Differences in retinal neovascular tissue and vitreous humour in patients with type 1 and type 2 diabetes

Antiangiogenic AAV2 gene therapy with a truncated form of soluble VEGFR-2 reduces the growth of choroidal neovascularization in mice after intravitreal injection

Pathological angiogenesis related to neovascularization in the eye is mediated through vascular endothelial growth factors (VEGFs) and their receptors. Ocular neovascular-related diseases are mainly treated with anti-VEGF agents. In this study we evaluated the efficacy and safety of novel gene therapy using adeno associated virus 2 vector expressing a truncated form of soluble VEGF receptor-2 fused to the Fc-part of human IgG1 (AAV2-sVEGFR-2-Fc) to inhibit ocular neovascularization in laser induced choroidal neovascularization (CNV) in mice. The biological activity of sVEGFR-2-Fc was determined in vitro. It was shown that sVEGFR-2-Fc secreted from ARPE-19 cells was able to bind to VEGF-A₁₆₅ and reduce VEGF-A₁₆₅ induced cell growth and survival. A single intravitreal injection (IVT) of AAV2-sVEGFR-2-Fc (1 μl, 4.7 × 10¹² vg/ml) one-month prior laser photocoagulation did not cause any changes in the retinal morphology and significantly suppressed fluorescein leakage at 7, 14, 21 and 28 days post-lasering compared to controls. Macrophage infiltration was observed after the injection of both AAV2-sVEGFR-2-Fc and PBS. Our findings indicate that AAV2 mediated gene delivery of the sVEGFR-2-Fc efficiently reduces formation of CNV and could be developed to a therapeutic tool for the treatment of retinal diseases associated with neovascularization.

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.

Mechanistic dissection of diabetic retinopathy using the protein-metabolite interactome

Purpose

The current study aims to determine the molecular mechanisms of diabetic retinopathy (DR) using the protein-protein interactome and metabolome map. We examined the protein network of novel biomarkers of DR for direct (physical) and indirect (functional) interactions using clinical target proteins in different models.

Methods

We used proteomic tools including 2-dimensional gel electrophoresis, mass spectrometry analysis, and database search for biomarker identification using in vivo murine and human model of diabetic retinopathy and in vitro model of oxidative stress. For the protein interactome and metabolome mapping, various bioinformatic tools that include STRING and OmicsNet were used.

Results

We uncovered new diabetic biomarkers including prohibitin (PHB), dynamin 1, microtubule-actin crosslinking factor 1, Toll-like receptor (TLR 7), complement activation, as well as hypothetical proteins that include a disintegrin and metalloproteinase (ADAM18), vimentin III, and calcium-binding C2 domain-containing phospholipid-binding switch (CAC2PBS) using a proteomic approach. Proteome networks of protein interactions with diabetic biomarkers were established using known DR-related proteome data. DR metabolites were interconnected to establish the metabolome map. Our results showed that mitochondrial protein interactions were changed during hyperglycemic conditions in the streptozotocin-treated murine model and diabetic human tissue.

Conclusions

Our interactome mapping suggests that mitochondrial dysfunction could be tightly linked to various phases of DR pathogenesis including altered visual cycle, cytoskeletal remodeling, altered lipid concentration, inflammation, PHB depletion, tubulin phosphorylation, and altered energy metabolism. The protein-metabolite interactions in the current network demonstrate the etiology of retinal degeneration and suggest the potential therapeutic approach to treat DR.

Pro-angiogenic Role of Insulin: From Physiology to Pathology

The underlying molecular mechanisms involve in the regulation of the angiogenic process by insulin are not well understood. In this review article, we aim to describe the role of insulin and insulin receptor activation on the control of angiogenesis and how these mechanisms can be deregulated in human diseases. Functional expression of insulin receptors and their signaling pathways has been described on endothelial cells and pericytes, both of the main cells involved in vessel formation and maturation. Consequently, insulin has been shown to regulate endothelial cell migration, proliferation, and in vitro tubular structure formation through binding to its receptors and activation of intracellular phosphorylation cascades. Furthermore, insulin-mediated pro-angiogenic state is potentiated by generation of vascular growth factors, such as the vascular endothelial growth factor, produced by endothelial cells. Additionally, diseases such as insulin resistance, obesity, diabetes, and cancer may be associated with the deregulation of insulin-mediated angiogenesis. Despite this knowledge, the underlying molecular mechanisms need to be elucidated in order to provide new insights into the role of insulin on angiogenesis.

