Profile of intraocular tumour necrosis factor-α and interleukin-6 in diabetic subjects with different degrees of diabetic retinopathy

Biochemical Changes in Anterior Chamber of the Eye in Diabetic Patients-A Review

This article aims to provide a comprehensive review of the biochemical changes observed in the anterior chamber of the eye in diabetic patients. The increased levels of inflammatory markers, alterations in antioxidant defense mechanisms, and elevated levels of advanced glycation end products (AGEs) in the aqueous humor (AH) are explored. Additionally, the impact of these biochemical changes on diabetic retinopathy progression, increased intraocular pressure, and cataract formation is discussed. Furthermore, the diagnostic and therapeutic implications of these findings are presented. This study explores potential biomarkers for detecting diabetic eye disease at an early stage and monitoring its progression. An investigation of the targeting of inflammatory and angiogenic pathways as a potential treatment approach and the role of antioxidant agents in managing these biochemical changes is performed.

Retinal inflammation in murine models of type 1 and type 2 diabetes with diabetic retinopathy

AIMS/HYPOTHESIS

The loss of pericytes surrounding the retinal vasculature in early diabetic retinopathy underlies changes to the neurovascular unit that lead to more destructive forms of the disease. However, it is unclear which changes lead to loss of retinal pericytes. This study investigated the hypothesis that chronic increases in one or more inflammatory factors mitigate the signalling pathways needed for pericyte survival.

METHODS

Loss of pericytes and levels of inflammatory markers at the mRNA and protein levels were investigated in two genetic models of diabetes, Ins2Akita/+ (a model of type 1 diabetes) and Leprdb/db (a model of type 2 diabetes), at early stages of diabetic retinopathy. In addition, changes that accompany gliosis and the retinal vasculature were determined. Finally, changes in retinal pericytes chronically incubated with vehicle or increasing amounts of IFNγ were investigated to determine the effects on pericyte survival. The numbers of pericytes, microglia, astrocytes and endothelial cells in retinal flatmounts were determined by immunofluorescence. Protein and mRNA levels of inflammatory factors were determined using multiplex ELISAs and quantitative reverse transcription PCR (qRT-PCR). The effects of IFNγ on the murine retinal pericyte survival-related platelet-derived growth factor receptor β (PDGFRβ) signalling pathway were investigated by western blot analysis. Finally, the levels of cell death-associated protein kinase C isoform delta (PKCδ) and cleaved caspase 3 (CC3) in pericytes were determined by western blot analysis and immunocytochemistry.

RESULTS

The essential findings of this study were that both type 1 and 2 diabetes were accompanied by a similar progression of retinal pericyte loss, as well as gliosis. However, inflammatory factor expression was dissimilar in the two models of diabetes, with peak expression occurring at different ages for each model. Retinal vascular changes were more severe in the type 2 diabetes model. Chronic incubation of murine retinal pericytes with IFNγ decreased PDGFRβ signalling and increased the levels of active PKCδ and CC3.

CONCLUSIONS/INTERPRETATION

We conclude that retinal inflammation is involved in and sustains pericyte loss as diabetic retinopathy progresses. Moreover, IFNγ plays a critical role in reducing pericyte survival in the retina by reducing activation of the PDGFRβ signalling pathway and increasing PKCδ levels and pericyte apoptosis.

Diabetic Macular Edema: Current Understanding, Molecular Mechanisms and Therapeutic Implications

Diabetic retinopathy (DR), with increasing incidence, is the major cause of vision loss and blindness worldwide in working-age adults. Diabetic macular edema (DME) remains the main cause of vision impairment in diabetic patients, with its pathogenesis still not completely elucidated. Vascular endothelial growth factor (VEGF) plays a pivotal role in the pathogenesis of DR and DME. Currently, intravitreal injection of anti-VEGF agents remains as the first-line therapy in DME treatment due to the superior anatomic and functional outcomes. However, some patients do not respond satisfactorily to anti-VEGF injections. More than 30% patients still exist with persistent DME even after regular intravitreal injection for at least 4 injections within 24 weeks, suggesting other pathogenic factors, beyond VEGF, might contribute to the pathogenesis of DME. Recent advances showed nearly all the retinal cells are involved in DR and DME, including breakdown of blood-retinal barrier (BRB), drainage dysfunction of Müller glia and retinal pigment epithelium (RPE), involvement of inflammation, oxidative stress, and neurodegeneration, all complicating the pathogenesis of DME. The profound understanding of the changes in proteomics and metabolomics helps improve the elucidation of the pathogenesis of DR and DME and leads to the identification of novel targets, biomarkers and potential therapeutic strategies for DME treatment. The present review aimed to summarize the current understanding of DME, the involved molecular mechanisms, and the changes in proteomics and metabolomics, thus to propose the potential therapeutic recommendations for personalized treatment of DME.

The role of the adaptive immune system and T cell dysfunction in neurodegenerative diseases

The adaptive immune system and associated inflammation are vital in surveillance and host protection against internal and external threats, but can secondarily damage host tissues. The central nervous system is immune-privileged and largely protected from the circulating inflammatory pathways. However, T cell involvement and the disruption of the blood-brain barriers have been linked to several neurodegenerative diseases including Parkinson's disease, Alzheimer's disease, and multiple sclerosis. Under normal physiological conditions, regulatory T cells (Treg cells) dampen the inflammatory response of effector T cells. In the pathological states of many neurodegenerative disorders, the ability of Treg cells to mitigate inflammation is reduced, and a pro-inflammatory environment persists. This perspective review provides current knowledge on the roles of T cell subsets (e.g., effector T cells, Treg cells) in neurodegenerative and ocular diseases, including uveitis, diabetic retinopathy, age-related macular degeneration, and glaucoma. Many neurodegenerative and ocular diseases have been linked to immune dysregulation, but the cellular events and molecular mechanisms involved in such processes remain largely unknown. Moreover, the role of T cells in ocular pathologies remains poorly defined and limited literature is available in this area of research. Adoptive transfer of Treg cells appears to be a vital immunological approach to control ocular pathologies. Similarities in T cell dysfunction seen among non-ocular neurodegenerative diseases suggest that this area of research has a great potential to develop better therapeutic agents for ocular diseases and warrants further studies. Overall, this perspective review article provides significant information on the roles of T cells in numerous ocular and non-ocular neurodegenerative diseases.

