Open clinical study of eye-drops containing tetrapeptides derived from substance P and insulin-like growth factor-1 for treatment of persistent corneal epithelial defects associated with neurotrophic keratopathy

Cell therapy in the cornea: The emerging role of microenvironment

The cornea is an ideal testing field for cell therapies. Its highly ordered structure, where specific cell populations are sequestered in different layers, together with its accessibility, has allowed the development of the first stem cell-based therapy approved by the European Medicine Agency. Today, different techniques have been proposed for autologous and allogeneic limbal and non-limbal cell transplantation. Cell replacement has also been attempted in cases of endothelial cell decompensation as it occurs in Fuchs dystrophy: injection of cultivated allogeneic endothelial cells is now in advanced phases of clinical development. Recently, stromal substitutes have been developed with excellent integration capability and transparency. Finally, cell-derived products, such as exosomes obtained from different sources, have been investigated for the treatment of severe corneal diseases with encouraging results. Optimization of the success rate of cell therapies obviously requires high-quality cultured cells/products, but the role of the surrounding microenvironment is equally important to allow engraftment of transplanted cells, to preserve their functions and, ultimately, lead to restoration of tissue integrity and transparency of the cornea.

Corneal Neurotization: Essentials for The Facial Paralysis Surgeon

Deficits in corneal innervation lead to neurotrophic keratopathy (NK). NK is frequently associated with facial palsy, and corneal damage can be accelerated by facial palsy deficits. Corneal nerves are important regulators of limbal stem cells, which play a critical role in epithelial maintenance and healing. Nonsurgical treatments of NK have undergone recent innovation, and growth factors implicated in corneal epithelial renewal are a promising therapeutic avenue. However, surgical intervention with corneal neurotization (CN) remains the only definitive treatment of NK. CN involves the transfer of unaffected sensory donor nerve branches to the affected cornea, and a variety of donor nerves and approaches have been described. CN can be performed in a direct or indirect manner; employ the supraorbital, supratrochlear, infraorbital, or great auricular nerves; and utilize autograft, allograft, or nerve transfer alone. Unfortunately, comparative studies of these factors are limited due to the procedure's novelty and varied recovery timelines after CN. Regardless of the chosen approach, CN has been shown to be a safe and effective procedure to restore corneal sensation and improve visual acuity in patients with NK.

Substance P promotes transforming growth factor-β-induced collagen synthesis in human corneal fibroblasts

Corneal fibroblasts maintain homeostasis of the corneal stroma by mediating the synthesis and degradation of extracellular collagen, and these actions are promoted by transforming growth factor-β (TGF-β) and interleukin-1β (IL-1β), respectively. The cornea is densely innervated with sensory nerve fibers that are not only responsible for sensation but also required for physiological processes such as tear secretion and wound healing. Loss or dysfunction of corneal nerves thus impairs corneal epithelial wound healing and can lead to neurotrophic keratopathy. The sensory neurotransmitter substance P (SP) promotes corneal epithelial wound healing by enhancing the stimulatory effects of growth factors and fibronectin. We have now investigated the role of SP in collagen metabolism mediated by human corneal fibroblasts in culture. Although SP alone had no effect on collagen synthesis or degradation by these cells, it promoted the stimulatory effect of TGF-β on collagen type I synthesis without affecting that of IL-1β on the expression of matrix metalloproteinase-1. This effect of SP on TGF-β-induced collagen synthesis was accompanied by activation of p38 mitogen-activated protein kinase (MAPK) signaling and was attenuated by pharmacological inhibition of p38 or of the neurokinin-1 receptor. Our results thus implicate SP as a modulator of TGF-β-induced collagen type I synthesis by human corneal fibroblasts, and they suggest that loss of this function may contribute to the development of neurotrophic keratopathy.NEW & NOTEWORTHY This study investigates the role of substance P (SP) in collagen metabolism mediated by human corneal fibroblasts in culture. We found that, although SP alone had no effect on collagen synthesis or degradation by corneal fibroblasts, it promoted the stimulatory effect of transforming growth factor-β on collagen type I synthesis without affecting that of interleukin-1β on the expression of matrix metalloproteinase-1.

Corneal reinnervation in patients with severe neurotrophic keratopathy secondary to herpes zoster ophthalmicus after treatment with autologous serum tear drops

Purpose

To study potential corneal reinnervation and recovery of corneal sensation in patients with severe neurotrophic keratopathy (NK) secondary to herpes zoster ophthalmicus (HZO) after treatment with topical autologous serum tears (AST).

Method

Four cases of HZO with severe NK were followed clinically and by serial laser in vivo confocal microscopy (IVCM, HRT3/RCM, Heidelberg Engineering) before and during treatment with 20% AST drops eight times a day. Two masked observers reviewed the IVCM images and assessed corneal nerve alterations.

Results

At baseline, all patients had complete loss of corneal sensation. In addition, IVCM showed complete lack of the subbasal corneal nerve plexus in all patients. All four patients were refractory to conventional therapies and were treated with AST drops. All patients demonstrated significant nerve regeneration by IVCM within 3-7 months of treatment. The total nerve density increased to a mean ± SEM of 10,085.88±2,542.74 μm/mm2 at the last follow up. Corneal sensation measured by Cochet-Bonnet esthesiometry improved to a mean ± SEM of 3.50±1.30 cm. Interestingly, 3 of 4 patients developed stromal keratitis with ulceration within weeks of corneal reinnervation, which was reversed by adding topical steroids.

Conclusion

Autologous serum tears are effective in restoring corneal subbasal nerves and sensation in patients with severe NK secondary to HZO. However, this group of patients may require concurrent topical immunomodulation and antiviral therapy while on AST to prevent stromal keratitis.

The Role of Insulin-like Growth Factor (IGF) System in the Corneal Epithelium Homeostasis-From Limbal Epithelial Stem Cells to Therapeutic Applications

The corneal epithelium, comprising three layers of cells, represents the outermost portion of the eye and functions as a vital protective barrier while concurrently serving as a critical refractive structure. Maintaining its homeostasis involves a complex regenerative process facilitated by the functions of the lacrimal gland, tear film, and corneal nerves. Crucially, limbal epithelial stem cells located in the limbus (transitional zone between the cornea and the conjunctiva) are instrumental for the corneal epithelium integrity by replenishing and renewing cells. Re-epithelialization failure results in persistent defects, often associated with various ocular conditions including diabetic keratopathy. The insulin-like growth factor (IGF) system is a sophisticated network of insulin and other proteins essential for numerous physiological processes. This review examines its role in maintaining the corneal epithelium homeostasis, with a special focus on the interplay with corneal limbal stem cells and the potential therapeutic applications of the system components.

Neurotrophic keratitis: inflammatory pathogenesis and novel therapies

PURPOSE OF REVIEW

Neurotrophic keratitis is a rare degenerative disease characterized by decrease or absence of corneal sensation. Neurotrophic keratitis varies from mild forms with mild epitheliopathy to severe manifestations such as corneal ulceration, melting and perforation that can lead to irreversible visual loss. The cause of neurotrophic keratitis comprises a long list of diseases, medications, congenital or genetic conditions as well as trauma. The mechanism of neurotrophic keratitis is complex and multifactorial and its understanding is crucial to better address the treatment strategies. We aimed to review neurotrophic keratitis pathology, mechanisms and management.

RECENT FINDINGS

Corneal nerves are critical for the homeostasis of a healthy ocular surface. The lack of nerve-derived neuromediators and corneal-released neuropeptides, neuro-trophins and neurotrophic factors in neurotrophic keratitis leads to a decrease in trophic supply to corneal cells in addition to a decrease in afferent signaling to the brain. This results in pathological tear secretion, decreased blinking rate, corneal healing along with ocular surface and corneal inflammation. Lately, nerve growth factor in special gained emphasis as a treatment strategy targeting the disease mechanism rather than its manifestations. Other therapies, including surgical interventions, are in the pipeline of neurotrophic keratitis management. However, there are still no proper therapeutic guidelines and neurotrophic keratitis treatment remains challenging.