Targeting Tie2 for Treatment of Diabetic Retinopathy and Diabetic Macular Edema

Tie2 is a tyrosine kinase receptor located predominantly on vascular endothelial cells that plays a central role in vascular stability. Angiopoietin-1 (Angpt1), produced by perivascular cells, binds, clusters, and activates Tie2, leading to Tie2 autophosphorylation and downstream signaling. Activated Tie2 increases endothelial cell survival, adhesion, and cell junction integrity, thereby stabilizing the vasculature. Angiopoietin-2 (Angpt2) and vascular endothelial-protein tyrosine phosphatase (VE-PTP) are negative regulators increased by hypoxia; they inactivate Tie2, destabilizing the vasculature and increasing responsiveness to vascular endothelial growth factor (VEGF) and other inflammatory cytokines that stimulate vascular leakage and neovascularization. AKB-9778 is a small-molecule antagonist of VE-PTP which increases phosphorylation of Tie2 even in the presence of high Angpt2 levels. In preclinical studies, AKB-9778 reduced VEGF-induced leakage and ocular neovascularization (NV) and showed additive benefit when combined with VEGF suppression. In two clinical trials in diabetic macular edema (DME) patients, subcutaneous injections of AKB-9778 were safe and provided added benefit to VEGF suppression. Preliminary data suggest that AKB-9778 monotherapy improves diabetic retinopathy. These data suggest that Tie2 activation may be a valuable strategy to treat or prevent diabetic retinopathy.

Increased expression of angiogenic and inflammatory proteins in the vitreous of patients with ischemic central retinal vein occlusion

Background

Central retinal vein occlusion (CRVO) is a common disease characterized by a disrupted retinal blood supply and a high risk of subsequent vision loss due to retinal edema and neovascular disease. This study was designed to assess the concentrations of selected signaling proteins in the vitreous and blood of patients with ischemic CRVO.

Methods

Vitreous and blood samples were collected from patients undergoing surgery for ischemic CRVO (radial optic neurotomy (RON), n = 13), epiretinal gliosis or macular hole (control group, n = 13). Concentrations of 40 different proteins were determined by an ELISA-type antibody microarray.

Results

Expression of proteins enriched in the vitreous (CCL2, IGFBP2, MMP10, HGF, TNFRSF11B (OPG)) was localized by immunohistochemistry in eyes of patients with severe ischemic CRVO followed by secondary glaucoma. Vitreal expression levels were higher in CRVO patients than in the control group (CRVO / control; p < 0.05) for ADIPOQ (13.6), ANGPT2 (20.5), CCL2 (MCP1) (3.2), HGF (4.7), IFNG (13.9), IGFBP1 (14.7), IGFBP2 (1.8), IGFBP3 (4.1), IGFBP4 (1.7), IL6 (10.8), LEP (3.4), MMP3 (4.3), MMP9 (3.6), MMP10 (5.4), PPBP (CXCL7 or NAP2) (11.8), TIMP4 (3.8), and VEGFA (85.3). In CRVO patients, vitreal levels of CCL2 (4.2), HGF (23.3), IGFBP2 (1.23), MMP10 (2.47), TNFRSF11B (2.96), and VEGFA (29.2) were higher than the blood levels (vitreous / blood, p < 0.05). Expression of CCL2, IGFBP2, MMP10, HGF, and TNFRSF11B was preferentially localized to the retina and the retinal pigment epithelium (RPE).

Conclusion

Proteins related to hypoxia, angiogenesis, and inflammation were significantly elevated in the vitreous of CRVO patients. Moreover, some markers known to indicate atherosclerosis may be related to a basic vascular disease underlying RVO. This would imply that local therapeutic targeting might not be sufficient for a long term therapy in a systemic disease but hypothetically reduce local changes as an initial therapeutic approach.

