Molecules related to diabetic retinopathy in the vitreous and involved pathways.

Angiogenesis in diabetic retinopathy (DR) is a multifactorial process regulated by hypoxia-induced growth factors and inflammatory cytokines. In addition to the angiogenic switch, the proteolytic processing and altered synthesis of the extracellular matrix are critical steps in this disease. This study was performed to evaluate the levels of matrix metalloproteinase-2 and matrix metalloproteinase-9 (MMP-2 and MMP-9), angiopoietin-1 and angiopoietin-2 (Ang-1 and Ang-2), vascular endothelial growth factor (VEGF), erythropoietin (EPO) and transforming growth factor-β1 (totalTGFβ1) in the vitreous of diabetic eyes undergoing vitrectomy compared with control eyes operated because of macular hole or pucker. Prospective consecutive controlled observational study performed in the unit of vitreoretinal surgery in Finland during the years 2006-2008. Vitreous samples were collected before the start of the conventional 3-ppp vitrectomy. Vitreous MMP-2 and MMP-9, Ang-1 and Ang-2, VEGF, EPO and TGFβ1 concentrations were measured from 69 patients with Type 1 or 2 diabetes and 40 controls. Comparison of eyes with DR with controls revealed that the mean vitreous concentrations of proMMP-2 (p = 0.0015), totalMMP-2 (p = 0.0011), proMMP-9 (p = 0.00001), totalMMP-9 (p < 0.00001), Ang-2 (p < 0.00001), VEGF (p < 0.00001), EPO (p < 0.00001) and totalTGFβ1 (p = 0.000026) were significantly higher in the former group. A multivariate logistic regression analysis suggested intravitreal Ang-2 concentration being the key marker of PDR (p = 0.00025) (OR = 1507.9). The main new finding is that the intravitreal concentrations of Ang-2 correlated significantly with MMP-9, VEGF, EPO and TGFβ1 levels in diabetic eyes undergoing vitrectomy. Thus, these factors could promote retinal angiogenesis synergistically.

The increased reactive oxygen species (ROS) caused by hyperglycemia (HG) is thought to be a key event in the pathogenesis of diabetic retinopathy. In diabetes, increased vascular endothelial growth factor (VEGF) expression is reported to increase ROS. Using a human RPE cell-line (ARPE-19), we investigated whether HG could promote the expression of VEGF independently of Angiotensin II through the prorenin receptor (PRR), via a NADPH oxidase (Nox)-dependent mechanism. HG significantly induced the expression of PRR, Nox2, Nox4, and VEGF. Also, PRR, Nox2/4, and Rac1 siRNAs, but not the control siRNA, significantly reduced the HG-induction of VEGF. Nox4 overexpression significantly potentiated PRR-induced stimulation of VEGF. Inhibitors of Nox significantly abolished HG-induction of VEGF. Both catalase and superoxide dismutase significantly attenuated VEGF induction by HG, indicative of the involvement of Nox-derived O2– and H2O2 signaling in regulation of VEGF regulation. In summary, Nox4-derived ROS signaling is implicated in the HG-induced increase of VEGF expression through PRR. Nox and redox signaling components can be considered as potential therapeutic targets for treatment of angiogenesis-dependent retinal diseases, including diabetic retinopathy.

BackgroundTo assess the association of lipid and lipid-derived toxic molecules in pathogenesis and severity of diabetic retinopathy (DR) in type 2 diabetes mellitus (T2DM).MethodsThe present cross-sectional study included 14 healthy individuals (HC) without T2DM, 22 T2DM subjects without DR (DNR), 24 T2DM subjects with mild non-proliferative DR (MNPDR), and 24 T2DM subjects with high-risk proliferative DR (HRPDR). All subjects underwent plasma and vitreous analysis for estimation of total lipid (TL), free fatty acid (FFA), lipid peroxides (LPOs) like malondialdehyde (MDA), 4-Hydroxy-noneal (HNE), the advanced lipoxidation end product (ALE) like Hexanoyl-lysine (HLY) and vascular endothelial growth factor (VEGF) following standard spectrophotometric and enzyme-linked immunosorbent assay (ELISA) methods respectively.ResultsThe concentration of TL, FFA, markers of lipid peroxidation and lipoxidation as well as VEGF in plasma and vitreous were found to be significantly elevated stepwise inT2DM subjects (HRPDR > MNPDR > DNR) compared to healthy controls (HC).Further, plasma conventional lipid components like total cholesterol (TCH), low density lipoprotein cholesterol (LDL-C) and triglycerides (TG), FFA and TL showed their significant positive correlations with vitreous level of different LPOs, ALE and VEGF in the DR group.ConclusionTotal lipid and lipid-derived detrimental biomolecules ultimately result in increased secretion of VEGF and thus not only add as associated mediators in the pathogenesis of DR, these also accelerate the severity of microangiopathy in T2DM.