SUMMARY

Neurotrophic keratitis may have a devastating outcome and treatment is still challenging. Understanding the disease pathology may assist in the development of new treatment strategies. Prompt disease recognition and immediate intervention are key factors to promote corneal healing and avoid further deterioration.

Conjunctival transcriptomics in ocular mucous membrane pemphigoid

PURPOSE

Ocular Mucous Membrane Pemphigoid (OcMMP) is an orphan disease characterized by chronic autoimmune-driven conjunctival inflammation leading to progressive scarring, debilitating symptoms, and blinding sequelae. This feasibility study aims to demonstrate conjunctival genetic transcriptomic analyses as a putative tool for interrogation of pathogenic signaling pathways in OcMMP.

METHODS

Conjunctival RNA profiling using the NanoString nCounter Human Fibrosis panel was undertaken on RNA extracted from conjunctival swabs obtained from 6 MMP patients (8 eyes; 4 M/2F; median age 78 [range 64-84] years); and 8 age-matched control participants (15 eyes; 3 M/5F; median age 69.5 [range 69-88] years). Data from 770 genes were analyzed with ROSALIND HyperScale architecture and stratified according to the level of clinically visible bulbar conjunctival inflammation. Normalization, fold-changes (≥+1.5-fold or ≤ -1.5-fold) and p-values adjustment (<0.05) using the Benjamini-Hochberg method were calculated.

RESULTS

93 differentially expressed genes (DEGs) were observed between OcMMP versus controls of which 48 were upregulated, and 45 downregulated. The top 4 upregulated DEGs represented fibrosis (COL3A1, COL1A1, FN1 and THBS1) while the key under-expressed genes (SCIN, HMGS2, XCL1/2) were indicative of ocular surface failure (goblet cell loss, keratinization, vulnerability to secondary infections). Forty-four pathways had a global significance score ≥2, the most significant being those related to extracellular matrix (ECM) remodeling, synthesis, and degradation. These pathways were accentuated in eyes with visible inflammation.

CONCLUSIONS

NanoString methodology acquired via a simple conjunctival swab identifies profibrotic genes in OcMMP group and differentiates inflamed eyes. Longitudinal sampling and following investigative intervention will further mechanistic insight and development of novel biomarkers to monitor disease progression.

Enhanced adipose-derived stem cells with IGF-1-modified mRNA promote wound healing following corneal injury

The cornea serves as an important barrier structure to the eyeball and is vulnerable to injuries, which may lead to scarring and blindness if not treated promptly. To explore an effective treatment that could achieve multi-dimensional repair of the injured cornea, the study herein innovatively combined modified mRNA (modRNA) technologies with adipose-derived mesenchymal stem cells (ADSCs) therapy, and applied IGF-1 modRNA (modIGF1)-engineered ADSCs (ADSCmodIGF1) to alkali-burned corneas in mice. The therapeutic results showed that ADSCmodIGF1 treatment could achieve the most extensive recovery of corneal morphology and function when compared not only with simple ADSCs but also IGF-1 protein eyedrops, which was reflected by the healing of corneal epithelium and limbus, the inhibition of corneal stromal fibrosis, angiogenesis and lymphangiogenesis, and also the repair of corneal nerves. In vitro experiments further proved that ADSCmodIGF1 could more significantly promote the activity of trigeminal ganglion cells and maintain the stemness of limbal stem cells than simple ADSCs, which were also essential for reconstructing corneal homeostasis. Through a combinatorial treatment regimen of cell-based therapy with mRNA technology, this study highlighted comprehensive repair in the damaged cornea and showed the outstanding application prospect in the treatment of corneal injury.

Healing of Chemical Injury-Related Persistent Corneal Epithelial Defects With Topical Insulin

PURPOSE

The purpose of this study was to evaluate the effectiveness of insulin eye drops for treating refractory persistent epithelial defects (PEDs).

METHODS

A prospective, single-center, case series was performed from March 2020 to September 2021. All patients were prescribed insulin eye drops for refractory PEDs that failed on maximum standard medical treatment (including serum eye drops). The drops were used 4 times/day. Patients were followed up at 2 weekly intervals with full slitlamp examination and serial anterior segment photography. The primary end point was resolution of the epithelial defect.

RESULTS

Eleven eyes of 10 patients were treated with insulin eye drops. The mean age of the cohort was 45.4 + 25 years with a mean follow-up of 195.7 + 114.3 days after re-epithelization. The most common causative condition was chemical injury (n = 5, 60%). Mean baseline PED defect was 41.3 + 55.2 mm 2 . Nine of 11 eyes (82%) fully re-epithelized within a mean time of 62.3 + 34.6 days (range 14-112). In 2 patients who did not achieve re-epithelization, one had a reduction in size from 12.25 mm 2 to 4.5 mm 2 and the other had no response. No recurrence in defect was observed in the group that had fully re-epithelized.

CONCLUSIONS

This study showed that the use of topical insulin eye drops led to a successful resolution of PED in 9 of 11 cases. We demonstrate the use of insulin for closure of PEDs in chemical eye injury. Larger controlled studies are required to further evaluate this novel therapy.

Use of Nicergoline as Adjunctive Treatment of Neurotrophic Keratitis in Routine Clinical Practice: A Case Series

PURPOSE

To describe the effectiveness and safety of nicergoline in patients with epithelial corneal defect or corneal ulcer due to neurotrophic keratitis (NK).

METHODS

A prospective case series review was performed in 14 patients with NK who started treatment with nicergoline as an off-label prescription from January to November 2020. Patients with a epithelial defect or corneal ulcer due to NK were treated with oral nicergoline.

RESULTS/SERIAL CASES

Complete corneal healing was observed in 10 (71.4%) of the 14 patients after 25.6 ± 26.60 days (range 7-90) with nicergoline. In three (21.5%) patients wound healing was not achieved, and one patient (7.1%) was lost to follow-up. The mean time between diagnosis and the starting of nicergoline was 10.92 ± 8.85 days (0-28). No adverse effects of nicergoline were observed.

CONCLUSION

Nicergoline as an adjunctive treatment for NK showed a potential use in the healing of epithelial defect in real-life clinical practice.

Exploration of biomimetic poly(γ-benzyl-L-glutamate) fibrous scaffolds for corneal nerve regeneration

Poly(γ-benzyl-L-glutamate) (PBG) made biomimetic scaffolds are explored as candidate materials for corneal nerve regeneration and neurotrophic keratopathy treatment. The PBG with built-in neurotransmitter glutamate was synthesized and fabricated into 3D fibrous scaffolds containing aligned fibers using electrospinning. In in vitro experiments, primary mouse trigeminal ganglia (TG) cells were used. Immunohistochemistry (IHC) analysis shows that TG cells cultured on PBG have no cytotoxic response for 21 days. Without any nerve growth factor, TG cells have the longest neurite length of 225.3 μm in the PBG group and 1.3 times the average length as compared with the polycaprolactone and no scaffold groups. Also, aligned fibers guide the neurite growth and extension unidirectionally. In vivo assays were carried out by intracorneal implantation of PBG on clinical New Zealand rabbits. The external eye photos and in vivo confocal microscopy (IVCM) show a low immune response. The corneal neural markers (βIII tubulin and SMI312) in the IHC analysis are consistent with the position stained by glutamate of implanted scaffolds, indicating that PBG induces neurogenesis. PBG exhibits mechanical stiffness to resist material deformation possibly caused by surgical operations. The results of this study demonstrate that PBG is suitable for corneal nerve regeneration and the treatment of neurotrophic keratopathy.

Immunomodulatory Role of Neuropeptides in the Cornea

The transparency of the cornea along with its dense sensory innervation and resident leukocyte populations make it an ideal tissue to study interactions between the nervous and immune systems. The cornea is the most densely innervated tissue of the body and possesses both immune and vascular privilege, in part due to its unique repertoire of resident immune cells. Corneal nerves produce various neuropeptides that have a wide range of functions on immune cells. As research in this area expands, further insights are made into the role of neuropeptides and their immunomodulatory functions in the healthy and diseased cornea. Much remains to be known regarding the details of neuropeptide signaling and how it contributes to pathophysiology, which is likely due to complex interactions among neuropeptides, receptor isoform-specific signaling events, and the inflammatory microenvironment in disease. However, progress in this area has led to an increase in studies that have begun modulating neuropeptide activity for the treatment of corneal diseases with promising results, necessitating the need for a comprehensive review of the literature. This review focuses on the role of neuropeptides in maintaining the homeostasis of the ocular surface, alterations in disease settings, and the possible therapeutic potential of targeting these systems.