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

BACKGROUND

Diabetic retinopathy is a major complication of diabetes mellitus, where in its most advanced form ischemic changes lead to the development of retinal neovascularization, termed proliferative diabetic retinopathy (PDR). While the development of PDR is often associated with angiogenic and inflammatory cytokines, studies differ on which cytokines are implicated in disease pathogenesis and on the strength of these associations. We therefore conducted a systematic review and meta-analysis to quantitatively assess the existing body of data on intraocular cytokines as biomarkers in PDR.

METHODS

A comprehensive search of the literature without year limitation was conducted to January 18, 2021, which identified 341 studies assessing vitreous or aqueous cytokine levels in PDR, accounting for 10379 eyes with PDR and 6269 eyes from healthy controls. Effect sizes were calculated as standardized mean differences (SMD) of cytokine concentrations between PDR and control patients.

RESULTS

Concentrations (SMD, 95% confidence interval, and p-value) of aqueous IL-1β, IL-6, IL-8, MCP-1, TNF-α, and VEGF, and vitreous IL-2, IL-4, IL-6, IL-8, angiopoietin-2, eotaxin, erythropoietin, GM-CSF, GRO, HMGB-1, IFN-γ, IGF, IP-10, MCP-1, MIP-1, MMP-9, PDGF-AA, PlGF, sCD40L, SDF-1, sICAM-1, sVEGFR, TIMP, TNF-α, and VEGF were significantly higher in patients with PDR when compared to healthy nondiabetic controls. For all other cytokines no differences, failed sensitivity analyses or insufficient data were found.

CONCLUSIONS

This extensive list of cytokines speaks to the complexity of PDR pathogenesis, and informs future investigations into disease pathogenesis, prognosis, and management.

Inflammatory cytokines and retinal nonperfusion area in quiescent proliferative diabetic retinopathy

PURPOSE

We sought to investigate the association between inflammatory cytokine levels and retinal capillary nonperfusion area in eyes with quiescent proliferative diabetic retinopathy (PDR).

METHODS

Samples of aqueous humor were collected from 67 eyes (n = 42 patients) with treatment-naïve PDR. Levels of interleukin (IL)-10, IL-1β, IL-6, IL-8, monocyte chemoattractant protein 1 (MCP-1), and tumor necrosis factor-α (TNF-α) were obtained using multiplex bead assay. Areas of capillary nonperfusion at the posterior pole and peripheral retina were measured via ultra-widefield fluorescein angiography and correlated with cytokine levels.

RESULTS

The levels of IL-10, IL-6, IL-8, MCP-1, and TNF-α were positively correlated with the nonperfusion area of the peripheral retina (r = 0.298, 0.401, 0.265, 0.435, and 0.393; all P ≤ 0.030). There were positive correlations between IL and 10, IL-6, IL-8, MCP-1, and TNF-α (all R ≥ 0.247; all P ≤ 0.043). IL-1β did not show a significant correlation with the nonperfusion area (P = 0.972 for posterior pole and 0.392 for periphery) but was positively correlated with TNF-α (r = 0.334; P = 0.006).

CONCLUSIONS

An increased level of inflammation was observed in PDR eyes with larger nonperfusion areas, which suggests inflammation as a possible target for suppressing PDR progression associated with nonperfusion.

Interleukins and redox impairment in type 2 diabetes mellitus: mini-review and pilot study

BACKGROUND

Type 2 diabetes mellitus (T2DM) represents a leading cause of morbidity and premature mortality, low-grade inflammation being acknowledged as a key contributor to its development and progression. A tailored therapeutic approach, based on sensitive and specific biomarkers, could allow a more accurate analysis of disease susceptibility/prognostic and of the response to treatment.

OBJECTIVES

This mini-review and pilot study had two main goals: (1) reviewing the most recent literature encompassing the use of interleukins as inflammatory markers influenced by the redox imbalances in T2DM and (2) assessing parameters that conjunctly evaluate the redox impairment and inflammatory burden of T2DM patients, taking into consideration smoking status, as such group-specific biomarkers are scarcely reported in literature.

METHODS

Firstly, PubMed database was surveyed to select and review the relevant studies employing interleukins as T2DM biomarkers and to assess if studies using combined inflammatory-redox indices were reported. Then, routine biochemical parameters were assessed in a pilot study -T2DM patients with 3 subgroups: non-smokers, smokers and ex-smokers, were compared to a control group of non-diabetic, apparently healthy non-smokers. Protein (AOPPs, AGEs), lipid/HDL (Amplex Red-based method) oxidative damage and inflammatory status (CRP, IL-1β, IL-6, IL-10) biomarkers were assessed. Cytokine ratios and 2 oxidative-inflammatory status indices were developed (IH1 and IH2) and evaluated.

RESULTS

We observed significant differences in terms of serum redox and inflammatory status (AOPPs, AGEs, CRP, CRP/HDL, CRP/IL-6, IL-10/IL-6, IH1) between T2DM patients compared to control and, moreover, between the subgroups formed considering smoking status (CRP, CRP/HDL, IH1). Glycemic control strongly influenced inflammatory status biomarkers: glycemia was positively correlated with the inflammatory parameters (CRP/IL-10) and inversely with the anti-inflammatory ones (IL-10, IL-10/IL-1β ratio).

CONCLUSIONS

Several of the assessed parameters may possess prognostic value for diabetics, especially when comparing subgroups with a different smoking history and could prove useful in clinical practice for assessing disease progress and therapeutic efficacy.

Possible roles of anti-type II collagen antibody and innate immunity in the development and progression of diabetic retinopathy

The pathogenesis of both diabetic retinopathy (DR) and rheumatoid arthritis (RA) has recently been considered to involve autoimmunity. Serum and synovial fluid levels of anti-type II collagen antibodies increase early after the onset of RA, thus inducing immune responses and subsequent hydrarthrosis and angiogenesis, which resemble diabetic macular edema and proliferative DR (PDR), respectively. We previously reported that DR is also associated with increased serum levels of anti-type II collagen antibodies. Retinal hypoxia in DR may induce pericytes to express type II collagen, resulting in autoantibody production against type II collagen. As the result of blood-retinal barrier disruption, anti-type II collagen antibodies in the serum come into contact with type II collagen around the retinal vessels. A continued loss of pericytes and type II collagen around the retinal vessels may result in a shift of the immune reaction site from the retina to the vitreous. It has been reported that anti-inflammatory M2 macrophages increased in the vitreous of PDR patients, accompanied by the activation of the NOD-like receptor family pyrin domain-containing 3 (NLRP3) inflammasome, a key regulator of innate immunity. M2 macrophages promote angiogenesis and fibrosis, which might be exacerbated and prolonged by dysregulated innate immunity.

