Diabetic keratopathy: Insights and challenges

Interconnections between diabetic corneal neuropathy and diabetic retinopathy: diagnostic and therapeutic implications

Diabetic corneal neuropathy and diabetic retinopathy are ocular complications occurring in the context of diabetes mellitus. Diabetic corneal neuropathy refers to the progressive damage of corneal nerves. Diabetic retinopathy has traditionally been considered as damage to the retinal microvasculature. However, growing evidence suggests that diabetic retinopathy is a complex neurovascular disorder resulting from dysfunction of the neurovascular unit, which includes both the retinal vascular structures and neural tissues. Diabetic retinopathy is one of the leading causes of blindness and is frequently screened for as part of diabetic ocular screening. However, diabetic corneal neuropathy is commonly overlooked and underdiagnosed, leading to severe ocular surface impairment. Several studies have found that these two conditions tend to occur together, and they share similarities in their pathogenesis pathways, being triggered by a status of chronic hyperglycemia. This review aims to discuss the interconnection between diabetic corneal neuropathy and diabetic retinopathy, whether diabetic corneal neuropathy precedes diabetic retinopathy, as well as the relation between the stage of diabetic retinopathy and the severity of corneal neuropathy. We also endeavor to explore the relevance of a corneal screening in diabetic eyes and the possibility of using corneal nerve measurements to monitor the progression of diabetic retinopathy.

Oxygen uptake at the ocular surface in diabetic animals is impaired in response to central corneal injury

Poor wound healing is one of the most devastating complications in late-stage diabetic patients. The avascular cornea does not rely on circulation for its oxygen consumption, uptaking it mainly from the atmosphere. Previous studies demonstrated that oxygen uptake (O2U) in diabetic experimental animals and patients is significantly lower than in the non-diabetic condition. Our recent experiments show that upon wounding of the central cornea the O2U decreased across the ocular surface, followed by two increases at 6-24 h, and at 72 h, which appeared to be important for proper wound healing. It is however not known whether the two distinct O2U increases are maintained in diabetic ocular surface in response to corneal injury. In this study, we used an optic-fiber oxygen micro-sensor to measure O2U across the ocular surface of streptozotocin (STZ)- induced diabetic mice and age-matched control mice following injury to the central cornea. We found that the injury causes an immediate and substantial reduction of O2U across the ocular surface. O2U in non-diabetic corneas increases at 2-6 h post wounding (hpw), decreasing again before the second rise to peak at 72 hpw, especially at the limbus. O2U in the diabetic cornea decreases more markedly than that of non-diabetic control. This defective diabetic O2U persisted, precluding the two dynamic rises in O2U, leading to a failure in recovery. Altogether, our results suggest a previously unknown mechanism of a defective O2U response to injury in the diabetic ocular surface, which warrants further research and may lead to new therapeutic paths.

Pigment epithelium-derived factor (PEDF) promotes survival and contraction of myoepithelial cells in lacrimal gland

PEDF is critical for general health of the ocular surface. In order to study mechanisms of PEDF's action in lacrimal gland (LG) secretion, these visual structures were studied in a PEDF deficient (Pedf-/-) mouse model using biochemical, histochemical, and morphometric analyses. In Pedf-/- animals there were several ocular surface and LG disturbances not seen in controls. Notably, changes in body and LG weight, corneal sensitivity, tear film, ocular surface damage, and size of acini comprising the LG were evident. Survival of myoepithelial cells (MECs) surrounding the acini showed a PEDF survival dependence as there were significant reduction in MEC-specific P63 cells and Bcl2 expression levels, and increased TUNEL positive cells in PEDF deficient mice. Expression levels of the major contractile MEC proteins, α-SMA, calponin, and keratin 14, were also reduced with PEDF gene deletion and MECs contraction apparatus impaired, since oxytocin significantly reduced acinar area in controls but had no effect in PEDF deficient LGs, although the oxytocin receptor (OXTR) was expressed in both PEDF genotypes. These findings suggest that PEDF is essential to MECs survival and contractile function, and tear homeostasis on the ocular surface. Treatment with PEDF is likely to alleviate ocular-related conditions in diseases associated with dry eye as well as promote healthy MEC cell function in other secretory glands of the body.

CD4+CD25- T-Cell-Secreted IFN-γ Promotes Corneal Nerve Degeneration in Diabetic Mice

Purpose

This study aimed to explore the relationship between corneal nerve degeneration and elevated dendritic cells (DCs) in diabetic keratopathy.

Methods

Corneas from diabetic and healthy mice were analyzed using single-cell RNA sequencing. Corneal nerve density and DC and T-cell infiltration were quantified through whole-mount corneal staining. Freshly isolated mouse trigeminal ganglion (TG) neurons were co-cultured with immature DCs, mature DCs, activated CD8+ T cells, and CD4+CD25- T cells. TG neurite outgrowth was assessed to identify potential effector cells driving corneal nerve degeneration. In addition, interferon-gamma (IFN-γ) and blocking antibodies were used to evaluate their effects on TG neurite outgrowth and corneal nerve degeneration in mice.

Results

Compared with age-matched healthy mice, diabetic mice exhibited a significant reduction in corneal nerve density and sensitivity, along with increased infiltration of DCs, CD4+ T cells, and CD8+ T cells. In vitro co-culture experiments revealed that CD4+CD25- T cells, rather than DCs and CD8+ T cells, significantly inhibited TG neurite outgrowth. Among cytokines, elevated IFN-γ in diabetic corneas impaired TG neurite outgrowth and induced corneal nerve degeneration, whereas IL-4 and IL-17 had no such effect. Blocking IFN-γ alleviated CD4+CD25- T-cell-induced inhibition of TG neurite outgrowth and corneal nerve degeneration in diabetic mice.

Conclusions

CD4+CD25- T cells, but not DCs or CD8+ T cells, contribute to corneal nerve degeneration in diabetic mice, a process partially mediated by IFN-γ.

Mesenchymal stem cell-derived exosomes carry miR-125a-5p to improve diabetic keratopathy by regulating endoplasmic reticulum stress

BACKGROUND

Diabetic keratopathy is a prevalent but sometimes ignored visual condition in diabetic patients, which significantly affects patients with diabetes mellitus (DM) in terms of their visual acuity. Exosomes regulate diabetes-related conditions like diabetic keratopathy (DK) by secreting their components into the body.

OBJECTIVE

Aim to investigate the effect and mechanism of mesenchymal stem cell (MSC)-derived exosome miR-125a-5p on DK.

METHODS

Transmission electron microscopy, along with nanoparticle tracking analysis, was used to determine the morphology and size of exosomes. To evaluate cell viability, proliferation, and migration, Western blotting and RT-qPCR methods were used. CCK-8, cell cloning, and scratch assays were used to measure protein levels and mRNA expression.

RESULTS

High glucose treatment of corneal epithelial cells weakened cell viability, proliferation and migration, and the level of miR-125a-5p was significantly reduced. It has been proposed that elevated levels of miR-125a-5p could enhance cell viability, proliferation, and migration, can inhibit endoplasmic reticulum stress induced by high glucose, which is the same as the effect of endoplasmic reticulum stress inhibitors.

CONCLUSION

Mouse bone marrow MSC-derived exosome miR-125a-5p repairs corneal epithelial cell viability and proliferation as well as migration ability to improve DK by inhibiting high glucose-induced endoplasmic reticulum stress.

Fabrication of a 3D Corneal Model Using Collagen Bioink and Human Corneal Stromal Cells

Corneal transplantation remains a critical treatment option for individuals with corneal disorders, but it faces challenges such as rejection, high associated medical costs, and donor scarcity. A promising alternative for corneal replacement involves fabricating artificial cornea from a patient's own cells. Our study aimed to leverage bioprinting to develop a corneal model using human corneal stromal cells embedded in a collagen-based bioink. We generated both cellular and acellular collagen I (COL I) constructs. Cellular constructs were cultured for up to 4 weeks, and gene expression analysis was performed to assess extracellular matrix (ECM) remodeling and fibrotic markers. Our results demonstrated a significant decrease in the expression of COL I, collagen III (COL III), vimentin (VIM), and vinculin (VCL), indicating a dynamic remodeling process towards a more physiologically relevant corneal ECM. Overall, our study provides a foundational framework for developing customizable, corneal replacements using bioprinting technology. Further research is necessary to optimize the bioink composition and evaluate the functional and biomechanical properties of these bioengineered corneas.

Norepinephrine regulates epithelial-derived neurotrophins expression and sensory nerve regeneration through ADRB2 receptor

Norepinephrine (NE) is mainly released by sympathetic nerve terminals to act on organs and tissues. After corneal epithelial debridement, we found that the sympathetic nerve fibers penetrated the limbus and regenerated toward the cornea within 24 h post-wounding. Topical NE application recapitulated the characteristics of delayed corneal epithelial wound healing and nerve regeneration in healthy mice, accompanied by the partial depletion of multiple neurotrophins, such as nerve growth factor and glial cell-derived nerve growth factor. Moreover, the diabetes mellitus (DM) mice exhibited corneal sensory nerve dysfunction and increased plasma and corneal NE contents, which were rescued by 6-hydroxydopamine (6-OHDA) and bretylium. In the cell culture model, the conditioned medium of NE-treated corneal epithelial cells inhibited trigeminal ganglion (TG) neurite outgrowth, which was reversed by the β2 adrenergic receptor (ADRB2) antagonist, but not by the β1 adrenergic receptor (ADRB1) antagonist. Topical application of the ADRB2 antagonist recovered the expression of corneal neurotrophins, and promoted corneal epithelial and nerve regeneration in DM mice. Taken together, the NE-ADRB2 axis regulates corneal neurotrophin expression and nerve regeneration in mice. Topical application of the ADRB2 antagonist may represent a promising therapeutic strategy for diabetic corneal sensory nerve dysfunction.

