Serum and aqueous humor adiponectin levels correlate with diabetic retinopathy development and progression

The potential role of adipokines and hepatokines in age-related ocular diseases

Age-related ocular diseases, including diabetic retinopathy (DR), age-related macular degeneration (AMD), cataract and glaucoma may lead to visual impairment and even to blindness. Metabolic diseases, such as obesity and metabolic dysfunction-associated steatotic liver disease (MASLD) have emerged as potential risk factors of age-related ocular diseases, especially DR. Visceral adiposity has been associated with increased risk of DR and AMD in most clinical studies, although body mass index has to-date provided conflicting association with DR and AMD. In addition, obesity is recognized as a risk factor of cataract and glaucoma. Similarly to obesity, MASLD appears to be associated with DR in patients with type 1 diabetes mellitus, but probably not in those with type 2 diabetes mellitus. A potential positive association between MASLD and AMD, glaucoma and cataract is supported by limited evidence to-date, thus needing further investigation. Altered secretion patterns of adipokines (adiponectin, leptin, lipocalin-2, resistin) and hepatokines [adropin, fetuin-A, fibroblast growth factor (FGF)-21, retinol binding protein (RBP)-4] seem to disrupt ocular homeostasis and contribute to the development of age-related ocular diseases in the context of obesity and MASLD. In this regard, novel adipokine-based and hepatokine-based therapies may be added to the treatment options for ocular diseases in the future. This narrative review aimed to summarize evidence on the interconnection of obesity and MASLD with age-related ocular diseases, with a specific focus on the roles of adipokines and hepatokines as mediators of these potential associations.

Association of serum adiponectin and leptin levels with inner retinal thickness among individuals with or without elevated HbA1c

Inner retinal thinning precedes clinical evidence of retinopathy in prediabetes and diabetes mellitus (DM), and may contribute to retinopathy development and progression. Serum levels of the adipokines leptin and adiponectin are inversely related in the setting of impaired glucose homeostasis, but their potential association with inner retinal thickness is unknown. In this prospective study, both eyes from 24 individuals with prediabetes or type 2 DM (glycated hemoglobin [HbA1c] ≥ 5.7) and 16 controls (HbA1c < 5.7) underwent spectral-domain optical coherence tomography imaging of the macula, and thickness of the nerve fiber layer (NFL) and ganglion cell layer-inner plexiform layer (GCL-IPL) was analyzed in each subfield of the Early Treatment Diabetic Retinopathy Study grid. Serum samples were collected and metabolic factors, including adiponectin and leptin, were measured. Adjusted regression analyses revealed inverse associations of these adipokines with NFL thickness that did not differ between prediabetes/DM and controls, but differential positive associations of adiponectin with GCL-IPL thickness only in the prediabetes/DM group. The results of our pilot study suggest opposing roles for adiponectin and leptin in the retina, similar to their relationship in systemic disease, and suggest that serum adiponectin may represent a potential clinical biomarker for inner retinal thickness in patients with elevated HbA1c.

Updates on medical and surgical managements of diabetic retinopathy and maculopathy

Diabetic retinopathy (DR) and diabetic macular edema (DME) are leading causes of vision loss globally. This is a comprehensive review focused on both medical and surgical management strategies for DR and DME. This review highlights the epidemiology of DR and DME, with a particular emphasis on the Asia-Pacific region, urban-rural disparities, ethnic variations, and grading methodologies. We examine various risk factors for DR, including glycemic control, hypertension, hyperlipidemia, obesity, chronic kidney disease, sex, myopia, pregnancy, and cataract surgery. Furthermore, we explore potential biomarkers in serum, proteomics, metabolomics, vitreous, microRNA, and genetics that may aid in the detection and management of DR. In addition to medical management, we review the evidence supporting systemic and ocular treatments for DR/DME, including anti-vascular endothelial growth factor (anti-VEGF) agents, anti-inflammatory agents, biosimilars, and integrin inhibitors. Despite advancements in treatment options such as pan-retinal photocoagulation and anti-VEGF agents, a subset of cases still progresses, necessitating vitrectomy. Challenging diabetic vitrectomies pose difficulties due to complex fibrovascular proliferations, incomplete posterior vitreous detachment, and fragile, ischemic retinas, making membrane dissection risky and potentially damaging to the retina. In this review, we address the question of challenging diabetic vitrectomies, providing insights and strategies to minimize complications. Additionally, we briefly explore newer modalities such as 3-dimensional vitrectomy and intra-operative optical coherence tomography as potential tools in diabetic vitrectomy. In conclusion, this review provides a comprehensive overview of both medical and surgical management options for DR and DME. It underscores the importance of a multidisciplinary approach, tailored to the needs of each patient, to optimize visual outcomes and improve the quality of life for those affected by these sight-threatening conditions.

