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Method Article
Here we demonstrate a novel approach to using high resolution spectral-domain optical coherence tomography (HR-SD-OCT) to assist delivery of gene therapy agents into the subretinal space, assess its areal coverage, and characterize photoreceptor vitality.
HR-SD-OCT is utilized to monitor the progression of photoreceptor degeneration in live mouse models, assess the delivery of therapeutic agents into the subretinal space, and to evaluate toxicity and efficacy in vivo. HR-SD-OCT uses near infrared light (800-880 nm) and has optics specifically designed for the unique optics of the mouse eye with sub-2-micron axial resolution. Transgenic mouse models of outer retinal (photoreceptor) degeneration and controls were imaged to assess the disease progression. Pulled glass microneedles were used to deliver sub retinal injections of adeno-associated virus (AAV) or nanoparticles (NP) via a trans-scleral and trans-choroidal approach. Careful positioning of the needle into the subretinal space was required prior to a calibrated pressure injection, which delivers fluid into the sub retinal space. Real time subretinal surgery was conducted on our retinal imaging system (RIS). HR-SD-OCT demonstrated progressive uniform retinal degeneration due to expression of a toxic mutant human mutant rhodopsin (P347S) (RHOP347S) transgene in mice. HR-SD-OCT allows rigorous quantification of all the retinal layers. Outer nuclear layer (ONL) thickness and photoreceptor outer segment length (OSL) measurements correlate with photoreceptor vitality, degeneration, or rescue. The RIS delivery system allows real-time visualization of subretinal injections in neonatal (~P10-14) or adult mice, and HR-SD-OCT immediately determines success of delivery and maps areal extent. HR-SD-OCT is a powerful tool that can evaluate the success of subretinal surgery in mice, in addition to measuring vitality of photoreceptors in vivo. HR-SD-OCT can also be used to identify uniform animal cohorts to evaluate the extent of retinal degeneration, toxicity, and therapeutic rescue in preclinical gene therapy research studies.
Researchers are developing gene therapies for a variety of retinal and retinal degenerative diseases with hopes of translating novel therapeutics into treatments for human disease1,2,3,4,5,6,7,8,9,10,11. Time domain or spectral domain optical coherence tomography (SD-OCT) has been used to investigate the aspects of outer retinal degeneration in specific mouse models of disease12,13,14. HR-SD-OCT has not, however, been extensively used in the context of optimizing evaluation of mouse models to determine the rate and spatial uniformity of retinal degeneration, or in the context of preclinical evaluation of gene based therapeutics, for example, to assess rescue, toxicity, or the spatial extent of vector delivery8,15,16. Once a mouse model is fully characterized, the HR-SD-OCT data can serve as an informative and reliable resource to measure the impact of therapeutics to exert rescue or toxicity in mouse models of retinal degeneration17. Many groups are using subretinal injection as a method of vector delivery due to its efficiency at transducing photoreceptors and retinal pigment epithelium (RPE) cells. However, this remains a difficult method to master, given that it is typically done by free-hand surgery from the corneal surface, and is often fraught with cataracts, bleeding, and unintended retinal detachments occurring simply by manipulation of the posterior vitreous. Many groups still attempt subretinal injections blindly and deliver the virus using manual injections with relatively large diameter stainless steel needles (34G)8,17,18,19,20,21,22, and a few uses optical coherence tomography (OCT) imaging to confirm proper delivery of vector to the retina8,17,20,22. Some improvements in the method have recently been described using microscale needles driven by a micromanipulator22.