Cornea Oculomics: A Clinical Blueprint for Extending Corneal Diagnostics and Artificial Intelligence in Systemic Health Insights

Oculomics is an emerging field that leverages ophthalmic imaging data to identify biomarkers of systemic disease, facilitating early diagnosis and risk stratification. Despite its growing recognition, gaps remain in the literature regarding the clinical applications of oculomics. Various systemic diseases-including metabolic disorders (e.g., diabetes mellitus), infectious diseases (e.g., COVID-19), neurodegenerative diseases (e.g., dementia), hematologic disorders (e.g., thalassemia), autoimmune conditions (e.g., rheumatoid arthritis), and genetic syndromes (e.g., Fabry disease)-exhibit ocular manifestations detectable through in vivo confocal microscopy and anterior segment optical coherence tomography, among other imaging modalities. Increasing evidence supports the role of corneal imaging in identifying systemic disease biomarkers, a process further enhanced by artificial intelligence-driven analyses. This review synthesizes the current findings on corneal biomarkers of systemic disease, their ophthalmic imaging correlates, and the expanding role of corneal oculomics in translational medicine. Additionally, we explore future directions for integrating oculomics into clinical practice and biomedical research.

Decoding the corneal immune microenvironment in healthy and diabetic mice during corneal wound healing

Diabetic keratopathy (DK) is an underdiagnosed ocular complication of diabetes mellitus. The changes of ocular immune microenvironment contribute to the pathogenesis of DK, while precise mechanisms remain inadequately understood. Here, we employed single-cell RNA sequencing (scRNA-seq) to elucidate the transcriptional alterations of immune cells from diabetic and healthy control mouse corneas during homeostasis and wound healing. Unbiased clustering analysis unveiled 3 major cell subsets and 11 subdivided cell clusters, including T cells, monocyte lineages, and neutrophil subpopulations. The further sub-clustering analysis demonstrated that T cells exhibited cytotoxicity characteristics in both homeostasis and wound healing of diabetic cornea. Moreover, dendritic cells preferred the migratory and maturation phenotype and may recruit and maintain cytotoxic T cells. Macrophages in diabetic cornea preferred the pro-inflammatory M1 phenotype. Under injury conditions, diabetic corneal neutrophils exhibited a more mature and functional possession of neutrophil extracellular traps (NETs). Furthermore, cell-cell communication revealed that the immune cells exhibited hyperactivation and pro-inflammatory responses, while the monocyte lineages exhibited the activating effect on T cells in diabetic cornea. This study represents the inaugural effort to establish a comprehensive scRNA-Seq transcriptomic profile of corneal immune cells during wound healing in healthy and diabetic mice, which offers a valuable reference for subsequent investigations into the pathological roles of immune cells in DK.

Novel full-thickness biomimetic corneal model for studying pathogenesis and treatment of diabetic keratopathy

Diabetic keratopathy (DK), a significant complication of diabetes, often leads to corneal damage and vision impairment. Effective models are essential for studying DK pathogenesis and evaluating potential therapeutic interventions. This study developed a novel biomimetic full-thickness corneal model for the first time, incorporating corneal epithelial cells, stromal cells, endothelial cells, and nerves to simulate DK conditions in vitro. By exposing the model to a high-glucose (HG) environment, the pathological characteristics of DK, including nerve bundle disintegration, compromised barrier integrity, increased inflammation, and oxidative stress, were successfully replicated. Transcriptomic analysis revealed that HG downregulated genes associated with axon and synapse formation while upregulating immune response and oxidative stress pathways, with C-C Motif Chemokine Ligand 5 (CCL5) identified as a key hub gene in DK pathogenesis. The therapeutic effects of Lycium barbarum glycopeptide (LBGP) were evaluated using this model and validated in db/db diabetic mice. LBGP promoted nerve regeneration, alleviated inflammation and oxidative stress in both in vitro and in vivo models. Notably, LBGP suppressed the expression of CCL5, highlighting its potential mechanism of action. This study establishes a robust biomimetic platform for investigating DK and other corneal diseases, and identifies LBGP as a promising therapeutic candidate for DK. These findings provide valuable insights into corneal disease mechanisms and pave the way for future translational research and clinical applications.

PI3K signaling and lysyl oxidase is critical to corneal stroma fibrosis following mustard gas injury

Sulfur mustard gas (SM), an alkylating and vesicating agent, has been used frequently in many wars and conflicts. SM exposure to the eye results in several corneal abnormalities including scar/fibrosis formation. However, molecular mechanism for SM induced corneal fibrosis development is poorly understood. After SM insult to the eye, excessive synthesis/secretion of extracellular matrix components (ECM) including collagen (COL) I, COL III, and lysyl oxidase (LOX) by corneal myofibroblasts causes corneal fibrosis, however, precise mechanism remains elusive. This study tested the hypothesis that Phosphoinositide 3-kinase (PI3K) signaling alterations post SM in cornea enhances stromal ECM synthesis and corneal fibrosis. New Zealand White Rabbits were used. The right eyes were exposed to SM (200 mg-min/m3) and left eye to the air for 8min at MRI Global. Rabbit corneas were collected on day-3, day-7, and day-14 for molecular analysis. SM exposure caused a significant increase in mRNA expression of PI3K, AKT, COL I, COL III, and LOX and protein levels of LOX in a time-dependent manner in rabbit corneas. The in vitro studies were performed with human corneal stromal fibroblasts (hCSFs) by growing cultures in -/+ nitrogen mustard (NM) and LY294002, a PI3K specific inhibitor, for 30min, 8h, 24h, 48h, and 72h. NM significantly increased mRNA and protein levels of PI3K, AKT, COL I, COL III, and LOX. On the contrary, LY294002 in NM hCSFs significantly reduced PI3K, AKT, COL I, COL III, and LOX protein expression. We concluded that PI3K signaling mediates stromal collagen synthesis and LOX production following SM injury.

Clodronate liposome treatment contributes to the nerve regeneration in corneal nerve involvement of diabetic mice

The dense nerve and thin vascular structure of the corneal tissue provide the refractive function in healthy eyes. Diabetes mellitus causes ocular complications including corneal opacification because of corneal nerve degeneration. Diabetic neurotrophic keratopathy is characterized by reduced corneal sensitivity, delayed corneal wound healing, and nerve degeneration. Neurotization and vascularization inhibit each other in the cornea. Macrophages contribute to the corneal neovascularization. To investigate the role of macrophage in neurotrophic keratopathy, clodronate liposome was subconjunctivally injected into diabetic db/db mice with neurotrophic keratopathy. The clodronate liposome treatment decreased F4/80+ macrophage infiltration into the corneal epithelium, and improved corneal nerve involvement in diabetic db/db mice. Furthermore, we found that Il1b and Il34 mRNA expression was increased in the corneal epithelium of clodronate-treated diabetic db/db mice. These cytokines contribute to the maintenance of nerve tissues via microglia and nerve regeneration; however, their role in corneal nerve involvement remains unknown. Notably, the intraocular injection of recombinant IL-1β and IL-34 promoted nerve regeneration in the cornea of diabetic db/db mice. These results suggest that clodronate liposome treatment contributes to nerve regeneration during corneal involvement via IL-1β and IL-34 signaling.

Enhancing Corneal Sensitivity in Diabetic Patients Through an Innovative Ophthalmic Solution: In Vivo and Vitro Results

Background/Objectives: Diabetes is a well-recognised factor inducing a plethora of corneal alterations ranging from dry eye to reduced corneal sensibility, epithelial defects, and reduced cicatrisation. This cohort study aimed to assess the efficacy of a novel ophthalmic solution combining cross-linked hyaluronic acid (CHA), chondroitin sulfate (CS), and inositol (INS) in managing diabetes-induced corneal alterations. Specifically, it evaluated the solution's impact on the tear breakup time (TBUT), the ocular surface disease index (OSDI), and corneal sensitivity after three months of treatment. Additionally, the solution's potential to promote wound healing was examined. Methods: Two different populations were retrieved from the database; the first one was composed of 20 diabetic subjects treated for three months with the ophthalmic CAH-CS (OPHTAGON srl, Rome, Italy), while the second group was composed of 20 diabetic subjects who did not want to use any eye lubricant or other treatment. The outcome measures were the TBUT, the OSDI score, and the corneal sensitivity measured using a Cochet-Bonnet aesthesiometer. To investigate the wound-healing properties, in vitro tests were conducted using two cell lines, comparing the results of scratch tests with and without the solution. Results: The results indicate that CHA-CS significantly improved the tear film stability, as evidenced by an increased TBUT and a reduction in dry eye symptoms reflected by lower OSDI scores. Moreover, the solution was associated with an enhanced corneal sensitivity in treated patients. In wound-healing assays, CHA-CS promoted cell motility, suggesting a supportive role in tissue repair compared to untreated cells. Conclusions: Collectively, the results suggest that CHA-CS could serve as an innovative tool for the treatment of diabetic patients with corneal alterations and delayed corneal sensitivity. Clinical trial registration number: Clinical Trial.gov NCT06573606.

