Topical Administration of GLP-1 Receptor Agonists Prevents Retinal Neurodegeneration in Experimental Diabetes

Topical administration of GLP-1 eyedrops improves retinal ganglion cell function by facilitating presynaptic GABA release in early experimental diabetes

JOURNAL/nrgr/04.03/01300535-202602000-00048/figure1/v/2025-05-05T160104Z/r/image-tiff Diabetic retinopathy is a prominent cause of blindness in adults, with early retinal ganglion cell loss contributing to visual dysfunction or blindness. In the brain, defects in γ-aminobutyric acid synaptic transmission are associated with pathophysiological and neurodegenerative disorders, whereas glucagon-like peptide-1 has demonstrated neuroprotective effects. However, it is not yet clear whether diabetes causes alterations in inhibitory input to retinal ganglion cells and whether and how glucagon-like peptide-1 protects against neurodegeneration in the diabetic retina through regulating inhibitory synaptic transmission to retinal ganglion cells. In the present study, we used the patch-clamp technique to record γ-aminobutyric acid subtype A receptor-mediated miniature inhibitory postsynaptic currents in retinal ganglion cells from streptozotocin-induced diabetes model rats. We found that early diabetes (4 weeks of hyperglycemia) decreased the frequency of GABAergic miniature inhibitory postsynaptic currents in retinal ganglion cells without altering their amplitude, suggesting a reduction in the spontaneous release of γ-aminobutyric acid to retinal ganglion cells. Topical administration of glucagon-like peptide-1 eyedrops over a period of 2 weeks effectively countered the hyperglycemia-induced downregulation of GABAergic mIPSC frequency, subsequently enhancing the survival of retinal ganglion cells. Concurrently, the protective effects of glucagon-like peptide-1 on retinal ganglion cells in diabetic rats were eliminated by topical administration of exendin-9-39, a specific glucagon-like peptide-1 receptor antagonist, or SR95531, a specific antagonist of the γ-aminobutyric acid subtype A receptor. Furthermore, extracellular perfusion of glucagon-like peptide-1 was found to elevate the frequencies of GABAergic miniature inhibitory postsynaptic currents in both ON- and OFF-type retinal ganglion cells. This elevation was shown to be mediated by activation of the phosphatidylinositol-phospholipase C/inositol 1,4,5-trisphosphate receptor/Ca 2+ /protein kinase C signaling pathway downstream of glucagon-like peptide-1 receptor activation. Moreover, multielectrode array recordings revealed that glucagon-like peptide-1 functionally augmented the photoresponses of ON-type retinal ganglion cells. Optomotor response tests demonstrated that diabetic rats exhibited reductions in visual acuity and contrast sensitivity that were significantly ameliorated by topical administration of glucagon-like peptide-1. These results suggest that glucagon-like peptide-1 facilitates the release of γ-aminobutyric acid onto retinal ganglion cells through the activation of glucagon-like peptide-1 receptor, leading to the de-excitation of retinal ganglion cell circuits and the inhibition of excitotoxic processes associated with diabetic retinopathy. Collectively, our findings indicate that the γ-aminobutyric acid system has potential as a therapeutic target for mitigating early-stage diabetic retinopathy. Furthermore, the topical administration of glucagon-like peptide-1 eyedrops represents a non-invasive and effective treatment approach for managing early-stage diabetic retinopathy.

Glucagon-Like Peptide 1 Receptor Agonist Stimulation Inhibits Laser-Induced Choroidal Neovascularization by Suppressing Intraocular Inflammation

Purpose

The glucagon-like peptide-1 receptor (GLP-1R), a diabetes therapy target, is expressed in multiple organs and is associated with neuroprotective, anti-inflammatory, and antitumor effects, particularly in cardiac and cerebral tissues. Although GLP-1's role in diabetic and ischemic retinopathies is well-studied, its influence on choroidal neovascularization (CNV) in exudative age-related macular degeneration (AMD) remains unclear. This study explored the effects of GLP-1 on CNV using a laser-induced mouse model.

Methods

The anti-angiogenic effects of GLP-1 were tested using ex vivo sprouting assays in 3-week-old C57BL/6J mice. In 6-week-old mice, GLP-1R localization in laser-induced CNV lesions was analyzed via immunohistochemistry. Liraglutide, a GLP-1R agonist, was administered subcutaneously for 7 days or by single intravitreal injection post-laser. Eyeballs collected on days 1 to 7 post-laser were analyzed using RT-qPCR for GLP-1R expression and inflammatory cytokines.

Results

GLP-1R-positive cells were detected in CNV lesions and were expressed in Iba-1-positive activated microglia or macrophages. They also expressed in abnormal retinal pigment epithelial cells and surrounding normal endothelial cells. NOD-like receptor protein 3 (NLRP3) inflammasome signaling was observed near CNV. Liraglutide inhibited angiogenesis in ex vivo assays and significantly reduced CNV formation with both subcutaneous and intravitreal administration. Additionally, Liraglutide inhibited expression of NLRP3, IL-1β, IL-6, and TNF expression compared with healthy controls. Intravitreal GLP-1R antagonist reduced subcutaneous effects.

Conclusions

Liraglutide suppresses CNV formation, likely via NLRP3 inflammasome inhibition. Intraocular GLP-1R appears to mediate anti-CNV effects, supporting GLP-1R agonists as potential adjunctive therapy for exudative AMD and warranting further investigation into its safety and clinical feasibility.

Characterization and Role of Glucagon-Like Peptide 1 Receptor in the Lacrimal Gland: Novel Insights into Diabetic Dry Eye Pathogenesis

This study aimed to investigate the expression of glucagon-like peptide 1 receptor (GLP-1R) in the lacrimal gland and explore the effects of topical application of GLP-1R agonist on lacrimal gland function in a murine model of type 1 diabetes. Tear secretion was evaluated using phenol red threads, RNA sequencing was used to explore gene expression profiles associated with hyperglycemia-induced lacrimal gland injuries, and histologic analysis was conducted to evaluate the degree of damage. The expression of GLP-1R in the lacrimal gland was first identified, and a down-regulation trend associated with diabetes was observed. RNA-sequencing data from lacrimal gland tissues revealed that differentially expressed genes were enriched in inflammatory response pathways. Histologic analysis demonstrated persistent hyperglycemia-induced infiltration of inflammatory cells and progressive fibrosis in the lacrimal gland, resulting in atrophy and diminished tear secretion. Topical application of liraglutide effectively attenuated inflammation and alleviated fibrosis, thus promoting tear production in diabetic mice. Additionally, local intervention with liraglutide promoted autophagy degradation function in the lacrimal gland. This study represents the first validation of GLP-1R expression in the lacrimal gland and its down-regulation induced by diabetes. Additionally, these findings demonstrate that topical administration of liraglutide eye drops, a GLP-1R agonist, can effectively mitigate hyperglycemia-induced damage in the lacrimal gland while enhancing tear secretion.

Blueberry Anthocyanin Extracts (BAEs) Protect Retinal and Retinal Pigment Epithelium Function from High-Glucose-Induced Apoptosis by Activating GLP-1R/Akt Signaling

Diabetic retinopathy is a severe diabetes complication leading to vision impairment and blindness primarily due to the disruption of insulin signaling in the retina. This study investigated the protective effects of blueberry anthocyanin extracts (BAEs) and its main component, anthocyanin-3-glucoside (C3G), in the retinas of diabetic mice and ARPE-19 cells under high-glucose (HG) conditions. The results showed that diabetic mice suffered significant weight loss, elevated glycemic levels, and increased retinal cell apoptosis after 10 weeks. Treatment with various doses of BAEs resulted in a significant reduction in glycemic levels, weight stabilization, decreased levels of inflammatory cytokines, and inhibition of retinal cell apoptosis. These findings suggested that BAEs possess hypoglycemic properties, potentially mitigating diabetes-induced retinal damage by modulating associated signaling pathways. Immunoblotting analysis revealed that persistent hyperglycemia impaired the Akt/GSK3β signaling pathway in diabetic mice, while high doses of BAEs significantly restored the function of these pathways and promoted GLP-1 release, enhancing GLP-1R expression in the retina and potentially mitigating retinal injury. Finally, studies on the effects of C3G on ARPE-19 cell models deficient in REDD1 under HG conditions showed that C3G protected cells from HG damage through the GLP-1R/Akt signaling pathway. In conclusion, this research provides valuable insights into the therapeutic potential of BAEs and C3G for managing diabetes-related ocular complications.

Relationship of OCT-Based Diabetic Retinal Neurodegeneration to the Development and Progression of Diabetic Retinopathy: A Cohort Study

Purpose

To evaluate the relationship between diabetic retinal neurodegeneration (DRN), as quantified by optical coherence tomography (OCT), to the development of diabetic retinopathy (DR), progression of DR, and development of proliferative DR (PDR).

Methods

This was a prospective cohort study, including 385 eyes with no DR or nonproliferative DR at baseline. The thicknesses of the macular ganglion cell-inner plexiform layer (m-GCIPL), macular retinal nerve fiber layer, and peripapillary RNFL (p-RNFL) were measured using Cirrus OCT (Carl Zeiss Meditec, Dublin, CA, USA). DR outcomes were determined from macula- and optic disc-centered fundus photographs, following the modified Airlie House classification system. Cox proportional hazards models were used to estimate hazard ratio (HR) adjusting for age, mean arterial blood pressure, diabetes mellitus duration, HbA1c, diabetic kidney disease, axial length, OCT signal strength, and disc area (for p-RNFL only).