We present an integrated approach which aids in the positioning of the needle, and the injections are facilitated by a custom directed stereo ophthalmoscope designed in the lab specifically for visualizing inside the small eye of the mouse17,23. The use of pulled glass micro needles in conjunction with the stereotaxic micromanipulator provide better control of needle placement with no surgical cut down required (i.e., through conjunctivae and connective tissue) prior to injection. The use of the pressure regulated micro injector helps deliver consistent injection volumes, and the injection can be done with much greater stability, precision, and much slower than manual injections performed by a hand-held syringe, thereby decreasing the occurrence of bubble injection into the eye. The smaller needle helps prevent leakage following needle withdrawal because the path is self-sealing. To assess the extent of injection/delivery, many investigative groups rely on finding and assessing the areal extent of enhanced green fluorescence protein (EGFP) expression in the retina (expression construct delivered by the vector) at the experimental end point (euthanasia) to confirm successful injections11,19,20,24. This approach (not utilizing OCT) to verify surgical success wastes an enormous amount of resources in surgical procedural time and animals, since all animals with (unknown) surgical failures need to be maintained, followed with repetitive measures until euthanasia and eye harvest (when EGFP is measured). Confirmation of the location of injection in the retina can be improved using HR-SD-OCT to demonstrate that the injection is located between the correct layers of the retina (i.e. the subretinal space). HR-SD-OCT can also be used to immediately delineate unsuccessful attempts (surgical failures) to identify relevant variables in real surgical time to improve upon the approach. We found that HR-SD-OCT provides numerous advantages in preclinical gene therapy studies by allowing rapid quantitative evaluation of outer retinal degeneration, allowing identification/culling of study animals which do not meet experimental criteria (e.g., incorrect subretinal injection), and to direct follow-up imaging to the region of the eye where vector was delivered (where preclinical effect is most likely) as well as control regions where vector was not delivered. Since its development, the use of SD-OCT has continued to be accepted and used by ophthalmology researchers and is now considered the standard of retinal imaging in retinal scientific studies in mouse or rodent models13,25. HR-SD-OCT and its software capabilities were utilized in unique integrated ways to further the goal of successful quantitative gene therapy in mouse models at every step in the process, including animal model selection, characterization of degeneration in chosen disease models, therapeutic delivery, mapping of vector delivery, and toxicity/efficacy evaluation. The use of HR-SD-OCT allows for more efficient drug discovery at every level of the process. Here we describe these approaches that are used in our RNA Drug Discovery program.
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Animal protocols were reviewed and approved by the Institutional Animal Care and Use Committees of the VA WNY HCS and the University at Buffalo-SUNY. Animals were used according to the stipulations of the Association for Research in Vision and Ophthalmology (ARVO) and the Declaration of Helsinki.
1. Mouse Models
2. Mouse Eye Gel
3. HR-SD-OCT Imaging
4. Assessing the Presence, Rate, and Uniformity of Model Outer Retinal Degenerations
5. Intraocular Injections
NOTE: Details on use of the RIS are further elaborated in a recent study23.
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Assessing the Presence, Rate and Uniformity of Model Outer Retinal Degeneration
Measurements of the ONL were recorded from the OPL to the ELM, defining the limits of the ONL using the caliper tool provided in the instrument software. The goal was to map the progression of outer retinal degeneration in a partially humanized adRP mouse model. Comparable images from a control C57BL/6(J) mouse and an hC1/hC1//mWT/mWT mouse model, expressing two copies of the mutant huma...
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HR-SD-OCT provides a simple method for characterization of potential animal models of human disease to determine their usefulness in testing potential therapeutics. The ability to quickly and reliably characterize a potential animal model of human disease is critical to the process of therapeutic drug discovery (e.g., replacement gene therapy, ribozyme or shRNA knockdown gene therapy, combined gene therapy). HR-SD-OCT provides a simple, quick, and non-invasive method for evaluating retinal health that can be use...
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Commercial Relationships: MCB: None; JMS: None. The retinal imaging system (RIS)23 used in this study is a novel device of substantial use to any group seeking to conduct gene therapy delivery studies in mice, rodents, or small animals. While the authors have no conflicts to declare with respect to this device at this time, the University at Buffalo- SUNY and the Veterans Administration have rights in the intellectual property and may seek to commercialize this instrument in the future.
This material is based upon work supported, in part, by the Department of Veterans Affairs (VA), Veterans Health Administration, Office of Research and Development (Biomedical Laboratory Research and Development) (VA Merit Grant 1I01BX000669). JMS is employed, in part, as Staff Physician-Scientist, Ophthalmology, by VA WNY; MCB is employed, in part, by VA WNY. The study was conducted at, and supported in part by, the Veterans Administration Western New York Healthcare System (Buffalo, NY). Contents do not represent the views of the Department of Veterans Affairs or the United States Government. Also supported, in major part, by NIH/NEI R01 grant EY013433 (PI: JMS), NIH/NEI R24 grant EY016662 (UB Vision Infrastructure Center, PI: M Slaughter, Director- Biophotonics Module: JMS), an Unrestricted Grant to the Department of Ophthalmology/University at Buffalo from Research to Prevent Blindness (New York, NY), and a grant from the Oishei Foundation (Buffalo, NY). We acknowledge the gift of the hC1 transgenic RHOP347S line and the exon 1 mouse RHO knockout from Dr. Janis Lem (Tufts New England Medical Center, Boston, MA), and the gift of the NHR-E transgene model in the heterozygous state on the mouse exon 2 RHO knockout background from Drs. G. Jane Farrar and Peter Humphries (Trinity College, Dublin, IRE).
