Gold nanorod in vivo molecular imaging of choroidal neovascularization using OCT and photoacoustic microscopy in rabbits

Abstract

Purpose : Enhanced detection of choroidal neovascularization (CNV) can lead to improved visual acuity in patients by providing targeted treatment and monitoring of disease progression. This study uses functionalized gold nanorods conjugated with targeting RGD peptides (GNR-RGD) as contrast agents in the presence of a custom-built photoacoustic microscopy (PAM) and OCT imaging system. This combination is used to optimally distinguish the margins of CNV in rabbits.

Methods : CNV models were generated in two groups of New Zealand rabbits. 3 rabbits received laser-induced RVO with 50 mg/kg Rose Bengal and laser illumination. A pulse duration of 0.5 s and a laser spot size of 75 µm were used with a power of 150 mW for the first 20 spots and 300 mW for an additional 20 spots. 3 other rabbits received subretinal injection of 750 ng human vascular endothelial growth factor (VEGF-165) at a concentration of 100 µL/mL in 1% bovine serum albumin mixed with 20 µL Matrigel. The models were monitored for 28 days until CNV had developed. All then received IV injection of 0.4 mL of targeting GNR-RGD (2.5 mg/mL). The injection was synchronously monitored with PAM and OCT and further imaged using fundus photography, OCT, PAM, FA, and ICGA at 2, 8, 24, and 72h and 5-14 days post-injection to provide visualization of GNR.

Results : IV administration of GNR-RGD into rabbit CNV models yielded a signal enhancement of 27.2-fold for PAM and 171.4% for OCT. The OCT and PAM signal peaked at 48 h post-injection. The PAM images were obtained at 578 and 700 nm, which permitted improved discernment of normal vasculature from CNV. Histological analysis and TUNEL assay showed no evidence of cell damage or death.

Conclusions : These images demonstrate that GNR-RGD can effectively localize to CNV regions to provide improved contrast and molecular imaging. For this reason, contrast-enhanced PAM and OCT provide a possible method of precise detection of CNV without harming ocular structures.

This is a 2021 ARVO Annual Meeting abstract.

 

(a) Fundus image showing retinal and choroidal vessels. (b) FA image showing CNV. (c) OCT showing retinal layers. (d) PAM images obtained at 578 and 700 nm. (Left) Vessel network with high contrast at excitation wavelength of 578 nm due to absorption of hemoglobin. (Middle) No signal on PAM acquired at 700 nm pre-injection. (Right) In vivo distribution of GNR-RGD at CNV 2 h post-injection.

 

Schematic of GNR modification and imaging.