Optical quality of the diabetic eye: a review

Diabetes mellitus is a metabolic disorder characterized by the presence of chronic hyperglycaemia. Several structural, morphological, and physiological changes in each of ocular component have been described in detail during the past decades. Due to these abnormalities, the diabetic patient undergoes a degradation of the retinal image by an increase of higher ocular aberrations and ocular scattering coming from mainly tear film, cornea, and crystalline lens. This review aims to provide an overview of current knowledge about the effects of diabetes mellitus in these optical phenomena and its consequence on the visual quality of the diabetic patient.

Molecular and pathological studies in the posterior interosseous nerve of diabetic and non-diabetic patients with carpal tunnel syndrome

AIMS/HYPOTHESIS

We sought to establish the molecular and pathological changes predisposing diabetic and non-diabetic patients to the development of carpal tunnel syndrome (CTS).

METHODS

The posterior interosseous nerve (PIN) was biopsied in 25 diabetic and 19 non-diabetic patients undergoing carpal tunnel decompression for CTS. Detailed morphometric and immunohistological analyses were performed in the nerve biopsy.

RESULTS

In diabetic patients median nerve distal motor latency was prolonged (p < 0.05 vs non-diabetic patients), PIN myelinated fibre density (p < 0.05), fibre area (p < 0.0001) and axon area (p < 0.0001) were reduced, the percentage of unassociated Schwann cell profiles (p < 0.0001) and unmyelinated axon density (p < 0.0001) were increased and the axon diameter was reduced (p < 0.0001). Endoneurial capillary basement membrane area was increased (p < 0.0001) in diabetic patients, but endothelial cell number was increased (p < 0.01) and luminal area was reduced (p < 0.05) in non-diabetic patients with CTS. There was no difference in the expression of hypoxia-inducible factor 1α between diabetic and non-diabetic patients with CTS. However, the expression of vascular endothelial growth factor A (VEGF) (p < 0.05) and its receptors VEGFR-1 (p < 0.01) and VEGFR-2 (p < 0.05) was significantly increased in diabetic patients, particularly those with type 1 diabetes, and related to the severity of nerve fibre pathology.

CONCLUSIONS/INTERPRETATION

This study demonstrates increased nerve fibre and microvascular pathology in relation to enhanced expression of VEGF and its receptors in a non-compressed nerve in diabetic compared with non-diabetic patients with CTS. It therefore provides a potential molecular and pathological basis for the predisposition of diabetic patients to the development of CTS.

Importance of insulin resistance to vascular repair and regeneration

Metabolic insulin resistance is apparent across a spectrum of clinical disorders, including obesity and diabetes, and is characterized by an adverse clustering of cardiovascular risk factors related to abnormal cellular responses to insulin. These disorders are becoming increasingly prevalent and represent a major global public health concern because of their association with significant increases in atherosclerosis-related mortality. Endogenous repair mechanisms are thought to retard the development of vascular disease, and a growing evidence base supports the adverse impact of the insulin-resistant phenotype upon indices of vascular repair. Beyond the impact of systemic metabolic changes, emerging data from murine studies also provide support for abnormal insulin signaling at the level of vascular cells in retarding vascular repair. Interrelated pathophysiological factors, including reduced nitric oxide bioavailability, oxidative stress, altered growth factor activity, and abnormal intracellular signaling, are likely to act in conjunction to impede vascular repair while also driving vascular damage. Understanding of these processes is shaping novel therapeutic paradigms that aim to promote vascular repair and regeneration, either by recruiting endogenous mechanisms or by the administration of cell-based therapies.