Retinal Neurodegeneration in Diabetes: an Emerging Concept in Diabetic Retinopathy

PURPOSE OF REVIEW

Diabetic retinopathy (DR), the leading cause of blindness in working-aged adults, remains clinically defined and staged by its vascular manifestations. However, early retinal neurodegeneration may precede vascular pathology, suggesting that this neuronal damage may contribute to disease pathogenesis and represent an independent target for intervention. This review will discuss the evidence and implications for diabetic retinal neurodegeneration.

RECENT FINDINGS

A growing body of literature has identified progressive retinal thinning and visual dysfunction in patients with diabetes even prior to the onset of DR, though advances in retinal vascular imaging suggest that vascular remodeling and choroidal changes occur during these early stages as well. Animal models of diabetes and in vitro studies have also suggested that diabetes may directly affect the retinal neural and glial tissue, providing support to the concept that diabetic retinal neurodegeneration occurs early in the disease and suggesting potentially relevant molecular pathways. Diabetic retinal neurodegeneration may represent a "preclinical" manifestation of diabetic retinal disease and remains an active area of investigation. As the natural history and molecular mechanisms become increasingly understood, it may lead to upcoming developments in not only the treatment options but also the clinical definition of DR.

Cyanidin-3-o-glucoside (C3G) inhibits vascular leakage regulated by microglial activation in early diabetic retinopathy and neovascularization in advanced diabetic retinopathy

Cyanidin-3-O-glucoside (C3G) is a kind of anthocyanin which shows strong anti-inflammation, anti-tumor and anti-oxidant properties. This paper was designed to explore the potential effects of C3G on diabetic retinopathy (DR). C57BL/6 mice were administrated with streptozotocin (STZ) or vehicle control for the establishment of diabetic models. To simulate hyperglycemia and hypoxia, D-glucose (30 mM) and CoCl₂ (200 μm/l) were utilized to treat HRECs, respectively. The migration, invasion, inflammation and tube formation abilities of cells were evaluated with the adoption of wound healing, transwell, ELISA and tube formation assays, respectively. Besides, immunofluorescence staining was utilized to detect proliferation and retinal vessels. Evans blue permeation assay were performed to evaluate the vascular leakage in DR mice. Moreover, western blot and qPCR were used to quantify the mRNA and protein expressions of ionized calcium-binding adapter molecule (Iba)-1 and tight junction proteins. Results showed that C3G alleviated the inflammation, microglial activation and angiogenesis in DR mice. Moreover, the proliferation and inflammation of BV2 cells induced by high glucose (HG) were suppressed by C3G. Evans blue permeation assay demonstrated the potency of C3G in attenuating vascular leakage. In addition, C3G suppressed the migration, invasion and angiogenesis of human retinal endothelial cells (HRECs) DR model in vitro.By confirming the role of C3G in inhibiting vascular leakage regulated by microglia activation in early DR and angiogenesis in advanced DR, this study pointed out the potential of C3G as a therapeutic drug for DR management.

Comparisons of Vitreal Angiogenic, Inflammatory, Profibrotic Cytokines, and Chemokines Profile between Patients with Epiretinal Membrane and Macular Hole

Objectives

Idiopathic epiretinal membrane (iERM) or idiopathic macular hole (iMH) is frequently used as a “healthy” control in comparison of vitreous cytokines with other vitreoretinal diseases. This study aimed to investigate if there is a difference in vitreal cytokines expression between patients with iERM and iMH.

Methods

In this prospective study, all subjects received standard pars plana vitrectomy surgery, and 0.5 ml of native vitreous sample was extracted during the vitrectomy. Luminex technology and enzyme-linked immunosorbent assay were used to profile the concentration of 52 classic angiogenic, inflammatory, and profibrotic cytokines and chemokines. Statistical analyses were performed by the Mann–Whitney U test, followed by multiple comparisons by the Bonferroni correction.

Results

Vitreal samples from 13 iERM and 24 iMH were studied. Of the 52 tested cytokines, 41 were similar in expression, and 5 were under the detection limit, while 6 cytokines (MMP-8, Eotaxin, MIP-1a, RANTES, TGF-β2, and IL-4) were differently expressed between two groups (p < 0.05). Nevertheless, these significances disappeared after the adjustment of Bonferroni correction.

Conclusion

The tested cytokines showed similar expression between iERM and iMH patients. This indicates that eyes with iERM or iMH can be together served as “healthy” controls.

The Vitreous Ecosystem in Diabetic Retinopathy: Insight into the Patho-Mechanisms of Disease

Diabetic retinopathy is one of the leading causes of blindness in the world with the incidence of disease ever-increasing worldwide. The vitreous humor represents an extensive and complex interactive arena for cytokines in the diabetic eye. In recent decades, there has been significant progress in understanding this environment and its implications in disease pathophysiology. In this review, we investigate the vitreous ecosystem in diabetic retinopathy at the molecular level. Areas of concentration include: the current level of knowledge of growth factors, cytokine and chemokine mediators, and lipid-derived metabolites in the vitreous. We discuss the molecular patho-mechanisms of diabetic retinopathy based upon current vitreous research.

Common genetic variants and pathways in diabetes and associated complications and vulnerability of populations with different ethnic origins

Diabetes mellitus is a complex and heterogeneous metabolic disorder which is often pre- or post-existent with complications such as cardiovascular disease, hypertension, inflammation, chronic kidney disease, diabetic retino- and nephropathies. However, the frequencies of these co-morbidities vary among individuals and across populations. It is, therefore, not unlikely that certain genetic variants might commonly contribute to these conditions. Here, we identified four single nucleotide polymorphisms (rs5186, rs1800795, rs1799983 and rs1800629 in AGTR1, IL6, NOS3 and TNFA genes, respectively) to be commonly associated with each of these conditions. We explored their possible interplay in diabetes and associated complications. The variant allele and haplotype frequencies at these polymorphic loci vary among different super-populations (African, European, admixed Americans, South and East Asians). The variant alleles are particularly highly prevalent in different European and admixed American populations. Differential distribution of these variants in different ethnic groups suggests that certain drugs might be more effective in selective populations rather than all. Therefore, population specific genetic architectures should be considered before considering a drug for these conditions.