Neuroimmune crosstalk in the cornea: The role of immune cells in corneal nerve maintenance during homeostasis and inflammation

In the cornea, resident immune cells are in close proximity to sensory nerves, consistent with their important roles in the maintenance of nerves in both homeostasis and inflammation. Using in vivo confocal microscopy in humans, and ex vivo immunostaining and fluorescent reporter mice to visualize corneal sensory nerves and immune cells, remarkable progress has been made to advance our understanding of the physical and functional interactions between corneal nerves and immune cells. In this review, we summarize and discuss recent studies relating to corneal immune cells and sensory nerves, and their interactions in health and disease. In particular, we consider how disrupted corneal nerve axons can induce immune cell activity, including in dendritic cells, macrophages and other infiltrating cells, directly and/or indirectly by releasing neuropeptides such as substance P and calcitonin gene-related peptide. We summarize growing evidence that the role of corneal intraepithelial immune cells is likely different in corneal wound healing versus other inflammatory-dominated conditions. The role of different types of macrophages is also discussed, including how stromal macrophages with anti-inflammatory phenotypes communicate with corneal nerves to provide neuroprotection, while macrophages with pro-inflammatory phenotypes, along with other infiltrating cells including neutrophils and CD4⁺ T cells, can be inhibitory to corneal re-innervation. Finally, this review considers the bidirectional interactions between corneal immune cells and corneal nerves, and how leveraging this interaction could represent a potential therapeutic approach for corneal neuropathy.

Modulating the tachykinin: Role of substance P and neurokinin receptor expression in ocular surface disorders

Substance P (SP) is a tachykinin expressed by various cells in the nervous and immune systems. SP is predominantly released by neurons and exerts its biological and immunological effects through the neurokinin receptors, primarily the neurokinin-1 receptor (NK1R). SP is essential for maintaining ocular surface homeostasis, and its reduced levels in disorders like diabetic neuropathy disrupt the corneal tissue. It also plays an essential role in promoting corneal wound healing by promoting the migration of keratocytes. In this review, we briefly discuss the structure, expression, and function of SP and its principal receptor NK1R. In addition, SP induces pro-inflammatory effects through autocrine or paracrine action on the immune cells in various ocular surface pathologies, including dry eye disease, herpes simplex virus keratitis, and Pseudomonas keratitis. We provide an in-depth review of the pathogenic role of SP in various ocular surface diseases and several new approaches developed to counter the immune-mediated effects of SP either through modulating its production or blocking its target receptor.

Neurotization of the human cornea - A comprehensive review and an interim report

We present a comprehensive review of existing literature on surgical corneal neurotization (SCN) as a treatment modality for neurotrophic keratopathy (NK) with an interim report of seven cases where SCN was performed using the indirect approach and followed up till 18 months postoperatively to look for improvement in ocular surface, corneal sensations, and nerve regeneration by using in vivo confocal microscopy (IVCM). A literature search was performed for publications with keywords “corneal nerves,” “neurotization,” “esthesiometry,” “corneal anesthesia,” and “neurotrophic keratopathy.” All literature available till December 31, 2020 was reviewed and included to describe NK and its management options, particularly SCN. NK is associated with absent or reduced corneal sensations and is managed using a step-ladder algorithm ranging from medical management for symptomatic relief to surgical corneal neurotization. Both direct and indirect approaches of SCN have a favorable outcome with reduced surgical morbidity in the indirect approach using sural nerve graft. Post neurotization, corneal sensation recovery may take up to 3–6 months, while nerve regeneration on confocal microscopy can take as long as 6 months–1 year.

New Pharmacological Approaches for the Treatment of Neurotrophic Keratitis

Neurotrophic keratitis (NK) is a rare degenerative condition that is caused by damage to the trigeminal nerve, with partial or complete loss of corneal sensory innervation. The loss of innervation leads to impaired healing of corneal epithelium, which subsequently results in punctate epithelial erosions, persistent epithelial defects, corneal ulcers and corneal perforation. Management of NK is often supportive and aims to promote epithelial healing and prevent progression of disease. Multiple novel pharmacological approaches have been proposed to address the underlying pathophysiology of NK, which are discussed in this paper.

Roles of Epithelial and Mesenchymal TRP Channels in Mediating Inflammatory Fibrosis

The maintenance of normal vision is dependent on preserving corneal transparency. For this to occur, this tissue must remain avascular and its stromal architecture needs to be retained. Epithelial transparency is maintained provided the uppermost stratified layers of this tissue are composed of terminally differentiated non-keratinizing cells. In addition, it is essential that the underlying stromal connective tissue remains avascular and scar-free. Keratocytes are the source of fibroblasts that are interspersed within the collagenous framework and the extracellular matrix. In addition, there are sensory nerve fibers whose lineage is possibly either neural crest or mesenchymal. Corneal wound healing studies have been undertaken to delineate the underlying pathogenic responses that result in the development of opacification following chemical injury. An alkali burn is one type of injury that can result in severe and long- lasting losses in ocular transparency. During the subsequent wound healing process, numerous different proinflammatory cytokines and proteolytic enzymes undergo upregulation. Such increases in their expression levels induce maladaptive expression of sustained stromal inflammatory fibrosis, neovascularization, and losses in the smooth optical properties of the corneal outer surface. It is becoming apparent that different transient receptor potential channel (TRP) isoforms are important players in mediating these different events underlying the wound healing process since injury upregulates both their expression levels and functional involvement. In this review, we focus on the involvement of TRPV1, TRPA1 and TRPV4 in mediating some of the responses that underlie the control of anterior ocular tissue homeostasis under normal and pathological conditions. They are expressed on both different cell types throughout this tissue and also on corneal sensory nerve endings. Their roles have been extensively studied as sensors and transducers of environmental stimuli resulting from exposure to intrinsic modulators and extrinsic ligands. These triggers include alteration of the ambient temperature and mechanical stress, etc., that can induce pathophysiological responses underlying losses in tissue transparency activated by wound healing in mice losses in tissue transparency. In this article, experimental findings are reviewed about the role of injury-induced TRP channel activation in mediating inflammatory fibrotic responses during wound healing in mice.

Treatment of Non-Infectious Corneal Injury: Review of Diagnostic Agents, Therapeutic Medications, and Future Targets

Corneal injuries can occur secondary to traumatic, chemical, inflammatory, metabolic, autoimmune, and iatrogenic causes. Ocular infection may frequently occur concurrent to corneal injury; however, antimicrobial agents are excluded from this present review. While practitioners may primarily rely on clinical examination techniques to assess these injuries, several pharmacological agents, such as fluorescein, lissamine green, and rose bengal, can be used to formulate a diagnosis and develop effective treatment strategies. Practitioners may choose from several analgesic medications to help with patient comfort without risking further injury or delaying ocular healing. Atropine, cyclopentolate, scopolamine, and homatropine are among the most frequently used medications for this purpose. Additional topical analgesic agents may be used judiciously to augment patient comfort to facilitate diagnosis. Steroidal anti-inflammatory agents are frequently used as part of the therapeutic regimen. A variety of commonly used agents, including prednisolone acetate, loteprednol, difluprednate, dexamethasone, fluorometholone, and methylprednisolone are discussed. While these medications are effective for controlling ocular inflammation, side effects, such as elevated intraocular pressure and cataract formation, must be monitored by clinicians. Non-steroidal medications, such as ketorolac, bromfenac, nepafenac, and diclofenac, are additionally used for their efficacy in controlling ocular inflammation without incurring side effects seen with steroids. However, these agents have their own respective side effects, warranting close monitoring by clinicians. Additionally, ophthalmologists routinely employ several agents in an off-label manner for supplementary control of inflammation and treatment of corneal injuries. Patients with corneal injuries not infrequently have significant ocular surface disease, either as a concurrent pathology or as an exacerbation of previously existing disease. Several agents used in the management of ocular surface disease have also been found to be useful as part of the therapeutic armamentarium for treatment of corneal injuries. For example, several antibiotics, such as doxycycline and macrolides, have been used for their anti-inflammatory effects on specific cytokines that are upregulated during acute injuries. There has been a recent wave of interest in amniotic membrane therapies (AMTs), including topical, cryopreserved and dehydrated variants. AMT is particularly effective in ocular injuries with violation of corneal surface integrity due to its ability to promote re-epithelialization of the corneal epithelium. Blood-based therapies, including autologous serum tears, plasma-enriched growth factor eyedrops and autologous blood drops, have additionally been explored in small case series for effectiveness in challenging and recalcitrant cases. Protection of the ocular surface is also a vital component in the treatment of corneal injuries. Temporary protective methods, such as bandage contact lenses and mechanical closure of the eyelids (tarsorrhaphy) can be particularly helpful in selective cases. Glue therapies, including biologic and non-biologic variants, can also be used in cases of severe injury and risk of corneal perforation. Finally, there are a variety of recently introduced and in-development agents that may be used as adjuvant therapies in challenging patient populations. Neurotrophic corneal disease may occur as a result of severe or chronic injury. In such cases, recombinant human nerve growth factor (cenegermin), topical insulin, and several other novel agents may be an alternate and effective option for clinicians to consider.

