Corneal Reinnervation for Neurotrophic Keratopathy – Evaluation of Topical and Microsurgical Treatment Approaches in a Standardized, Preclinical, In-vivo Long-term Model of Neurotrophic Keratopathy in Thy1-GFP+ Rats
Clinical Neurology; Neurosurgery and Neuroradiology
Final Report Abstract
Corneal nerve fibers provide sensation and maintain the renewal and repair process in the corneal epithelium. Insufficient corneal innervation can cause neurotrophic keratopathy, a degenerative ocular surface disease that may culminate in blindness. However, it is presently unclear why insufficient innervation impairs epithelial renewal and repair. We hypothesized that stem cell activity in the cornea is dependent on the presence of nerve fibers and regulated through paracrine communication. We analyzed the gene expression profile in the corneal limbus on a single cell level and found a well-defined cell cluster among which Schwann cells and limbal stem cells communicate via several ligandreceptor interactions. We observed that this communication pattern changes when the cornea initiates an epithelial healing process in response to epithelial injury. We identified candidate genes that may be involved in limbal stem cell regulation and therefore may represent promising therapeutic agents for promoting stem cell activity in patients suffering from corneal denervation and impaired epithelial healing. In addition, we evaluated a novel therapeutic approach to promote corneal reinnervation using sustained delivery of Tacrolimus to the ocular surface through a biodegradable drug delivery system (DDS). We demonstrated that application of the DDS accelerates corneal epithelial reinnervation with minimal systemic “off-target” drug exposure. We then adapted the polymeric DDS to create a biodegradable Tacrolimus releasing implant for peripheral nerve surgery. With the clinical translation in mind, we developed a DDS with adjustable size and drug loading for application in large and small caliber nerves, releasing therapeutic doses of bioactive Tacrolimus over 31 days. We observed that implantation around surgically repaired peripheral nerves accelerates nerve regeneration and functional recovery in preclinical rodent models while systemic drug exposure is reduced by 80% compared to systemic delivery. After it served its therapeutic purpose, the DDS degrades within 120 days into biocompatible by-products. Given its easy “off the shelf” applicability, and preclinical efficacy and safety, this system may provide a readily translatable approach to promote nerve fiber regeneration and accelerate functional recovery in patients undergoing nerve surgery or suffering from insufficient corneal innervation. In spring 2020 the SARS-CoV2 pandemic hit Canada and non-covid related research was put on hold indefinitely. Frontline health care workers at the Hospital for sick children (SickKids) faced dire shortages of N95 masks, due to the unprecedented worldwide demand. The staff was instructed to reuse one mask over their whole shift, or even longer, potentially resulting in accumulation of contagious material on the mask surface and thus risking the health and safety of personnel and patients. In response to this crisis, we assembled an interdisciplinary research team led by SickKids researchers to evaluate rescue strategies to mitigate the depletion of masks. We hypothesized that inactivating accumulated pathogens in disposable respirators without affecting the respirators’ protective properties may enable safe reuse and thus help to alleviate the global shortage temporarily. As sterilization methods regularly used in health care institutions potentially degrade disposable respirators and thereby affect filtration efficiency, we investigated alternative strategies. We demonstrated that thermal disinfection for 60 minutes at 70°C in commercially available holding cabinets reliably inactivates SARS-CoV-2 on disposable N95 respirators without affecting their protective performance. The capacity of the tested holding cabinets allows for the reprocessing of hundreds of masks simultaneously. We published our results in the Canadian medical association journal concluding that this method provides a feasible, effective, and rapidly scalable strategy for high and low-tech regions and thereby may help to protect front-line workers from job-related risk of infection during the COVID-19 pandemic globally. Based on our results, SickKids collected and stored used masks from frontline personnel as an emergency plan to make the quicky available for decontamination, if needed.
Publications
- Effect of moist heat reprocessing of N95 respirators on SARS-CoV-2 inactivation and respirator function. Cmaj (2020)
S.C. Daeschler, N. Manson, K. Joachim, A.W.H. Chin, K. Chan, P.Z. Chen, A. Jones, K. Tajdaran, K. Mirmoeini, J.J. Zhang, J.T. Maynes, L. Zhang, M. Science, A. Darbandi, D. Stephens, F. Gu, L.L.M. Poon, and G.H. Borschel
(See online at https://doi.org/10.1503/cmaj.201203) - Corneal Neurotization. in: C.-H.J. Tzou, and A. Rodríguez- Lorenzo, (Eds.), Facial Palsy: Techniques for Reanimation of the Paralyzed Face, Springer International Publishing, Cham, 2021, pp. 269-281
S.C. Daeschler, R. Zuker, A. Ali, and G.H. Borschel
(See online at https://doi.org/10.1007/978-3-030-50784-8_26) - Strategies to Improve Cross-Face Nerve Grafting in Facial Paralysis. Facial Plastic Surgery Clinics 29 (2021) 423-430
S.C. Daeschler, R. Zuker, and G.H. Borschel
(See online at https://doi.org/10.1016/j.fsc.2021.03.009) - Optical Tissue Clearing Enables Rapid, Precise and Comprehensive Assessment of Three-Dimensional Morphology in Experimental Nerve Regeneration Research. Neural regeneration research 17 (2022) 1348-1356
S.C. Daeschler, J. Zhang, T. Gordon, and G.H. Borschel
(See online at https://doi.org/10.4103/1673-5374.329473)