Cytokines associated with hemorrhage in proliferative diabetic retinopathy

PURPOSE

To investigate aqueous cytokine levels in association with hemorrhage in proliferative diabetic retinopathy (PDR) in patients with type 2 diabetes mellitus.

METHODS

Sixty-six eyes with treatment-naïve PDR, including 26 hemorrhagic and 40 nonhemorrhagic eyes were included in this institutional study. Aqueous humor levels of interleukin (IL)-1b, IL-6, IL-8, IL-10, monocyte chemoattractant protein (MCP)-1, tumor necrosis factor (TNF)-α, vascular endothelial growth factor (VEGF), and soluble VEGF receptor-1 were obtained by multiplex bead assay. Visual acuity and hemorrhage area measurements were obtained, and correlations between cytokine levels and hemorrhage were identified.

RESULTS

Levels of MCP-1, TNF-α, and VEGF were higher in hemorrhagic eyes (1506.77 vs. 2131.31 pg/mL, 0.43 vs. 0.63 pg/mL, and 103.96 vs. 206.96 pg/mL; P = 0.050, 0.022, and 0.027, respectively). The levels of IL-8, MCP-1, TNF-α, and VEGF showed positive correlation with visual acuity (P = 0.019, 0.015, 0.001, and 0.014, respectively). The hemorrhage area revealed positive correlation with TNF-α and VEGF levels (P = 0.001 and < 0.001, respectively).

CONCLUSION

The presence and amount of hemorrhage in PDR were associated not only with VEGF concentration, but also with the levels of certain inflammatory cytokines, suggesting a role of both VEGF and inflammation in hemorrhagic eyes.

The role of IL-6-174 G/C polymorphism and intraocular IL-6 levels in the pathogenesis of ocular diseases: a systematic review and meta-analysis

Interleukin-6 (IL-6) is one of the key regulators behind the inflammatory and pathological process associated with ophthalmic diseases. The role of IL-6-174 G/C polymorphism as well as intraocular IL-6 levels among various eye disease patients differ across studies and has not been systematically reviewed. Thus, this study aims to provide a summary to understand the relationship between IL-6 and ophthalmic disease. In total, 8,252 and 11,014 subjects for IL-6-174 G/C and intraocular levels of IL-6, respectively, were retrieved from PubMed, Scopus and Web of Science. No association was found between IL-6-174 G/C polymorphisms with ocular diseases. Subgroup analyses revealed a suggestive association between the GC genotype of IL-6-174 G/C with proliferative diabetic retinopathy (PDR). Further, the level of intraocular IL-6 among ocular disease patients in general was found to be higher than the control group [standardized mean difference (SMD) = 1.41, 95% confidence interval (CI) 1.24-1.58, P < 0.00001]. Closer examination through subgroup analyses yielded similar results in several ocular diseases. This study thus indicates that the IL-6-174 G/C polymorphism does not predispose patients to ocular disease, although the GC genotype is likely to be a genetic biomarker for PDR. Moreover, intraocular IL-6 concentrations are related to the specific manifestations of the ophthalmic diseases. Further studies with larger sample sizes are warranted to confirm this conclusion.

Increased levels of cytokines in the aqueous humor correlate with the severity of diabetic retinopathy

AIMS

To determine the associations between the levels of certain cytokines in the aqueous humor and the severity of diabetic retinopathy.

METHODS

A total of 103 patients (one eye per patient) who received intravitreal injection with ranibizumab for diabetic retinopathy were enrolled and divided into 3 groups: nonproliferative diabetic retinopathy (NPDR) with macular edema group (42 eyes), proliferative diabetic retinopathy (PDR) group (40 eyes) and neovascular glaucoma due to PDR (NVG-PDR) group (21 eyes). The concentrations of interleukin (IL)-6, IL-8, IL-10, vascular endothelial growth factor (VEGF), transforming growth factor-β (TGF-β), vascular cell adhesion molecule-1 (VCAM-1), intercellular adhesion molecule-1 (ICAM-1), and monocyte chemoattractant protein-1 (MCP-1) in the aqueous humor were measured.

RESULTS

In this study, 42, 40 and 21 patients (one eye per patient) were included in the NPDR, PDR and NVG-PDR groups, respectively. The median concentrations of IL-6, IL-8, IL-10, VEGF, TGF-β, VCAM-1, ICAM-1 and MCP-1 in the groups were measured. The levels of these 8 cytokines increased with the severity of diabetic retinopathy, especially in the NVG-PDR group. Compared with those in the NPDR group, the aqueous concentrations of these 8 cytokines were higher in the PDR group and were the highest in the NVG-PDR group. There were significant differences in all cytokines among the three groups (P < 0.05). Multivariate analysis showed that in the NPDR and PDR groups, the risk of PDR associated with elevated levels of TGF-β (P = 0.0004, OR 1.11, 95% CI [1.05-1.18]) and ICAM-1 (P = 0.0408, OR 10.75, 95% CI [1.10-104.61]). In the PDR and NVG groups, the risk of NVG associated with elevated levels of IL-10 (P = 0.0486, OR 0.7040, 95% CI [0.4966, 0.9979]), VEGF (P = 0.0279, OR 0.9963, 95% CI [0.9931, 0.9996]), and VCAM-1 (P = 0.0316, OR 0.9998, 95% CI [0.9996, 0.99998]). In the three groups, the risk of developing NVG associated with elevated levels of TGF-β (P < 0.001, OR 1.04, 95% CI [1.02, 1.05]).

CONCLUSIONS

The levels of these eight cytokines in the aqueous humor increased with the severity of diabetic retinopathy, especially in NVG-PDR. This study suggests that TGF-β, ICAM-1, IL-10, VEGF, and VCAM-1 may play a role in the progression of diabetic retinopathy, especially TGF-β, which may plays a significant role in NVG-PDR. These cytokines potentially may be used as biomarkers to predict the progress of diabetic retinopathy, contribute to the choice of treatment options and/or monitor treatment responses.