Mechanistic investigations of diabetic ocular surface diseases

With the global prevalence of diabetes mellitus over recent decades, more patients suffered from various diabetic complications, including diabetic ocular surface diseases that may seriously affect the quality of life and even vision sight. The major diabetic ocular surface diseases include diabetic keratopathy and dry eye. Diabetic keratopathy is characterized with the delayed corneal epithelial wound healing, reduced corneal nerve density, decreased corneal sensation and feeling of burning or dryness. Diabetic dry eye is manifested as the reduction of tear secretion accompanied with the ocular discomfort. The early clinical symptoms include dry eye and corneal nerve degeneration, suggesting the early diagnosis should be focused on the examination of confocal microscopy and dry eye symptoms. The pathogenesis of diabetic keratopathy involves the accumulation of advanced glycation end-products, impaired neurotrophic innervations and limbal stem cell function, and dysregulated growth factor signaling, and inflammation alterations. Diabetic dry eye may be associated with the abnormal mitochondrial metabolism of lacrimal gland caused by the overactivation of sympathetic nervous system. Considering the important roles of the dense innervations in the homeostatic maintenance of cornea and lacrimal gland, further studies on the neuroepithelial and neuroimmune interactions will reveal the predominant pathogenic mechanisms and develop the targeting intervention strategies of diabetic ocular surface complications.

Risk factors for corneal epithelial wound healing: Can sex play a role?

PURPOSE

To determine if sex is associated with corneal epithelial wound healing time in patients with persistent corneal epithelial defects (PCEDs).

METHODS

Retrospective case series on patients with PCED from November 2014 to January 2019. Records of 127 patients with diagnosis of PCED were reviewed. Patients with an epithelial defect that lasted more than two weeks in the absence of an active corneal infection were included. Main outcome was corneal epithelial wound healing time.

RESULTS

55 patients (29 males) with a mean age of 65.3 ± 16.5 years were included. No difference was found between female and male patients in terms of risk factors, age, treatment strategies or intervals between visits (median of 15 days in females and 12 days in males; p = 0.24). Median duration of the PCED was 51 days (IQR 32-130), with a median number of 5 clinical visits (IQR 4-8). Female patients had significantly longer healing times (p = 0.004) and a corresponding increase in the number of clinical visits (median of 7 visits vs. 5 clinical visits in males, p = 0.012).

CONCLUSION

Results from this study suggest female patients with PCED might have a longer corneal epithelial wound healing duration and may therefore require earlier intervention.

Neurotrophic keratopathy and Wallenberg – Zakharchenko syndrome: a clinical case

BACKGROUND: Degenerative changes of cornea after transection of the trigeminal nerve were first described by F. Magendie in 1824. Neurotrophic keratopathy is considered to be an orphan disease which lately has been recognized more and more often. According to literature data, neurotropchic keratopathy affects 5 individuals in 10,000. The diagnosis is difficult due to the lack of information about this condition, the rare occurrence and the presence of a large number of etiological factors. AIM: To determine the causes of the neurotrophic keratopathy development and the treatment tactics in a patient with a neurological disease. The article presents a case of neurotrophic keratopathy in a patient with Wallenberg Zakharchenko syndrome. Because of the fact that neurotrophic keratopathy was diagnosed late and the correct treatment did not start in time, further progression of the pathological process in the cornea could not be avoided. Periodic recurrence of neurotrophic keratopathy is associated with an underlying chronic neurological disease. CONCLUSIONS: Neurotrophic keratopathy requires early diagnosis. In certain clinical cases, for the successful treatment of this pathology, it is necessary to prescribe systemic therapy.

Use of Plasma Rich in Growth Factors and ReGeneraTing Agent Matrix for the Treatment of Corneal Diseases

This study aimed to investigate the use of Plasma Rich in Growth Factors (PRGF) associated with tissue ReGeneraTing Agent (RGTA) drops for the treatment of noninfectious corneal ulcers. RGTA treatment was applied (one drop every two days); however, if ulcer closure was not achieved, PRGF eye drops treatment was added (four times/day). The time taken to reach the ulcer closure, the Best Corrected Visual Acuity (BCVA), intraocular pressure (IOP), Visual Analog Scale (VAS, in terms of frequency and severity of symptoms), and Ocular Surface Disease Index (OSDI) were evaluated. Seventy-four patients (79 eyes) were included, and the mean age was 56.8 ± 17.3 years. The neurotrophic corneal ulcer was the most frequent disorder (n = 27, 34.2%), mainly for herpes virus (n = 15, 19.0%). The time of PRGF eye drops treatment associated with the RGTA matrix was 4.2 ± 2.2 (1.5–9.0) months, and the follow-up period was 44.9 ± 31.5 months. The ulcer closure was achieved in 76 eyes (96.2%). BCVA, VAS and OSDI improved from the baseline (p < 0.001), and IOP remained unchanged (p = 0.665). RGTA and PRGF in noninfectious ulcers were effective and could be a therapeutic alternative for this type of corneal disease.

The management of neurotrophic keratitis

PURPOSE OF REVIEW

The management of neurotrophic keratitis (NK) has evolved in the last decade. The present article reviews updated management guidelines of this entity, as well as future innovations in the field.

RECENT FINDINGS

The advent of confocal microscopy has allowed for the first time to image corneal nerves. In addition, multiple novel topical treatments such as nerve growth factor have improved the prognosis of this disease, with many other in the pipeline. Finally, corneal nerve restoration is now possible with corneal neurotization procedures.

SUMMARY

Many novel treatments based on agents that stimulate nerve regrowth are now available to treat NK. Improvement in neurotization procedures could also address advanced stages of this disease with surgery.

The two-faced effects of nerves and neuropeptides in corneal diseases

Corneal nerves are instrumental to maintain cornea integrity through regulation of key physiological functions such as tear secretion, blink reflex, and neuropeptide turnover. Corneal nerve injury/stimulation can follow many insults including mechanical/chemical trauma, infections and surgeries. Nerve disruption initiates a process named neurogenic inflammation which leads to edema, pain, and recruitment and activation of leukocytes. Interestingly, leukocyte influx in the cornea can further damage nerves by releasing inflammatory mediators-including neuropeptides. The clinical outcome of neuroinflammation can be beneficial or detrimental to corneal integrity. On one side, it ensures prompt wound healing and prevents infections. On the other, prolonged and/or deranged neuroinflammation can permanently disrupt corneal integrity and impair vision. The cornea is an ideal site to study peripheral neuroinflammation and neurogenic inflammation since it receives the highest density of sensory nerves of the entire body. We will review the corneal nerve anatomy and neurochemistry, discuss the beneficial and detrimental effects of neurogenic inflammation in corneal wound healing, inflammatory processes, and pain. We will also examine the emerging remote impact of corneal nerve disruption on the trigeminal ganglion and the brain, highlighting the key role of neuropeptide Substance P. Finally, we will discuss the clinical relevance of such neuroinflammatory network in the context of severe and highly prevalent ocular diseases, including potential treatments.