Diabetic macular oedema (DMO) is an important cause of vision loss in patients with diabetes mellitus. The underlying mechanisms of DMO, on both macrocellular and microcellular levels, are discussed in this review. The pathophysiology of DMO can be described as a process whereby hyperglycaemia leads to overlapping and inter-related pathways that play a role not only in the initial vascular events, but also in the continued tissue insult that leads to chronic DMO. On a macrocellular level, DMO is believed to be in part caused by alterations in hydrostatic pressure, oxygen tension, oncotic pressure and shear stress. Three key components of the microvascular pathways include angiogenic factor expression, inflammation and oxidative stress. These molecular mediators, acting in conjunction with macrocellular factors, which are all stimulated in part by the hyperglycaemia and hypoxia, can have a direct endothelial effect leading to hyperpermeability, disruption of vascular endothelial cell junctions, and leukostasis. The interactions, signalling events and feedback loops between the various molecules are complicated and are not completely understood. However, by attempting to understand the pathways involved in DMO, we can help guide new treatment options targeted towards specific factors or mediators.

Diabetic retinopathy, characterized as a microangiopathy and neurodegenerative disease, is the leading cause of visual impairment in diabetic patients. Many clinical features observed in diabetic retinopathy, such as capillary occlusion, acellular capillaries and retinal non-perfusion, aggregate retinal ischemia and represent relatively late events in diabetic retinopathy. In fact, retinal microvascular injury is an early event in diabetic retinopathy involving multiple biochemical alterations, and is manifested by changes to the retinal neurovascular unit and its cellular components. Currently, intravitreal anti-vascular endothelial growth factor therapy is the first-line treatment for diabetic macular edema, and benefits the patient by decreasing the edema and improving visual acuity. However, a significant proportion of patients respond poorly to anti-vascular endothelial growth factor treatments, indicating that factors other than vascular endothelial growth factor are involved in the pathogenesis of diabetic macular edema. Accumulating evidence confirms that low-grade inflammation plays a critical role in the pathogenesis and development of diabetic retinopathy as multiple inflammatory factors, such as interleukin-1β, monocyte chemotactic protein-1 and tumor necrosis factor -α, are increased in the vitreous and retina of diabetic retinopathy patients. These inflammatory factors, together with growth factors such as vascular endothelial growth factor, contribute to blood-retinal barrier breakdown, vascular damage and neuroinflammation, as well as pathological angiogenesis in diabetic retinopathy, complicated by diabetic macular edema and proliferative diabetic retinopathy. In addition, retinal cell types including microglia, Müller glia, astrocytes, retinal pigment epithelial cells, and others are activated, to secrete inflammatory mediators, aggravating cell apoptosis and subsequent vascular leakage. New therapies, targeting these inflammatory molecules or related signaling pathways, have the potential to inhibit retinal inflammation and prevent diabetic retinopathy progression. Here, we review the relevant literature to date, summarize the inflammatory mechanisms underlying the pathogenesis of diabetic retinopathy, and propose inflammation-based treatments for diabetic retinopathy and diabetic macular edema.

Vascular Endothelial Growth Factor

Diabetic nephropathy often co-exists with other manifestations of microangiopathy, in particular retinopathy. Recent clinical evidence suggests that inhibition of the renin-angiotensin system in humans can delay the development and/or progression of diabetic nephropathy and perhaps also retinopathy. The benefits of this therapeutic strategy may in part be explained by inhibition of the nonhaemodynamic actions of angiotensin II (Ang II). The recognized nonhaemodynamic actions of Ang II include the augmented release of many growth factors. Ang II can stimulate the release of vascular endothelial growth factor (VEGF) from human vascular tissues. VEGF is a family of potent cytokines which act to induce angiogenesis and markedly increase microvascular permeability. VEGF is abundantly expressed in the renal glomerulus, specifically within the podocyte, where its function is unknown. VEGF is also expressed in the retina and increased retinal VEGF expression occurs in diabetes and has been implicated in the pathogenesis of diabetic retinopathy. This review considers the potential clinical significance of Ang II-induced VEGF expression, if any, in the pathogenesis of diabetic nephropathy and retinopathy.