Concentrations of Selected Cytokines and Vascular Endothelial Growth Factor in Aqueous Humor and Serum of Diabetic Patients

Purpose: To investigate the aqueous humor and serum levels of selected cytokines and vascular endothelial growth factor (VEGF) in diabetic patients, implicating their role in the pathogenesis of diabetic eye complications.Materials and methods:   Atotal of 65 patients (27 males and 38 females) who underwent cataract surgery were recruited into the study. The study group consisted of 30 cataract patients with type 2 diabetes mellitus, and this group was divided into two subgroups: 14 patients with diabetic retinopathy (DR group) and 16 patients without DR (NDR group). The control group consisted of 35 non-diabetic cataract subjects.Results: Patients in the DR group had significantly higher aqueous humor concentrations of interleukin (IL)-1β, IL-6, IL-8, IL-10, monocyte chemotactic protein (MCP-1) and VEGF. Likewise, serum concentrations of IL-1β, IL-6, IL-8, IL-12, TNF-α and IFN-γ were significantly higher in the DR group as compared to the controls. Aqueous humor concentrations of IL-1β, IL-8, MCP-1 and VEGF were significantly higher in the DR group as compared with the NDR group.Conclusion: Our findings support the hypothesis that chronic inflammation and a disturbance of the immune system play important roles in the pathogenesis of diabetic cataract and DR.

Human vitreous in proliferative diabetic retinopathy: Characterization and translational implications

Diabetic retinopathy (DR) is one of the leading causes of visual impairment in the working-age population. DR is a progressive eye disease caused by long-term accumulation of hyperglycaemia-mediated pathological alterations in the retina of diabetic patients. DR begins with asymptomatic retinal abnormalities and may progress to advanced-stage proliferative diabetic retinopathy (PDR), characterized by neovascularization or preretinal/vitreous haemorrhages. The vitreous, a transparent gel that fills the posterior cavity of the eye, plays a vital role in maintaining ocular function. Structural and molecular alterations of the vitreous, observed during DR progression, are consequences of metabolic and functional modifications of the retinal tissue. Thus, vitreal alterations reflect the pathological events occurring at the vitreoretinal interface. These events are caused by hypoxic, oxidative, inflammatory, neurodegenerative, and leukostatic conditions that occur during diabetes. Conversely, PDR vitreous can exert pathological effects on the diabetic retina, resulting in activation of a vicious cycle that contributes to disease progression. In this review, we recapitulate the major pathological features of DR/PDR, and focus on the structural and molecular changes that characterize the vitreal structure and composition during DR and progression to PDR. In PDR, vitreous represents a reservoir of pathological signalling molecules. Therefore, in this review we discuss how studying the biological activity of the vitreous in different in vitro, ex vivo, and in vivo experimental models can provide insights into the pathogenesis of PDR. In addition, the vitreous from PDR patients can represent a novel tool to obtain preclinical experimental evidences for the development and characterization of new therapeutic drug candidates for PDR therapy.

The relationship of blood cell-associated inflammatory indices and diabetic retinopathy: a Meta-analysis and systematic review

AIM

To explore the correlation between several blood cell-associated inflammatory indices including mean platelet volume (MPV), platelet distribution width (PDW), neutrophil to lymphocyte ratio (NLR) and platelet-lymphocyte ratio (PLR), and the presence and severity of diabetic retinopathy (DR).

METHODS

We searched for eligible studies from PubMed, EMBASE, Web of Science and CNKI up to December 13, 2017. Standardized mean difference (SMD) calculated with confidence interval (CI) of 95% was used to estimate the values of those indices.

RESULTS

A total of 31 studies were included in the present Meta-analysis. As compared with type 2 diabetes mellitus (T2DM) patients without DR, the values of MPV, PDW, NLR, and PLR were higher in patients with DR (SMD=0.67; 95%CI: 0.36 to 0.98; SMD=0.51; 95%CI: 0.27 to 0.75; SMD=0.77; 95%CI: 0.49 to 1.05 and SMD=1.18; 95%CI: 0.07 to 2.28). Additionally, it was also observed that MPV was closely correlated with the severity of DR.

CONCLUSION

MPV, PDW, NLR, and PLR could be recommended as diagnostic biomarkers for DR, and MPV could be applied to assess the severity of DR.

Interleukin-6 and Diabetic Retinopathy: A Systematic Review and Meta-Analysis

BACKGROUND

Interleukin-6 (IL-6) is produced by a variety of cells involved in inflammation and acts as local intensification signals in pathological processes associated with chronic eye inflammation. This meta-analysis was performed to provide a better understanding of the relationship between IL-6 and diabetic retinopathy.

METHODS

The study was started with systematic search for literatures by using the PubMed, Web of Science and Embase online databases. The standard mean difference (SMD) and its 95% confidence intervals (CIs) were was included and then pooled with a random effects model.

RESULTS

Thirty-one articles, containing1099 DR patients and 1010 controls, were included in this meta-analysis. The level of IL-6 in the DR group was found to be higher than that in the control group (SMD: 2.12, 95% CI: 1.53-2.70, p < 0.00001).Obvious heterogeneity existed between the studies (p < 0.00001, I² = 96%). So a subgroup analysis and sensitivity analysis were performed. Removing the sensitivity studies, the stability of the overall treatment effect was good. Subgroup analysis showed that the levels of IL-6 in case group were observed to be higher than those in the control group; and the IL-6 levels in the proliferative diabetic retinopathy (PDR) group were also higher than those in the non-proliferative diabetic retinopathy (NPDR) group. (SMD: 0.78, 95% CI: 0.26-1.31, p=  0.003) Conclusion: The results from this current meta-analysis indicated that increased level of IL-6 generally exist in DR patients. And it may associated with the severity of DR. However, large-scale and high-quality studies in future are required to confirm the present findings.

Tumor necrosis factor-α and diabetic retinopathy: Review and meta-analysis

BACKGROUND

Tumor necrosis factor-alpha (TNF-α) is produced by multinuclear giant cells and acts as local intensification signals in pathological processes associated with chronic eye inflammation. This meta-analysis was performed to provide a better understanding of the relationship between TNF-α and diabetic retinopathy (DR).

METHOD

Online electric databases were searched to retrieve all relevant articles published before October 2017. The standard mean difference (SMD) and their 95% confidence intervals (CI) were included and then pooled with a random effects model.