Interleukin-5: an indicator of mild cognitive impairment in patients with type 2 diabetes mellitus - a comprehensive investigation ranging from bioinformatics analysis to clinical research

PURPOSE

Neuroinflammation constitutes an underlying mechanism for cognitive impairment. Here, we endeavor to scrutinize the potential contribution of interleukin-5 (IL-5) towards mild cognitive impairment (MCI), and to assess its diagnostic value for MCI in patients with type 2 diabetes mellitus (T2DM).

METHODS

RNA-seq was used to explore the potential neuroinflammation factors in the hippocampus of diabetic mice with cognitive decline. Additionally, the promising risk factor was verified in animals. Finally, the association between IL-5 levels and cognitive function and its diagnostic value for MCI were assessed.

RESULTS

In animals, up-regulated IL-5 mRNA and protein levels were detected by RNA-seq and (or) verified experiments in the hippocampus of diabetic db/db mice with cognitive decline, compared to those of db/m mice without diabetes. In human, compared to diabetic patients without MCI, those with MCI demonstrate elevated levels of IL-5. It is natively associated with Montreal Cognitive Assessment (MoCA) scores, reflecting global cognitive function, and positively correlated with Trail Making Test A (TMTA) scores, reflecting information processing speed. Furthermore, an elevated level of IL-5 is identified as a risk factor for MCI, and a factor that influences TMTA scores. Finally, it is recommended that the cut-off value for IL-5 in the diagnosis of MCI is 22.98 pg/mL, with a sensitivity of 68.6% and specificity of 72.9%.

CONCLUSIONS

IL-5 is considered a risk factor for MCI in T2DM patients and is associated with their performance in information processing speed. Moreover, an elevated level of IL-5 is a plausible biomarker for MCI in T2DM patients.

Changes in aqueous and vitreous inflammatory cytokine levels in nonproliferative diabetic retinopathy: systematic review and meta-analysis

OBJECTIVE

Diabetic retinopathy is a complication of diabetes mellitus with the potential for significant patient morbidity. Although changes to intraocular inflammatory cytokines are integral to disease pathogenesis, studies have been inconsistent about which exact cytokines are associated with diabetic retinopathy. We aimed to quantitatively summarize proangiogenic and proinflammatory cytokines in nonproliferative diabetic retinopathy (NPDR), given its frequency among those with diabetes mellitus.

METHODS

A systematic literature search without year limitation to February 21, 2022, identified 59 studies assessing vitreous or aqueous cytokine levels in NPDR, encompassing 1378 eyes with NPDR and 1288 eyes from nondiabetic controls. Effect sizes were generated as standardized mean differences (SMD) of cytokine concentrations between patients with NPDR and controls.

RESULTS

Concentrations (SMD, 95% confidence interval, and p value) of aqueous interleukin-6 (IL-6) (2.58, 1.17-3.99; p = 0.0003), IL-8 (1.56, 0.39-2.74; p = 0.009), IL-17 (13.55, 7.50-19.59; p < 0.001), transforming growth factor beta (TGF-β) (2.44, 1.02-3.85; p = 0.0007) and vascular endothelial growth factor (VEGF) (1.35, 0.76-1.93; p < 0.00001), and vitreous VEGF (1.49, 0.60-2.37; p = 0.001) were significantly higher in patients with NPDR when compared with those of healthy controls.

CONCLUSIONS

These cytokines may serve as disease markers of the biochemical alterations seen in NPDR and may guide interventions, as we move into an era of more targeted therapeutics.

Epiretinal Membrane: Correlations Among Clinical, Immunohistochemical, and Biochemical Features and Their Prognostic Implications

Purpose

To investigate correlations among clinical, immunohistochemical, and biochemical characteristics of epiretinal membranes (ERMs) and their prognostic implications.