Results

After a median follow-up of 6.2 years (range 5.0-7.7 years), 79 eyes developed DR, 99 eyes developed DR progression, and 38 eyes developed PDR. Thinner mean and sectorial m-GCIPL thicknesses were significantly associated with higher risk of DR development, with HRs ≥ 1.373 (1.023-1.843), except for the superonasal and superotemporal sectors. Similar to DR development, thinner m-GCIPL thicknesses were significantly associated with DR progression and PDR development, with HRs ranging from 1.306 (1.094-1.559) to 2.331 (1.524-3.566). Additionally, the inclusion of inferior m-GCIPL thickness significantly improved the predictive discrimination for DR development (C statistics: 0.661 vs. 0.705, P < 0.001), and DR progression (C statistics: 0.704 vs. 0.729, P < 0.001), as well as inferotemporal m-GCIPL for PDR development (C statistic: 0.917 vs. 0.930, P < 0.001) beyond established risk factors.

Conclusions

OCT measurements that elucidate DRN may enhance prognostic identification and predictive discrimination of DR development, DR progression, and PDR development beyond established risk factors.

Glucagon-like Peptide-1 Receptor Agonist Impact on Chronic Ocular Disease Including Age-Related Macular Degeneration

PURPOSE

Glucagon-like peptide-1 receptor agonists (GLP-1RAs) have been shown to exert neuroprotective and anti-inflammatory effects across multiple organ systems. This study investigated whether GLP-1RAs influence the risk for age-related ocular diseases.

DESIGN

Retrospective cohort study.

PARTICIPANTS

This study used an electronic health records platform of patients in the United States. Patients > 60 years with at least 5 years of ophthalmology follow-up and medication prescription documentation were included. There were 5 medication groups: GLP-1RA, metformin, insulin, statin, or aspirin users. Cohorts were propensity matched (1:1) on demographics and chronic disease risk factors.

MAIN OUTCOME MEASURES

Outcomes of cataract, ocular hypertension, primary open-angle glaucoma, nonexudative age-related macular degeneration (AMD), and exudative AMD were compared 5 years after initial medication prescription. We then examined earlier time points within the 5-year period. Significance was defined as P < 0.05 with a hazard ratio (HR) threshold of > 1.1 or < 0.9.

RESULTS

Of the 9669 patients taking GLP-1RAs, 84.4% had a diagnosis of diabetes with an average body mass index (BMI) of 36.2 kg/m2. Propensity-matched cohorts demonstrated that GLP-1RAs were associated with a reduced hazard of nonexudative AMD compared with metformin (HR, 0.68; 95% CI, 0.56-0.84), insulin (HR, 0.72; 95% CI, 0.58-0.89), and statins (HR, 0.70; 95% CI, 0.57-0.87). These findings were validated compared with aspirin and in an independent older cohort of patients. This significant reduction appeared after 3 years compared with metformin (HR, 0.69; 95% CI, 0.52-0.91), insulin (HR, 0.66; 95% CI, 0.5-0.87), and statins (HR, 0.67; 95% CI, 0.51-0.88). Time course results were validated using independent cohorts of propensity-matched patients taking medications for 3 years. Notably, GLP-1RAs also significantly reduced the risk of exudative AMD (HR, 0.70; 95% CI, 0.58-0.84) and primary open-angle glaucoma (HR, 0.58; 95% CI, 0.45-0.76) compared with insulin after 3 years. Use of GLP-1RAs showed no persistent impact on the risk of cataract formation or ocular hypertension compared with other medications.

CONCLUSIONS

This study suggests that GLP-1RAs may reduce the risk of multiple age-related ocular diseases and the need for future prospective studies to validate these findings.

FINANCIAL DISCLOSURE(S)

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

Semaglutide: Nonarteritic Anterior Ischemic Optic Neuropathy in the FDA adverse event reporting system - A disproportionality analysis

Semaglutide, a glucagon-like peptide-1 (GLP-1) receptor agonist, is used for type 2 diabetes (T2D) and approved for obesity by the FDA in 2022 and in Europe in 2023. Its increasing use has raised concerns about access for T2D patients and potential adverse events (AE), such as Nonarteritic Anterior Ischemic Optic Neuropathy (NAION). This study investigates the association between semaglutide and these AE using the FDA Adverse Event Reporting System (FAERS). We conducted a disproportionality analysis using FAERS data. AE were identified using MedDRA Preferred Terms (PTs) and related terms. OpenVigil 2.1 was used for data extraction and analysis. This system is a spontaneous safety surveillance database for drugs. The participants are patients who reported AE related to GLP-1 receptor agonists in the FAERS database from January 1, 2004, to September 30, 2024. Reporting Odds Ratios (ROR) and Proportional Reporting Ratios (PRR) were calculated to assess the association between GLP-1 receptor agonists and the AE. Semaglutide showed a significant ROR and PRR for NAION, suggesting a stronger association compared to other GLP-1 receptor agonists. The findings suggest a disproportionate reporting signal for semaglutide and NAION. The mechanisms behind these associations are not fully understood but may involve effects on the hypothalamus and vascular health. Further research is necessary to confirm these findings ensure the safe use of semaglutide, given the potential risk associated with this rare but severe adverse event.

Impact of glucagon-like peptide-1 receptor agonists on diabetic retinopathy: A meta-analysis of clinical studies emphasising retinal changes as a primary outcome

BACKGROUND

To determine if glucagon-like peptide-1 receptor agonists (GLP-1RA) are associated with the development and progression of diabetic retinopathy (DR).

METHODS

A systematic search was conducted on PubMed, Cochrane Library, and Embase from inception to February 2024 to identify clinical studies reporting the development of and changes in DR as the primary outcome in patients with type 2 diabetes taking GLP-1RA, insulin, or oral antidiabetic medication (OAD). Two researchers independently completed the search and referred to a third as necessary. Data for meta-analysis was pooled using a random-effects model.

RESULTS

Analysis of seven studies representing 242 537 patients showed a significantly decreased risk of incidence of DR between GLP-1RA and insulin use (RR = 0.66, 95% CI (0.48, 0.91), p = 0.01). There was no difference in the risk of DR complications (e.g., vitreous haemorrhage, retinal detachment, or requiring treatment with intravitreal injections, lasers, vitrectomy). Between GLP-1RA and OAD use, there was no difference in the risk of incidence of DR, while there was a significantly increased risk of DR complications (RR = 1.39, 95% CI (1.07, 1.80), p = 0.01).

CONCLUSION

Our findings indicate no elevated risk of incidence of DR linked to GLP-1RA compared to insulin. In fact, GLP-1RA may offer potential advantages over insulin regarding the overall incidence of DR. The increased risk of DR requiring treatment and associated complications in the GLP-1RA group compared to OAD may be due to the transient progression of DR associated with a rapid decrease in HbA1c - a phenomenon not specific to GLP-1RA and warrants further investigation.

Reversible bilateral central scotoma under scotopic conditions associated with oral semaglutide

Introduction

Semaglutide is a glucagon-like peptide-1 receptor agonist that treats type 2 diabetes mellitus and can be used as an adjunct for weight loss when combined with exercise and diet. Here we report a case of a bilateral, incongruent central visual scotoma under scotopic conditions in a board-certified ophthalmologist associated with semaglutide use that resolved quickly following medication discontinuation.

Case report

A 72-year-old male ophthalmologist (JAD) started 3.0 mg daily oral semaglutide (Rybelsus) to help with weight loss and seventeen days after treatment initiation developed a small, round central scotoma in his right eye that enlarged over several days. After two days a similar but smaller scotoma developed in his left eye. These symptoms were present only under scotopic conditions and were not visible in daylight or artificially lit conditions. When symptoms developed in the left eye, the medication was discontinued, and all symptoms completely resolved two days later. A subsequent clinical evaluation revealed no abnormalities on macular optical coherence tomography, fundus photography, fundus autofluorescence or Humphrey visual field.

Conclusions

This case of a bilateral central scotoma under scotopic conditions that resolved after medication discontinuation expands the knowledge of potential side effects from this increasingly popular diabetic and weight loss medication.

Incretin-based therapy: a new horizon in diabetes management

Diabetes mellitus, a metabolic syndrome characterized by hyperglycemia and insulin dysfunction, often leads to serious complications such as neuropathy, nephropathy, retinopathy, and cardiovascular disease. Incretins, gut peptide hormones released post-nutrient intake, have shown promising therapeutic effects on these complications due to their wide-ranging biological impacts on various body systems. This review focuses on the role of incretin-based therapies, particularly Glucagon-like peptide-1 (GLP-1) agonists and dipeptidyl peptidase-4 (DPP-4) inhibitors, in managing diabetes and its complications. We also discuss the potential of novel agents like semaglutide, a recently approved oral compound, and dual/triple agonists targeting GLP-1/GIP, GLP-1/glucagon, and GLP-1/GIP/glucagon receptors, which are currently under investigation. The review aims to provide a comprehensive understanding of the beneficial impacts of natural incretins and the therapeutic potential of incretin-based therapies in diabetes management.

