Corneal collagen as a potential therapeutic target in dry eye disease

A highly selective inhibitor of discoidin domain receptor-1 (DDR1-IN-1) protects corneal epithelial cells from YAP/ACSL4-mediated ferroptosis in dry eye

BACKGROUND AND PURPOSE

This study investigated the involvement of discoidin domain receptor (DDR) in dry eye and assessed the potential of specific DDR inhibitors as a therapeutic strategy for dry eye by exploring the underlying mechanism.

EXPERIMENTAL APPROACH

Dry eye was induced in Wistar rats by applying 0.2% benzalkonium chloride (BAC), after which rats were treated topically for 7 days with DDR1-IN-1, a selective inhibitor of DDR1. Clinical manifestations of dry eye were assessed on Day-7 post-treatment. Histological evaluation of corneal damage was performed using haematoxylin and eosin (H&E) staining. In vitro, immortalized human corneal epithelial cells (HCECs) exposed to hyperosmotic stress (HS) were treated with varying doses of DDR1-IN-1 for 24 h. The levels of lipid peroxidation in dry eye corneas or HS-stimulated HCECs were assessed. Protein levels of DDR1/DDR2 and related pathways were detected by western blotting. The cellular distribution of acyl-CoA synthetase long chain family member 4 (ACSL4) and Yes-associated protein (YAP) was evaluated using immunohistochemistry or immunofluorescent staining.

KEY RESULTS

In dry eye corneas, only DDR1 expression was significantly up-regulated compared with normal controls. DDR1-IN-1 treatment significantly alleviated dry eye symptoms in vivo. The treatment remarkably reduced lipid hydroperoxide (LPO) levels and suppressed the expression of ferroptosis markers, particularly ACSL4. Overexpression or reactivation of YAP diminished the protective effects of DDR1-IN-1, indicating the involvement of the Hippo/YAP pathway in DDR1-targeted therapeutic effects.

CONCLUSIONS AND IMPLICATIONS

This study confirms the significance of DDR1 in dry eye and highlights the potential of selective DDR1 inhibitor(s) for dry eye treatment.

A Phase 2 Trial to Test Safety and Efficacy of ST-100, a Unique Collagen Mimetic Peptide Ophthalmic Solution for Dry Eye Disease

Objective

Dry eye disease (DED) is a worldwide source of ocular discomfort. This first-in-human phase 2 clinical study determined the efficacy of treating signs and symptoms of DED using an ophthalmic solution of synthesized mimetic of human collagen (ST-100).

Design

This double-masked, randomized, study compared high (60 μg/mL) and low (22 μg/mL) dose ST-100 to vehicle utilizing the Ora, Inc. Controlled Adverse Environment (CAE) during a 28-day period.

Participants

Participants included males and females ≥ 18 years of age with signs and symptoms of DED for ≥ 6 months that worsened during CAE exposure who were not taking any topical prescription therapeutic.

Intervention

Participants applied ST-100 or vehicle placebo topically to both corneas (1 drop) twice daily via a blow-fill-sealed preservative-free container.

Main Outcome Measures

The prespecified primary efficacy sign end point was mean change from baseline (CFB) in total corneal fluorescein staining, and the primary symptom end point was mean CFB in ocular discomfort. A secondary prespecified efficacy end point was CFB in unanesthetized Schirmer's test for tear film production.

Results

Of 160 subjects in the intent-to-treat population (112 female, 48 male, median age 64), 146 completed the study. Total corneal fluorescein staining CFB improved for high-dose ST-100, with superiority over vehicle when both eyes were considered together (2-sample t test: P = 0.0394). High-dose ST-100 was superior to vehicle in Schirmer's CFB for the study eye (least squares mean difference [confidence interval] = 2.3 [0.6, 4.0], P = 0.0094). For study eyes, the proportion of Schirmer's test responders (CFB ≥ 10 mm, Schirmer's responder rate) was 12.2% for high-dose ST-100 versus 0.0% for vehicle (P = 0.0266). The CFB for ocular discomfort score improved in study eyes for high- and low-dose ST-100 (paired t test, P = 0.0133, P = 0.0151, respectively) but without superiority over vehicle (ANCOVA: P = 0.5696, P = 0.8968, respectively). ST-100 Schirmer's responders also demonstrated total elimination of worsening of corneal fluorescein stain during the stress of CAE sessions.