Specular microscopy findings in diabetic patients: a systematic review and meta-analysis

OBJECTIVE

To evaluate the specular microscopy findings in patients with diabetes mellitus (DM) through a systematic review and meta-analysis.

METHODS

A systematic search with the appropriate keyword was done in the online databases including PubMed, Scopus, and Web of Sciences. The records were imported into EndNote software and duplicated records were removed. The title, abstract, and full text of the articles were evaluated carefully. STATA software also was used for all data analyses. The mean difference (MD) and 95% confidence intervals (95% CIs) were used to examine the data.

RESULTS

After a systematic search, 781 records were evaluated and finally, 14 of them were selected for final analysis. The results showed that the mean differences in average cell size (MD = 21.22, 95% CI 10.43, 32.01, P 0.001), central corneal thickness (MD = 9.90, 95% CI 6.07, 13.73, P 0.001), and coefficient of variation (MD = 1.11, 95% CI 0.11, 2.11, P = 0.03) were higher in diabetic patients in comparison with healthy cases. However, the mean differences in endothelial cell density (MD = -114.29, 95% CI -158.34, -70.24, P 0.001) and hexagonal cell ratio (MD = -3.52, 95% CI -5.79, -1.25, P < 0.001) were lower in diabetic cases.

CONCLUSIONS

Patients with DM have higher average cell size, corneal thickness, and coefficient of variation. On the other hand, the endothelial cell density and hexagonal cell ratio were reduced in diabetic cases.

Corneal epithelial-stromal constructs to study differences associated with diabetes mellitus

Diabetes mellitus (DM) is a common metabolic disease associated with severe macrovascular and microvascular complications that influence nearly every tissue in the body, including the anterior and posterior segments of the eye. In the cornea, DM is associated with recurrent epithelial erosion and reduced wound-healing capacity, which increases the risk of corneal scarring. We previously developed a co-culture model of the cornea consisting of immortalized human corneal epithelial cells (hCE-TJ) overlaying a self-assembled stromal layer generated by human corneal fibroblasts (hCFs) over a 4-week period. In this study, we investigated epithelial-stromal constructs generated from hCFs derived from subjects with Type 1 (T1DM) or 2 diabetes (T2DM) compared to controls. We found that T2DM constructs exhibited a disrupted epithelium and a thicker, stratified stromal layer compared to controls or T1DM. Both T1DM and T2DM stromal constructs expressed lower expression of thrombospondin-1 in isolated extracellular vesicles (EVs) compared to controls with no significant difference observed in the presence of epithelial cells, suggesting that reduced provisional matrix secretion in the corneal stroma may be a factor that promotes delayed corneal wound healing in diabetes. The tetraspanins are established extracellular vesicle (EV) markers and include CD63, CD81, and CD9, and were highly expressed by EVs in all three cell types. Control corneal stromal fibroblasts produced more and larger EVs when compared to T1DM and T2DM hCF-derived EVs, supporting a role for altered cell-cell communication in the context of DM. Further characterization of EVs and their cargo is expected to aid in the development of targeted treatments to improve corneal wound healing.

The Role of Immune Cells and Signaling Pathways in Diabetic Eye Disease: A Comprehensive Review

Diabetic eye disease (DED) encompasses a range of ocular complications arising from diabetes mellitus, including diabetic retinopathy, diabetic macular edema, diabetic keratopathy, diabetic cataract, and glaucoma. These conditions are leading causes of visual impairments and blindness, especially among working-age adults. Despite advancements in our understanding of DED, its underlying pathophysiological mechanisms remain incompletely understood. Chronic hyperglycemia, oxidative stress, inflammation, and neurodegeneration play central roles in the development and progression of DED, with immune-mediated processes increasingly recognized as key contributors. This review provides a comprehensive examination of the complex interactions between immune cells, inflammatory mediators, and signaling pathways implicated in the pathogenesis of DED. By delving in current research, this review aims to identify potential therapeutic targets, suggesting directions of research for future studies to address the immunopathological aspects of DED.

Recent advances in NLRP3 inflammasome in corneal diseases: Preclinical insights and therapeutic implications

NLRP3 inflammasome is a cytosolic multiprotein complex formed in response to exogenous environmental stress and cellular damage. The three major components of the NLRP3 inflammasome are the innate immunoreceptor protein NLRP3, the adapter protein apoptosis-associated speck-like protein containing a C-terminal caspase activation and recruitment domain, and the inflammatory protease enzyme caspase-1. The integrated NLRP3 inflammasome triggers the activation of caspase-1, leading to GSDMD-dependent pyroptosis and facilitating the maturation and release of inflammatory cytokines, namely interleukin (IL)-18 and IL-1β. However, the inflammatory responses mediated by the NLRP3 inflammasome exhibit dual functions in innate immune defense and cellular homeostasis. Aberrant activation of the NLRP3 inflammasome matters in the etiology and pathophysiology of various corneal diseases. Corneal alkali burn can induce pyroptosis, neutrophil infiltration, and corneal angiogenesis via the activation of NLRP3 inflammasome. When various pathogens invade the cornea, NLRP3 inflammasome recognizes pathogen-associated molecular patterns or damage-associated molecular patterns to engage in pro-inflammatory and anti-inflammatory mechanisms. Moreover, chronic inflammation and proinflammatory cascades mediated by the NLRP3 inflammasome contribute to the pathogenesis of diabetic keratopathy. Furthermore, overproduction of reactive oxygen species, mitochondrial dysfunction, and toll-like receptor-mediated activation of nuclear factor kappa B drive the stimulation of NLRP3 inflammasome and participate in the progression of dry eye disease. However, there still exist controversies regarding the regulatory pathways of the NLRP3 inflammasome. In this review, we provide a comprehensive overview of recent advancements in the function of NLRP3 inflammasome in corneal diseases and its regulatory pathways primarily through studies using animal models. Furthermore, we explore prospects for pharmacologically targeting pathways associated with NLRP3.

The role of topical insulin in ocular surface restoration: A review

Corneal epithelial defects are one of the most common ocular disorders. Restoring corneal integrity is crucial to reduce pain and regain function, but in cases of neurotrophic or desensitized corneas, healing can be significantly delayed. Treating neurotrophic corneas is challenging for ophthalmologists, and surgical intervention is often indicated to manage refractory cases that are unresponsive to medical therapy. Over the last decade, as more expensive therapeutics reach the market, topical insulin has returned to the forefront as an affordable option to improve corneal wound healing. There is still a paucity of data on the use and the efficacy of topical insulin, with no consensus regarding its indications, preparation, or posology. Here we review the literature on topical insulin for corneal and ocular surface pathologies, with a focus on the current evidence, its mechanisms of action, and its safety profile. Additionally, we share our experience in the field and provide a potential framework for future research.

PET imaging for the early evaluation of ocular inflammation in diabetic rats by using [18F]-DPA-714

Ocular complications of diabetes mellitus (DM) are the leading cause of vision loss. Ocular inflammation often occurs in the early stage of DM; however, there are no proven quantitative methods to evaluate the inflammatory status of eyes in DM. The 18 kDa translocator protein (TSPO) is an evolutionarily conserved cholesterol binding protein localized in the outer mitochondrial membrane. It is a biomarker of activated microglia/macrophages; however, its role in ocular inflammation is unclear. In this study, fluorine-18-DPA-714 ([18F]-DPA-714) was evaluated as a specific TSPO probe by cell uptake, cell binding assays and micro positron emission tomography (microPET) imaging in both in vitro and in vivo models. Primary microglia/macrophages (PMs) extracted from the cornea, retina, choroid or sclera of neonatal rats with or without high glucose (50 mM) treatment were used as the in vitro model. Sprague-Dawley (SD) rats that received an intraperitoneal administration of streptozotocin (STZ, 60 mg/kg once) were used as the in vivo model. Increased cell uptake and high binding affinity of [18F]-DPA-714 were observed in primary PMs under hyperglycemic stress. These findings were consistent with cellular morphological changes, cell activation, and TSPO up-regulation. [18F]-DPA-714 PET imaging and biodistribution in the eyes of DM rats revealed that inflammation initiates in microglia/macrophages in the early stages (3 weeks and 6 weeks), corresponding with up-regulated TSPO levels. Thus, [18F]-DPA-714 microPET imaging may be an effective approach for the early evaluation of ocular inflammation in DM.

Tear Fluid Progranulin as a Noninvasive Biomarker for the Monitoring of Corneal Innervation Changes in Patients With Type 2 Diabetes Mellitus

Purpose

This study aimed to investigate the expression levels of progranulin (PGRN) in the tears of patients with diabetic retinopathy (DR) versus healthy controls. Additionally, we sought to explore the correlation between PGRN levels and the severity of ocular surface complications in patients with diabetes.

Methods

In this prospective, single-visit, cross-sectional study, patients with DR (n = 48) and age-matched healthy controls (n = 22) were included and underwent dry eye examinations. Tear fluid was collected, and its components were analyzed using the Luminex assay. The subbasal nerve plexus of all participants was evaluated by in vivo confocal microscopy.