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Name | Company | Catalog Number | Comments |
C57BL6 (J) | Jackson Laboratories | 664 | |
N129R- | N/A | N/A | |
2HRho 1T/1T | N/A | N/A | |
Envisu R-2200 Ocular Coherence Tomography Instrument (OCT) | Bioptigen | 90-R2200-U1-120. | |
Retinal Imaging System (RIS) | In-house | N/A | |
Stemi 2000C Microscope | Zeiss | 000000-1106-133 | |
P-97 Flaming/Brown micropipette puller | Sutter Instrument Co | p-97 | |
MMN-33 micro manipulator | Narishige USA | MMN-33 | |
PLI-100 micro injector | Harvard Apparatus | 64-1736 | |
Micropipette Holder (Rotating) | In-house | N/A | |
Micropipette Storage Receptacle | World Precision Instruments Inc. | E210 | |
Borosilicate glass capillary tubes 1.5-1.8 X 100mm, | Harvard Apparatus | 30-0053 | |
2,2,2-Tribromoethanol | SIGMA Aldrich | T48402-25G | |
Tert-amyl Alcohol | SIGMA Aldrich | 240486-100ML | |
Atropine Sulfate Ophthalmic Solution, USP 1% | Akorn Inc. | NDC 17478-215-05 | |
Goniovisc | BioVision Limited | NDC 17238-610-15 | |
Cyclopentolate Hydrochloride Ophthalmic Solution, USP 2% | Akorn Inc. | NDC 17478-097-10 | |
Gentamicin Sulfate Ointment USP, 0.1% | Perigo | NDC 45802-046-35 | |
Systane Ultra | Alcon Laboratories, Inc. | 9006619-1013 | |
Tetracaine Hydrochloride | Bausch and Lomb | NDC 24208-920-64 | |
Ophthalmic Solution, USP 0.5% | Bausch and Lomb | NDC 24208-920-64 | |
DPBS | Gibco Life Technologies | 14190-136 | |
Virus Preparations | ViGene /UNC | N/A | |
Gold nanorods | NANOPARTz | D12M-850-1.75 | |
Fluorescein Sulfate AK-FLUOR 25% | Akorn Inc. | NDC 17478-250-20 | |
Coverslips | Fisher Scientific | 12-548-A | |
Forceps | Milton | 18-825 | |
Needles 30 guage | Beckton Dickenson | W11604 | |
Syringes | Beckton Dickenson | 309659 | |
Bioptigen software Package | Bioptigen | N/A | |
Proparacaine Hydrochloride Ophthalmic Solution, USP 0.5% | Akorn Inc. | NDC 17478-263-12 | |
Windows Excel | Microsoft | N/A | |
Adobe Illustrator | Adobe | ||
Scale | Mettler | ||
Scissors | World Precision Instruments | ||
Ear punch | Nat’l band | ||
CL 100 Light source | Welch Allyn | CL100 | |
Nitrogen Gas | Jackson Welding Supply | N/A | |
Heated Water bath | Neslab | RTE-140 | |
Heating plate | In House | N/A | |
Heating mat | Cincinnatti Sub Zero | 273 | |
Clay mouse holder | Plast.i.clay American Art Clay Co. | N/A | |
Betadine | MedLine | NDC53329-938-06 | |
Cotton Tip Applicators | American Health Service | Ctag | |
EtOH 70% | Fisher Scientific | BP2818-100 | |
Gloves Nitrile | VWR | 89038-272 | |
Diagnosys ERG Color Dome instrument | Diagnosys Inc. | D125 | |
Contact lenses | In-house | N/A | |
Diagnosys Software | Diagnosys Inc. | N/A | |
Origin 6.1 software | OriginLab Corp. | N/A | |
Reference electrodes | Ocuscience | F-Thread Electrode (DTL) 24” |
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