RESULTS

A total of 16 articles with 1286 participants were included in this meta-analysis. No difference in the level of TNF-α was found between DR patients and healthy controls (SMD = 0.39, 95% CI = -0.09 to 0.68, P = 0.01). Subgroup analysis showed that with respect to the level of TNF-α, the association was significant for studies conducted in Europe (SMD: 0.57, 95% CI: 0.11-1.02, P = 0.01), patients with type 1 DM (SMD: 1.06, 95% CI: 0.09-2.04, P = 0.03), studies based on serum samples (SMD: 0.57, 95% CI: 0.12-1.02, P = 0.01) and studies with a sample size >50 (SMD: 0.39, 95% CI: 0.03-0.75, P = 0.04).

CONCLUSION

The results this meta-analysis indicated that the level of TNF-α in DR patients was significantly different from that in the healthy controls, so TNF-α represents a candidate biomarker for DR.

The Role of Microglia in Diabetic Retinopathy: Inflammation, Microvasculature Defects and Neurodegeneration

Diabetic retinopathy is a common complication of diabetes mellitus, which appears in one third of all diabetic patients and is a prominent cause of vision loss. First discovered as a microvascular disease, intensive research in the field identified inflammation and neurodegeneration to be part of diabetic retinopathy. Microglia, the resident monocytes of the retina, are activated due to a complex interplay between the different cell types of the retina and diverse pathological pathways. The trigger for developing diabetic retinopathy is diabetes-induced hyperglycemia, accompanied by leukostasis and vascular leakages. Transcriptional changes in activated microglia, mediated via the nuclear factor kappa-light-chain-enhancer of activated B cells (NFκB) and extracellular signal–regulated kinase (ERK) signaling pathways, results in release of various pro-inflammatory mediators, including cytokines, chemokines, caspases and glutamate. Activated microglia additionally increased proliferation and migration. Among other consequences, these changes in microglia severely affected retinal neurons, causing increased apoptosis and subsequent thinning of the nerve fiber layer, resulting in visual loss. New potential therapeutics need to interfere with these diabetic complications even before changes in the retina are diagnosed, to prevent neuronal apoptosis and blindness in patients.

Outcome of Surgical Treatment in Late-Onset Capsular Block Syndrome

Purpose

To further investigate the pathogenesis of late-onset capsular block syndrome (CBS) and to evaluate the safety of surgical treatment.

Methods

Seven patients diagnosed with late-onset CBS were retrospectively analyzed. Anterior chamber depth (ACD), intraocular pressure (IOP), refractive diopter, and best-corrected visual acuity (BCVA) before and after surgery were recorded. The opaque substance was tested with Western blot, and a flow cytometer multiple array assay system was utilized to evaluate the levels of inflammatory cytokines from opaque substance and aqueous humor, respectively.

Results

Patients who had undergone surgical treatment showed a significant BCVA and spherical equivalent refractive error improvement (P = 0.002, P = 0.021, resp.). Nevertheless, ACD and IOP before and after surgery were in normal range with no difference (P = 0.165, P = 0.749, resp.). αB-crystallin and βB-crystallin were detected in all opaque substances. Tumor necrosis factor-alpha (TNF-α) and interlukin-1β (IL-1β) levels in opaque substance were significantly higher than those in aqueous humor (P = 0.038, P = 0.007, resp.), while IL-2 and IL-6 were not detected in any samples.

Conclusions

Opaque substance is derived from human lens epithelial cells. Inflammatory cytokines may be involved in the pathogenesis of late-onset CBS. In addition, surgical treatment is an effective approach. This trial is registered with ChiCTR-IOR-17011287.

Inflammation and N-formyl peptide receptors mediate the angiogenic activity of human vitreous humour in proliferative diabetic retinopathy

AIMS/HYPOTHESIS

Angiogenesis and inflammation characterise proliferative diabetic retinopathy (PDR), a major complication of diabetes mellitus. However, the impact of inflammation on the pathogenesis of PDR neovascularisation has not been elucidated. Here, we assessed the capacity of PDR vitreous fluid to induce pro-angiogenic/proinflammatory responses in endothelium and the contribution of the inflammation-related pattern recognition N-formyl peptide receptors (FPRs) in mediating these responses.

METHODS

Pooled and individual pars plana vitrectomy-derived PDR vitreous fluid ('PDR vitreous') samples were assessed in endothelial cell proliferation, motility, sprouting and morphogenesis assays, and for the capacity to induce proinflammatory transcription factor activation, reactive oxygen species production, intercellular junction disruption and leucocyte-adhesion molecule upregulation in these cells. In vivo, the pro-angiogenic/proinflammatory activity of PDR vitreous was tested in murine Matrigel plug and chick embryo chorioallantoic membrane (CAM) assays. Finally, the FPR inhibitors Boc-Phe-Leu-Phe-Leu-Phe (Boc-FLFLF) and Ac-L-Arg-Aib-L-Arg-L-Cα(Me)Phe-NH₂ tetrapeptide (UPARANT) were evaluated for their capacity to affect the biological responses elicited by PDR vitreous.

RESULTS

PDR vitreous activates a pro-angiogenic/proinflammatory phenotype in endothelial cells. Accordingly, PDR vitreous triggers a potent angiogenic/inflammatory response in vivo. Notably, the different capacity of individual PDR vitreous samples to induce neovessel formation in the CAM correlates with their ability to recruit infiltrating CD45⁺ cells. Finally, the FPR inhibitor Boc-FLFLF and the novel FPR antagonist UPARANT inhibit neovessel formation and inflammatory responses triggered by PDR vitreous in the CAM assay.

CONCLUSIONS/INTERPRETATION

This study provides evidence that inflammation mediates the angiogenic activity of PDR vitreous and paves the way for the development of FPR-targeting anti-inflammatory/anti-angiogenic approaches for PDR therapy.

Indications of lymphatic endothelial differentiation and endothelial progenitor cell activation in the pathology of proliferative diabetic retinopathy

PURPOSE

Proliferative diabetic retinopathy (PDR) is characterized by ischaemia- and inflammation-induced neovascularization, but the pathological vascular differentiation in PDR remains poorly characterized. Here, endothelial progenitor and growth properties, as well as potential lymphatic differentiation, were investigated in the neovascular membrane specimens from vitrectomized patients with PDR.