Ocular and Plasma Pharmacokinetics of Sitagliptin Eye Drops: Preclinical Data

Background/Objectives: Early stages of diabetic retinopathy are currently considered an unmet medical need due to the lack of effective treatments beyond proper monitoring and control of glycemia and blood pressure. Sitagliptin eye drops have emerged as a new therapeutic approach against early stages of the disease, as they can prevent its main hallmarks, including both neurodegeneration and microvascular impairment. Interestingly, all of these effects occur without any glycemic systemic improvement. In the present study, we aimed to investigate the pharmacokinetics and distribution of the drug within the eye and plasma. Methods: A total of 48 male New Zealand rabbits were treated with topical administration (eye drops) of sitagliptin at two concentrations: 5 mg/mL and 10 mg/mL. Blood, iris/ciliary body, retina/choroid, aqueous humor, and vitreous humor samples were collected at specific intervals post-administration (10 and 30 min and 1, 3, 6, 15, and 24 h), processed, and analyzed using an LC-MS/MS method. The pharmacokinetics of sitagliptin were then calculated, and statistical comparisons were performed. Results: Our findings indicate that sitagliptin reaches the retina prior to the aqueous and vitreous humors, suggesting that its absorption follows the transscleral route. Additionally, systemic absorption was minimal and below pharmacologically active concentrations. Conclusions: These results support the use of an eye drop formulation for the treatment of diabetic retinopathy and other retinal diseases.

The Effect of Glucagon-Like Peptide-1 Receptor Agonists on Diabetic Retinopathy at a Tertiary Care Center

Objective

The potential association between diabetic retinopathy (DR) worsening and glucagon-like peptide-1 receptor agonists (GLP-1RA) has affected therapeutic management of diabetic patients but remains controversial. This study compared rates of DR development or progression in patients on GLP-1RA to those on SGLT-2 inhibitors (SGLT-2I).

Design

Retrospective cohort study.

Subjects

Nine hundred eighty-one patients with diabetes mellitus taking GLP-1RA or SGLT-2I, the latter serving as controls, between 2012 and 2023.

Methods

Patients were one-to-one greedy matched by propensity scores on race/ethnicity, age, smoking status, baseline body mass index and hemoglobin A1c %, type of diabetes mellitus, baseline DR status and history of DR procedures, duration of drug use, whether they had taken both drug types, and change in hemoglobin A1c % after 1 year on the drug.

Main Outcome Measures

The primary outcome was clinical DR development or progression (termed "worsening") detected by International Classification of Diseases (ICD), 10th edition codes, confirmed by manual review, on GLP-1RA compared with SGLT-2I after propensity score matching. Secondary outcomes included DR worsening indicated by need for procedures due to complications, and time-to-first DR worsening event.

Results

The study included 692 GLP-1RA users and 289 SGLT-2I users. The mean follow-up periods for GLP-1RA versus SGLT-2I use were 1.54 (standard deviation [SD] 1.82) years and 1.38 (SD 1.56) years, respectively. The rates of clinical worsening were 2.3% and 2.8%, respectively. After propensity score matching, an association was not identified between GLP1-RA and DR worsening neither clinically by ICD-10 codes (odds ratio [OR] = 0.33, 95% confidence interval [CI]: 0.11-1.03) nor by indication for procedures (OR = 0.50, 95% CI 0.13-2.00). Time-to-first DR worsening did not differ between the groups in Kaplan-Meier analysis. The most common type of clinical worsening event for both drug types was vitreous hemorrhage (43.7% and 50% of worsening events in GLP-1RA and SGLT-2I users, respectively). The most common DR procedure indicated was anti-VEGF injections (34% and 35% of GLP-1RA and SGLT-2I events, respectively).

Conclusions

Diabetic retinopathy worsening, either clinically or by procedures, was not associated with GLP-1RA compared with SGLT-2I, both before and after propensity score matching on all analyses, including time-to-first worsening event.

Financial Disclosures

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

Diabetic retinopathy: New concepts of screening, monitoring, and interventions

The science of diabetes care has progressed to provide a better understanding of the oxidative and inflammatory lesions and pathophysiology of the neurovascular unit within the retina (and brain) that occur early in diabetes, even prediabetes. Screening for retinal structural abnormalities, has traditionally been performed by fundus examination or color fundus photography; however, these imaging techniques detect the disease only when there are sufficient lesions, predominantly hemorrhagic, that are recognized to occur late in the disease process after significant neuronal apoptosis and atrophy, as well as microvascular occlusion with alterations in vision. Thus, interventions have been primarily oriented toward the later-detected stages, and clinical trials, while demonstrating a slowing of the disease progression, demonstrate minimal visual improvement and modest reduction in the continued loss over prolonged periods. Similarly, vision measurement utilizing charts detects only problems of visual function late, as the process begins most often parafoveally with increasing number and progressive expansion, including into the fovea. While visual acuity has long been used to define endpoints of visual function for such trials, current methods reviewed herein are found to be imprecise. We review improved methods of testing visual function and newer imaging techniques with the recommendation that these must be utilized to discover and evaluate the injury earlier in the disease process, even in the prediabetic state. This would allow earlier therapy with ocular as well as systemic pharmacologic treatments that lower the and neuro-inflammatory processes within eye and brain. This also may include newer, micropulsed laser therapy that, if applied during the earlier cascade, should result in improved and often normalized retinal function without the adverse treatment effects of standard photocoagulation therapy.

Glucagon-Like Peptide-1 Receptor Agonists are Not Associated with an Increased Risk of Progressing to Vision-Threatening Diabetic Retinopathy

PURPOSE

Glucagon-like peptide-1 receptor agonists (GLP-1RA) are used to treat type 2 diabetes mellitus (DM) by augmenting insulin release and sensitivity. We assessed the overall risk for development of vision-threatening diabetic retinopathy (VTDR), proliferative diabetic retinopathy (PDR), and diabetic macular edema (DME), among GLP-1RA users.

METHODS

A retrospective cohort of patients with NPDR newly started on a GLP-1RA from a national insurance claims database was compared to a cohort of patients treated with other oral anti-diabetic agents and matched for age, sex, race, index year, and number of active diabetic medications. Exclusions occurred for < 2 years in the database before diagnosis; prior diagnoses of PDR, DME, vitreous hemorrhage, and/or other retinal vascular diseases; and prior intraocular treatment for VTDR.

RESULTS

A total of 6093 users of GLP-1RA were matched to 14,122 controls. In the GLP-1RA cohort, 632 (10.1%), 76 (1.2%), and 544 (8.9%) patients progressed to VTDR, PDR, or DME, respectively. This is compared to 1332 (9.5%) VTDR, 165 (1.2%) PDR, or 1148 (8.1%) DME in the control group. Accounting for underlying DM severity with IPTW, no difference in hazard was seen in the GLP-1RA cohort compared to controls for progression to VTDR (HR = 1.02, 95%CI: 0.92-1.14 p = 0.69), DME (HR = 1.06, 95%CI: 0.95-1.1.9, p = 0.31), or PDR (HR = 0.81, 95%CI: 0.58-1.12, p = 0.20).

CONCLUSION

We found no difference in the risk for vision-threatening diabetic retinopathy, nor for its component diseases, DME or PDR, with GLP-1RA use compared to other oral anti-hyperglycemic agents in patients with NPDR.

Comparative Effectiveness of Glucagon-Like Peptide-1 Receptor Agonists, Sodium-Glucose Cotransporter 2 Inhibitors, Dipeptidyl Peptidase-4 Inhibitors, and Sulfonylureas for Sight-Threatening Diabetic Retinopathy

OBJECTIVE

To investigate whether the choice of glucose-lowering agent for type 2 diabetes (T2D) impacts a patient's risk of developing sight-threatening diabetic retinopathy complications.

DESIGN

Retrospective observational database study emulating an idealized target trial.

SUBJECTS

Adult (≥21 years) enrollees in United States commercial, Medicare Advantage, and Medicare fee-for-service plans from January 1, 2014, to December 31, 2021, with T2D and moderate cardiovascular disease (CVD) risk who had no baseline history of advanced diabetic retinal complications, initiating treatment with glucagon-like peptide-1 receptor agonists (GLP-1 RA), sodium-glucose cotransporter 2 inhibitors (SGLT2i), dipeptidyl peptidase-4 inhibitors (DPP-4i), and sulfonylureas.

METHODS

We used inverse propensity scoring weights in time-to-event Cox proportional hazards models.

MAIN OUTCOME MEASURES

Treatment for either diabetic macular edema or proliferative diabetic retinopathy.

RESULTS

The final study population included 371 698 patients, of whom 42 265 initiated GLP-1 RA, 53 476 initiated SGLT2i, 78 444 initiated DPP-4i, and 197 513 initiated sulfonylurea agents. The probability of treatment for sight-threatening retinopathy within 2 and 5 years was 0.3% and 0.7% for patients initiating SGLT2i (median follow-up 830 [interquartile range (IQR), 343-1401] days), 0.4% and 1.0% for GLP-1 RA (669 [IQR, 256-1167] days), 0.4% and 0.9% for DPP-4i (1263 [IQR, 688-1938] days), and 0.5% and 1.2% for sulfonylurea (1223 [IQR, 662-1879] days). Sodium-glucose cotransporter 2 inhibitors use was associated with a lower risk of treatment for sight-threatening retinopathy compared with all other medication classes, including GLP-1 RA (hazard ratio [HR], 0.73; 95% confidence interval [CI], 0.55-0.97), DPP-4i (HR, 0.79; 95% CI, 0.64-0.97), and sulfonylurea (HR, 0.61; 95% CI, 0.50-0.74). Glucagon-like peptide-1 receptor agonists use was associated with a similar risk of sight-threatening retinopathy as DPP-4i (HR, 1.07; 95% CI, 0.85-1.35) and sulfonylurea (HR, 0.83; 95% CI, 0.67-1.03).