Methods

This prospective study included 120 patients with idiopathic ERM who underwent vitrectomy. Preoperative and postoperative best-corrected visual acuity (BCVA) and optical coherence tomography (OCT) were measured. Surgical ERM tissues underwent immunohistochemistry (IHC) analysis, and vitreous samples were analyzed for cytokine levels. Statistical analysis assessed associations among BCVA, OCT metrics (ERM stage, inner-retinal irregularity index [IRII], ellipsoid zone disruption [EZD]), IHC features (cell density, protein expression), and cytokines.

Results

The average age of the participants was 70.2 ± 7.6 years, and ERM stages were distributed as Stage 2 in 34 eyes (28.3%), Stage 3 in 54 eyes (45.0%), and Stage 4 in 32 eyes (26.7%). Advancing ERM stage was linked with worsening visual outcomes, higher preoperative IRII, increased EZD incidence, increased ERM cellularity, and elevated TGF-β1 level. Protein expression for myofibroblasts (αSMA), glial cells (GFAP), hyalocytes (CD45), and retinal pigment epithelium (RPE) cells (PRPH2) correlated positively with ERM stage. Multivariate analysis showed preoperative IRII significantly correlated with preoperative BCVA, GFAP, PRPH2, and type I collagen. TGF-β1 was significantly associated with preoperative IRII, αSMA, type I collagen, and N-cadherin, but not with postoperative BCVA. Postoperative BCVA was significantly correlated with preoperative BCVA, preoperative IRII, preoperative EZD, αSMA, and PRPH2.

Conclusions

Early-stage ERM is associated with better visual prognosis, fewer inner and outer retinal changes in OCT, and fewer epithelial-mesenchymal transition-related alterations in ERM tissues. Key prognostic indicators for postoperative BCVA include preoperative BCVA, IRII, EZD, myofibroblasts, and RPE cells. TGF-β1 promotes the transdifferentiation of intraocular cells, impacting OCT features directly and visual outcomes indirectly.

The role of adiponectin and its receptor signaling in ocular inflammation-associated diseases

Ocular inflammation-associated diseases are leading causes of global visual impairment, with limited treatment options. Adiponectin, a hormone primarily secreted by adipose tissue, binds to its receptors, which are widely distributed throughout the body, exerting powerful physiological regulatory effects. The protective role of adiponectin in various inflammatory diseases has gained increasing attention in recent years. Previous studies have confirmed the presence of adiponectin and its receptors in the eyes. Furthermore, adiponectin and its analogs have shown potential as novel drugs for the treatment of inflammatory eye diseases. This article summarizes the evidence for the interplay between adiponectin and inflammatory eye diseases and provides new perspectives on the diagnostic and therapeutic possibilities of adiponectin.

Integrative analysis of Mendelian randomization and gene expression profiles reveals a null causal relationship between adiponectin and diabetic retinopathy

Observational studies have been conducted to investigate the correlation between adiponectin and diabetic retinopathy (DR), but no consistent relationship has been established. In this study, we employed an integrative analysis that combined Mendelian randomization (MR) and bioinformatics analyses to comprehensively explore the association between DR and adiponectin, aiming to provide a unified answer of their relationship. Using the inverse-variance weighted (IVW) method, the odd ratio (OR) of developing DR per 1 mg/dL increment in genetically predicted log-transformed adiponectin concentration was estimated to be 0.949 (P = 0.557). Other robust MR methods produced consistent results, confirming the absence of a causal effect of adiponectin on DR. Additionally, the expression levels of the six adiponectin-related genes showed no significant differences among normal controls, individuals with diabetes but without DR, and those with DR Furthermore, the biological pathways enriched by these genes were not strongly relevant to DR. At both the individual gene and pathway levels, there were no overlaps between the adiponectin-related genes and the differentially expressed genes, indicating a lack of association between adiponectin and DR based on gene expression profiles. In summary, the integrative analysis, which combined MR and bioinformatics data mining, yielded compelling evidence supporting the notion that adiponectin is not a risk factor for DR.