[Methods and clinical significance of the condition of corneal nerve fibers]

The review provides basic information about embryology, structural features, biochemical composition, functions and classification of corneal nerve fibers, and describes anatomical, histological and functional diagnostic techniques for corneal nerves. Each method for analyzing the structure of the nerve fiber, its advantages and disadvantages are described in detail, including the history of the development of confocal microscopy (laser and light) and esthesiometry (contact and non-contact). The article also presents the criteria according to which the structure of the nerve fiber is estimated using laser confocal microscopy, and the shortcomings of these criteria. Additionally, the article reports on the futility of the use of modern esthesiometry methods.

Temporal evolution of the biological response to laser-induced refractive index change (LIRIC) in rabbit corneas

Laser-induced refractive index change (LIRIC) is a new, non-incisional, non-ablative, femtosecond photo-modification technique being developed for vision correction in humans. Prior, exvivo studies showed intra-tissue refractive index change to induce minimal cell death, restricted to the laser focal zone in the corneal stroma, and with no observable damage to the epithelium or endothelium. Here, we used live rabbits to ascertain longer-term consequences of LIRIC in vivo. Specifically, we assessed cell death, fibrosis, corneal nerve distribution, endothelial cell density, and corneal structure for up to 3 months after LIRIC. A +2.5 D gradient-index LIRIC Fresnel lens was inscribed inside 20 applanated corneas of Dutch Belted rabbits, over a circular region of the mid-stroma measuring 4.5 mm in diameter. Twelve additional rabbit eyes were used as applanation-only controls to differentiate the effects of laser treatment and suction applanation on biological and structural parameters. In vivo optical measurements were performed pre-operatively, then immediately, 2, 4, and 12 weeks after the procedure, to measure endothelial cell density and changes in corneal structure. Groups of four rabbits were sacrificed at 4 hours, 2, 4, and 12 weeks after LIRIC for histological determinations; the TUNEL assay was used to evaluate cell death, H&E staining was used to assess inflammatory infiltration, and immunostaining for α-smooth muscle actin (α-SMA) and βIII tubulin (Tuj-1) was performed to assess myofibroblast differentiation and corneal nerve distribution, respectively. Consistent with prior ex vivo data, only minimal cell death was observed in the laser focal zone, with TUNEL-positive cells restricted to the stromal region of refractive index change 4 h after LIRIC. No TUNEL-positive cells were evident anywhere in the cornea 2, 4, or 12 weeks after LIRIC. Applanation-only corneas were completely TUNEL-negative. Neither LIRIC-treated nor applanation-only eyes exhibited α-SMA-positive staining or altered corneal nerve distributions at any of the time points examined. In vivo confocal imaging revealed normal endothelial cell densities in all eyes (whether LIRIC-treated or applanation-only) at all time points. Optical coherence tomography showed suction applanation to cause a temporary decrease in central corneal thickness, which returned to normal within 4 h. Corneas into which LIRIC Fresnel lenses were written while applanated did not undergo major structural or shape changes beyond the temporary thinning already described for suction applanation. The present findings suggest that LIRIC patterns, which generated a clinically-relevant refractive correction in the mid-stromal region of live rabbit corneas, induced little-to-no disruption to corneal structure and biology for 3 months after the procedure. This affirms the relative safety of LIRIC and predicts that compared to traditional laser vision correction surgeries, common post-operative complications such as dry eye, haze, or patient discomfort may be entirely avoided.

Corneal neurotization for neurotrophic keratopathy: Review of surgical techniques and outcomes

Neurotrophic keratopathy is a degenerative disease in which damage to the corneal nerves leads to corneal hypoesthesia. Injuries to neurotrophic corneas are notoriously difficult to treat and have traditionally been approached with supportive management. However, recent progress in the field of corneal neurotization has given new direction for addressing nerve loss directly by stimulating new nerve growth onto the cornea from nearby sensory nerves transferred to the perilimbal region. Herein, we review the surgical techniques utilized in corneal neurotization, including direct transfers and the use of nerve grafts. Considerations in surgical approach, as well as factors that influence prognosis and outcomes of the surgical intervention are also discussed.

Advances in the Medical Management of Neurotrophic Keratitis

Neurotrophic Keratitis (NK) is a degenerative disorder of the cornea characterized by decreased or absent sensory corneal innervation, corneal epitheliopathy and impaired healing.The clinical presentation of NK can range from persistent epithelial defects to corneal perforation and management is often both challenging and protracted. Historically, the management of NK has consisted of non-specific strategies to facilitate corneal epithelial healing such as lubrication, bandage contact lenses and tarsorrhaphy. Recent advances in the development of therapeutics for NK have provided new and efficacious targeted strategies for its management.In this article, we review recombinant human nerve growth factor (Cenegermin), currently approved for clinical use in the United States and Europe, as well as other promising therapeutic options that are in pre-clinical development such as thymosine β4, connexin43 inhibitors, and artificial extracellular matrix components.

On the Horizon: Biologics and Nutrients for Neurotrophic Keratitis

ABSTRACT

Neurotrophic keratitis (NK), a potentially sight-threatening corneal disease, still does not have a specific treatment. The reduction or complete loss of corneal sensation, the most important factor in its pathogenesis, is one of the most important factors that complicate the treatment of corneal wound healing. In addition, the visual outcome may be adversely affected because of aggressive stromal fibrosis in severe NK cases. Basically, the current management of NK aims to accelerate wound healing and prevent the progression. However, new therapeutic agents, particularly developed depending on cell type-specific healing mechanisms are required for better visual outcomes. In recent years, several studies have started to use new promising areas of translational research, including gene therapy, stem cell therapy, miRNA, and bioengineering. Evidence has emerged that future treatment strategies for NK will be designed by the results of these studies. In this review, it is aimed to summarize scientific data of new treatment modalities for NK.

Nerve Growth Factor as an Ocular Therapy: Applications, Challenges, and Future Directions

Nerve growth factor (NGF), the prototypical neurotrophin first discovered in the 1950s, has recently garnered increased interest as a therapeutic agent promoting neuronal health and regeneration. After gaining orphan drug status within the last decade, NGF-related research and drug development has accelerated. The purpose of this article is to review the preclinical and clinical evidence of NGF in various applications, including central and peripheral nervous system, skin, and ophthalmic disorders. We focus on the ophthalmic applications including not only the FDA-approved indication of neurotrophic keratitis but also retinal disease and glaucoma. NGF represents a promising therapy whose therapeutic profile is evolving. The challenges related to this therapy are reviewed, along with possible solutions and future directions.

Insulin-Like Growth Factor 2 As a Possible Neuroprotective Agent and Memory Enhancer-Its Comparative Expression, Processing and Signaling in Mammalian CNS

A number of studies performed on rodents suggest that insulin-like growth factor 2 (IGF-2) or its analogs may possibly be used for treating some conditions like Alzheimer’s disease, Huntington’s disease, autistic spectrum disorders or aging-related cognitive impairment. Still, for translational research a comparative knowledge about the function of IGF-2 and related molecules in model organisms (rats and mice) and humans is necessary. There is a number of important differences in IGF-2 signaling between species. In the present review we emphasize species-specific patterns of IGF-2 expression in rodents, humans and some other mammals, using, among other sources, publicly available transcriptomic data. We provide a detailed description of Igf2 mRNA expression regulation and pre-pro-IGF-2 protein processing in different species. We also summarize the function of IGF-binding proteins. We describe three different receptors able to bind IGF-2 and discuss the role of IGF-2 signaling in learning and memory, as well as in neuroprotection. We hope that comprehensive understanding of similarities and differences in IGF-2 signaling between model organisms and humans will be useful for development of more effective medicines targeting IGF-2 receptors.