Conclusions

ST-100 significantly improved tear production and related outcomes in DED and was well-tolerated in reducing symptoms.

Financial Disclosures

Proprietary or commercial disclosure may be found in the Footnotes and Disclosures at the end of this article.

Novel treatments for dry eye syndrome

Dry eye syndrome (DES) is a prevalent and multifactorial disease that leads to a self-perpetuating cycle of inflammation and damage to the ocular surface. This results in symptoms such as redness, burning, and blurred vision, which can negatively affect a patient's quality of life. While treatments are available to manage DES, they only temporarily relieve symptoms. Furthermore, long-term use of certain medications can cause harm to the ocular surface. Therefore, there is a need for safer and effective treatments for DES. This review highlights the latest advancements in DES therapy, providing valuable insights into ongoing efforts to improve patient outcomes.

Smart coating by thermo-sensitive Pluronic F-127 for enhanced corneal healing via delivery of biological macromolecule progranulin

As a leading cause of vision impairment and blindness, corneal alkali burns lead to long-term visual deterioration or even permanent visual impairment while effective treatment strategies remain a challenge. Herein, a thermo-sensitive hydrogel with the combination of multi-functional protein progranulin (PGRN), a biological macromolecule consisting of several hundred amino acids and possessing a high molecular weight, is efficiently prepared through a convenient stirring and mixing at the low temperature. The hydrogel can be easily administrated to the ocular surface contacting with the cornea, which can be immediately transformed into gel-like state due to the thermo-responsive behavior, realizing a site-specific coating to isolate further external stimulation. The smart coating not only exhibits excellent transparency and biocompatibility, but also presents a constant delivery of PGRN, creating a nutritious and supportive micro-environment for the ocular surface. The results show that the prepared functional hydrogel can efficiently suppress inflammation, accelerate re-epithelization, and intriguingly enhance axonal regeneration via modulation of multiple signaling pathways, indicating the novel designed HydrogelPGRN is a promising therapy option for serious corneal injury.

Collagen mimetic peptide repair of the corneal nerve bed in a mouse model of dry eye disease

The intraepithelial sub-basal nerve plexus of the cornea is characterized by a central swirl of nerve processes that terminate between the apical cells of the epithelium. This plexus is a critical component of maintaining homeostatic function of the ocular surface. The cornea contains a high concentration of collagen, which is susceptible to damage in conditions such as neuropathic pain, neurotrophic keratitis, and dry eye disease. Here we tested whether topical application of a collagen mimetic peptide (CMP) is efficacious in repairing the corneal sub-basal nerve plexus in a mouse model of ocular surface desiccation. We induced corneal tear film reduction, epithelial damage, and nerve bed degradation through a combination of environmental and pharmaceutical (atropine) desiccation. Mice were subjected to desiccating air flow and bilateral topical application of 1% atropine solution (4× daily) for 2 weeks. During the latter half of this exposure, mice received topical vehicle [phosphate buffered saline (PBS)] or CMP [200 μm (Pro-Pro-Gly)₇, 10 μl] once daily, 2 h prior to the first atropine treatment for that day. After euthanasia, cornea were labeled with antibodies against βIII tubulin to visualize and quantify changes to the nerve bed. For mice receiving vehicle only, the two-week desiccation regimen reduced neuronal coverage of the central sub-basal plexus and epithelial terminals compared to naïve, with some corneas demonstrating complete degeneration of nerve beds. Accordingly, both sub-basal and epithelial βIII tubulin-labeled processes demonstrated increased fragmentation, indicative of nerve disassembly. Treatment with CMP significantly reduced nerve fragmentation, expanded both sub-basal and epithelial neuronal coverage compared to vehicle controls, and improved corneal epithelium integrity, tear film production, and corneal sensitivity. Together, these results indicate that topical CMP significantly counters neurodegeneration characteristic of corneal surface desiccation. Repairing underlying collagen in conditions that damage the ocular surface could represent a novel therapeutic avenue in treating a broad spectrum of diseases or injury.