CONCLUSIONS

Sodium-glucose cotransporter 2 inhibitors use was associated with a lower risk of sight-threatening diabetic retinopathy among adults with T2D and moderate CVD risk compared with other glucose-lowering therapies. Glucagon-like peptide-1 receptor agonists do not confer increased retinal risk, relative to DPP-4i and sulfonylurea medications.

FINANCIAL DISCLOSURE(S)

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

New Insights into the Pleiotropic Actions of Dipeptidyl Peptidase-4 Inhibitors Beyond Glycaemic Control

Dipeptidyl peptidase-4 (DPP-4) is a multifunctional serine ectopeptidase that cleaves and modifies a plethora of substrates, including regulatory peptides, cytokines and chemokines. DPP-4 is implicated in the regulation of immune response, viral entry, cellular adhesion, metastasis and chemotaxis. Regarding its numerous substrates and extensive expression inside the body, multitasking DPP-4 has been assumed to participate in different pathophysiological mechanisms. DPP-4 inhibitors or gliptins are increasingly used for the treatment of type 2 diabetes mellitus. Several reports from experimental and clinical studies have clarified that DPP-4 inhibitors exert many beneficial pleiotropic effects beyond glycaemic control, which are mediated by anti-inflammatory, anti-oxidant, anti-fibrotic and anti-apoptotic actions. The present review will highlight the most recent findings in the literature about these pleiotropic effects and the potential mechanisms underlying these benefits, with a specific focus on the potential effectiveness of DPP-4 inhibitors in coronavirus disease-19 and diabetic kidney disease.

Glucagon-like Peptide 1 Receptor Agonist use and the effect on diabetic retinopathy: An uncertain relationship

Glucagon-like Peptide 1 Receptor Agonists (GLP-1 RAs) are a group of relatively novel medications for the treatment of diabetes mellitus. These medications can mimic the naturally occurring incretins of the body, which promote the release of insulin in response to hyperglycaemia. The anti-glycaemic effects of these medications can be profound and carry other metabolic benefits such as promoting weight loss. Clinical trials have shown GLP-1 RAs are safe to use from a cardiovascular perspective. However, some trials have suggested a link between GLP-1 RA use and worsening diabetic retinopathy. The conclusions surrounding this link are poorly established as data is drawn primarily from cardiovascular outcome trials. If an association does exist, a possible explanation might be the observed phenomenon of early worsening diabetic retinopathy with rapid correction of hyperglycaemic states. Trials which look at diabetic retinopathy as a primary outcome in relation to use of GLP-1 RAs are sparse and warrant investigation given the growing use of this group of medications. Therefore currently, it is uncertain what effect, beneficial or adverse, GLP-1 RA use has on diabetic retinopathy. This article provides an overview of GLP-1 RA use as a treatment for diabetes mellitus and the current understanding of their relationship with diabetic retinopathy.

Vildagliptin ameliorates intrapulmonary vasodilatation and angiogenesis in chronic common bile duct ligation-induced hepatopulmonary syndrome in rat

INTRODUCTION

Experimental hepatopulmonary syndrome (HPS) is best reproduced in the rat common bile duct ligation (CBDL) model. Vildagliptin (Vild) is an anti-hyperglycemic drug that exerts beneficial anti-inflammatory, anti-oxidant and anti-fibrotic effects. Therefore, the present search aimed to explore the possible effectiveness of Vild in CBDL-induced HPS model.

METHODS

Four groups of male Wistar rats which weigh 220-270 g were used, including the normal control group, the sham control group, the CBDL group and CBDL+Vild group. The first three groups received i.p. saline, while the last group was treated with i.p. Vild (10 mg/kg/day) from the 15th to 28th day of the experiment.

RESULTS

CBDL decreased the survivability and body weight of rats, increased diameter of the pulmonary vessels, and altered the arterial blood gases and the liver function parameters. Additionally, it increased the pulmonary expressions of endothelin-1 (ET-1) and tumor necrosis factor-α (TNF-α) mRNA as well as endothelial nitric oxide synthase (eNOS), inducible nitric oxide synthase (iNOS) and vascular endothelial growth factor-A (VEGF-A) proteins. The CBDL rats also exhibited elevation of the pulmonary interleukin-6 (IL-6), dipeptidyl peptidase-4 (DPP-4) and nitric oxide (NO) levels along with reduction of the pulmonary total anti-oxidant capacity and glucagon-like peptide-1 (GLP-1) levels. Vild mitigated these alterations and improved the histopathological abnormalities caused by CBDL.

CONCLUSION

Vild effectively attenuated CBDL-induced HPS through its anti-oxidant and anti-inflammatory effects along with its modulatory effects on ET-1/NOS/NO and TNF-α/IL-6/VEGF-A signaling implicated in the regulation of intrapulmonary vasodilatation and angiogenesis, respectively.

Retinopathy risk factors in patients with type 2 diabetes on liraglutide

Liraglutide, a glucagon-like peptide 1 receptor agonist, effectively treats type 2 diabetes(T2D) by lowering glucose levels, suppressing glucagon release, and promoting insulin secretion. Liraglutide has been shown to reduce body weight and glycated hemoglobin (HbA1c) levels and improve cardiovascular outcomes. However, evidence regarding the association between liraglutide and diabetic retinopathy in the Middle East is insufficient. Therefore, this study aimed to investigate the characteristics and risk factors of diabetic retinopathy in patients with T2D treated with liraglutide in Saudi Arabia. This retrospective cohort study was conducted on patients (≥14 years) with T2D treated with liraglutide between 2015 and 2021, who had a documented retinopathy assessment at baseline before liraglutide initiation and during follow-up, at King Abdulaziz Medical City (KAMC), Riyadh. Data collection included demographic information, retinopathy status, body mass index (BMI), and HbA1c level at baseline and follow-up after liraglutide use. The study included 181 patients with a mean age of 58.2 (9.8) years. Of these, 72.9% were females. At baseline, the median weight (interquartile range) was 88 (77-100) kg, diabetes duration was 19 (13-23.5) years, and HbA1c level was 9% (8-10%). Total of 69.6% were on insulin, 22.7% were on oral hypoglycemic agents, and 7.7% were on no other medications in addition to liraglutide. After a median of 2 years follow-up, both HbA1c level and weight decreased significantly (P < .001). Seventy-one of the 87 patients (81.6%) without retinopathy at baseline continued to show no retinopathy. Among patients with retinopathy at baseline, 25.5% showed improvement and 44.7% showed no change. In the multivariate binary mixed effect analysis, factors significantly associated with retinopathy were: use of insulin (odds ratio [OR]:2.68; 95% confidence interval [CI]: 1.18-6.09, P = .019), older age (OR:1.03; 95% CI: 1.00-1.06; P = .022), higher HbA1c level (OR:1.17; 95% CI: 1.02-1.34; P = .024), Hypertension (OR:2.56; 95% CI: 1.13-5.76; P=<.0001) and longer diabetes duration (OR:1.04; 95% CI: 1.00-1.08; P = .024). In conclusion, liraglutide use caused significant reductions in the HbA1c level and weight of patients with T2D. Most patients showed no change in retinopathy status after liraglutide use.

Glucagon-like peptide-1 receptor agonists rescued diabetic vascular endothelial damage through suppression of aberrant STING signaling

Glucagon-like peptide-1 receptor agonists (GLP-1 RAs) protect against diabetic cardiovascular diseases and nephropathy. However, their activity in diabetic retinopathy (DR) remains unclear. Our retrospective cohort study involving 1626 T2DM patients revealed superior efficacy of GLP-1 RAs in controlling DR compared to other glucose-lowering medications, suggesting their advantage in DR treatment. By single-cell RNA-sequencing analysis and immunostaining, we observed a high expression of GLP-1R in retinal endothelial cells, which was down-regulated under diabetic conditions. Treatment of GLP-1 RAs significantly restored the receptor expression, resulting in an improvement in retinal degeneration, vascular tortuosity, avascular vessels, and vascular integrity in diabetic mice. GO and GSEA analyses further implicated enhanced mitochondrial gene translation and mitochondrial functions by GLP-1 RAs. Additionally, the treatment attenuated STING signaling activation in retinal endothelial cells, which is typically activated by leaked mitochondrial DNA. Expression of STING mRNA was positively correlated to the levels of angiogenic and inflammatory factors in the endothelial cells of human fibrovascular membranes. Further investigation revealed that the cAMP-responsive element binding protein played a role in the GLP-1R signaling pathway on suppression of STING signaling. This study demonstrates a novel role of GLP-1 RAs in the protection of diabetic retinal vasculature by inhibiting STING-elicited inflammatory signals.