Association between adipocytokines and diabetic retinopathy: a systematic review and meta-analysis

Background

Diabetic retinopathy (DR) is a common complication of diabetes. The adipocytokines are closely associated with the occurrence and development of diabetes and its related complications. Literature confirms that the level of adiponectin in patients with DR is significantly higher; however, the relationship between other adipocytokines (leptin, chemerin, apelin, and omentin-1) and DR remains unclear.

Aim

This study aimed to systematically evaluate the association between adipocytokines (leptin, chemerin, apelin, and omentin-1) and DR.

Methods

The PubMed, Web of Science, Embase, EBSCO and Willy databases were used to search for potential studies with keywords such as "diabetic retinopathy" or "DR" in combination with the terms "leptin," "chemerin", "apelin" or "omentin-1" in the search titles or abstracts. Standardized mean differences (SMD) with corresponding 95% confidence intervals (CIs) were determined as the results of the meta-analysis.

Results

After screening, 18 articles were included in the meta-analysis including 750 DR cases and 993 controls. Leptin and chemerin levels in patients with DR were significantly higher than those in the control group (SMD: 0.68, 95% CI [0.1, 1.26]; SMD: 0.79, 95% CI [0.35, 1.23]). The omentin-1 levels in patients with DR were significantly lower than those in the controls (SMD: -0.85, 95% CI [-1.08, -0.62]).

Conclusions

To the best of our knowledge, this is the first meta-analysis to evaluate the leptin, chemerin, apelin, and omentin-1 levels in patients with DR. Further high-quality studies are warranted to support the association between these adipocytokines and DR.

Systematic review registration

https://www.crd.york.ac.uk/PROSPERO/display_record.php?RecordID=443770, identifier CRD42023443770.

Adiponectin: A "Friendly adipokine" in Diabetic Retinopathy?

PURPOSE

Adiponectin has also been associated with diabetic retinopathy, a diabetic microvascular complication. However, the mechanism of action of adiponectin in retinopathy is still under investigation. This review summarizes emerging evidence on the association with diabetic retinopathy in type 2 diabetes.

METHODS

We reviwed papers from 2004 to 2022 and included studies related to retinopathy and its association with blood and intraocular adiponectin in type 2 diabetes.

RESULTS

Most of the studies analyzed in this review suggested an association between the diabetic retinopathy progression and intraocular, serum, or plasma adiponectin levels. Increased levels of adiponectin contributed to the development of the disease in diabetic patients. In a minority of studies, it was indicated an inversely proportional relationship between adiponectin concentration and diabetic retinopathy severity.

CONCLUSION

The high levels of adiponectin in diabetic patients may be related to the decrease in renal clearance. Under this situation, if the predominant isoform is globular adiponectin, this may explain the retinopathy progression, considering a pro-inflammatory response induced by this isoform. However, the actions of adiponectin in diabetic retinopathy pathophysiology are still controversial.

A Mediterranean Diet May Be Protective in the Development of Diabetic Retinopathy

The Mediterranean diet is recognized as one of the healthiest available dietary patterns. This perception results from its beneficial effects on the cardiovascular system and, also, on hypertension, diabetes, and cancer compared with other diets. Its impact on the course of diabetes is assessed in the available scientific literature; however, little information is available about its impact on diabetic retinopathy. The MD is characterized mainly by the consumption of fish, seafood, foods of plant origin, and fresh fruit and vegetables. It is also recommended to consume legumes, which are a source of folic acid, magnesium, iron, and dietary fiber. High consumption of nuts and unrefined grains is also recommended in the MD. Marine fish provide polyunsaturated acids from the omega-3 group. Olive oil plays a very important role, especially olive oil obtained from mechanical pressing. Additionally, olive oil contains vitamins E, K, and polyphenols. Polyphenols, which are present in a diverse range of vegetables, fruits, and seeds, have the ability to decrease oxidative stress, inflammation, and insulin resistance. Resveratrol is naturally found in grape skins and seeds, as well as in peanuts and berries, and is a constituent of red wine. Resveratrol can inhibit increased vascular leakage and loss of pericytes and regulate the level of VEGF protein in the retina, thus inhibiting the development of DR. Consumption of fruits, vegetables, fish, and olive oil may be correlated with a lower risk of diabetic retinopathy. This paper presents the definition of the Mediterranean diet and its influence on the course of diabetes and diabetic retinopathy.

