in place in-vivo, or removed and incubated ex-vivo. After 3 days, we determined: (1) β-Gal protein levels, by ELISA; (2) endothelial VCAM-1 and ICAM-1 expression, and inflammation, by immunohistochemistry; or (3) endothelial function, by isometric vasomotor studies. The importance of neutrophils (PMN) was examined by inducing neutropenia with vinblastine. Results: A total of 68 rabbit CA were studied. (1) β-Gal expression was reduced 4-fold in in-vivo CA compared with paired ex-vivo CA (n=18, p < 0.001). Increasing viral titer > 5 × 10 9 pfu/ml had little effect on β-Gal expression in-vivo. (2) Endothelial PMN were not seen ex-vivo but increased with viral titer in-vivo (21.9 ± 4.2 PMN/section at 8 × 10 9 pfu/ml vs. 2.0 ± 2.4 at 1 × 10 9 pfu/ml; p < 0.01). (3)Phenylephrine-induced contraction was unaffected by gene transfer. In contrast, endothelial dependent relaxation to acetylcholine (ACh) was greatly impaired (31 ± 6.0 % relaxation at 1 × 10 11 pfu/ml vs. 53 ± 5.8 % in control CA, at 10 .. μM ACh; p < 0.01). (4) Vinblastine-induced neutropenia virtually abolished PMN infiltration in CA, and improved ACh dependent relaxation. Conclusions: In vivo vascular adenoviral gene transfer can result in endothelial injury, impaired vasomotor function, and greatly reduced transgene expression. Acute endothelial toxicity is mediated largely by PMN. However, we identify a "window" of viral titer for optimal vascular adenoviral gene transfer, between 1 and 5 × 10 9 pfu/ml, when transgene expression is high but vessel injury is minimized.


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