Redox Regulation of Immunometabolism in Microglia Underpinning Diabetic Retinopathy

Diabetic retinopathy (DR) is the leading cause of visual impairment and blindness among the working-age population. Microglia, resident immune cells in the retina, are recognized as crucial drivers in the DR process. Microglia activation is a tightly regulated immunometabolic process. In the early stages of DR, the M1 phenotype commonly shifts from oxidative phosphorylation to aerobic glycolysis for energy production. Emerging evidence suggests that microglia in DR not only engage specific metabolic pathways but also rearrange their oxidation-reduction (redox) system. This redox adaptation supports metabolic reprogramming and offers potential therapeutic strategies using antioxidants. Here, we provide an overview of recent insights into the involvement of reactive oxygen species and the distinct roles played by key cellular antioxidant pathways, including the NADPH oxidase 2 system, which promotes glycolysis via enhanced glucose transporter 4 translocation to the cell membrane through the AKT/mTOR pathway, as well as the involvement of the thioredoxin and nuclear factor E2-related factor 2 antioxidant systems, which maintain microglia in an anti-inflammatory state. Therefore, we highlight the potential for targeting the modulation of microglial redox metabolism to offer new concepts for DR treatment.

Role of myeloid cells in ischemic retinopathies: recent advances and unanswered questions

Myeloid cells including microglia and macrophages play crucial roles in retinal homeostasis by clearing cellular debris and regulating inflammation. These cells are activated in several blinding ischemic retinal diseases including diabetic retinopathy, where they may exert both beneficial and detrimental effects on neurovascular function and angiogenesis. Myeloid cells impact the progression of retinal pathologies and recent studies suggest that targeting myeloid cells is a promising therapeutic strategy to mitigate diabetic retinopathy and other ischemic retinal diseases. This review summarizes the recent advances in our understanding of the role of microglia and macrophages in retinal diseases and focuses on the effects of myeloid cells on neurovascular injury and angiogenesis in ischemic retinopathies. We highlight gaps in knowledge and advocate for a more detailed understanding of the role of myeloid cells in retinal ischemic injury to fully unlock the potential of targeting myeloid cells as a therapeutic strategy for retinal ischemia.

Special Issue: "Anti-inflammatory Effects of Glucagon-like Peptide-1"

From the failure of gut extracts in diabetic patients' therapy to the effective action in cardiovascular outcomes [...].

Compound Danshen dripping pills prevent early diabetic retinopathy: roles of vascular protection and neuroprotection

Introduction: Diabetic retinopathy (DR) represents a major cause of adult blindness, and early discovery has led to significant increase in the number of patients with DR. The drugs currently used for treatment, such as ranibizumab, mainly focus on the middle and late periods of DR, and thus do not meet the clinical need. Here, the potential mechanisms by which compound Danshen Dripping Pills (CDDP) might protect against early DR were investigated. Methods: Db/db mice were used to establish a DR model. The initial weights and HbA1c levels of the mice were monitored, and retinal pathology was assessed by hematoxylin-eosin (HE) staining. The vascular permeability of the retina and thickness of each retinal layer were measured, and electroretinogram were performed together with fundus fluorescein angiography and optical coherence tomography. The levels of inflammatory factors were examined in retinal tissue, as well as those of intercellular adhesion molecule 1 (ICAM-1), IL-6, and monocyte chemoattractant protein 1 (MCP-1) in the serum using ELISA. Immunohistochemistry was used to evaluate levels of vascular endothelial growth factor (VEGF), B-cell lymphoma 2 (Bcl-2), and Bclassociated X protein (Bax). Retinal cell injury and apoptosis were examined by TdT-mediated dUTP Nick End Labeling (TUNEL) assays. Results: The data showed that CDDP significantly improved cellular disarrangement. Imaging data indicated that CDDP could reduce vascular permeability and the amplitude of oscillatory potentials (OPs), and restore the thickness of the ganglion cell layer. Moreover, CDDP reduced the expression levels of inflammatory factors in both the retina and serum. Conclusion: These findings strongly suggest that CDDP prevents early DR through vascular and neuroprotection.

Associations of antidiabetic drugs with diabetic retinopathy in people with type 2 diabetes: an umbrella review and meta-analysis

Background

Diabetic retinopathy (DR) is the most frequent complication of type 2 diabetes and remains the leading cause of preventable blindness. Current clinical decisions regarding the administration of antidiabetic drugs do not sufficiently incorporate the risk of DR due to the inconclusive evidence from preceding meta-analyses. This umbrella review aimed to systematically evaluate the effects of antidiabetic drugs on DR in people with type 2 diabetes.

Methods

A systematic literature search was undertaken in Medline, Embase, and the Cochrane Library (from inception till 17th May 2022) without language restrictions to identify systematic reviews and meta-analyses of randomized controlled trials or longitudinal studies that examined the association between antidiabetic drugs and DR in people with type 2 diabetes. Two authors independently extracted data and assessed the quality of included studies using the AMSTAR-2 (A MeaSurement Tool to Assess Systematic Reviews) checklist, and evidence assessment was performed using the GRADE (Grading of recommendations, Assessment, Development and Evaluation). Random-effects models were applied to calculate relative risk (RR) or odds ratios (OR) with 95% confidence intervals (CI). This study was registered with PROSPERO (CRD42022332052).

Results

With trial evidence from 11 systematic reviews and meta-analyses, we found that the use of glucagon-like peptide-1 receptor agonists (GLP-1 RA), sodium-glucose cotransporter-2 inhibitors (SGLT-2i), or dipeptidyl peptidase-4 inhibitors (DPP-4i) was not statistically associated with the risk of DR, compared to either placebo (RR: GLP-1 RA, 0.98, 0.89-1.08; SGLT-2i, 1.00, 95% CI 0.79-1.27; DPP-4i, 1.17, 0.99-1.39) or other antidiabetic drugs. Compared to other antidiabetic drugs, meglitinides (0.34, 0.01-8.25), SGLT-2i (0.73, 0.10-5.16), thiazolidinediones (0.92, 0.67-1.26), metformin (1.15, 0.81-1.63), sulphonylureas (1.24, 0.93-1.65), and acarbose (4.21, 0.44-40.43) were not statistically associated with the risk of DR. With evidence from longitudinal studies only, insulin was found to have a higher risk of DR than other antidiabetic drugs (OR: 2.47, 95% CI: 2.04-2.99).

Conclusion

Our results indicate that antidiabetic drugs are generally safe to prescribe regarding the risk of DR among people with type 2 diabetes. Further robust and large-scale trials investigating the effects of insulin, meglitinides, and acarbose on DR are warranted.

Systematic review registration

https://www.crd.york.ac.uk/prospero/display_record.php?RecordID=332052, identifier CRD42022332052.

Blocking Hemopexin With Specific Antibodies: A New Strategy for Treating Diabetic Retinopathy

Hemopexin (HPX) is overexpressed in the retina of patients with diabetes and induces the breakdown of the blood-retinal barrier in vitro. The aim of this study was to evaluate whether HPX blockade by specific antibodies (aHPX) could avoid vascular leakage in vivo and microvascular angiogenesis in vitro and ex vivo. For this purpose, the effect of intravitreal (IVT) injections of aHPX on vascular leakage was evaluated in db/db mice and rats with streptozotocin-induced diabetes using the Evans Blue method. Retinal neurodegeneration and inflammation were also evaluated. The antiangiogenic effect of aHPX on human retinal endothelial cells (HRECs) was tested by scratch wound healing and tube formation using standardized methods, as well as by choroidal sprouting assays from retinal explants obtained in rats. We found that IVT injection of aHPX significantly reduced vascular leakage, retinal neurodegeneration, and inflammation. In addition, treatment with aHPX significantly reduced HREC migration and tube formation induced by high glucose concentration and suppressed choroidal sprouting even after vascular endothelial growth factor stimulation, with this effect being higher than obtained with bevacizumab. The antipermeability and antiangiogenic effects of IVT injection of aHPX suggest the blockade or inhibition of HPX as a new strategy for the treatment of advanced stages of diabetic retinopathy.

ARTICLE HIGHLIGHTS

Hemopexin (HPX) is the best-characterized permeability factor in steroid-sensitive nephrotic syndrome. We have previously reported that HPX is overexpressed in the retina of patients with diabetes and induces the breakdown of the blood-retinal barrier in vitro. Here, we report that intravitreal injection of anti-HPX antibodies significantly reduces vascular leakage, retinal neurodegeneration, and inflammation in diabetic murine models and that the immunoneutralization of HPX exerts a significant antiangiogenic effect in vitro and in retinal explants. The blockade of HPX can be considered as a new therapy for advanced stages of diabetic retinopathy.

Glucagon-Like Peptide-1 Receptor Agonist and Risk of Diabetic Retinopathy in Patients with Type 2 Diabetes Mellitus: A Systematic Review and Meta-analysis of Randomized Placebo-Controlled Trials

BACKGROUND

Glucagon-like peptide 1 receptor agonists (GLP-1RAs) exhibit glucose-lowering, weight-reducing, and blood pressure-lowering effects. Nevertheless, a debate exists concerning the association between GLP-1RA treatment and the risk of diabetic retinopathy (DR) in patients diagnosed with type 2 diabetes mellitus (T2DM).

OBJECTIVE

To ascertain the risk of DR in patients with T2DM undergoing GLP-1RA treatment, we conducted a meta-analysis utilizing data derived from randomized placebo-controlled studies (RCTs).

METHODS

A comprehensive literature search was conducted using PubMed, Cochrane Library, Web of Science, and EMBASE. We focused on RCTs involving the use of GLP-1RAs in patients with T2DM. Utilizing R software, we compared the risk of DR among T2DM patients undergoing GLP-1RA treatment. The Cochrane risk of bias method was employed to assess the research quality.

RESULTS

The meta-analysis incorporated data from 20 RCTs, encompassing a total of 24,832 T2DM patients. Across all included trials, randomization to GLP-1 RA treatment did not demonstrate an increased risk of DR (odds ratio = 1.17; 95% CI 0.98-1.39). Furthermore, no significant heterogeneity or publication bias was detected in the analysis.