Leptin-VEGF crosstalk in excess body mass and related disorders: A systematic review

By 2030, it is expected that a billion people will have suffer from obesity. Adipose tissue synthesizes leptin, an adipokine that affects cardiovascular risk. Leptin intensifies the synthesis of vascular endothelial growth factor (VEGF). Our study reviews recent reports on leptin-VEGF crosstalk in obesity and related disorders. PubMed, Web of Science, Scopus, and Google Scholar were searched. One hundred and one articles involving human, animal, and in vitro research were included. In vitro studies show the crucial role of interaction between endothelial cells and adipocytes and hypoxia as a factor that intensifies leptin's effects on VEGF. Leptin-VEGF crosstalk promotes the progression of cancer. The animal research reveal that a high-fat diet enhances leptin and VEGF crosstalk. Genetic and epigenetic mechanisms and procreator-offspring programming may be involved in leptin-VEGF crosstalk. Some female-specific characteristics of leptin-VEGF relation in obesity were observed. The human studies have shown that increased leptin and VEGF synthesis and leptin-VEGF crosstalk are factors linking obesity with elevated cardiovascular risk. The studies of the last 10 years documented a range of significant aspects of leptin-VEGF crosstalk specific for obesity and related disorders, shedding new light on the link between obesity and increased cardiovascular risk.

Potential Protective Function of Adiponectin in Diabetic Retinopathy

Adiponectin, one of the most ubiquitous adipokines found in the blood, plays a major role in glucolipid metabolism and energy metabolism and regulation. In recent years, a growing body of research indicates that adiponectin also plays a significant role in diabetic retinopathy. In the present review, we specifically address the protective effects of adiponectin on the development and progression of diabetic retinopathy through improvement in insulin resistance, alleviation of oxidative stress, limiting of inflammation, and prevention of vascular remodeling, with the aim to explore new potential approaches and targets for the prevention and treatment of diabetic retinopathy.

The Correlation between Waist Circumference and the Pro-Inflammatory Adipokines in Diabetic Retinopathy of Type 2 Diabetes Patients

Central obesity is one of the major risk factors for type 2 diabetes mellitus (DM), and the most common complication of DM is diabetic retinopathy. However, the exact relationship between obesity and DR remains unknown. In this study, we evaluate the effect of obesity on DR by comparing the aqueous humor-derived adipokines. For the analysis, 37 DR patients and 29 non-DR-patients participated. To evaluate the obesity of the patients, body mass index (BMI) and waist circumference (WC) were used. By comparing the concentrations of adipokines obtained from the aqueous humor of the two groups, the relationship between DR and adipokines was analyzed. In addition, by analyzing the correlation between obesity and adipokines in patients, the relationship between central obesity and DR was finally confirmed. The WC was significantly higher in patients than in the non-patient group. The concentrations of all adipokines compared in this study were significantly higher in the DR group than in the non-DM group (p < 0.05). Among them, adiponectin, leptin, TNF-α, Factor D (adipsin), lipocalin-2 (NGAL), Serpin E1 (PAI-1), and CXCL8 (IL-8) were confirmed to have a positive correlation with central obesity (defined as WC). These findings suggest that central obesity is strongly associated with the risk of DR.

Adiponectin Paradox More Evident in Non-Obese Than in Obese Patients with Diabetic Microvascular Complications

AIMS/INTRODUCTION

Adiponectin is generally regarded as a beneficial molecule, protecting against insulin resistance and atherosclerosis, and its serum levels are low in individuals with obesity as well as in those with type 2 diabetes (T2DM). However, several clinical studies have shown associations between high adiponectin values and major health concerns. These conflicting findings are termed the "adiponectin paradox". Similarly, these paradoxical adiponectin elevations were observed in patients with diabetic microvascular complications. This cross-sectional study aimed to identify differences in factors, including adiponectin, related to diabetic vascular complications between non-obese and obese patients.

MATERIALS AND METHODS

Study patients with T2DM were non-obese (n=197) or obese (n=197), matched by a propensity score model adjusted with age and gender. Independent factors for each of the microvascular complications were determined using multivariate logistic regression analyses.