Results

Patients with DR exhibited more severe dry eye symptoms, along with a reduction in nerve fiber density, length, and branch density within the subbasal nerve plexus, accompanied by an increase in the number of dendritic cells. Tear PGRN levels were also significantly lower in patients with diabetes than in normal controls, and the levels of some inflammatory factors (TNF-α, IL-6, and MMP-9) were higher in patients with DR. Remarkably, the PGRN level significantly correlated with nerve fiber density (R = 0.48, P < 0.001), nerve fiber length (R = 0.65, P < 0.001), and nerve branch density (R = 0.69, P < 0.001).

Conclusions

Tear PGRN levels might reflect morphological changes in the corneal nerve plexus under diabetic conditions, suggesting that PGRN itself is a reliable indicator for predicting the advancement of neurotrophic keratopathy in patients with diabetes.

Translational Relevance

PGRN insufficiency on the ocular surface under diabetic conditions was found to be closely associated with nerve impairment, providing a novel perspective to discover the pathogenesis of diabetic complications, which could help in developing innovative therapeutic strategies.

Limbal stem cells carried by a four-dimensional -printed chitosan-based scaffold for corneal epithelium injury in diabetic rabbits

Methods: Herein, we obtained and characterized deltaN p63- and adenosine triphosphate-binding cassette subfamily G member 2-expressing limbal stem cells (LSCs). Chitosan and carboxymethyl chitosan (CTH) were cross-linked to be an in situ thermosensitive hydrogel (ACH), which was printed through four-dimensional (4D) printing to obtain a porous carrier with uniform pore diameter (4D-CTH). Rabbits were injected with alloxan to induce diabetes mellitus (DM). Following this, the LSC-carrying hydrogel was spread on the surface of the cornea of the diabetic rabbits to cure corneal epithelium injury. Results: Compared with the control group (LSCs only), rapid wound healing was observed in rabbits treated with LSC-carrying 4D-CTH. Furthermore, the test group also showed better corneal nerve repair ability. The results indicated the potential of LSC-carrying 4D-CTH in curing corneal epithelium injury. Conclusion: 4D-CTH holds potential as a useful tool for studying regenerative processes occurring during the treatment of various diabetic corneal epithelium pathologies with the use of stem cell-based technologies.

Topical insulin in neurotrophic keratopathy after diabetic vitrectomy

To assess the efficacy and safety of topical insulin (TI) for treating neurotrophic keratopathy (NK) within one-month post-diabetic vitrectomy (DV) compared to conventional non-invasive measures, we conducted this retrospective case-control study including all eyes that developed acute NK (stages 2 and 3) following DV between October 2020 and June 2023. The control group included NK cases managed with preservative-free lubricant eye drops and prophylactic topical antibiotics. In contrast, the study group included NK cases treated with TI [1 unit per drop] four times daily, in addition to the previously mentioned treatment. The primary outcome measure was time to epithelial healing. Secondary outcome measures included any adverse effect of TI or the need for amniotic membrane transplantation (AMT). During the study period, 19 patients with a mean age of 49.3 ± 8.6 years received TI versus 18 controls with a mean age of 52.5 ± 10.7 years. Corneal epithelial healing was significantly faster in the TI-treated group compared to controls, with a mean difference of 12.16 days (95% CI 6.1-18.3, P = 0.001). Survival analysis indicated that the insulin-treated group had 0% and 20% of NK stages 2 and 3, respectively, that failed to achieve corneal epithelial healing, compared to 20% and 66.7% for the control group (P < 0.001). In the control group, two eyes required AMT due to progressive thinning. Additionally, three patients in the control group, progressing to stage 3 NK, were switched to TI, achieving healing after a mean of 14 days. No adverse effects were reported in the TI-treated group. Our study suggests that TI can effectively and safely promote the healing of NK after DV.

Insulin eye drops improve corneal wound healing in STZ-induced diabetic mice by regulating corneal inflammation and neuropeptide release

INTRODUCTION

In recent years, insulin eye drops have attracted increasing attention from researchers and ophthalmologists. The aim of this study was to investigate the efficacy and possible mechanism of action of insulin eye drops in diabetic mice with corneal wounds.

METHODS

A type 1 diabetes model was induced, and a corneal epithelial injury model of 2.5 mm was established. We used corneal fluorescein staining, hematoxylin-eosin (H-E) staining and the Cochet-Bonnet esthesiometer to examine the process of wound healing. Subsequently, the expression levels of Ki-67, IL-1β, β3-tubulin and neuropeptides, including substance P (SP) and calcitonin gene-related peptide (CGRP), were examined at 72 h after corneal injury.

RESULTS

Fluorescein staining demonstrated an acceleration of the recovery of corneal epithelial injury in diabetic mice compared with the saline treatment, which was further evidenced by the overexpression of Ki-67. Moreover, 72 h of insulin application attenuated the expression of inflammatory cytokines and neutrophil infiltration. Remarkably, the results demonstrated that topical insulin treatment enhanced the density of corneal epithelial nerves, as well as neuropeptide SP and CGRP release, in the healing cornea via immunofluorescence staining.

CONCLUSIONS

Our results indicated that insulin eye drops may accelerate corneal wound healing and decrease inflammatory responses in diabetic mice by promoting nerve regeneration and increasing levels of neuropeptides SP and CGRP.

Analyzing the changing trend of corneal biomechanical properties under different influencing factors in T2DM patients

To analyze the changing trend of CH and CRF values under different influencing factors in T2DM patients. A total of 650 patients with T2DM were included. We discovered that the course of T2DM, smoking history, BMI, and FBG, DR, HbA1c, TC, TG, and LDL-C levels were common risk factors for T2DM, while HDL-C levels were a protective factor. Analyzing the CH and CRF values according to the course of diabetes, we discovered that as T2DM continued to persist, the values of CH and CRF gradually decreased. Moreover, with the increase in FBG levels and the accumulation of HbA1c, the values of CH and CRF gradually decreased. In addition, in patients with HbA1c (%) > 12, the values of CH and CRF decreased the most, falling by 1.85 ± 0.33 mmHg and 1.28 ± 0.69 mmHg, respectively. Compared with the non-DR group, the CH and CRF values gradually decreased in the mild-NPDR, moderate-NPDR, severe-NPDR and PDR groups, with the lowest CH and CRF values in the PDR group. In patients with T2DM, early measurement of corneal biomechanical properties to evaluate the change trend of CH and CRF values in different situations will help to identify and prevent diabetic keratopathy in a timely manner.

Novel electro-spun fabrication of blended polymeric nanofibrous wound closure materials loaded with catechin to improve wound healing potential and microbial inhibition for the care of diabetic wound

Diabetic wound infections caused by the multiplication of infectious pathogens and their antibiotic resistance. Wound infection evident by bacterial colonization and other factors, such as the virulence and host immune factors. In this context, we need discover appropriate treatment and effective antibiotics for wound infection control. Considering this, we synthesized catechin-loaded polyvinyl alcohol/Chitosan (PVA/CS) based nanofiber for multifunctional wound healing. The physicochemical and biological properties of fabricated nanofiber, were systematically evaluated by various spectroscopy and microscopy techniques. The CA@PVA/CS nanofiber exhibited a high level of antibacterial and antioxidant effects. The nanofibers showed effective control in gram-positive and negative wound infectious bacterial multiplication at the lowest concentration. Based on the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) cell viability study CA@PVA/CS nanofiber shows excellent biocompatibility against L929 cells. In wound, scratch assay results revealed that the CA@PVA/CS treated group shows enhanced cell migration and cell proliferation within 48 h. The synthesis of antioxidant, antibacterial, and biocompatible nanofiber exposes their potential for effective wound healing. Current research hypothesized catechin loaded PVA/CS nanofiber could be a multifunctional and low-cost material for diabetic wound care application. Fabricated nanofiber would be improved skin tissue regeneration and public health hygiene.

Identification and Validation of the Pyroptosis-Related Hub Gene Signature and the Associated Regulation Axis in Diabetic Keratopathy

Background

Diabetic keratopathy (DK) poses a significant challenge in diabetes mellitus, yet its molecular pathways and effective treatments remain elusive. The aim of our research was to explore the pyroptosis-related genes in the corneal epithelium of the streptozocin-induced diabetic rats.

Methods

After sixteen weeks of streptozocin intraperitoneal injection, corneal epithelium from three diabetic rats and three normal groups underwent whole-transcriptome sequencing. An integrated bioinformatics pipeline, including differentially expressed gene (DEG) identification, enrichment analysis, protein-protein interaction (PPI) network, coexpression, drug prediction, and immune deconvolution analyses, identified hub genes and key drivers in DK pathogenesis. These hub genes were subsequently validated in vivo through RT-qPCR.

Results

A total of 459 DEGs were screened out from the diabetic group and nondiabetic controls. Gene Set Enrichment Analysis highlighted significant enrichment of the NOD-like receptor, Toll-like receptor, and NF-kappa B signaling pathways. Intersection of DEGs and pyroptosis-related datasets showed 33 differentially expressed pyroptosis-related genes (DEPRGs) associated with pathways such as IL-17, NOD-like receptor, TNF, and Toll-like receptor signaling. A competing endogenous RNA network comprising 16 DEPRGs, 22 lncRNAs, 13 miRNAs, and 3 circRNAs was constructed. After PPI network, five hub genes (Nfkb1, Casp8, Traf6, Ptgs2, and Il18) were identified as upregulated in the diabetic group, and their expression was validated by RT-qPCR in streptozocin-induced rats. Immune infiltration characterization showed that diabetic corneas owned a higher proportion of resting mast cells, activated NK cells, and memory-resting CD4 T cells. Finally, several small compounds including all-trans-retinoic acid, Chaihu Shugan San, dexamethasone, and resveratrol were suggested as potential therapies targeting these hub genes for DK.