CONCLUSION

The results of this systematic review and meta-analysis indicate that the administration of GLP-1 RA is not associated with an increased risk of DR. PROSPERO REGISTRATION IDENTIFIER: CRD42023413199.

Alleviate oxidative stress in diabetic retinopathy: antioxidant therapeutic strategies

OBJECTIVES

This review outlines the function of oxidative stress in DR and discusses therapeutic strategies to treat DR with antioxidants.

METHODS

Published papers on oxidative stress in DR and therapeutic strategies to treat DR with antioxidants were collected and reviewed via database searching on PubMed.

RESULTS

The abnormal development of DR is a complicated process. The pathogenesis of DR has been reported to involve oxidative stress, despite the fact that the mechanisms underlying this are still not fully understood. Excessive reactive oxygen species (ROS) accumulation can damage retina, eventually leading to DR. Increasing evidence have demonstrated that antioxidant therapy can alleviate the degeneration of retinal capillaries in DR.

CONCLUSION

Oxidative stress can play an important contributor in the pathogenesis of DR. Furthermore, animal experiments have shown that antioxidants are a beneficial therapy for treating DR, but more clinical trial data is needed.

Intravitreal Injection of ZYAN1 Restored Autophagy and Alleviated Oxidative Stress in Degenerating Retina via the HIF-1α/BNIP3 Pathway

Mitochondrial autophagy plays a contributary role in the pathogenesis of retina degeneration (RD). ZYAN1 is a novel proline hydroxylase domain (PHD) inhibitor that can enhance the expression of hypoxia-inducible factor 1-alpha (HIF-1α). This study investigated whether ZYAN1 could alleviate progressive photoreceptor loss and oxidative damage in a pharmacologically induced RD model via the modulation of mitophagy. ZYAN1 was injected into the vitreous body of the RD model, and the retinal autophagy level was analyzed. The therapeutic effects of ZYAN1 were evaluated via a function examination, a morphological assay, in situ reactive oxygen species (ROS) detection, and an immunofluorescence assay. It was shown that the thickness of the outer nuclear layer (ONL) increased significantly, and visual function was efficiently preserved via ZYAN1 treatment. The mitochondria structure of photoreceptors was more complete in the ZYAN1-treated mice, and the number of autophagosomes also increased significantly. Membrane disc shedding and ROS overproduction were alleviated after ZYAN1 treatment, and the axonal cilia were more structurally intact. A Western blot analysis showed that the expression levels of the autophagy-related proteins LC3-B, Beclin-1, and ATG5 increased significantly after ZYAN1 treatment, while the expression of P62 was down-regulated. Moreover, the expression levels of HIF-1α and BNIP3 were up-regulated after ZYAN1 treatment. Therefore, an intravitreal injection of ZYAN1 can act as part of the pharmacologic strategy to modulate mitophagy and alleviate oxidative stress in RD. These findings enrich our knowledge of RD pathology and provide insights for the discovery of a therapeutic molecule.

An Update on Strategies to Deliver Protein and Peptide Drugs to the Eye

In the past few decades, advancements in protein engineering, biotechnology, and structural biochemistry have resulted in the discovery of various techniques that enhanced the production yield of proteins, targetability, circulating half-life, product purity, and functionality of proteins and peptides. As a result, the utilization of proteins and peptides has increased in the treatment of many conditions, including ocular diseases. Ocular delivery of large molecules poses several challenges due to their high molecular weight, hydrophilicity, unstable nature, and poor permeation through cellular and enzymatic barriers. The use of novel strategies for delivering protein and peptides such as glycoengineering, PEGylation, Fc-fusion, chitosan nanoparticles, and liposomes have improved the efficacy, safety, and stability, which consequently expanded the therapeutic potential of proteins. This review article highlights various proteins and peptides that are useful in ocular disorders, challenges in their delivery to the eye, and strategies to enhance ocular bioavailability using novel delivery approaches. In addition, a few futuristic approaches that will assist in the ocular delivery of proteins and peptides were also discussed.

Liraglutide intervention improves high-glucose-induced reactive gliosis of Müller cells and ECM dysregulation

Reactive gliosis of Müller cells plays an important role in the pathogenesis of diabetic retinopathy (DR). Liraglutide, a glucagon-like peptide-1 receptor (GLP-1R) agonist, has been shown to improve DR by inhibiting reactive gliosis. However, the mechanism of inhibition has yet to be elucidated. This study investigated the effects of liraglutide on Müller glia reactivity in the early stages of DR and the underlying mechanisms. Proteomics combined with bioinformatics analysis, HE staining, and immunofluorescence staining revealed ganglion cell loss, reactive gliosis of Müller cells, and extracellular matrix (ECM) imbalance in rats with early stages of DR. High glucose (HG) exposure up-regulated GFAP and TNF-α expression and down-regulated ITGB1 expression and FN1 content in extracellular fluid in rMC1 cells, thereby promoting reactive gliosis. GLP-1R knockdown and HG+DAPT inhibition experiments show that liraglutide balances ECM levels by inhibiting activation of the Notch1/Hes1 pathway and ameliorates high-glucose-induced Müller glia reactivity. Thus, the study provides new targets and ideas for improvement of DR in early stages.

Retinoid X Receptor Activation Prevents Diabetic Retinopathy in Murine Models

Previously, the RXR agonist UAB126 demonstrated therapeutic potential to treat obese mice by controlling blood glucose levels (BGL) and altering the expression of genes associated with lipid metabolism and inflammatory response. The purpose of the study was to assess the effects of UAB126 on the progression of diabetic retinopathy (DR) in rodent models of type 1 diabetes (T1D), streptozotocin-induced, and type 2 diabetes (T2D), in db/db mice. UAB126 treatment was delivered either by oral gavage for 6 weeks or by topical application of eye drops for 2 weeks. At the end of the treatment, the retinal function of diabetic mice was assessed by electroretinography (ERG), and their retinal tissue was harvested for protein and gene expression analyses. Bone-marrow cells were isolated and differentiated into bone marrow-derived macrophages (BMDMs). The glycolysis stress test and the 2-DG glucose uptake analysis were performed. Our results demonstrated that in the UAB126-treated diabetic BMDMs, the ECAR rate and the 2-DG uptake were improved as compared to untreated diabetic BMDMs. In UAB126-treated diabetic mice, hyperglycemia was reduced and associated with the preservation of ERG amplitudes and enhanced AMPK activity. Retinas from diabetic mice treated with topical UAB126 demonstrated an increase in Rxr and Ppar and the expression of genes associated with lipid metabolism. Altogether, our data indicate that RXR activation is beneficial to preclinical models of DR.

Exendin-4 promotes retinal ganglion cell survival and function by inhibiting calcium channels in experimental diabetes

Progressive damage of retinal ganglion cells (RGCs) is observed in early diabetic retinopathy. Intracellular Ca2+ overload mediated by Ca2+ influx through voltage-gated Ca2+ channels (VGCCs) is involved in neurodegeneration, whereas glucagon-like peptide-1 (GLP-1) provides neuroprotection. However, whether GLP-1 plays a neuroprotective role in diabetic retinas by modulating VGCCs remains unknown. We found that eye drops of exendin-4, a long-acting GLP-1 receptor (GLP-1R) agonist, prevented the increase of L-type Ca2+ current (ILCa) densities of RGCs induced by 4-week hyperglycemia and promoted RGC survival by suppressing L-type VGCC (L-VGCC) activity in streptozotocin-induced diabetic rats. Moreover, exendin-4-induced suppression of ILCa in RGCs may be mediated by a GLP-1R/Gs/cAMP-PKA/ryanodine/Ca2+/calmodulin/calcineurin/PP1 signaling pathway. Furthermore, exendin-4 functionally improved the light-evoked spiking ability of diabetic RGCs. These results suggest that GLP-1R activation enhances cAMP to PP1 signaling and that PP1 inactivates L-VGCCs by dephosphorylating them, thereby reducing Ca2+ influx, which could protect RGCs against excitotoxic Ca2+ overload.

The protective role of GLP-1 in neuro-ophthalmology

Despite recent advancements in the field of neuro-ophthalmology, the rising rates of neurological and ophthalmological conditions, mismatches between supply and demand of clinicians, and an aging population underscore the urgent need to explore new therapeutic approaches within the field. Glucagon-like peptide 1 receptor agonists (GLP-1RAs), traditionally used in the treatment of type 2 diabetes, are becoming increasingly appreciated for their diverse applications. Recently, GLP-1RAs have been approved for the treatment of obesity and recognized for their cardioprotective effects. Emerging evidence indicates some GLP-1RAs can cross the blood-brain barrier and may have neuroprotective effects. Therefore, this article aims to review the literature on the neurologic and neuro-ophthalmic role of glucagon-like peptide 1 (GLP-1). This article describes GLP-1 peptide characteristics and the mechanisms mediating its known role in increasing insulin, decreasing glucagon, delaying gastric emptying, and promoting satiety. This article identifies the sources and targets of GLP-1 in the brain and review the mechanisms which mediate its neuroprotective effects, as well as implications for Alzheimer's disease (AD) and Parkinson's disease (PD). Furthermore, the preclinical works which unravel the effects of GLP-1 in ocular dynamics and the preclinical literature regarding GLP-1RA use in the management of several neuro-ophthalmic conditions, including diabetic retinopathy (DR), glaucoma, and idiopathic intracranial hypertension (IIH) are discussed.