RESULTS

The prevalence of nephropathy was high in obese T2DM patients. In addition to long diabetes duration, elevated adiponectin was a common characteristic of patients with microvascular complications. Logistic regression analyses for microvascular complications revealed adiponectin to be highly related to retinopathy (odds ratio [OR], 1.138; 95%confidence intervals [CI], 1.004-1.289, p<0.001), nephropathy (OR, 1.192; CI, 1.077-1.319, p<0.001) and neuropathy (OR, 1.217; CI, 1.071-1.384, p<0.001), in non-obese patients. In contrast, the association between adiponectin values and complications was modest in obese patients.

CONCLUSION

Adiponectin regulation in response to vascular damage differed between non-obese and obese patients, suggesting that adiponectin regulation is compromised by fat accumulation. Assuming that paradoxical elevation of adiponectin in vascular damage is a compensatory response, we speculate that responsive upregulation might be insufficient in obese patients. These newly-recognized differences in adiponectin values might lead to novel insights into adiponectin regulation and our understanding of the adiponectin paradox.

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.

Adiponectin Ameliorates Hyperglycemia-Induced Retinal Endothelial Dysfunction, Highlighting Pathways, Regulators, and Networks

Background

The pathophysiology of diabetic retinopathy (DR) is multifaced. A low level of circulating adiponectin (APN) in type 2 diabetes is associated with microvasculature complications, and its role in the evolution of DR is complex.

Aim

This study is designed to explore the potential impact of APN in the pathogenesis of DR, linking the changes in cellular and biological processes with the pathways, networks, and regulators involved in its actions.

Methods

Human microvascular retinal endothelial cells (HMRECs) were exposed to 30mM glucose (HG) and treated with globular adiponectin (30μg/mL) for 24 hours. The cells were evaluated for reactive oxidative stress (ROS) and apoptosis. RT-PCR profile arrays were utilized to evaluate the profile of genes involved in endothelial functions, angiogenesis, extracellular matrix, and adhesion molecules for hyperglycemic HMRECs treated with adiponectin. In addition, the barrier function, leukocyte migration, and angiogenesis were evaluated. The differential expressed genes (DEGs) were outlined, and bioinformatic analysis was applied.

Results

Adiponectin suppresses ROS production and apoptosis in HMRECs under HG conditions. Adiponectin improved migration and barrier functions in hyperglycemic cells. The bioinformatic analysis highlighted that the signaling pathways of integrin, HMGB1, and p38 AMPK, are mainly involved in the actions of APN on HMRECs. APN significantly affects molecular functions, including the adhesion of cells, chemotaxis, migration of WBCs, and angiogenesis. STAT3, NFKB, IKBKB, and mir-8 are the top upstream regulators, which affect the expressions of the genes of the data set, while TNF and TGFB1 are the top regulators.

Conclusion

Adiponectin significantly counteracts hyperglycemia at various cellular and molecular levels, reducing its impact on the pathophysiological progression towards DR in vitro using HMRECs. Adiponectin ameliorates inflammatory response, oxidative stress, and endothelial barrier dysfunction using a causal network of NFBk complex, TNF, and HMGB1 and integrin pathways.

Adiponectin accumulation in the retinal vascular endothelium and its possible role in preventing early diabetic microvascular damage

Adiponectin (APN), a protein abundantly secreted from adipocytes, has been reported to possess beneficial effects on cardiovascular diseases in association with its accumulation on target organs and cells by binding to T-cadherin. However, little is known about the role of APN in the development of diabetic microvascular complications, such as diabetic retinopathy (DR). Here we investigated the impact of APN on the progression of early retinal vascular damage using a streptozotocin (STZ)-induced diabetic mouse model. Our immunofluorescence results clearly showed T-cadherin-dependent localization of APN in the vascular endothelium of retinal arterioles, which was progressively decreased during the course of diabetes. Such reduction of retinal APN accompanied the early features of DR, represented by increased vascular permeability, and was prevented by glucose-lowering therapy with dapagliflozin, a selective sodium-glucose co-transporter 2 inhibitor. In addition, APN deficiency resulted in severe vascular permeability under relatively short-term hyperglycemia, together with a significant increase in vascular cellular adhesion molecule-1 (VCAM-1) and a reduction in claudin-5 in the retinal endothelium. The present study demonstrated a possible protective role of APN against the development of DR.