Integrating network pharmacology, transcriptomics, and molecular simulation to reveal the mechanism of tert-butylhydroquinone for treating diabetic retinopathy

Aim: The aim of the study was to establish the relationship between levels of vascular endothelial growth factor (VEGF) in blood and severity of diabetic retinopathy (DR). Background: The importance of VEGF in the pathogenesis of DR is evident from numerous studies demonstrating a significant increase in VEGF levels in samples obtained from the eye. However, a correlation between blood levels of VEGF and DR has not been conclusively proven or disproven. In this article, we demonstrate the relationship between blood levels of VEGF and the severity of DR. Materials and Methods: This is a hospital-based descriptive analytic study. The study population consisted of 75 Type 2 diabetic patients attending outpatient department for routine DR screening. After obtaining informed consent, 5 ml of blood was drawn from each patient and estimated for the levels of serum VEGF. The data thus obtained were correlated with the grade of DR. Additional parameters studied were duration of diabetes mellitus (DM), hemoglobin levels, blood urea, serum creatinine, fasting blood sugar (FBS) and random blood sugar (RBS), and hemoglobin A1c (HBA1c) levels. Statistical analysis used in this study was Chi-square test, Student's t-test, independent one sample t-test, and analysis of variance using SPSS software version. 19. Results: Overall mean VEGF levels for the study population of 75 diabetic patients were 577.01 ± 291.13 pg/ml. The average duration of DM in the study population was 7.2 years. The average hemoglobin level in the study population was 11.53 ± 2.00 g/dl. The mean urea levels in mg/dl of the whole population were 35.47 ± 25.80 mg/dl. The mean creatinine levels for the population were 1.42 ± 1.55 mg/dL. The mean RBS levels for the whole population were 228.95 ± 74.499 mg/dL. The mean FBS levels for the 75 patients were 165.87 ± 59.04 mg/dl. The mean HBA1c levels were 9.49 ± 2.37%. Conclusion: Levels of blood VEGF are elevated in diabetic patients regardless of whether they have DR or not. There is no statistically significant relationship between blood levels of VEGF and the severity of DR. Even though severe grades of DR showed more anemia, there is no statistically significant relationship between anemia and DR. The levels of urea and creatinine were elevated in the more severe grade of DR. VEGF, therefore, could present a potential treatment and preventive strategy for not only DR but also DM and its complications in general.

Diabetic retinopathy (DR) is a severe diabetes-induced eye disease, in which its pathological phenomena basically include abnormal proliferation, migration, and angiogenesis of microvascular endothelial cells in the retina. Long non-coding RNAs (lncRNAs) have been proven to be important regulators in various biological processes, but their participation in DR remains largely undiscovered. In the present study, we aimed to unveil the role of lncRNA small nucleolar RNA host gene 16 (SNHG16) in regulating the functions of human retinal microvascular endothelial cells (hRMECs) under a high-glucose (HG) condition. We found that SNHG16 expression was significantly upregulated in hRMECs treated with HG. Functionally, SNHG16 could facilitate hRMEC proliferation, migration, and angiogenesis. Moreover, SNHG16 was associated with nuclear factor κB (NF-κB) and phosphatidylinositol 3-kinase (PI3K)/AKT pathways. Mechanistically, SNHG16 could promote hRMEC dysfunction by sequestering microRNA (miR)-146a-5p and miR-7-5p to act as a competing endogenous RNA (ceRNA) with interleukin-1 receptor-associated kinase 1 (IRAK1) and insulin receptor substrate 1 (IRS1). In conclusion, our results illustrated the potential role of SNHG16 in facilitating hRMEC dysfunction under HG treatment, providing a novel approach for DR therapy.