METHODS

The expression of pan-endothelial CD31 (PECAM-1), ETS-related gene (ERG), α-smooth muscle actin (α-SMA), and stem/progenitor cell marker CD117 (c-kit) and cell proliferation marker Ki67 was investigated along with the markers of lymphatic endothelial differentiation (vascular endothelial growth factor receptor (VEGFR)-3; prospero-related homeobox gene-1 (Prox-1), lymphatic vessel endothelial receptor [LYVE)-1 and podoplanin (PDPN)] by immunohistochemistry. Lymphocyte antigen CD45 and pan-macrophage marker CD68 were likewise investigated.

RESULTS

All specimens displayed CD31, ERG and α-SMA immunoreactivity in irregular blood vessels. Unexpectedly, VEGFR3 and Prox-1 lymphatic marker positive vessels were also detected in several tissues. Prox-1 was co-expressed with CD117 in lumen-lining endothelial cells and adjacent cells, representing putative endothelial stem/progenitor cells and pro-angiogenic perivascular cells. Immunoreactivity of CD45 and CD68 was detectable in all investigated diabetic neovessel specimens. PDPN immunoreactivity was also detected in irregular lumen-forming structures, but these cells lacked CD31 and ERG that mark blood and lymphatic endothelium.

CONCLUSIONS

Although the inner part of human eye is physiologically devoid of lymphatic vessels, lymphatic differentiation associated with endothelial stem/progenitor cell activation may be involved in the pathogenesis of human PDR. Further studies are warranted to elucidate whether targeting lymphatic factors could be beneficial in the treatment of patients with the sight-threatening forms of DR.

The Expression of GDF-15 in the Human Vitreous in the Presence of Retinal Pathologies with an Inflammatory Component

PURPOSE

The presence of growth differentiation factor-15 (GDF-15), a protein implicated in the regulation of the inflammatory response, was investigated in the vitreous of patients with vitreoretinal disorders.

METHODS

Vitreous and plasma samples were collected from patients with idiopathic epiretinal membrane (IERM), macular hole (MH), rhegmatogenous retinal detachment (RRD), nucleus drop (ND), or proliferative diabetic retinopathy (PDR). GDF-15 concentrations were measured using ELISA.

RESULTS

The vitreous levels of GDF-15 were higher in ND (5) and PDR (14) patients (1494 ± 243 and 904 ± 138 pg/mL, respectively) than RRD (3), MH (3), and IERM (8) patients (302 ± 160, 288 ± 24, and 254 ± 91 pg/mL, respectively). The vitreous levels of GDF-15 were significantly higher in patients with inflammatory vitreoretinal disorders (p < 0.0001).

CONCLUSIONS

This is the first report showing that GDF-15 appears to be expressed in the vitreous, and that its expression is significantly higher in the presence of a vitreoretinal disorder in which there is an inflammatory component.

Increased intravitreal adenosine 5'-triphosphate, adenosine 5'-diphosphate and adenosine 5'-monophosphate levels in patients with proliferative diabetic retinopathy

PURPOSE

Extracellular purines play important role in ocular physiology, diabetes, vascular remodelling and adaptation to inflammation. This study was aimed to evaluate intravitreal purine levels in patients with diabetic retinopathy (DR) and other non-vascular vitreoretinal eye diseases.

METHODS

Vitreous samples were collected at the start of the three-port pars plana vitrectomy. Study group comprised 55 eyes operated due to sight-threatening forms of DR, including eyes of 24 patients with proliferative DR. Of the 143 non-diabetic controls, 112 had rhegmatogenous retinal detachment and 31 macular hole or pucker. Intravitreal purine concentrations were determined using a combination of bioluminescent [adenosine 5'-triphosphate (ATP), adenosine 5'-diphosphate (ADP)] and fluorometric [adenosine 5'-monophosphate (AMP), adenosine, inosine] enzyme-coupled sensing assays.

RESULTS

Compared with non-diabetic controls, DR eyes contained significantly higher (p < 0.01) concentrations of ATP (4.2 ± 0.6 versus 34.5 ± 13.7 nm; mean ± SEM), ADP (19.5 ± 2.7 versus 43.7 ± 14.5 nm) and AMP (1290 ± 115 versus 1876 ± 190 nm). Intravitreal adenosine and inosine levels varied within submicromolar to low micromolar range, and their concentrations did not differ between the groups studied.

CONCLUSIONS

High concentrations of intravitreal nucleotides ATP, ADP and AMP may be related to the pathogenesis of sight-threatening forms of DR.

Serum and vitreous levels of visfatin in patients with diabetic retinopathy

Background

Angiogenesis plays an important role in the mechanism of diabetic retinopathy (DR). Visfatin, a recently identified adipokine, is thought to possess an angiogenic effect. The aim of our study was to investigate serum and vitreous levels of visfatin in patients with proliferative diabetic retinopathy (PDR) and non-PDR (NPDR).

Material/Methods

A total of 280 diabetic patients (124 without DR, 56 with NPDR, and 100 with PDR) and 78 control subjects were enrolled in this study. Serum and vitreous levels of visfatin were measured by enzyme-linked immunosorbent assay (ELISA).

Results

Serum and vitreous visfatin levels in PDR patients were significantly elevated compared with those in the other 3 groups. NPDR patients showed elevated vitreous visfatin levels compared with patients without DR. However, no significant differences in serum visfatin levels were found between NPDR patients and patients without DR. In addition, control subjects had significantly lower levels of serum and vitreous visfatin compared with diabetic patients without DR, NPDR patients, and PDR patients.

Conclusions

Serum and vitreous visfatin levels are associated with the presence and severity of DR.

Bone morphogenetic protein 2: a potential new player in the pathogenesis of diabetic retinopathy