Progressive Thinning of Retinal Nerve Fiber Layer/Ganglion Cell Layer (RNFL/GCL) as Biomarker and Pharmacological Target of Diabetic Retinopathy

Diabetes-driven retinal neurodegeneration has recently been shown to be involved in the initial phases of diabetic retinopathy, raising the possibility of setting up a preventive strategy based on early retinal neuroprotection. To make this possible, it is crucial to identify a biomarker for early retinal neurodegeneration. To this end, in this study, we verified and confirmed that, in the Akita mouse model of diabetes, the thinning of the retinal nerve fiber layer/ganglion cell layer (the RNFL/GCL-the layer that contains the retinal ganglion cells) precedes the death of these same cells, suggesting that this dysfunction is a possible biomarker of retinal neurodegeneration. We then confirmed the validity of this assumption by starting a neuroprotective treatment (based on nerve growth factor eye drops) in concert with the first demonstration of RNFL/GCL thinning. In this way, it was possible not only to avoid the loss of retinal ganglion cells but also to prevent the subsequent development of the microvascular stage of diabetic retinopathy. In conclusion, in the case of diabetes, the thinning of the RNFL/GCL appears to be both a valid biomarker and a pharmacological target of diabetic retinopathy; it precedes the development of vascular dysfunctions and represents the ideal starting point for prevention.

GLP-1R agonists demonstrate potential to treat Wolfram syndrome in human preclinical models

AIMS/HYPOTHESIS

Wolfram syndrome is a rare autosomal recessive disorder caused by pathogenic variants in the WFS1 gene. It is characterised by insulin-dependent diabetes mellitus, optic nerve atrophy, diabetes insipidus, hearing loss and neurodegeneration. Considering the unmet treatment need for this orphan disease, this study aimed to evaluate the therapeutic potential of glucagon-like peptide 1 receptor (GLP-1R) agonists under wolframin (WFS1) deficiency with a particular focus on human beta cells and neurons.

METHODS

The effect of the GLP-1R agonists dulaglutide and exenatide was examined in Wfs1 knockout mice and in an array of human preclinical models of Wolfram syndrome, including WFS1-deficient human beta cells, human induced pluripotent stem cell (iPSC)-derived beta-like cells and neurons from control individuals and individuals affected by Wolfram syndrome, and humanised mice.

RESULTS

Our study shows that the long-lasting GLP-1R agonist dulaglutide reverses impaired glucose tolerance in WFS1-deficient mice, and that exenatide and dulaglutide improve beta cell function and prevent apoptosis in different human WFS1-deficient models including iPSC-derived beta cells from people with Wolfram syndrome. Exenatide improved mitochondrial function, reduced oxidative stress and prevented apoptosis in Wolfram syndrome iPSC-derived neural precursors and cerebellar neurons.

CONCLUSIONS/INTERPRETATION

Our study provides novel evidence for the beneficial effect of GLP-1R agonists on WFS1-deficient human pancreatic beta cells and neurons, suggesting that these drugs may be considered as a treatment for individuals with Wolfram syndrome.

Topical and systemic GLP-1R agonist administration both rescue retinal ganglion cells in hypertensive glaucoma

Glaucomatous neurodegeneration, a blinding disease affecting millions worldwide, has a need for the exploration of new and effective therapies. Previously, the glucagon-like peptide-1 receptor (GLP-1R) agonist NLY01 was shown to reduce microglia/macrophage activation, rescuing retinal ganglion cells after IOP elevation in an animal model of glaucoma. GLP-1R agonist use is also associated with a reduced risk for glaucoma in patients with diabetes. In this study, we demonstrate that several commercially available GLP-1R agonists, administered either systemically or topically, hold protective potential in a mouse model of hypertensive glaucoma. Further, the resulting neuroprotection likely occurs through the same pathways previously shown for NLY01. This work contributes to a growing body of evidence suggesting that GLP-1R agonists represent a viable therapeutic option for glaucoma.

Inflammation: The Link between Neural and Vascular Impairment in the Diabetic Retina and Therapeutic Implications

The etiology of diabetic retinopathy (DR) is complex, multifactorial and compromises all the elements of the retinal neurovascular unit (NVU). This diabetic complication has a chronic low-grade inflammatory component involving multiple inflammatory mediators and adhesion molecules. The diabetic milieu promotes reactive gliosis, pro-inflammatory cytokine production and leukocyte recruitment, which contribute to the disruption of the blood retinal barrier. The understanding and the continuous research of the mechanisms behind the strong inflammatory component of the disease allows the design of new therapeutic strategies to address this unmet medical need. In this context, the aim of this review article is to recapitulate the latest research on the role of inflammation in DR and to discuss the efficacy of currently administered anti-inflammatory treatments and those still under development.

Semaglutide-eye-catching results

Semaglutide is a glucagon-like peptide-1 receptor agonist used either orally every day or subcutaneously once a week for the treatment of type 2 diabetes mellitus and, more recently, at higher doses, for the treatment of obesity. Both diseases are reaching epidemic proportions and often coexist, posing patients with a high risk for cardiovascular disease and death. Therefore, an agent such as semaglutide, which offers clinically significant weight loss and cardiovascular benefits, is essential and will be increasingly used in high-risk patients. However, during the SUSTAIN clinical trial program (Semaglutide Unabated Sustainability in treat-ment of type 2 diabetes), a safety issue concerning the progression and worsening of diabetic retinopathy emerged. The existing explanation so far mainly supports the role of the magnitude and speed of HbA1c reduction, a phenomenon also associated with insulin treatment and bariatric surgery. Whether and to which extent the effect is direct is still a matter of debate and an intriguing topic to investigate for suitable preventative and rehabilitative purposes. In this minireview, we will summarize the available data and suggest guidelines for a comprehensive semaglutide clinical utilization until new evidence becomes available.

Caffeine and the Risk of Diabetic Retinopathy in Type 2 Diabetes Mellitus: Findings from Clinical and Experimental Studies

The aim of this study was to assess the potential benefits of caffeine intake in protecting against the development of diabetic retinopathy (DR) in subjects with type 2 diabetes (T2D). Furthermore, we tested the effect of topical administration of caffeine on the early stages of DR in an experimental model of DR. In the cross-sectional study, a total of 144 subjects with DR and 147 individuals without DR were assessed. DR was assessed by an experienced ophthalmologist. A validated food frequency questionnaire (FFQ) was administered. In the experimental model, a total of 20 mice were included. One drop (5 μL) of caffeine (5 mg/mL) (n = 10) or vehicle (5 μL PBS, pH 7.4) (n = 10) was randomly administered directly onto the superior corneal surface twice daily for two weeks in each eye. Glial activation and retinal vascular permeability were assessed using standard methods. In the cross-sectional study in humans, the adjusted-multivariable model showed that a moderate and high (Q2 and Q4) caffeine intake had a protective effect of DR (odds ratio (95% confidence interval) = 0.35 (0.16-0.78); p = 0.011 and 0.35 (0.16-0.77); p = 0.010, respectively). In the experimental model, the administration of caffeine did not improve either reactive gliosis or retinal vascular permeability. Our results suggest a dose-dependent protective effect of caffeine in the development of DR, while the potential benefits of antioxidants in coffee and tea should also be considered. Further research is needed to establish the benefits and mechanisms of caffeinated beverages in the development of DR.

Glucagon-like peptide-1 receptor agonists and diabetic retinopathy: nationwide cohort and Mendelian randomization studies

BACKGROUND

The ability of glucagon-like peptide-1 receptor agonists (GLP-1 RAs) to decrease certain microvascular events has called for the investigation of GLP-1 RAs against diabetic retinopathy (DR), but the evidence is limited. By combining data from observational and Mendelian randomization (MR) studies, we aimed to investigate whether GLP-1 RAs decrease the risk of DR.

METHODS

We combined data from several Swedish Registers and identified patients with incident type 2 diabetes being treated with GLP-1 RAs between 2006 and 2015, and matched them to diabetic patients who did not use GLP-1 RAs as the comparisons. The Cox proportional hazards models were applied to assess the risk of DR. We further performed the summary-data-based MR (SMR) analyses based on the Genotype-Tissue Expression databases and the Genome-Wide Association Study of DR from the FinnGen consortium.

RESULTS

A total of 2390 diabetic patients were treated with GLP-1 RAs and the incidence of DR was 5.97 per 1000 person-years. Compared with diabetic patients who did not use GLP-1 RAs having an incidence of 12.85 per 1000 person-years, the adjusted hazard ratio (HR) of DR was 0.42 [95% confidence interval (CI), 0.29-0.61]. Genetically-predicted GLP1R expression (the target of GLP-1 RAs) showed an inverse association with background [odds ratio (OR)=0.83, 95% CI, 0.71-0.97] and severe nonproliferative DR (OR=0.72, 95% CI, 0.53-0.98), and a non-significant association with overall (OR=0.97, 95% CI, 0.92-1.03) and proliferative DR (OR=0.98, 95% CI, 0.91-1.05).

CONCLUSIONS

Both observational and mendelian randomization analyses showed a significantly lower risk of DR for patients treated with GLP-1 RAs, which calls for further studies to validate these findings.