Conclusions

The identified and validated hub genes, Nfkb1, Casp8, Traf6, Ptgs2, and Il18, may play crucial roles in DK pathogenesis and serve as therapeutic targets.

Effects of Diabetes Mellitus on Corneal Immune Cell Activation and the Development of Keratopathy

Diabetes mellitus (DM) is one of the most prevalent diseases globally, and its prevalence is rapidly increasing. Most patients with a long-term history of DM present with some degree of keratopathy (DK). Despite its high incidence, the underlying inflammatory mechanism of DK has not been elucidated yet. For further insights into the underlying immunopathologic processes, we utilized streptozotocin-induced mice to model type 1 DM (T1D) and B6.Cg-Lepob/J mice to model type 2 DM (T2D). We evaluated the animals for the development of clinical manifestations of DK. Four weeks post-induction, the total frequencies of corneal CD45+CD11b+Ly-6G- myeloid cells, with enhanced gene and protein expression levels for the proinflammatory cytokines TNF-α and IL-1β, were higher in both T1D and T2D animals. Additionally, the frequencies of myeloid cells/mm2 in the sub-basal neural plexus (SBNP) were significantly higher in T1D and T2D compared to non-diabetic mice. DK clinical manifestations were observed four weeks post-induction, including significantly lower tear production, corneal sensitivity, and epitheliopathy. Nerve density in the SBNP and intraepithelial terminal endings per 40x field were lower in both models compared to the normal controls. The findings of this study indicate that DM alters the immune quiescent state of the cornea during disease onset, which may be associated with the progressive development of the clinical manifestations of DK.

Regenerative Therapy for Corneal Scarring Disorders

The cornea is a transparent and vitally multifaceted component of the eye, playing a pivotal role in vision and ocular health. It has primary refractive and protective functions. Typical corneal dysfunctions include opacities and deformities that result from injuries, infections, or other medical conditions. These can significantly impair vision. The conventional challenges in managing corneal ailments include the limited regenerative capacity (except corneal epithelium), immune response after donor tissue transplantation, a risk of long-term graft rejection, and the global shortage of transplantable donor materials. This review delves into the intricate composition of the cornea, the landscape of corneal regeneration, and the multifaceted repercussions of scar-related pathologies. It will elucidate the etiology and types of dysfunctions, assess current treatments and their limitations, and explore the potential of regenerative therapy that has emerged in both in vivo and clinical trials. This review will shed light on existing gaps in corneal disorder management and discuss the feasibility and challenges of advancing regenerative therapies for corneal stromal scarring.

Electroacupuncture regulates the P2X7R-NLRP3 inflammatory cascade to relieve decreased sensation on ocular surface of type 2 diabetic rats with dry eye

Dry eye (DE) is a prevalent ocular surface disease in patients with type 2 diabetes (T2DM). However, current medications are ineffective against decreased sensation on the ocular surface. While electroacupuncture (EA) effectively alleviates decreased sensation on ocular surface of DE in patients with T2DM, the neuroprotective mechanism remains unclear. This study explored the pathogenesis and therapeutic targets of T2DM-associated DE through bioinformatics analysis. It further investigated the underlying mechanism by which EA improves decreased sensation on the ocular surface of DE in rats with T2DM. Bioinformatic analysis was applied to annotate the potential pathogenesis of T2DM DE. T2DM and DE was induced in male rats. Following treatment with EA and fluorometholone, comprehensive metrics were assessed. Additionally, the expression patterns of key markers were studied. Key targets such as NLRP3, Caspase-1, and NOD-like receptor signaling may be involved in the pathogenesis of T2DM DE. EA treatment improved ocular measures. Furthermore, EA potently downregulated P2X7R, NLRP3, apoptosis-associated speck-like protein containing a CARD (ASC), and Caspase-1 expression within the trigeminal ganglion and spinal trigeminal nucleus caudalis. Targeted P2X7R antagonist (A-438079) and agonist (BzATP) employed as controls to decipher the biochemistry of the therapeutic effects of EA showed an anti-inflammatory effect with A-438079, while BzATP blocked the anti-inflammatory effect of EA. EA relieved DE symptoms and attenuated inflammatory damage to sensory nerve pathways in T2DM rats with DE. These findings suggest a crucial role of EA inhibition of the P2X7R-NLRP3 inflammatory cascade to provide these benefits.

Diabetic Ocular Surface Has Defects in Oxygen Uptake Revealed by Optic Fiber Microsensor

Purpose

Diabetes mellitus causes diabetic keratopathy (DK). This and other ocular surface disorders are underdiagnosed and problematic for affected patients as well as recipients of diabetic donor corneas. Thus, it is important to find noninvasive means to facilitate determination of the potentially vision-threatening DK. It has been reported that diabetic corneas uptake significantly less oxygen (O2) than healthy controls. However, an integral assessment of the ocular surface is missing.

Methods

Using an optic-fiber O2 micro-sensor (optrode) we demonstrated recently that the healthy ocular surface displays a unique spatiotemporal map of O2 consumption. We hypothesize that diabetes impairs the spatiotemporal profile of O2 uptake at the ocular surface.

Results

Using streptozotocin (STZ)-induced diabetic mice, we found diminished O2 uptake and loss of the unique pattern across the ocular surface. A diabetic cornea consumes significantly less O2 at the bulbar conjunctiva and limbus, but not the central and peripheral cornea, compared to controls. Further, we show that, contrary to the healthy cornea, the diabetic cornea does not increase the O2 consumption at the limbus in the evening as the normal control.

Conclusions

Altogether, our measurements reveal a previously unknown impairment in O2 uptake at the diabetic cornea, making it a potential tool to diagnose ocular surface abnormalities and suggesting a new etiology mechanism.

Lack of Elevated Expression of TGFβ3 Contributes to the Delay of Epithelial Wound Healing in Diabetic Corneas

Purpose

To investigate the mechanisms underlying the differential roles of TGFβ1 and TGFβ3 in accelerating corneal epithelial wound healing (CEWH) in diabetic (DM) corneas, with normoglycemia (NL) corneas as the control.

Methods

Two types of diabetic mice, human corneal organ cultures, mouse corneal epithelial progenitor cell lines, and bone marrow-derived macrophages (BMDMs) were employed to assess the effects of TGFβ1 and TGFβ3 on CEWH, utilizing quantitative PCR, western blotting, ELISA, and whole-mount confocal microscopy.

Results

Epithelial debridement led to an increased expression of TGFβ1 and TGFβ3 in cultured human NL corneas, but only TGFβ1 in DM corneas. TGFβ1 and TGFβ3 inhibition was significantly impeded, but exogenous TGFβ1 and, more potently, TGFβ3 promoted CEWH in cultured TKE2 cells and in NL and DM C57BL6 mouse corneas. Wounding induced similar levels of p-SMAD2/SMAD3 in NL and DM corneas but weaker ERK1/2, Akt, and EGFR phosphorylation in DM corneas compared to NL corneas. Whereas TGFβ1 augmented SMAD2/SMAD3 phosphorylation, TGFβ3 preferentially activated ERK, PI3K, and EGFR in healing DM corneas. Furthermore, TGFβ1 and TGFβ3 differentially regulated the expression of S100a9, PAI-1, uPA/tPA, and CCL3 in healing NL and DM corneas. Finally, TGFβ1 induced the expression of M1 macrophage markers iNOS, CD86, and CTGF, whereas TGFβ3 promoted the expression of M2 markers CD206 and NGF in BMDMs from db/db or db/+ mice.

Conclusions

Hyperglycemia disrupts the balanced expression of TGFβ3/TGFβ1, resulting in delayed CEWH, including impaired sensory nerve regeneration in the cornea. Supplementing TGFβ3 in DM wounds may hold therapeutic potential for accelerating delayed wound healing in diabetic patients.

Effects of hypoxia in the diabetic corneal stroma microenvironment

Corneal dysfunctions associated with Diabetes Mellitus (DM), termed diabetic keratopathy (DK), can cause impaired vision and/or blindness. Hypoxia affects both Type 1 (T1DM) and Type 2 (T2DM) surprisingly, the role of hypoxia in DK is unexplored. The aim of this study was to examine the impact of hypoxia in vitro on primary human corneal stromal cells derived from Healthy (HCFs), and diabetic (T1DMs and T2DMs) subjects, by exposing them to normoxic (21% O2) or hypoxic (2% O2) conditions through 2D and 3D in vitro models. Our data revealed that hypoxia affected T2DMs by slowing their wound healing capacity, leading to significant alterations in oxidative stress-related markers, mitochondrial health, cellular homeostasis, and endoplasmic reticulum health (ER) along with fibrotic development. In T1DMs, hypoxia significantly modulated markers related to membrane permeabilization, oxidative stress via apoptotic marker (BAX), and protein degradation. Hypoxic environment induced oxidative stress (NOQ1 mediated reduction of superoxide in T1DMs and Nrf2 mediated oxidative stress in T2DMs), modulation in mitochondrial health (Heat shock protein 27 (HSP27), and dysregulation of cellular homeostasis (HSP90) in both T1DMs and T2DMs. This data underscores the significant impact of hypoxia on the diabetic cornea. Further studies are warranted to delineate the complex interactions.

