Emerging strategies of engineering retinal organoids and organoid-on-a-chip in modeling intraocular drug delivery: current progress and future perspectives

Retinal diseases are a rising concern as major causes of blindness in an aging society; therapeutic options are limited, and the precise pathogenesis of these diseases remains largely unknown. Intraocular drug delivery and nanomedicines offering targeted, sustained, and controllable delivery are the most challenging and popular topics in ocular drug development and toxicological evaluation. Retinal organoids (ROs) and organoid-on-a-chip (ROoC) are both emerging as promising in-vitro models to faithfully recapitulate human eyes for retinal research in the replacement of experimental animals and primary cells. In this study, we review the generation and application of ROs resembling the human retina in cell subtypes and laminated structures and introduce the emerging engineered ROoC as a technological opportunity to address critical issues. On-chip vascularization, perfusion, and close inter-tissue interactions recreate physiological environments in vitro, whilst integrating with biosensors facilitates real-time analysis and monitoring during organogenesis of the retina representing engineering efforts in ROoC models. We also emphasize that ROs and ROoCs hold the potential for applications in modeling intraocular drug delivery in vitro and developing next-generation retinal drug delivery strategies.

In Situ Formation of Injectable Gelatin Methacryloyl (GelMA) Hydrogels for Effective Intraocular Delivery of Triamcinolone Acetonide

A novel drug delivery system designed for intraocular injection, gelatin methacryloyl (GelMA), has attracted much attention due to its sustained-release character and low cytotoxicity. We aimed to explore the sustained drug effect of GelMA hydrogels coupled with triamcinolone acetonide (TA) after injection into the vitreous cavity. The GelMA hydrogel formulations were characterized using scanning electron microscopy, swelling measurements, biodegradation, and release studies. The biological safety effect of GelMA on human retinal pigment epithelial cells and retinal conditions was verified by in vitro and in vivo experiments. The hydrogel exhibited a low swelling ratio, resistance to enzymatic degradation, and excellent biocompatibility. The swelling properties and in vitro biodegradation characteristics were related to the gel concentration. Rapid gel formation was observed after injection, and the in vitro release study confirmed that TA-hydrogels have slower and more prolonged release kinetics than TA suspensions. In vivo fundus imaging, optical coherence tomography measurements of retinal and choroid thickness, and immunohistochemistry did not reveal any apparent abnormalities of retinal or anterior chamber angle, and ERG indicated that the hydrogel had no impact on retinal function. The GelMA hydrogel implantable intraocular device exhibited an extended duration, in situ polymerization, and support cell viability, making it an attractive, safe, and well-controlled platform for treating the posterior segment diseases of the eye.

Immunology and Pathology in Ocular Drug Development

Clear vision is dependent on features that protect the anatomical integrity of the eye (cornea and sclera) and those that contribute to internal ocular homeostasis by conferring hemangiogenic (avascular tissues and antiangiogenic factors), lymphangiogenic (lack of draining lymphatics), and immunologic (tight junctions that form blood-ocular barriers, immunosuppressive cells, and modulators) privileges. The later examples are necessary components that enable the eye to maintain an immunosuppressive environment that responds to foreign invaders in a deviated manner, minimizing destructive inflammation that would impair vision. These conditions allowed for the observations made by Medawar, in 1948, of delayed rejection of allogenic tissue grafts in the anterior chamber of mouse eye and permit the sequestration of foreign invaders (eg, Toxoplasma gondii) within the retina of healthy individuals. Yet successful development of intraocular drugs (biologics and delivery devices) has been stymied by adverse ocular pathology, much of which is driven by immune pathways. The eye can be intolerant of foreign protein irrespective of delivery route, and endogenous ocular cells have remarkable plasticity when recruited to preserve visual function. This article provides a review of current understanding of ocular immunology and the potential role of immune mechanisms in pathology observed with intraocular drug delivery.

Intraocular mitomycin C use in the treatment and prophylaxis of proliferative vitreoretinopathy in severe traumatic retinal detachments

PURPOSE

To evaluate the anatomic and visual outcomes of a new intraocular mitomycin c (MMC) application technique in the treatment of severe traumatic retinal detachment (RD) with advance proliferative vitreoretinopathy (PVR).

METHODS

The records of 15 eyes of 14 patients who underwent vitreoretinal surgery and intraoperative MMC application were reviewed retrospectively.

SURGICAL TECHNIQUE

After performing complicated vitreoretinal surgical procedures (Pars plana vitrectomy, PVR membrane stripping, large retinotomy/retinectomies and intraocular foreign body removal if found etc. . .) retina was attached with perfluorocarbon liquid (PFCL) and partial fluid-air exchange. Endolaser was performed. PFCL was removed to the posterior borders of retinochoroidal wounds, breaks or retinectomy sites. The remaining PFCL was enough to cover and prevent MMC contact with the posterior vital structures including optic disc, macula and underlying RPE and major vascular arcades. Ciliary epithelium and other anterior segment structures were protected from MMC contact with the use of air in the rest of the eye. Then, a 10 µg/mL concentrated MMC solution was carefully injected above the PFCL bubble until it covered PVR or potential areas of PVR development and removed after 60 s. Finally, the remaining PFCL was removed and all eyes were filled with silicone oil. The patients were followed at least 6 months after silicone oil removal. Visual and anatomic outcomes were determined during follow-up period.

RESULTS

The mean follow-up time was 19.6 ± 6 months (range 12-27 months). About 100% retinal attachment was achieved with one vitreoretinal surgery during the follow-up period. PVR was not detected around the retinal breaks or retinotomy sites in any eye. Limited macular epiretinal membrane was detected in two eyes and subsequently peeled during silicone oil removal. Preoperative visual acuities were hand motions in seven eyes and light perception in eight eyes. Nine of 15 eyes had a visual acuity of ⩾0.1 during the follow-up period. The mean preoperative visual acuity was logMAR 2.16 ± 0.15 and postoperative visual acuity was 0.80 ± 0.50 (p = 0.001). There were no additional complications related to intraoperative MMC use during follow-up period.

CONCLUSION

Temporary intraocular MMC use in vitreoretinal surgery yielded good anatomic and visual outcomes after the treatment of traumatic RDs with PVR or those with high risk of PVR development. Furthermore, MMC application appeared to prevent further PVR development after vitreoretinal surgery.

Future opportunities in diabetic retinopathy research

PURPOSE OF REVIEW

The risk of vision loss from diabetic retinopathy has fallen dramatically over the past 3 decades with improvements in diabetes and blood pressure treatments, and with advances in laser surgery and intraocular drug delivery. Nevertheless, diabetes continues to be a major cause of blindness. This study summarizes the state of the art in diabetic retinopathy research and provides a perspective on opportunities for future investigations.

RECENT FINDINGS

New insights into the pathophysiology of diabetes and diabetic retinopathy will improve metabolic control. Structure-function analyses are revealing new details of diabetic retinopathy. Intraocular drug therapy provides improved visual outcomes. Together these steps will yield better means to detect and quantify vision loss, and to develop patient-specific treatments to preserve vision for persons with diabetes.

SUMMARY

Retinopathy is one of the most successfully treated complications of diabetes and will continue to be an important area of research for patients and their families.

Novel Approaches for Retinal Drug and Gene Delivery

The ARVO 2014 minisymposium on "Novel Approaches for Retinal Drug and Gene Delivery" was held on May 6, 2014 in Orlando, FL. The main intent of the symposium was to review recent advances in retinal drug and gene delivery with specific emphasis on novel approaches that address current limitations and have the potential to translate into clinical practice. The symposium was sponsored by Translational Vision Science and Technology.