Collagen as a Biomaterial for Skin and Corneal Wound Healing

The cornea and the skin are two organs that form the outer barrier of the human body. When either is injured (e.g., from surgery, physical trauma, or chemical burns), wound healing is initiated to restore integrity. Many cells are activated during wound healing. In particular, fibroblasts that are stimulated often transition into repair fibroblasts or myofibroblasts that synthesize extracellular matrix (ECM) components into the wound area. Control of wound ECM deposition is critical, as a disorganized ECM can block restoration of function. One of the most abundant structural proteins in the mammalian ECM is collagen. Collagen type I is the main component in connective tissues. It can be readily obtained and purified, and short analogs have also been developed for tissue engineering applications, including modulating the wound healing response. This review discusses the effect of several current collagen implants on the stimulation of corneal and skin wound healing. These range from collagen sponges and hydrogels to films and membranes.

Collagen Mimetic Peptides Promote Adherence and Migration of ARPE-19 Cells While Reducing Inflammatory and Oxidative Stress

Epithelial cells of multiple types produce and interact with the extracellular matrix to maintain structural integrity and promote healthy function within diverse endogenous tissues. Collagen is a critical component of the matrix, and challenges to collagen’s stability in aging, disease, and injury influence survival of adherent epithelial cells. The retinal pigment epithelium (RPE) is important for maintaining proper function of the light-sensitive photoreceptors in the neural retina, in part through synergy with the collagen-rich Bruch’s membrane that promotes RPE adherence. Degradation of Bruch’s is associated with RPE degeneration, which is implicated early in age-related macular degeneration, a leading cause of irreversible vision loss worldwide. Collagen mimetic peptides (CMPs) effectively repair damage to collagen helices, which are present in all collagens. Our previous work indicates that in doing so, CMPs promote survival and integrity of affected cells and tissues in models of ocular injury and disease, including wounding of corneal epithelial cells. Here, we show that CMPs increase adherence and migration of the ARPE-19 line of human RPE cells challenged by digestion of their collagen substrate. Application of CMPs also reduced both ARPE-19 secretion of pro-inflammatory cytokines (interleukins 6 and 8) and production of reactive oxygen species. Taken together, these results suggest that repairing collagen damaged by aging or other pathogenic processes in the posterior eye could improve RPE adherence and survival and, in doing so, reduce the inflammatory and oxidative stress that perpetuates the cycle of destruction at the root of age-related diseases of the outer retina.

Intraocular Delivery of a Collagen Mimetic Peptide Repairs Retinal Ganglion Cell Axons in Chronic and Acute Injury Models

Vision loss through the degeneration of retinal ganglion cell (RGC) axons occurs in both chronic and acute conditions that target the optic nerve. These include glaucoma, in which sensitivity to intraocular pressure (IOP) causes early RGC axonal dysfunction, and optic nerve trauma, which causes rapid axon degeneration from the site of injury. In each case, degeneration is irreversible, necessitating new therapeutics that protect, repair, and regenerate RGC axons. Recently, we demonstrated the reparative capacity of using collagen mimetic peptides (CMPs) to heal fragmented collagen in the neuronal extracellular milieu. This was an important step in the development of neuronal-based therapies since neurodegeneration involves matrix metalloproteinase (MMP)-mediated remodeling of the collagen-rich environment in which neurons and their axons exist. We found that intraocular delivery of a CMP comprising single-strand fractions of triple helix human type I collagen prevented early RGC axon dysfunction in an inducible glaucoma model. Additionally, CMPs also promoted neurite outgrowth from dorsal root ganglia, challenged in vitro by partial digestion of collagen. Here, we compared the ability of a CMP sequence to protect RGC axons in both inducible glaucoma and optic nerve crush. A three-week +40% elevation in IOP caused a 67% degradation in anterograde transport to the superior colliculus, the primary retinal projection target in rodents. We found that a single intravitreal injection of CMP during the period of IOP elevation significantly reduced this degradation. The same CMP delivered shortly after optic nerve crush promoted significant axonal recovery during the two-week period following injury. Together, these findings support a novel protective and reparative role for the use of CMPs in both chronic and acute conditions affecting the survival of RGC axons in the optic projection to the brain.

