Kelsey Kubelick , C. Ross Ethier, PhD
The trabecular meshwork (TM) is a fluid drainage tissue in the anterior eye that regulates intraocular pressure (IOP), and cell death at the TM is related to progression of glaucoma. Thus, novel glaucoma treatments seek to deliver stem cells to regenerate the TM and thus reduce IOP. Currently, histology is the gold standard for monitoring stem cell delivery and localization, but destructive sample preparation limits its use. To expedite development and clinical translation, longitudinal stem cell tracking in vivo is desirable. Thus, we are developing an ultrasound and photoacoustic (US/PA) imaging platform for tracking mesenchymal stem cells (MSCs) in the anterior eye.
To achieve this goal, MSCs were tagged with one of two custom-made optical absorbers: gold nanospheres (AuNSs) or Prussian blue nanocubes (PBNCs). MSCs were tagged by incubation with particles in vitro and then collected and washed to remove excess particles. Tagged MSCs were injected into porcine anterior segments in culture, perfused with media at a physiological flow rate of 2.5 µL/min to circulate tagged MSCs in the anterior chamber, and US/PA datasets were acquired.
Ultrasound imaging visualized anatomical landmarks (gray scale), and melanin-rich tissues produced strong signals with single-wavelength PA imaging (red scale) (Fig 1A). An increase in PA signal upon injection of AuNS-MSCs was observed (Fig 1B). The imaging platform was further developed to include 3D US/PA imaging (Fig 1C). Multi-wavelength PA imaging and spectroscopic analysis distinguished AuNS-MSCs and melanin at 5 hours post-injection (Fig 1D). To improve delivery efficiency, we used photomagnetic PBNC-MSCs. In proof-of-concept studies, a disc magnet pulled PBNC-MSCs to the cornea and held the cells in place for 24 hours (Fig 1E).
Our US/PA imaging platform has the ability to monitor stem cell location in the anterior eye, specifically facilitating real-time image-guided delivery with potential for longitudinal monitoring in vivo. Current efforts focus on magnetic guidance to the TM to improve delivery efficiency (Fig 1F).
- Kubelick KP, Snider EJ, Ethier CR, Emelianov S. Development of a stem cell tracking platform for ophthalmic applications using ultrasound and photoacoustic imaging. Theranostics. 2019;9(13):3812-24.
- Kubelick KP, Snider EJ, Ethier CR, Emelianov S. Photoacoustic properties of anterior ocular tissues. Journal of Biomedical Optics. 2019 May;24(5):056004.
- Snider EJ, Kubelick KP, Tweed K, Kim RK, Li Y, Gao K, Read AT, Emelianov S, Ethier CR. Improving stem cell delivery to the trabecular meshwork using magnetic nanoparticles. Scientific Reports. 2018 Aug 16;8(1):12251.