Calreticulin accelerates corneal wound closure and mitigates fibrosis: Potential therapeutic applications

The processes involved in regeneration of cutaneous compared to corneal tissues involve different intrinsic mechanisms. Importantly, cutaneous wounds involve healing by angiogenesis but vascularization of the cornea obscures vision. Previous studies showed that topically applied calreticulin (CALR) healed full-thickness excisional animal wounds by a tissue regenerative process markedly enhancing repair without evoking angiogenesis. In the current study, the application of CALR in a rabbit corneal injury model: (1) accelerated full wound closure by 3 days (2) accelerated delayed healing caused by corticosteroids, routinely used to prevent post-injury inflammation, by 6 days and (3) healed wounds without vascularization or fibrosis/hazing. In vitro, CALR stimulated proliferation of human corneal epithelial cells (CE) and corneal stromal cells (keratocytes) by 1.5-fold and 1.4-fold, respectively and induced migration of CE cells and keratocytes, by 72% and 85% compared to controls of 44% and 59%, respectively. As a marker of decreased fibrosis, CALR treated corneal wounds showed decreased immunostaining for α-smooth muscle actin (α-SMA) by keratocytes and following CALR treatment in vitro, decreased the levels of TGF-β2 in human CE cells and α-SMA in keratocytes. CALR has the potential to be a novel therapeutic both, to accelerate corneal healing from various injuries and in conjunction with corticosteroids.

Pharmaceutical applications of chitosan in skin regeneration: A review

Skin regeneration is the process that restores damaged tissues. When the body experiences trauma or surgical incisions, the skin and tissues on the wound surface become damaged. The body repairs this damage through complex physiological processes to restore the original structural and functional states of the affected tissues. Chitosan, a degradable natural bioactive polysaccharide, has attracted widespread attention partly owing to its excellent biocompatibility and antimicrobial properties; additionally, a modified form of this compound has been shown to promote skin regeneration. This review evaluates the recent research progress in the application of chitosan to promote skin regeneration. First, we discuss the basic principles of the extraction and preparation processes of chitosan from its source. Subsequently, we describe the functional properties of chitosan and the optimization of these properties through modification. We then focus on the existing chitosan-based biomaterials developed for clinical applications and their corresponding effects on skin regeneration, particularly in cases of diabetic and burn wounds. Finally, we explore the challenges and prospects associated with the use of chitosan in skin regeneration. Overall, this review provides a reference for related research and contributes to the further development of chitosan-based products in cutaneous skin regeneration.

Diabetic Keratopathy: Redox Signaling Pathways and Therapeutic Prospects

Diabetes mellitus, the most prevalent endocrine disorder, not only impacts the retina but also significantly involves the ocular surface. Diabetes contributes to the development of dry eye disease and induces morphological and functional corneal alterations, particularly affecting nerves and epithelial cells. These changes manifest as epithelial defects, reduced sensitivity, and delayed wound healing, collectively encapsulated in the context of diabetic keratopathy. In advanced stages of this condition, the progression to corneal ulcers and scarring further unfolds, eventually leading to corneal opacities. This critical complication hampers vision and carries the potential for irreversible visual loss. The primary objective of this review article is to offer a comprehensive overview of the pathomechanisms underlying diabetic keratopathy. Emphasis is placed on exploring the redox molecular pathways responsible for the aberrant structural changes observed in the cornea and tear film during diabetes. Additionally, we provide insights into the latest experimental findings concerning potential treatments targeting oxidative stress. This endeavor aims to enhance our understanding of the intricate interplay between diabetes and ocular complications, offering valuable perspectives for future therapeutic interventions.

Inhibition of miR-144-3p/FOXO1 Attenuates Diabetic Keratopathy Via Modulating Autophagy and Apoptosis

Purpose

Diabetic keratopathy (DK) is a vision-threatening disease that occurs in people with diabetes. Mounting evidence indicates that microRNAs (miRNAs) are indispensable in nerve regeneration within DK. Herein, the role of miRNAs associated with DK, especially focusing on autophagy and apoptosis regulation, was investigated.

Methods

To identify differentially expressed miRNAs, we performed miRNA sequencing on trigeminal ganglion (TG) tissues derived from streptozotocin-induced type 1 diabetic mellitus (T1DM) and normal mice. MiR-144-3p was chosen for the subsequent experiments. To explore the regulatory role of miR-144-3p in DK, miRNA antagomir was utilized to inhibit miR-144-3p expression. Bioinformatic tools were used to predict the target genes of miR-144-3p, and a dual-luciferase reporter assay was then applied for validation. Autophagy and apoptosis activities were measured utilizing TUNEL staining, immunofluorescence staining, and Western blotting.

Results

Overall, 56 differentially expressed miRNAs were detected in diabetic versus control mice. In the diabetic mouse TG tissue, miR-144-3p expression was aberrantly enhanced, whereas decreasing its expression contributed to improved diabetic corneal re-epithelialization and nerve regeneration. Fork-head Box O1 (FOXO1) was validated as a target gene of miR-144-3p. Overexpression of FOXO1 could prevent both inadequate autophagy and excessive apoptosis in DK. Consistently, a specific miR-144-3p inhibition enhanced autophagy and prevented apoptosis in DK.

Conclusions

In this study, our research confirmed the target binding relationship between miR-144-3p and FOXO1. Inhibiting miR-144-3p might modulate autophagy and apoptosis, which could generate positive outcomes for corneal nerves via targeting FOXO1 in DK.

Protective effect of pituitary adenylate cyclase activating polypeptide in diabetic keratopathy

Diabetic keratopathy (DK) is the major complication of the cornea characterizing diabetes-affected patients. This ocular pathology is correlated with the hyperglycemic state leading to delayed corneal wound healing and recurrent corneal ulcers. Pituitary adenylate cyclase-activating polypeptide (PACAP) is a neuropeptide with widespread distribution throughout the body, and exerting cytoprotective effects in the neural and non-neuronal parts of the eye, including the cornea. The purpose of the present study was to investigate whether changes in PACAP expression can concur for delayed epithelial wound healing in diabetic cornea and whether the protective effect of the peptide could be mediated through the activation of the EGFR signaling pathway, which has been reported to be impaired in DK. Expression and distribution of PACAP, PAC1R, and EGFR were investigated through immunohistochemistry analysis in the cornea of normal and diabetic rats. The role of the peptide on wound healing during DK was evaluated in an in vitro model represented by rabbit corneal epithelial cells grown in high glucose conditions. Western blotting and immunofluorescence analysis were used to examine the ability of PACAP to induce the activation of the EGFR/ERK1/2 signaling pathway. Our results showed that in diabetic cornea the expression of PACAP, PAC1R, and EGFR is drastically reduced. The treatment with PACAP via PAC1R activation enhanced cell viability and corneal epithelium wound healing in cells grown under high glucose conditions. Furthermore, both EGFR and ERK1/2 signaling was induced upon the peptide treatment. Overall, our results showed the trophic efficiency of PACAP for enhancing the corneal epithelium re-epithelialization suggesting that the peptide could be beneficially valuable as a treatment for DK.

Oxidative stress in the eye and its role in the pathophysiology of ocular diseases

Oxidative stress occurs through an imbalance between the generation of reactive oxygen species (ROS) and the antioxidant defense mechanisms of cells. The eye is particularly exposed to oxidative stress because of its permanent exposure to light and due to several structures having high metabolic activities. The anterior part of the eye is highly exposed to ultraviolet (UV) radiation and possesses a complex antioxidant defense system to protect the retina from UV radiation. The posterior part of the eye exhibits high metabolic rates and oxygen consumption leading subsequently to a high production rate of ROS. Furthermore, inflammation, aging, genetic factors, and environmental pollution, are all elements promoting ROS generation and impairing antioxidant defense mechanisms and thereby representing risk factors leading to oxidative stress. An abnormal redox status was shown to be involved in the pathophysiology of various ocular diseases in the anterior and posterior segment of the eye. In this review, we aim to summarize the mechanisms of oxidative stress in ocular diseases to provide an updated understanding on the pathogenesis of common diseases affecting the ocular surface, the lens, the retina, and the optic nerve. Moreover, we discuss potential therapeutic approaches aimed at reducing oxidative stress in this context.

Animal Models in Eye Research: Focus on Corneal Pathologies

The eye is a complex sensory organ that enables visual perception of the world. The dysfunction of any of these tissues can impair vision. Conduction studies on laboratory animals are essential to ensure the safety of therapeutic products directly applied or injected into the eye to treat ocular diseases before eventually proceeding to clinical trials. Among these tissues, the cornea has unique homeostatic and regenerative mechanisms for maintaining transparency and refraction of external light, which are essential for vision. However, being the outermost tissue of the eye and directly exposed to the external environment, the cornea is particularly susceptible to injury and diseases. This review highlights the evidence for selecting appropriate animals to better understand and treat corneal diseases, which rank as the fifth leading cause of blindness worldwide. The development of reliable and human-relevant animal models is, therefore, a valuable research tool for understanding and translating fundamental mechanistic findings, as well as for assessing therapeutic potential in humans. First, this review emphasizes the unique characteristics of animal models used in ocular research. Subsequently, it discusses current animal models associated with human corneal pathologies, their utility in understanding ocular disease mechanisms, and their role as translational models for patients.