Pigment Epithelium-Derived Factor Peptide Promotes Corneal Nerve Regeneration: An In Vivo and In Vitro Study

Purpose

To investigate the potential of a pigment epithelium-derived factor (PEDF) peptide 44-mer to promote nerve regeneration in a rabbit corneal nerve injury model to demonstrate its neurotrophic ability in cultivated mouse trigeminal neuron cells.

Methods

Subconjunctival or intrastromal injection of 44-mer on the cornea was performed in a rabbit model of corneal nerve injury created by corneal epithelial debridement. Immunocytochemical analysis (44-mer, anti-tubulin III, SMI312, CD11b, and α-SMA) and in vivo confocal microscopy were performed. Corneal sensation was estimated using a Cochet-Bonnet corneal esthesiometer. Primary cultivated mouse trigeminal neurons were used to examine the in vitro neurotrophic ability of 44-mer. The cellular morphology and the immunocytochemical staining with anti-tubulin III and SMI312 in different concentrations of 44-mer were compared, and a quantitative assessment of neurite outgrowth was performed.

Results

Immunohistochemical staining showed the retention of 44-mer in the corneal stroma for at least 7 days after a single dose of corneal intrastromal injection and promoted corneal nerve regeneration revealed by in vivo confocal microscopy. Corneal esthesiometer demonstrated gradual recovery of the corneal sensation in 44-mer-treated eyes with a lower corneal touch threshold than wounded vehicles and closer to baseline at 3 weeks after corneal injury (P < 0.001). In vitro studies showed a dose-dependent neurotrophic effect of 44-mer in cultivated trigeminal neuron cells.

Conclusions

The 44-mer showed in vivo and in vitro corneal neurotrophic abilities. Our results suggest that intrastromal injection of 44-mer into the corneal stroma may have a potential role in treating diseases related to corneal nerve damage.

Role of the Neurokinin-1 Receptor in the Promotion of Corneal Epithelial Wound Healing by the Peptides FGLM-NH2 and SSSR in Neurotrophic Keratopathy

Purpose

Neurotrophic keratopathy is a corneal epitheliopathy induced by trigeminal denervation that can be treated with eyedrops containing the neuropeptide substance P (or the peptide FGLM-NH₂ derived therefrom) and insulin-like growth factor 1 (or the peptide SSSR derived therefrom). Here, we examine the mechanism by which substance P (or FGLM-NH₂) promotes corneal epithelial wound healing in a mouse model of neurotrophic keratopathy.

Methods

The left eye of mice subjected to trigeminal nerve axotomy in the right eye served as a model of neurotrophic keratopathy. Corneal epithelial wound healing was monitored by fluorescein staining and slit-lamp examination. The distribution of substance P, neurokinin-1 receptor (NK-1R), and phosphorylated Akt was examined by immunohistofluorescence analysis. Cytokine and chemokine concentrations in intraocular fluid were measured with a multiplex assay.

Results

Topical administration of FGLM-NH₂ and SSSR promoted corneal epithelial wound healing in the neurotrophic keratopathy model in a manner sensitive to the NK-1R antagonist L-733,060. Expression of substance P and NK-1R in the superficial layer of the corneal epithelium decreased and increased, respectively, in model mice compared with healthy mice. FGLM-NH₂ and SSSR treatment suppressed the production of interleukin-1α, macrophage inflammatory protein 1α (MIP-1α) and MIP-1β induced by corneal epithelial injury in the model mice. It also increased the amount of phosphorylated Akt in the corneal epithelium during wound healing in a manner sensitive to prior L-733,060 administration.

Conclusions

The substance P–NK-1R axis promotes corneal epithelial wound healing in a neurotrophic keratopathy model in association with upregulation of Akt signaling and attenuation of changes in the cytokine-chemokine network.

CORNEAL NEUROTIZATION IN A PATIENT WITH SEVERE NEUROTROPHIC KERATOPATHY. CASE REPORT

PURPOSE

Neurotrophic keratopathy (NK) is a degenerative corneal disease caused by damage to the trigeminal innervation due to a decrease in corneal sensitivity or complete anaesthesia. Impaired corneal innervation leads to morphological and metabolic disorders of the epithelium. In addition, it also leads to the development of recurrent or persistent epithelial defects in corneal ulcers, which may progress to stromal lysis and corneal perforation. One possible solution for severe NK is reinnervation of the anaesthetic cornea (corneal neurotization) using the supraorbital nerve and an autologous sensory nerve graft (indirect neurotization). This article presents the results of corneal neurotization in a young male patient with persistent epithelial defects and corneal ulcers due to corneal denervation.

RESULTS

A 22-year-old man with a history of neurosurgery for astrocytoma of the cerebellum and trunk on the right side at the age of 2 years, was observed for postoperative paresis of the right facial nerve with lagophthalmos in his childhood. The presence of asymptomatic dysfunction of the right trigeminal nerve was also noted. At the age of 22 years, after right eyeball contusion, the vision of the right eye decreased and a persistent epithelial defect developed, followed by corneal ulceration. Due to the exhaustion of therapeutic options in a young patient with corneal anaesthesia, the cornea was reinnervated via the contralateral supraorbital nerve using an autologous sural nerve graft. Five months after the surgery, the sensitivity of the cornea of the right eye began to recover. After amniotic membrane transplantation, the extensive epithelial defect healed, and the opaque corneal stroma gradually cleared up.

CONCLUSION

The reinnervation of the anaesthetic cornea (corneal neurotization) using the supraorbital nerve and the autologous sensory nerve graft represents a new solution for severe NK treatment. The severe corneal condition in our patient healed after the surgery.

How scars shape the neural landscape: Key molecular mediators of TGF-β1's anti-neuritogenic effects

Following injury to the peripheral and central nervous systems, tissue levels of transforming growth factor (TGF)-β1 often increase, which is key for wound healing and scarring. However, active wound regions and scars appear to inhibit process outgrowth by regenerating neurons. We recently showed that corneal wound myofibroblasts block corneal nerve regeneration in vivo, and sensory neurite outgrowth in vitro in a manner that relies critically on TGF-β1. In turn, delayed, abnormal re-innervation contributes to long-term sensory dysfunctions of the ocular surface. Here, we exposed morphologically and biochemically-differentiated sensory neurons from the ND7/23 cell line to TGF-β1 to identify the intracellular signals regulating these anti-neuritogenic effects, contrasting them with those of Semaphorin(Sema)3A, a known inhibitor of neurite outgrowth. Neuronal morphology was quantified using phase-contrast imaging. Western blotting and specific inhibitors were then used to identify key molecular mediators. Differentiated ND7/23 cells expressed neuron-specific markers, including those involved in neurite extension and polarization. TGF-β1 increased phosphorylation of collapsin response mediator protein-2 (CRMP2), a molecule that is key for neurite extension. We now show that both glycogen synthase kinase (GSK)-3β and Smad3 modulate phosphorylation of CRMP2 after treatment with TGF-β1. GSK-3β appeared to exert a particularly strong effect, which could be explained by its ability to phosphorylate not only CRMP2, but also Smad3. In conclusion, TGF-β1's inhibition of neurite outgrowth in sensory neurons appears to be regulated through a highly-conserved signaling pathway, which involves the GSK-3β/CRMP-2 loop via both canonical and non-canonical mechanisms. It is hoped that by defining the signaling pathways that control neurite outgrowth in wound environments, it will become possible to identify optimal molecular targets to promote re-innervation following injury.

The progress in corneal translational medicine

Cornea tissue is in high demand by tissue donation centres globally, and thus tissue engineering cornea, which is the main topic of corneal translational medicine, can serve as a limitless alternative to a donated human cornea tissue. Tissue engineering aims to produce solutions to the challenges associated with conventional cornea tissue, including transplantation and use of human amniotic membrane (HAM), which have issues with storage and immune rejection in patients. Accordingly, by carefully selecting biomaterials and fabrication methods to produce these therapeutic tissues, the demand for cornea tissue can be met, with an improved healing outcome for recipients with less associated harmful risks. In this review paper, we aim to present the recent advancements in the research and clinical applications of cornea tissue, applications including biomaterial selection, fabrication methods, scaffold structure, cellular response to these scaffolds, and future advancements of these techniques.

