Digital optical imaging of green fluorescent proteins for tracking vascular gene expression: Feasibility study in rabbit and human cell models

PURPOSE: To investigate the feasibility of using a sensitive digital optical imaging technique to detect green fluorescent protein (GFP) expressed in rabbit vasculature and human arterial smooth muscle cells. MATERIALS AND METHODS: A GFP plasmid was transfected into human arterial smooth muscle cells to obtain a GFP-smooth muscle cell solution. This solution was imaged in cell phantoms by using a prototype digital optical imaging system. For in vivo validation, a GFP-lentivirus vector was transfected during surgery into the carotid arteries of two rabbits, and GFP-targeted vessels were harvested for digital optical imaging ex vivo. RESULTS: Optical imaging of cell phantoms resulted in a spatial resolution of 25 mum/pixel. Fluorescent signals were detected as diffusely distributed bright spots. At ex vivo optical imaging of arterial tissues, the average fluorescent signal was significantly higher (P < .05) in GFP-targeted tissues (mean <plus/minus> SD, 9,357.3 absolute units of density +/- 1,001.3) than in control tissues (5,633.7 absolute units of density +/- 985.2). Both fluorescence microscopic and immunohistochemical findings confirmed these differences between GFP-targeted and control vessels. CONCLUSION: The digital optical imaging system was sensitive to GFPs and may potentially provide an in vivo imaging tool to monitor and track vascular gene transfer and expression in experimental investigations.