Repeated Topical Administration of 3 nm Cerium Oxide Nanoparticles Reverts Disease Atrophic Phenotype and Arrests Neovascular Degeneration in AMD Mouse Models

Increased oxidative stress in the retina and retinal pigment epithelium is implicated in age-related macular degeneration (AMD). Antioxidant cerium oxide nanoparticles (CeO2NPs) have been used to treat degenerative retinal pathologies in animal models, although their delivery route is not ideal for chronic patient treatment. In this work, we prepared a formulation for ocular topical delivery that contains small (3 nm), nonaggregated biocompatible CeO2NPs. In vitro results indicate the biocompatible and protective character of the CeO2NPs, reducing oxidative stress in ARPE19 cells and inhibiting neovascularization related to pathological angiogenesis in both HUVEC and in in vitro models of neovascular growth. In the in vivo experiments, we observed the capacity of CeO2NPs to reach the retina after topical delivery and a subsequent reversion of the altered retinal transcriptome of the retinal degenerative mouse model DKOrd8 toward that of healthy control mice, together with signs of decreased inflammation and arrest of degeneration. Furthermore, CeO2NP eye drops' treatment reduced laser-induced choroidal neovascular lesions in mice by lowering VEGF and increasing PEDF levels. These results indicate that CeO2NP eye drops are a beneficial antioxidant and neuroprotective treatment for both dry and wet forms of AMD disease.

Transcriptomic Analysis Reveals That Retinal Neuromodulation Is a Relevant Mechanism in the Neuroprotective Effect of Sitagliptin in an Experimental Model of Diabetic Retinopathy

Synaptic dysfunction and neuronal damage have been extensively associated with diabetic retinopathy (DR). Our group evidenced that chronic hyperglycemia reduces the retinal expression of presynaptic proteins, which are crucial for proper synaptic function. The aim of the study was to explore the effect of topically administered sitagliptin, an inhibitor of the enzyme dipeptidyl peptidase-4, on the retinal expression patterns of an experimental model of DR. Transcriptome analysis was performed, comparing the retinas of 10 diabetic (db/db) mice randomly treated with sitagliptin eye drops (10 mg/mL) twice daily and the retinas of 10 additional db/db mice that received vehicle eye drops. Ten non-diabetic mice (db/+) were used as a control group. The Gene Ontology (GO) and Reactome databases were used to perform the gene set enrichment analysis (GSEA) in order to explore the most enriched biological pathways among the groups. The most differentiated genes of these pathways were validated through quantitative RT-PCR. Transcriptome analysis revealed that sitagliptin eye drops have a significant effect on retinal expression patterns and that neurotransmission is the most enriched biological process. Our study evidenced enriched pathways that contain genes involved in membrane trafficking, transmission across chemical synapses, vesicle-mediated transport, neurotransmitter receptors and postsynaptic signal transmission with negative regulation of signaling as a consequence of neuroprotector treatment with sitagliptin. This improves the modulation of the macromolecule biosynthetic process with positive regulation of cell communication, which provides beneficial effects for the neuronal metabolism. This study suggests that topical administration of sitagliptin ameliorates the abnormalities on presynaptic and postsynaptic signal transmission during experimental DR and that this improvement is one of the main mechanisms behind the previously demonstrated beneficial effects.

Will GLP-1 Analogues and SGLT-2 Inhibitors Become New Game Changers for Diabetic Retinopathy?

Diabetic retinopathy (DR) is the most frequent microvascular complication of diabetes mellitus (DM), estimated to affect approximately one-third of the diabetic population, and the most common cause of preventable vision loss. The available treatment options focus on the late stages of this complication, while in the early stages there is no dedicated treatment besides optimizing blood pressure, lipid and glycemic control; DR is still lacking effective preventive methods. glucagon-like peptide 1 receptor agonists (GLP-1 Ras) and sodium-glucose cotransporter 2 (SGLT-2) inhibitors have a proven effect in reducing risk factors of DR and numerous experimental and animal studies have strongly established its retinoprotective potential. Both drug groups have the evident potential to become a new therapeutic option for the prevention and treatment of diabetic retinopathy and there is an urgent need for further comprehensive clinical trials to verify whether these findings are translatable to humans.

Protective role of IGF-1 and GLP-1 signaling activation in neurological dysfunctions

Insulin-like growth factor-1 (IGF-1), a pleiotropic polypeptide, plays an essential role in CNS development and maturation. Glucagon-like peptide-1 (GLP-1) is an endogenous incretin hormone that regulates blood glucose levels and fatty acid oxidation in the brain. GLP-1 also exhibits similar functions and growth factor-like properties to IGF-1, which is likely how it exerts its neuroprotective effects. Recent preclinical and clinical evidence indicate that IGF-1 and GLP-1, apart from regulating growth and development, prevent neuronal death mediated by amyloidogenesis, cerebral glucose deprivation, neuroinflammation and apoptosis through modulation of PI3/Akt kinase, mammalian target of rapamycin (mTOR) and mitogen-activated protein kinase (MAPK/ERK). IGF-1 resistance and GLP-1 deficiency impair protective cellular signaling mechanisms, contributing to the progression of neurodegenerative diseases. Over the past decades, IGF-1 and GLP-1 have emerged as an essential component of the neuronal system and as potential therapeutic targets for several neurodegenerative and neuropsychiatric dysfunctions. There is substantial evidence that IGF-1 and GLP-1 analogues penetrate the blood-brain barrier (BBB) and exhibit neuroprotective functions, including synaptic formation, neuronal plasticity, protein synthesis, and autophagy. Conclusively, this review represents the therapeutic potential of IGF-1 and GLP-1 signaling target activators in ameliorating neurological disorders.

Topical nerve growth factor prevents neurodegenerative and vascular stages of diabetic retinopathy

Specific and effective preventive treatment for diabetic retinopathy (DR) is presently unavailable, mostly because the early stages of the complication have been, until recently, poorly understood. The recent demonstration that the vascular phase of DR is preceded and possibly caused by the neurodegeneration of retinal ganglion cells suggests that DR could, at least theoretically, be prevented through an early neuroprotective approach. The aims of our study were to clarify the natural history of diabetes-driven retinal neurodegeneration and to verify the possibility to prevent DR using topical nerve growth factor (NGF). The results of the study show that retinal neurodegeneration, characterized by the loss of retinal ganglion cells represents a relatively early phenomenon of diabetes (between 5 and 16 weeks of age), which tends to be self-limiting in the long run. Neurodegeneration is followed by the development of DR-related vascular dysfunctions, as confirmed by the development of acellular capillaries and the loss of retinal pericytes. Both retinal neurodegeneration and subsequent vascular dysfunction can be successfully prevented by topical NGF administration. These findings suggest that: 1) The first stage of DR consists in a self-limiting retinal neurodegeneration 2) The demonstrated effectiveness of topical NGF in the prevention of DR could be rapidly translated into clinical practice.

Anti-inflammatory effect of glucagon-like Peptide-1 receptor agonist on the neurosensory retina in an acute optic nerve injury rat model

PURPOSE

To explore the possibility of using glucagon-like peptide-1 receptor agonist (GLP-1RA) as a new treatment for neuroinflammation, by analyzing retinal pathological changes in an optic nerve crush rat model.

METHODS

Eight-week-old male Sprague-Dawley rats were divided into lixisenatide (LIX, n = 10), traumatic control (T-CON, n = 10), and normal control (n = 5) groups. The optic nerves of left eyes in the LIX and T-CON groups were crushed in a standardized manner. The LIX group was treated with subcutaneous injections of lixisenatide (200 μg/kg/day) for 5 days. One week after initiating treatment, quantitative polymerase chain reaction, Western blot, and immunohistochemistry analyses were performed on the retinal tissues of each group to identify inflammatory markers.

RESULTS

The LIX group showed significantly lower mRNA levels of interleukin 1 beta (IL-1β), tumor necrosis factor-alpha (TNF-α), thioredoxin interacting protein (TXNIP), and glial fibrillary acidic protein (GFAP) than the T-CON group. Also, the LIX group exhibited decreased TXNIP and GFAP expression compared with the T-CON group, and similar expression to the normal control group, according to Western blot analysis. Significantly increased immunohistochemistry staining of Brn3a and decreased TUNEL staining were seen in the LIX group compared with the T-CON group, indicating that lixisenatide contributes to retinal ganglion cell survival in cases of acute optic nerve injury.

CONCLUSIONS

Neuroinflammation was significantly reduced in lixisenatide-treated retinas compared with untreated retinas in our acute optic nerve injury rat model. The neuroprotective effect of lixisenatide indicates that it can serve a new treatment option against clinically intractable traumatic optic neuropathy.

DPP-4 inhibitors and GLP-1RAs: cardiovascular safety and benefits

Glucagon-like peptide-1 receptor agonists and dipeptidyl peptidase-4 inhibitors are commonly used treatments for patients with type 2 diabetes mellitus (T2DM). Both anti-diabetic treatments function by playing key modulatory roles in the incretin system. Though these drugs have been deemed effective in treating T2DM, the Food and Drug Administration (FDA) and some members of the scientific community have questioned the safety of these therapeutics relative to important cardiovascular endpoints. As a result, since 2008, the FDA has required all new drugs for glycemic control in T2DM patients to demonstrate cardiovascular safety. The present review article strives to assess the safety and benefits of incretin-based therapy, a new class of antidiabetic drug, on the health of patient cardiovascular systems. In the process, this review will also provide a physiological overview of the incretin system and how key components function in T2DM.