Corneal Neurotization and Novel Medical Therapies for Neurotrophic Keratopathy

Purpose of Review

Neurotrophic keratopathy (NK) is a degenerative corneal disease characterized by decreased corneal sensibility and impaired corneal healing. In this article, we review surgical techniques for corneal neurotization (CN) and novel medical therapies for the treatment of NK.

Recent Findings

In recent decades, there has been a paradigm shift in the treatment strategies for NK. New minimally invasive direct and indirect CN approaches have demonstrated efficacy at improving best-corrected visual acuity and central corneal sensation while decreasing surgical morbidity. In addition, several targeted medical therapies, such as recombinant human nerve growth factor (rhNGF), regenerating agents (RGTA), and nicergoline, have shown promise in improving corneal epithelial healing. Of these options, cenegermin (Oxervate®, Dompé), a topical biologic medication, has emerged as an approved medical treatment for moderate to severe NK.

Summary

NK is a challenging condition caused by alterations in corneal nerves, leading to impairment in sensory and trophic function with subsequent breakdown of the cornea. Conventional therapy for NK depends on the severity of disease and focuses primarily on protecting the ocular surface. In recent years, numerous CN techniques and novel medical treatments have been developed that aim to restore proper corneal innervation and promote ocular surface healing. Further studies are needed to better understand the long-term efficacy of these treatment options, their target populations, and the potential synergistic efficacy of combined medical and surgical treatments.

Diabetic keratopathy: Insights and challenges

Ocular complications from diabetes mellitus are common. Diabetic keratopathy, the most frequent clinical condition affecting the human cornea, is a potentially sight-threatening condition caused mostly by epithelial disturbances that are of clinical and research attention because of their severity. Diabetic keratopathy exhibits several clinical manifestations, including persistent corneal epithelial erosion, superficial punctate keratopathy, delayed epithelial regeneration, and decreased corneal sensitivity, that may lead to compromised visual acuity or permanent vision loss. The limited amount of clinical studies makes it difficult to fully understand the pathobiology of diabetic keratopathy. Effective therapeutic approaches are elusive. We summarize the clinical manifestations of diabetic keratopathy and discuss available treatments and up-to-date research studies in an attempt to provide a thorough overview of the disorder.

The IGF/Insulin-IGFBP Axis in Corneal Development, Wound Healing, and Disease

The insulin-like growth factor (IGF) family plays key roles in growth and development. In the cornea, IGF family members have been implicated in proliferation, differentiation, and migration, critical events that maintain a smooth refracting surface that is essential for vision. The IGF family is composed of multiple ligands, receptors, and ligand binding proteins. Expression of IGF type 1 receptor (IGF-1R), IGF type 2 receptor (IGF-2R), and insulin receptor (INSR) in the cornea has been well characterized, including the presence of the IGF-1R and INSR hybrid (Hybrid-R) in the corneal epithelium. Recent data also indicates that each of these receptors display unique intracellular localization. Thus, in addition to canonical ligand binding at the plasma membrane and the initiation of downstream signaling cascades, IGF-1R, INSR, and Hybrid-R also function to regulate mitochondrial stability and nuclear gene expression. IGF-1 and IGF-2, two of three principal ligands, are polypeptide growth factors that function in all cellular layers of the cornea. Unlike IGF-1 and IGF-2, the hormone insulin plays a unique role in the cornea, different from many other tissues in the body. In the corneal epithelium, insulin is not required for glucose uptake, due to constitutive activation of the glucose transporter, GLUT1. However, insulin is needed for the regulation of metabolism, circadian rhythm, autophagy, proliferation, and migration after wounding. There is conflicting evidence regarding expression of the six IGF-binding proteins (IGFBPs), which function primarily to sequester IGF ligands. Within the cornea, IGFBP-2 and IGFBP-3 have identified roles in tissue homeostasis. While IGFBP-3 regulates growth control and intracellular receptor localization in the corneal epithelium, both IGFBP-2 and IGFBP-3 function in corneal fibroblast differentiation and myofibroblast proliferation, key events in stromal wound healing. IGFBP-2 has also been linked to cellular overgrowth in pterygium. There is a clear role for IGF family members in regulating tissue homeostasis in the cornea. This review summarizes what is known regarding the function of IGF and related proteins in corneal development, during wound healing, and in the pathophysiology of disease. Finally, we highlight key areas of research that are in need of future study.

The effect of human platelet lysate on corneal nerve regeneration

AIM

This study aimed to test whether human platelet lysate (HPL) has neurotrophic ability for corneal nerve regeneration.

METHODS

We measured the neurotrophic factors in human peripheral serum (HPS) and two commercially available HPLs, UltraGRO and PLTMax. In vitro, we compared the growth rates, neuronal differentiation and immunostaining of neuron markers in mouse neuroblastoma cell line (Neuro-2a) and primary culture of mouse trigeminal ganglion cells that were cultivated in different concentrations of fetal bovine serum, HPS and HPL. In vivo, we created corneal wounds on Sprague Dawley rats with a rotating burr and evaluated the effects of topical HPL on wound healing and corneal nerve regeneration by in vivo confocal microscopy and corneal aesthesiometry.

RESULTS

HPLs had significantly higher concentrations of various neurotrophic factors compared with HPS (p<0.05). In Neuro-2a cells, 3% HPL was better at promoting neuronal growth and differentiation compared with HPS at the same concentration. HPL was also found to have superior neurotrophic effects compared with HPS in primary cultures of mouse trigeminal ganglion cells. In vivo, HPL-treated eyes had better corneal epithelial wound healing rate, nerve regeneration length and corneal touch threshold compared with eyes treated with artificial tears (p<0.05).

CONCLUSION

HPL has significantly higher concentrations of neurotrophic factors compared with HPS. It showed not only in vitro but also in vivo corneal neurotrophic abilities. Our results suggest that HPL may have a potential role in the treatment of diseases related to corneal nerve damage or degeneration.

Recent innovations with drugs in clinical trials for neurotrophic keratitis and refractory corneal ulcers

Introduction: Corneal ulcers normally resolve spontaneously because of the proliferative ability of the corneal epithelium; however, sometimes, epithelial healing is diminished, even when standard treatments are administered. Hence, the treatment of refractory corneal ulcers is challenging and is the subject of ongoing efforts in preclinical and clinical development. Emerging treatment approaches include thymosine β4, CODA001, and topical insulin. Cenegermin eye drops, containing recombinant human nerve growth factor and ReGenerating Agent, a matrix therapy agent, have recently been commercialized for the treatment of moderate to severe neurotrophic keratitis in adults.Areas covered: We describe emerging therapeutic approaches for the management of refractory corneal ulcers and treatments recently introduced to the market. Pubmed and Clinicaltrial.gov databases were first searched including the terms: "corneal ulcer" or "neurotrophic keratopathy" and "treatment." Each treatment was searched in the same databases separately.Expert opinion: Affections of the sensory corneal nerves are the main factor contributing to the pathophysiology of neurotrophic keratopathy; this explains the healing difficulties of this form of ulcer. Cenegermin is a promising therapy acting as a neurotrophic agent for corneal healing. ReGenerating Agent has led to rapid pain relief and corneal healing, but randomized clinical trials are still necessary for further assessment.

In Vivo Confocal Microscopy of Cornea in Patients with Terrien's Marginal Corneal Degeneration

This study was aimed at observing the morphological changes of the cornea with ocular in vivo confocal microscopy (IVCM) in patients with Terrien's marginal degeneration (TMD). Ten patients (20 eyes) with TMD treated in the Department of Ophthalmology, Xiangya Hospital, and 10 healthy controls (20 eyes) were included in the current study. A detailed slit lamp microscopy, anterior segment photography, and corneal IVCM examination were performed for each eye. The density of central and marginal corneal epithelial cells, stromal cells, and subepithelial nerve fibers was compared between the two groups using the Wilcoxon rank sum test. Compared with the control group, the corneal epithelial and endothelial cells in the TMD group showed granular highly reflective substances and thinner subepithelial nerve fibers. The uneven dot-like highly reflective substances without cell structures appeared in the stromal layer of the cornea. The density of central and marginal corneal epithelial cells, stromal cells, and subepithelial nerve fibers was lower in the TMD group (p < 0.05), and they were negatively correlated with severity of the disease (p < 0.05). Our study demonstrated that the density of corneal epithelial cells, stromal cells, and sensory plexus nerve fibers was significantly reduced in the TMD group. The pathological changes were more obvious in the marginal cornea, and it is correlated with severity of the disease.