Diabetes-Associated Hyperglycemia Causes Rapid-Onset Ocular Surface Damage

Purpose

The metabolic alterations due to chronic hyperglycemia are well-known to cause diabetes-associated complications. Short-term hyperglycemia has also been shown to cause many acute changes, including hemodynamic alterations and osmotic, oxidative, and inflammatory stress. The present study was designed to investigate whether diabetes-associated hyperglycemia can cause rapid-onset detrimental effects on the tear film, goblet cells, and glycocalyx and can lead to activation of an inflammatory cascade or cellular stress response in the cornea.

Methods

Mouse models of type 1 and type 2 diabetes were used. Tear film volume, goblet cell number, and corneal glycocalyx area were measured on days 7, 14, and 28 after the onset of hyperglycemia. Transcriptome analysis was performed to quantify changes in 248 transcripts of genes involved in inflammatory, apoptotic, and stress response pathways.

Results

Our data demonstrate that type 1 and type 2 diabetes-associated hyperglycemia caused a significant decrease in the tear film volume, goblet cell number, and corneal glycocalyx area. The decrease in tear film and goblet cell number was noted as early as 7 days after onset of hyperglycemia. The severity of ocular surface injury was significantly more in type 1 compared to type 2 diabetes. Diabetes mellitus also caused an increase in transcripts of genes involved in the inflammatory, apoptotic, and cellular stress response pathways.

Conclusions

The results of the present study demonstrate that diabetes-associated hyperglycemia causes rapid-onset damage to the ocular surface. Thus, short-term hyperglycemia in patients with diabetes mellitus may also play an important role in causing ocular surface injury and dry eye.

Limbal Epithelial Stem Cells in the Diabetic Cornea

Continuous replenishment of the corneal epithelium is pivotal for maintaining optical transparency and achieving optimal visual perception. This dynamic process is driven by limbal epithelial stem cells (LESCs) located at the junction between the cornea and conjunctiva, which is otherwise known as the limbus. In patients afflicted with diabetes, hyperglycemia-induced impairments in corneal epithelial regeneration results in persistent epithelial and other defects on the ocular surface, termed diabetic keratopathy (DK), which progressively diminish vision and quality of life. Reports of delayed corneal wound healing and the reduced expression of putative stem cell markers in diabetic relative to healthy eyes suggest that the pathogenesis of DK may be associated with the abnormal activity of LESCs. However, the precise role of these cells in diabetic corneal disease is poorly understood and yet to be comprehensively explored. Herein, we review existing literature highlighting aberrant LESC activity in diabetes, focusing on factors that influence their form and function, and emerging therapies to correct these defects. The consequences of malfunctioning or depleted LESC stocks in DK and limbal stem cell deficiency (LSCD) are also discussed. These insights could be exploited to identify novel targets for improving the management of ocular surface complications that manifest in patients with diabetes.

Immunoglobulin A levels and its correlation with neutrophil-to-lymphocyte ratio as inflammatory biomarkers for dry eye disease in type 2 diabetes: a retrospective study

Background

The neutrophil-to-lymphocyte ratio (NLR) and immunoglobulin A (IgA) level are commonly used as biomarkers for inflammation. Patients with type 2 diabetes (T2D) may experience an imbalance of tear film and inflammation, which can result in dry eye disease (DED). This study aimed to assess the levels of IgA and explore its correlation with the NLR as potential inflammatory biomarkers for dry eye disease in patients with T2D.

Methods

A retrospective study was conducted at the cornea clinic and diabetes centre of King Abdulaziz Medical City (Jeddah, Saudi Arabia). The study included patients with DED and the number of available T2D-DED patients determined the sample size. Neutrophil, lymphocyte, IgA and CRP (C-reactive protein) laboratory values were obtained from medical records and correlational analyses were performed.

Results

The study included 85 patients with an average age of 54 ± 14.4 years for the DED group (n=32) and 62 ± 13.9 years for the T2D-DED group (n=53). The age difference between the two groups was statistically significant (p 0.0001). The NLR values of the T2D-DED and DED groups were 3.203 ± 0.66 and 2.406 ± 0.46, respectively, with no significant difference (p<0.285). Similarly, there were no significant differences in neutrophil and lymphocyte values between the two groups. The IgA levels showed no significant variation between T2D-DED and DED groups (p<0.364). Spearman's correlation analysis in the DED group showed a significant negative correlation between IgA and lymphocyte (p=0.011; r= - 0.471) values and significant positive correlations between IgA and neutrophil (p=0.014; r=0.309) and NLR (p=0.052; r= - 0.283) values. In the T2D-DED group, a significant correlation was found between IgA and CRP values (p=0.032; r=0.33).

Conclusion

Although diabetic patients may exhibit higher levels of NLR and IgA that correlate with disease severity, our study did not find significant differences in NLR and IgA values between the two groups. These findings may guide future research and enhance understanding of the disease's underlying mechanisms.

Bibliometric and visual analysis of diabetes mellitus and pyroptosis from 2011 to 2022

OBJECTIVE

To visualize and analyze the published literature on diabetes mellitus and pyroptosis based on a bibliometric approach, so as to provide a comprehensive picture of the hot research directions and dynamic progress in this field.

METHODS

This study was based on the web of science core collection database to conduct a comprehensive search of the published literature in the field of diabetes mellitus and Pyroptosis from January 1985 to August 2022, including the published research literature in this field, as well as a visual analysis of the number of citations, year of publication, journal, author, research institution, country, and research topic.

RESULTS

A total of 139 literature on research related to diabetes mellitus and cellular scorch from 2011 to 2022 were retrieved, with a total of 3009 citations and a maximum of 255 citations for a single article, which had a first author Schmid-Burgk, JL The first author of this article is from Germany; among 20 publishing countries, China leads with 100 articles; among 222 publishing institutions, Harbin Medical University leads with 18 articles and 184 citations; among 980 authors, Chen, X from China tops the list of high-impact authors with 5 articles and 29 citations. Among the 98 journals, "CELL DEATH DISEASE" ranked first in both volume and high-impact journals with 4 articles and 29 citations. Among 349 keywords, "pyroptosis" ranked first with a cumulative frequency of 65 times. The cluster analysis was divided into three categories, chronic complications of diabetes mellitus and pyroptosis (67 articles), diabetes mellitus and pyroptosis (60 articles), and diabetes mellitus combined with other diseases and pyroptosis (12 articles), and the number of articles related to diabetes mellitus and its chronic complications increased rapidly from 2019, among which, diabetic cardiomyopathy (27 articles) had the highest number of articles.

CONCLUSIONS

Based on a comprehensive analysis of published literature in the field of diabetes mellitus and pyroptosis from 2011 to 2022, this study achieved a visual analysis of studies with significant and outstanding contributions to the field, thus framing a picture showing the development and changes in the field. At the same time, this study provides research information and direction for clinicians and investigators to conduct diabetes mellitus and pyroptosis-related research in the future.

Effects of Topical 1,25 and 24,25 Vitamin D on Diabetic, Vitamin D Deficient and Vitamin D Receptor Knockout Mouse Corneal Wound Healing

Delayed or prolonged corneal wound healing and non-healing corneas put patients at risk for ocular surface infections and subsequent stromal opacification, resulting in discomfort or visual loss. It is important to enhance corneal wound healing efficiency and quality. Vitamin D (Vit D) is both a hormone and a vitamin, and its insufficiency has been linked to immune disorders and diabetes. For this study, wound healing and recruitment of CD45+ cells into the wound area of normoglycemic and diabetic mice were examined following corneal epithelial debridement and treatment with 1,25-dihyroxyvitamin D (1,25 Vit D) or 24,25-dihydroxyvitamin D (24,25 Vit D). Treatment with topical 1,25-dihyroxyvitamin D (1,25 Vit D) resulted in significantly increased corneal wound healing rates of normoglycemic, diabetic and diabetic Vit D deficient mice. Furthermore, 24,25-dihydroxyvitamin D (24,25 Vit D) significantly increased corneal wound healing of diabetic Vit D deficient and Vit D receptor knockout (VDR KO) mice. In addition, CD45+ cell numbers were reduced in diabetic and VDR KO mouse corneas compared to normoglycemic mice, and 24,25 Vit D increased the recruitment of CD45+ cells to diabetic mouse corneas after epithelial debridement. CD45+ cells were found to infiltrate into the corneal basal epithelial layer after corneal epithelial debridement. Our data indicate that topical Vit D promotes corneal wound healing and further supports previous work that the Vit D corneal wound healing effect is not totally VDR-dependent.

Usage of topical insulin for the treatment of diabetic keratopathy, including corneal epithelial defects

BACKGROUND

Diabetic keratopathy (DK) occurs in 46%-64% of patients with diabetes and requires serious attention. In patients with diabetes, the healing of corneal epithelial defects or ulcers takes longer than in patients without diabetes. Insulin is an effective factor in wound healing. The ability of systemic insulin to rapidly heal burn wounds has been reported for nearly a century, but only a few studies have been performed on the effects of topical insulin (TI) on the eye. Treatment with TI is effective in treating DK.

AIM

To review clinical and experimental animal studies providing evidence for the efficacy of TI to heal corneal wounds.