Atrial Natriuretic Peptide Reduces Vascular Leakage and Choroidal Neovascularization

Diabetic retinopathy (DR) is the most common microvascular complication of diabetes mellitus (DM) and the leading cause of blindness in patients with DM. In the pathogenesis of DR, chronic hyperglycemia leads to biochemical and structural alterations in retinal blood vessels' wall, resulting in hyperpermeability and non-perfusion. Since vascular endothelial growth factor (VEGF) has been found to play a significant role in the pathogenesis of DR, this review sheds light on the effect of intravitreal anti-VEGF agents on retinal non-perfusion in patients with DR. Based on the existing literature, anti-VEGF agents have been shown to improve DR severity, although they cannot reverse retinal ischemia. The results of the published studies are controversial and differ based on the location of retinal non-perfusion, as well as the imaging modality used to assess retinal non-perfusion. In cases of macular non-perfusion, most of studies showed no change in both fundus fluorescein angiography (FFA) and optical coherence tomography (OCTA) in patients with DR treated with intravitreal anti-VEGF agents, while few studies reported worsening of non-perfusion with enlargement of foveal avascular zone (FAZ). Regarding peripheral ischemia, studies using wide-field-FFA demonstrated an improvement or stability in non-perfusion areas after anti-VEGF treatment. However, the use of wide-field-OCTA revealed no signs of re-perfusion of retinal vessels post anti-VEGF treatment. Further prospective studies with long follow-up and large sample size are still needed to draw solid conclusions.

Prevention of Age-Related Macular Degeneration–Like Retinopathy by Rapamycin in Rats

With increasing prevalence of diabetes and a progressively aging society, diabetic retinopathy is emerging as one of the global leading causes of blindness. Recent studies have shown that vascular endothelial growth factor (VEGF) plays a central role in the pathogenesis of diabetic retinopathy and anti-VEGF agents have become the first-line therapy for the vision-threatening disease. However, recent studies have also demonstrated that diabetic retinopathy is a multifactorial disease and that VEGF-independent mechanism(s) also underlie much of the pathological changes in diabetic retinopathy. Acrolein is a highly reactive unsaturated aldehyde and is implicated in protein dysfunction. As acrolein is common in air pollutants, previous studies have focused on it as an exogenous causative factor, for instance, in the development of respiratory diseases. However, it has been discovered that acrolein is also endogenously produced and induces cell toxicity and oxidative stress in the body. In addition, accumulating evidence suggests that acrolein and/or acrolein-conjugated proteins are associated with the molecular mechanisms in diabetic retinopathy. This review summarizes the pathological roles and mechanisms of endogenous acrolein production in the pathogenesis of diabetic retinopathy.

To assess the efficacy, duration of effect and safety of one intravitreal injection of bevacizumab in diabetic macular oedema (DMO). Bevacizumab (1 mg/0.04 ml) was injected intravitreally into eyes with DMO (29 with and nine without previous treatments). Best corrected visual acuity (BCVA), intraocular pressure and central retinal thickness (CRT) were measured; slit-lamp examination, macular biomicroscopy, optical coherence tomography and fluorescein angiography were performed before and at 2-4, 8 and 12 weeks post-injection. Best corrected VA and CRT were analysed in both groups. In the non-pretreated group, mean BCVA improved from 0.76 +/- 0.33 (baseline) to 0.57 +/- 0.30 and 0.54 +/- 0.27 at 2-4 weeks and 8 weeks post-injection, respectively (p = 0.02, p = 0.014, paired t-test). Mean CRT decreased from 632.4 +/- 196.0 microm (baseline) to 392.3 +/- 113.6 microm and 370.4 +/- 141.7 microm at the same time-points, respectively (p = 0.01, p = 0.01). There was no difference in BCVA or CRT at 12 weeks. In the pretreated group, mean BCVA improved from 0.62 +/- 0.30 (baseline) to 0.53 +/- 0.33 at 2-4 weeks post-injection (p = 0.01), and mean CRT decreased from 583.9 +/- 180.7 microm (baseline) to 404.1 +/- 197.9 microm at 2-4 weeks post-injection (p < 0.001). Mean BCVA was unchanged at 8 weeks and 12 weeks post-injection, although mean CRT remained lower at 8 weeks (p = 0.004). No ocular or systemic side-effects developed during follow-up. One intravitreal injection of bevacizumab for DMO seems to be effective and safe in both eyes that have been treated previously and eyes that have not. The therapeutic effect is temporary and repeat treatment may be needed.