Corneal Neurotization Improves Ocular Surface Health in a Novel Rat Model of Neurotrophic Keratopathy and Corneal Neurotization

Purpose

Corneal neurotization is a novel surgical procedure to reinnervate the cornea in patients with neurotrophic keratopathy (NK). We developed a rat model of NK and corneal neurotization to further investigate corneal neurotization as a treatment to improve maintenance and healing of the corneal epithelium.

Methods

Thy1-GFP+ Sprague Dawley rats were used to develop the model. Corneal denervation was performed via stereotactic electrocautery of the ophthalmomaxillary branch of the trigeminal nerve. Corneal neurotization was performed by guiding donor sensory axons from the contralateral infraorbital nerve into the cornea via two nerve grafts. Corneal imaging, including nerve density measurements and retrograde labeling were performed to validate the model. In vivo assays of corneal maintenance and repair were used to examine whether treatment with corneal neurotization improved healing in rats with NK.

Results

Corneal neurotization significantly increased corneal axon density in rats with NK (P < 0.01). Retrograde labeling of the cornea in rats with corneal neurotization labeled 206 ± 82 neurons in the contralateral trigeminal ganglion, confirming axons reinnervating the cornea derived from the contralateral infraorbital nerve. Corneal reinnervation after corneal neurotization improved corneal epithelial maintenance and corneal healing after injury (P < 0.01).

Conclusions

Donor nerve fibers reinnervate the insensate cornea after corneal neurotization and significantly improve corneal maintenance and repair. This model can be used to further investigate how corneal neurotization influences epithelial maintenance and repair in the context of NK.

Hyaluronic Acid Combined with Serum Rich in Growth Factors in Corneal Epithelial Defects

The aim of this study is to assess if an adhesive biopolymer, sodium hyaluronate (NaHA), has synergistic effects with s-PRGF (a serum derived from plasma rich in growth factors and a blood derivative that has already shown efficacy in corneal epithelial wound healing), to reduce time of healing or posology. In vitro proliferation and migration studies, both in human corneal epithelial (HCE) cells and in rabbit primary corneal epithelial (RPCE) cultures, were carried out. In addition, we performed studies of corneal wound healing in vivo in rabbits treated with s-PRGF, NaHA, or the combination of both. We performed immunohistochemistry techniques (CK3, CK15, Ki67, ß4 integrin, ZO-1, α-SMA) in rabbit corneas 7 and 30 days after a surgically induced epithelial defect. In vitro results show that the combination of NaHA and s-PRGF offers the worst proliferation rates in both HCE and RPCE cells. Addition of NaHA to s-PRGF diminishes the re-epithelializing capability of s-PRGF. In vivo, all treatments, given twice a day, showed equivalent efficacy in corneal epithelial healing. We conclude that the combined use of s-PRGF and HaNA as an adhesive biopolymer does not improve the efficacy of s-PRGF alone in the wound healing of corneal epithelial defects.

Impact of topical anti-fibrotics on corneal nerve regeneration in vivo

Recent work in vitro has shown that fibroblasts and myofibroblasts have opposing effects on neurite outgrowth by peripheral sensory neurons. Here, we tested a prediction from this work that dampening the fibrotic response in the early phases of corneal wound healing in vivo could enhance reinnervation after a large, deep corneal injury such as that induced by photorefractive keratectomy (PRK). Since topical steroids and Mitomycin C (MMC) are often used clinically for mitigating corneal inflammation and scarring after PRK, they were ideal to test this prediction. Twenty adult cats underwent bilateral, myopic PRK over a 6 mm optical zone followed by either: (1) intraoperative MMC (n = 12 eyes), (2) intraoperative prednisolone acetate (PA) followed by twice daily topical application for 14 days (n = 12 eyes), or (3) no post-operative treatment (n = 16 eyes). Anti-fibrotic effects of MMC and PA were verified optically and histologically. First, optical coherence tomography (OCT) performed pre-operatively and 2, 4 and 12 weeks post-PRK was used to assess changes in corneal backscatter reflectivity. Post-mortem immunohistochemistry was then performed at 2, 4 and 12 weeks post-PRK, using antibodies against α-smooth muscle actin (α-SMA). Finally, immunohistochemistry with antibodies against βIII-tubulin (Tuj-1) was performed in the same corneas to quantify changes in nerve distribution relative to unoperated, control cat corneas. Two weeks after PRK, untreated corneas exhibited the greatest amount of staining for α-SMA, followed by PA-treated and MMC-treated eyes. This was matched by higher OCT-based stromal reflectivity values in untreated, than PA- and MMC-treated eyes. PA treatment appeared to slow epithelial healing and although normal epithelial thickness was restored by 12 weeks-post-PRK, intra-epithelial nerve length only reached ∼1/6 normal values in PA-treated eyes. Even peripheral cornea (outside the ablation zone) exhibited depressed intra-epithelial nerve densities after PA treatment. Stromal nerves were abundant under the α-SMA zone, but appeared to largely avoid it, creating an area of sub-epithelial stroma devoid of nerve trunks. In turn, this may have led to the lack of sub-basal and intra-epithelial nerves in the ablation zone of PA-treated eyes 4 weeks after PRK, and their continuing paucity 12 weeks after PRK. Intra-operative MMC, which sharply decreased α-SMA staining, was followed by rapid restoration of nerve densities in all corneal layers post-PRK compared to untreated corneas. Curiously, stromal nerves appeared unaffected by the development of large, stromal, acellular zones in MMC-treated corneas. Overall, it appears that post-PRK treatments that were most effective at reducing α-SMA-positive cells in the early post-operative period benefited nerve regeneration the most, resulting in more rapid restoration of nerve densities in all corneal layers of the ablation zone and of the corneal periphery.

Post-herpes neurotrophic keratopathy: Aetiopathogenesis, clinical signs and current therapies

Neurotrophic keratopathy (NK) is a degenerative corneal disease caused by damage of trigeminal innervation. This leads to epithelial defects, ulceration and, eventually, perforation. Both herpes simplex and varicella zoster keratitis are reported to be the main causes of NK. Furthermore, prognosis in this type of NK is poor. Classic clinical findings in post-herpes NK are spontaneous epithelial breakdown, round and central epithelial defects with smooth edges, stromal melting and thinning, scarring, and neovascularisation. Although several medical and surgical treatments have been reported, no therapies are currently available to definitely restore corneal sensitivity. Therefore, NK remains a challenging disease to treat. In this review a summary is presented of the pathogenesis, manifestations, and current management of post-herpes NK. The role of antiviral treatment and varicella-zoster vaccination is also discussed. A description is also presented on both medical and surgical novel therapies, such as regenerative drugs and corneal neurotization.

Neprilysin inhibition promotes corneal wound healing

Neprilysin (NEP), an ectoenzyme that modulates inflammation by degrading neuropeptides, was recently identified in the human corneal epithelium. The cornea expresses many NEP substrates, but the function of NEP in homeostatic maintenance and wound healing of the cornea is unknown. We therefore investigated the role of this enzyme under naive and injured conditions using NEP-deficient (NEP-/-) and wild type (WT) control mice. In vivo ocular surface imaging and histological analysis of corneal tissue showed no differences in limbal vasculature or corneal anatomy between naive NEP-/- and WT mice. Histological examination revealed increased corneal innervation in NEP-/- mice. In an alkali burn model of corneal injury, corneal wound healing was significantly accelerated in NEP-/- mice compared to WT controls 3 days after injury. Daily intraperitoneal administration of the NEP inhibitor thiorphan also accelerated corneal wound healing after alkali injury in WT mice. Collectively, our data identify a previously unknown role of NEP in the cornea, in which pharmacologic inhibition of its activity may provide a novel therapeutic option for patients with corneal injury.