Vitreous mediators in retinal hypoxic diseases

The causes of retinal hypoxia are many and varied. Under hypoxic conditions, a variety of soluble factors are secreted into the vitreous cavity including growth factors, cytokines, and chemokines. Cytokines, which usually serve as signals between neighboring cells, are involved in essentially every important biological process, including cell proliferation, inflammation, immunity, migration, fibrosis, tissue repair, and angiogenesis. Cytokines and chemokines are multifunctional mediators that can direct the recruitment of leukocytes to sites of inflammation, promote the process, enhance immune responses, and promote stem cell survival, development, and homeostasis. The modern particle-based flow cytometric analysis is more direct, stable and sensitive than the colorimetric readout of the conventional ELISA but, similar to ELISA, is influenced by vitreous hemorrhage, disruption of the blood-retina barrier, and high serum levels of a specific protein. Finding patterns in the expression of inflammatory cytokines specific to a particular disease can substantially contribute to the understanding of its basic mechanism and to the development of a targeted therapy.

Vascular endothelial growth factors in retinal and choroidal neovascular diseases

Angiogenesis, or neovascularization, refers to development of new vessels from pre-existing vasculature. Retinal and choroidal neovascularization leads to oedema, haemorrhages, and fibrosis, causing visual impairment and blindness. In multiple studies, vascular endothelial growth factor (VEGF) has been shown to be the most important factor in ocular angiogenesis. Recently discovered anti-VEGF treatments have revolutionized the therapy of neovascular diseases in the eye. These agents have been shown not just to stop the angiogenic process and maintain visual acuity but also improve vision in a great proportion of patients at least during a 2-year follow-up. However, there are also problems with these agents and their delivery regimens, and new therapeutic strategies are needed. This review summarizes the most important growth factors participating in the angiogenic process in the retina and the choroid, diseases where angiogenesis plays the most devastating part causing visual impairment, as well as current antiangiogenic treatments for these diseases.

Increased IL-6 levels are not related to NF-κB or HIF-1α transcription factors activity in the vitreous of proliferative diabetic retinopathy

PURPOSE

The purpose was to assess the activity of nuclear factor (NF)-κB and hypoxia inducible factor (HIF)-1α transcription factors and the expression levels of inflammation markers [interleukin (IL)-6 and IL-8] in the vitreous of patients suffering from proliferative diabetic retinopathy (PDR) scheduled for elective vitreous surgery in a single academic-based retina practice in a prospective clinical study.

METHODS

Twenty-seven patients with PDR were enrolled in the study. The severity of retinopathy was classified (0, 1, 2, 3, 4) and the activity of neovascularization was graded (0, 1, 2, 3, 4) by the surgeon intraoperatively. Samples of the vitreous were collected during surgery, and the activity of NF-κB and HIF-1α transcription factors and the expression levels of IL-6 and IL-8 were measured.

RESULTS

The majority of samples fell into the retinopathy class 3 (n = 12) or 4 (n = 13). The level of IL-6 increased from 68.9 ± 46.8 pg/ml to 102.7 ± 94.1 pg/ml, and IL-8 increased from 165.1 ± 136.0 pg/ml to 521.0 ± 870.9 pg/ml (mean ± S.D., nonsignificant change: normality test followed with Mann-Whitney Rank Sum Test). According to the neovascularization activity, the samples fell into grade 1 (n = 7), 2 (n = 12) or 3 (n = 7). In IL-6, there was a statistically significant increase (P < .05) from grade 2 to 3: 58.6 ± 40.3 pg/ml and 158.4 ± 102.5 pg/ml, respectively (Kruskal-Wallis One-Way Analysis of Variance on Ranks followed with Dunn's Method). The level of IL-8 was as follows: in grade 1: 118.0 ± 62.4 pg/ml, in grade 2: 192.3 ± 127.1 pg/ml and in grade 3: 884.3 ± 1161.0 pg/ml (statistically nonsignificant change). There was a statistically significant linear regression between IL-6 and IL-8 (P < .001): IL-6 = 51.88 pg/ml + (0.092*IL-8), r = 0.772. Increased activity of the NF-κB and HIF-1α transcription factors was not observed.

CONCLUSION

Interleukin-6 is a candidate to indicate activity of neovascularization process in PDR. It might be a new molecular therapeutic target to regulate innate immunity response in vitreous.