New method effectively stains apoptotic retinal cells without requiring intraocular injections

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Azure Biosystems is excited to share the first published study that uses the Azure Sapphire Biomolecular Imager! We look forward to the role the Sapphire will play in future studies. Please continue to tag us in your studies using #ImagedbyAzure- we love to read your work.

What’s the problem, scientifically speaking?

Labeling neurons is critical for the diagnosis, prognosis, and treatment of retinal degenerative diseases. A common approach is to use a fluorescent probe to tag anionic phosphatidylserine (PS), which cells produce early in apoptosis in order to trigger phagocytosis. Until now, the only way to tag PS was by injecting the label directly into the eye. Not only is this a painful and invasive procedure, but the injection itself can promote retinal degeneration, making this method for labeling PS undesirable for monitoring disease progression.

Live imaging of apoptotic photoreceptors in vivo by retinal imaging
Live imaging of apoptotic photoreceptors in vivo by retinal imaging. (a) Representative fluorescence images of photoreceptors and fundus images of p25 RCS and WT rats 24 hours after PSVue-550 or HBSS solvent eyedrop application as indicated. (b) Quantification of fluorescence intensity after background subtraction in areas indicated by dashed lines. *P < 0.05 by Student’s t-test. (c) Photoreceptor fluorescence and (d) quantification as in b of fluorescence intensity maxima. *P < 0.05 Student’s t-test. (e) Photoreceptor fluorescence and (f) quantification of areas of fluorescent intensities specific to retinal quadrants. *P < 0.05; two-way ANOVA and Tukey post-hoc test. (b,d,f) All bars show mean ± SEM, n = 3 animals per group.

Technical barriers to labeling neurons

Labeling neurons is critical for the diagnosis, prognosis, and treatment of retinal degenerative diseases. A common approach is to use a fluorescent probe to tag anionic phosphatidylserine (PS), which cells produce early in apoptosis in order to trigger phagocytosis. Until now, the only way to tag PS was by injecting the label directly into the eye. Not only is this a painful and invasive procedure, but the injection itself can promote retinal degeneration, making this method for labeling PS undesirable for monitoring disease progression.

Technical barriers to labeling neurons

Until now, non-invasive PS probes have not been effective because they do not permeate the vitreous layer of the eye. Barriers in the eye make treatment of ocular disease difficult2, and previous work has focused on delivering PS probes effectively3.

What’s the solution?

Non-invasive in vivo fluorescence imaging of apoptotic retinal photoreceptors

In a study published in Scientific Reports by Mazzoni et al from Fordham University, the authors found Texas-red-conjugated PSVue-550, a commercially available probe, effectively binds to apoptotic photoreceptors when administered with an eye dropper1. Using this method, they were able to track disease progression in vivo using whole animal imaging and a retinal imaging system in both rat and mouse models of retinal degeneration.

The Sapphire Biomolecular Imager was used to confirm PSVue-550 penetration into the eye. Monitoring of disease progression is now possible in vivo using an eye dropper, replacing the need for injections.

A step in the right direction for human retinal disease

The work by Mazzoni et al. is a significant first step toward using this method in the study and treatment of human retinal disease. The Sapphire’s superior resolution, range, and sensitivity are regularly used for important advances in disease research around the world. Check out our full list of publications to read more.

Where can I learn more?

Click here to earn more about the Sapphire Biomolecular Imager and how it can enhance your research.

SOURCES

  1. Scientific Reports 2019 Feb 7; 9(1):1590. PMID: 30733587

  2. Pearce, W., Hsu, J., & Yeh, S. (2015). Advances in drug delivery to the posterior segment. Current opinion in ophthalmology, 26(3), 233–239.

  3. Qiu, et al. Single-Cell Resolution Imaging of Retinal Ganglion Apoptosis In Vivo Using a Cell-Penetrating Caspase Activatable Peptide Probe. PLOS ONE 9(2), e88855.

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