Diabetic retinopathy (DR) is one of the most common complications of diabetes mellitus. Vision loss in DR principally occurs due to breakdown of the blood-retinal barrier (BRB), leading to macular edema, retinal detachment and inner retinal and vitreous hemorrhage. Several growth factors have been shown to play crucial role in the development of these vascular changes; however, the cellular and molecular mechanisms of DR are not yet fully revealed. In the current study we investigated the role of bone morphogenetic protein-2 (BMP2) in DR. We examined the changes in the protein levels of BMP2 in human vitreous and retina in addition to the mouse retina of streptozotocin-induced diabetes. To detect the source of BMP2 during diabetes, human retinal endothelial cells (hRECs) were subjected to high glucose (HG) for 5 days and levels of BMP2 protein were analyzed in conditioned media of these cells relative to control. We also evaluated the effect of BMP2 on the levels of VEGF in cultured rat Müller cells (rMC1). In addition, we tested the pro-inflammatory effects of BMP2 by examining its effect on leukocyte adhesion to cultured hRECs, and levels of adhesion molecules and cytokines production. Finally, the effect of different concentrations of BMP2 on permeability of confluent monolayer of hRECs was evaluated using FITC-Dextran flux permeability assay and by measuring Transcellular Electrical Resistance (TER) using Electric Cell-substrate Impedance Sensing (ECIS). Our results show, for the first time, the up-regulation of BMP2 in diabetic human and mouse retinas in addition to its detection in vitreous of patients with proliferative DR (72 ± 7 pg/ml). In vitro, hRECs showed upregulation of BMP2 in HG conditions suggesting that these cells are a potential source of BMP2 in diabetic conditions. Furthermore, BMP2 induced VEGF secretion by Müller cells in-vitro; and showed a dose response in increasing permeability of cultured hRECs. Meanwhile, BMP2 pro-inflammatory effects were recognized by its ability to induce leukocyte adhesion to the hRECs, intercellular adhesion molecule-1 (ICAM-1) and upregulation of interleukin-6 and 8 (IL-6 and IL-8). These results show that BMP2 could be a contributing growth factor to the development of microvascular dysfunction during DR via enhancing both pro-angiogenic and inflammatory pathways. Our findings suggest BMP2 as a potential therapeutic target to prevent/treat DR.

Current trends in the monitoring and treatment of diabetic retinopathy in young adults

The diagnosis and treatment of diabetic retinopathy (DR) in young adults have significantly improved in recent years. Research methods have widened significantly, for example, by introducing spectral optical tomography of the eye. Invasive diagnostics, for example, fluorescein angiography, are done less frequently. The early introduction of an insulin pump to improve the administration of insulin is likely to delay the development of diabetic retinopathy, which is particularly important for young patients with type 1 diabetes mellitus (T1DM). The first years of diabetes occurring during childhood and youth are the most appropriate to introduce proper therapeutic intervention before any irreversible changes in the eyes appear. The treatment of DR includes increased metabolic control, laserotherapy, pharmacological treatment (antiangiogenic and anti-inflammatory treatment, enzymatic vitreolysis, and intravitreal injections), and surgery. This paper summarizes the up-to-date developments in the diagnostics and treatment of DR. In the literature search, authors used online databases, PubMed, and clinitrials.gov and browsed through individual ophthalmology journals, books, and leading pharmaceutical company websites.

Matrix metalloproteinase-10 plays an active role in microvascular complications in type 1 diabetic patients

AIMS/HYPOTHESIS

The role of metalloproteinase-10 (MMP-10) in type 1 diabetes is not known. We hypothesise that it plays a role in the onset and progression of diabetic nephropathy and retinopathy.

METHODS

Serum MMP-10 levels from 269 patients with type 1 diabetes were measured, and their association with microvascular complications was analysed. We also studied whether knocking out the Mmp10 gene influenced the extent of renal injury and retinal damage in a streptozotocin-induced diabetic mouse model.

RESULTS

The risk of nephropathy and proliferative retinopathy associated with the highest vs the lowest MMP-10 tertile was increased three to four times independently of the classical risk factors. Accordingly, renal function and morphology were better preserved in diabetic Mmp10 −⁄− mice than in their Mmp10 +/+ counterparts. There were more kidney-infiltrating macrophages in diabetic Mmp10+/+ mice, suggesting that MMP-10 contributes to the inflammatory response leading to microvascular complications. The loss of neuronal cells in the retinas of diabetic Mmp10 +/+ mice was higher than in Mmp10 −⁄− mice. Retinal inflammation was decreased in Mmp10 −⁄− mice, as indicated by their reduced retinal caspase-1 levels.

CONCLUSIONS/INTERPRETATION

MMP-10 is involved in the development of microvascular complications in type 1 diabetes and emerges as a potential therapeutic target for slowing down the evolution of diabetic nephropathy and retinopathy.

Overexpression of hemopexin in the diabetic eye: a new pathogenic candidate for diabetic macular edema

OBJECTIVE

Hemopexin is a well-recognized permeability factor in the kidney, but its potential role in blood-retinal barrier (BRB) breakdown has not been explored. The main aims of this study were as follows: 1) to determine hemopexin expression in the retina and its content in the vitreous fluid from diabetic patients with diabetic macular edema (DME) and nondiabetic patients, 2) to evaluate the effect of hemopexin on BRB permeability, and 3) to determine whether dexamethasone prevents an eventual hemopexin-induced hyperpermeability.

RESEARCH DESIGN AND METHODS

Biological material included 1) retinas from 10 diabetic donors with nonproliferative retinopathy and from 10 nondiabetic donors and 2) vitreous fluid from 14 patients with DME and 14 nondiabetic patients. Hemopexin and hemopexin receptor mRNA levels were measured by quantitative RT-PCR and hemopexin concentrations by ELISA. The effect of hemopexin on permeability in culture was evaluated in human retinal pigment epithelial (ARPE)-19 cells and bovine retinal endothelial cells. The experiments were repeated in the presence of hemopexin-neutralizing antibodies and dexamethasone.

RESULTS

A higher expression of hemopexin was detected in the retinal pigment epithelium (RPE) from diabetic patients in comparison with nondiabetic control subjects. Intravitreal hemopexin concentration was higher in patients with DME than in nondiabetic subjects. Hemopexin significantly increased permeability in ARPE-19 cells, which was prevented by both hemopexin-neutralizing antibodies and dexamethasone.

CONCLUSIONS

Hemopexin is overexpressed in the RPE of diabetic patients with DME and induces the breakdown of RPE cells in vitro. Dexamethasone was able to prevent hemopexin-induced hyperpermeability. Our results suggest that hemopexin can be considered a new pathogenic candidate for DME.

Therapeutic interventions against inflammatory and angiogenic mediators in proliferative diabetic retinopathy

The global prevalence of diabetes is estimated to be 336 million people, with diabetic complications contributing to significant worldwide morbidity and mortality. Diabetic retinopathy results from cumulative microvascular damage to the retina and inflammation is recognized as a critical driver of this disease process. This paper outlines the pathophysiology leading to proliferative diabetic retinopathy and highlights many of the inflammatory, angiogenic, and cytokine mediators implicated in the development and progression of this disease. We focus a detailed discussion on the current targeted therapeutic interventions used to treat diabetic retinopathy.