Restoring the Extracellular Matrix: A Neuroprotective Role for Collagen Mimetic Peptides in Experimental Glaucoma

Optic neuropathies are a major cause of visual disabilities worldwide, causing irreversible vision loss through the degeneration of retinal ganglion cell (RGC) axons, which comprise the optic nerve. Chief among these is glaucoma, in which sensitivity to intraocular pressure (IOP) leads to RGC axon dysfunction followed by outright degeneration of the optic projection. Current treatments focus entirely on lowering IOP through topical hypotensive drugs, surgery to facilitate aqueous fluid outflow, or both. Despite this investment in time and resources, many patients continue to lose vision, underscoring the need for new therapeutics that target neurodegeneration directly. One element of progression in glaucoma involves matrix metalloproteinase (MMP) remodeling of the collagen-rich extracellular milieu of RGC axons as they exit the retina through the optic nerve head. Thus, we investigated the ability of collagen mimetic peptides (CMPs) representing various single strand fractions of triple helix human type I collagen to protect RGC axons in an inducible model of glaucoma. First, using dorsal root ganglia maintained in vitro on human type I collagen, we found that multiple CMPs significantly promote neurite outgrowth (+35%) compared to vehicle following MMP-induced fragmentation of the α1(I) and α2(I) chains. We then applied CMP to adult mouse eyes in vivo following microbead occlusion to elevate IOP and determined its influence on anterograde axon transport to the superior colliculus, the primary RGC projection target in rodents. In glaucoma models, sensitivity to IOP causes early degradation in axon function, including anterograde transport from retina to central brain targets. We found that CMP treatment rescued anterograde transport following a 3-week +50% elevation in IOP. These results suggest that CMPs generally may represent a novel therapeutic to supplement existing treatments or as a neuroprotective option for patients who do not respond to IOP-lowering regimens.

Collagen Mimetic Peptides Promote Corneal Epithelial Cell Regeneration

The cornea of the eye is at risk for injury through constant exposure to the extraocular environment. A highly collagenous structure, the cornea contains several different types distributed across multiple layers. The anterior-most layer contains non-keratinized epithelial cells that serve as a barrier to environmental, microbial, and other insults. Renewal and migration of basal epithelial cells from the limbus involve critical interactions between secreted basement membranes, composed primarily of type IV collagen, and underlying Bowman's and stromal layers, which contain primarily type I collagen. This process is challenged in many diseases and conditions that insult the ocular surface and damage underlying collagen. We investigated the capacity of a collagen mimetic peptide (CMP), representing a fraction of a single strand of the damaged triple helix human type I collagen, to promote epithelial healing following an acute corneal wound. In vitro, the collagen mimetic peptide promoted the realignment of collagen damaged by enzymic digestion. In an in vivo mouse model, topical application of a CMP-containing formulation following a 360° lamellar keratectomy targeting the corneal epithelial layer accelerated wound closure during a 24 h period, compared to vehicle. We found that the CMP increased adherence of the basal epithelium to the underlying substrate and enhanced density of epithelial cells, while reducing variability in the regenerating layer. These results suggest that CMPs may represent a novel therapeutic to heal corneal tissue by repairing underlying collagen in conditions that damage the ocular surface.