METHODS

National and international databases, including PubMed and Scopus, were searched using relevant keywords, and additional manual searches were conducted to assess the effectiveness of TI application on corneal wound healing. Journal articles published from January 1, 2000 to December 1, 2022 were examined. The relevancy of the identified citations was checked against predetermined eligibility standards, and relevant articles were extracted and reviewed.

RESULTS

A total of eight articles were found relevant to be discussed in this review, including four animal studies and four clinical studies. According to the studies conducted, TI is effective for corneal re-epithelialization in patients with diabetes based on corneal wound size and healing rate.

CONCLUSION

Available animal and clinical studies have shown that TI promotes corneal wound healing by several mechanisms. The use of TI was not associated with adverse effects in any of the published cases. Further studies are needed to enhance our knowledge and understanding of TI in the healing of DK.

Interference of sympathetic overactivation restores limbal stem/progenitor cells function and accelerates corneal epithelial wound healing in diabetic mice

Diabetic keratopathy (DK), the diabetic complication in the cornea, is characterized by the delayed epithelial regeneration and sensory nerve degeneration. The involvement of limbal stem/progenitor cells (LSPCs) dysfunction has been reported, however the pathogenic mechanisms remain unclear. Here, we confirmed the dysfunction of LSPCs in diabetic mouse and human corneas. The sympathetic nerve in the cornea was adjacent to LSPCs, and the sympathetic overactivation was found in diabetic mice. Surgical and pharmacological ablation of sympathetic nerves rescued the LSPCs function and promoted corneal epithelial regeneration in diabetic mice. In contrast, both topical norepinephrine (NE) application and chemogenetic sympathetic overactivation directly impaired the stemness and proliferation characteristics of LSPCs, as well as the normal epithelial regeneration. Moreover, we identified that β2-adrenoceptor (Adrb2) was the predominant adrenergic receptor expressed in LSPCs by corneal limbal single-cell sequencing and real time PCR (RT-PCR) analysis of sorted LSPCs. The Adrb2 knockout mice exhibited the enhancement of epithelial regeneration and LSPCs function, compared with the wild-type mice. Similarly, topical application of the Adrb2 specific antagonist ICI 118, 551 effectively accelerated diabetic corneal epithelial regeneration with the restored LSPCs function. Mechanistically, sonic hedgehog (Shh) activity mediated the downstream effects of NE-Adrb2 signaling pathway in regulating LSPCs and epithelial regeneration. Taken together, our data revealed the involvement of sympathetic overactivation in the impairment of diabetic LSPCs function and corneal epithelial regeneration through the NE-Adrb2-Shh signaling pathway. The interference of sympathetic overactivation may provide novel treatment strategies for diabetic keratopathy.

Extracellular vesicles derived from mouse adipose-derived mesenchymal stem cells promote diabetic corneal epithelial wound healing through NGF/TrkA pathway activation involving dendritic cells

Diabetic keratopathy (DK) is a common ocular complication of diabetes in which the dendritic cells (DCs)-mediated inflammatory response plays an important role. Nerve growth factor (NGF)/Tropomyosin receptor kinase A (TrkA)-mediated inhibition of the nuclear factor kappa B (NF-κB) pathway can reduce inflammatory cytokine production. Extracellular vesicles (EVs) derived from mouse adipose-derived mesenchymal stem cells (mADSC-EVs) have been explored extensively as treatments for degenerative eye disease. However, mADSC-EVs is poorly studied in the DK models. In this study, we investigated the anti-inflammatory effects of mADSC-EVs and explored the underlying mechanisms in vitro and in vivo DK models. Our results showed that mADSC-EVs have significant therapeutic effects including increasing tear volume and the ratio of lacrimal gland/body weight, promoting corneal nerve regeneration, and sensation recovery in streptozotocin (STZ)-induced DK mice. In addition, mADSC-EVs significantly reduced the inflammatory response involving DCs, consistently up-regulated protein expression of the NGF/TrkA pathway, and importantly, reduced lipopolysaccharide (LPS)-mediated IL-6 and TNF-α expression and directly dependent on TrkA in the induced culture of bone marrow-derived DCs (BMDCs). Taken together, our findings revealed that mADSC-EVs promoted diabetic corneal epithelial wound healing through NGF/TrkA pathway activation involving DCs. Given the significant therapeutic efficacy of mADSC-EVs and its clinical application, mADSC-EVs appears to be a promising new therapy for DK.

Peroxisome proliferator-activated receptor-α (PPARα) regulates wound healing and mitochondrial metabolism in the cornea

Diabetes can result in impaired corneal wound healing. Mitochondrial dysfunction plays an important role in diabetic complications. However, the regulation of mitochondria function in the diabetic cornea and its impacts on wound healing remain elusive. The present study aimed to explore the molecular basis for the disturbed mitochondrial metabolism and subsequent wound healing impairment in the diabetic cornea. Seahorse analysis showed that mitochondrial oxidative phosphorylation is a major source of ATP production in human corneal epithelial cells. Live corneal biopsy punches from type 1 and type 2 diabetic mouse models showed impaired mitochondrial functions, correlating with impaired corneal wound healing, compared to nondiabetic controls. To approach the molecular basis for the impaired mitochondrial function, we found that Peroxisome Proliferator-Activated Receptor-α (PPARα) expression was downregulated in diabetic human corneas. Even without diabetes, global PPARα knockout mice and corneal epithelium-specific PPARα conditional knockout mice showed disturbed mitochondrial function and delayed wound healing in the cornea, similar to that in diabetic corneas. In contrast, fenofibrate, a PPARα agonist, ameliorated mitochondrial dysfunction and enhanced wound healing in the corneas of diabetic mice. Similarly, corneal epithelium-specific PPARα transgenic overexpression improved mitochondrial function and enhanced wound healing in the cornea. Furthermore, PPARα agonist ameliorated the mitochondrial dysfunction in primary human corneal epithelial cells exposed to diabetic stressors, which was impeded by siRNA knockdown of PPARα, suggesting a PPARα-dependent mechanism. These findings suggest that downregulation of PPARα plays an important role in the impaired mitochondrial function in the corneal epithelium and delayed corneal wound healing in diabetes.

The effect of a-Lipoic acid (ALA) on oxidative stress, inflammation, and apoptosis in high glucose-induced human corneal epithelial cells

PURPOSE

Oxidative stress and inflammation had been proved to play important role in the progression of diabetic keratopathy (DK). The excessive accumulation of AGEs and their bond to AGE receptor (RAGE) in corneas that cause the formation of oxygen radicals and the release of inflammatory cytokines, induce cell apoptosis. Our current study was aimed to evaluate the effect of ALA on AGEs accumulation as well as to study the molecular mechanism of ALA against AGE-RAGE axis mediated oxidative stress, apoptosis, and inflammation in HG-induced HCECs, so as to provide cytological basis for the treatment of DK.

METHODS

HCECs were cultured in a variety concentration of glucose medium (5.5, 10, 25, 30, 40, and 50 mM) for 48 h. The cell proliferation was evaluated by CCK-8 assay. Apoptosis was investigated with the Annexin V- fluorescein isothiocyanate (V-FITC)/PI kit, while, the apoptotic cells were determined by flow cytometer and TUNEL cells apoptosis Kit. According to the results of cell proliferation and cell apoptosis, 25 mM glucose medium was used in the following HG experiment. The effect of ALA on HG-induced HCECs was evaluated. The HCECs were treated with 5.5 mM glucose (normal glucose group, NG group), 5.5 mM glucose + 22.5 mM mannitol (osmotic pressure control group, OP group), 25 mM glucose (high glucose group, HG group) and 25 mM glucose + ALA (HG + ALA group) for 24 and 48 h. The accumulation of intracellular AGEs was detected by ELISA kit. The RAGE, catalase (CAT), superoxide dismutase 2 (SOD2), cleaved cysteine-aspartic acid protease-3 (Cleaved caspase-3), Toll-like receptors 4 (TLR4), Nod-like receptor protein 3 (NLRP3) inflammasome, interleukin 1 beta (IL-1 ß), and interleukin 18 (IL-18) were quantified by RT-PCR, Western blotting, and Immunofluorescence, respectively. Reactive oxygen species (ROS) production was evaluated by fluorescence microscope and fluorescence microplate reader.

RESULTS

When the glucose medium was higher than 25 mM, cell proliferation was significantly inhibited and apoptosis ratio was increased (P < 0.001). In HG environment, ALA treatment alleviated the inhibition of HCECs in a dose-dependent manner, 25 μM ALA was the minimum effective dose. ALA could significantly reduce the intracellular accumulation of AGEs (P < 0.001), activate protein and genes expression of CAT and SOD2 (P < 0.001), and therefore inhibited ROS-induced oxidative stress and cells apoptosis. Besides, ALA could effectively down-regulate the protein and gene level of RAGE, TLR4, NLRP3, IL-1B, IL-18 (P < 0.05), and therefore alleviated AGEs-RAGE-TLR4-NLRP3 pathway-induced inflammation in HG-induced HCECs.

CONCLUSION

Our study indicated that ALA could be a desired treatment for DK due to its potential capacity of reducing accumulation of advanced glycation end products (AGEs) and down-regulating AGE-RAGE axis-mediated oxidative stress, cell apoptosis, and inflammation in high glucose (HG)-induced human corneal epithelial cells (HCECs), which may provide cytological basis for therapeutic targets that are ultimately of clinical benefit.