Critical roles of miR-21 in promotions angiogenesis: friend or foe?

MiRNAs are small RNA strands that are managed following transcription and are of substantial importance in blood vessel formation. It is essential to oversee the growth, differentiation, death, movement and construction of tubes by angiogenesis-affiliated cells. If miRNAs are not correctly regulated in regard to angiogenesis, it can deteriorate the health and lead to various illnesses, which include cancer, cardiovascular disorder, critical limb ischemia, Crohn's disease, ocular diseases, diabetic microvascular complications, and more. Consequently, it is vital to understand the crucial part that miRNAs play in the development of blood vessels, so we can develop reliable treatment plans for vascular diseases. This write-up will assess the critical role of miR-21/exosomal miR-21 in managing angiogenesis associated with bone growth, wound recovery, and other pathological conditions like tumor growth, ocular illnesses, diabetes, and other diseases connected to formation of blood vessels. Previous investigations have demonstrated that miR-21 is present at higher amounts in certain cancerous cells, and it influences a multitude of genes that moderate the increased creation of blood vessels. Furthermore, studies demonstrated that exosomal miR-21 has the capacity to interact with endothelial cells to foster tumor angiogenesis. For that reason, this review explains the critical importance of miR-21/exosomal miR-21 in managing both healthy and diseased states of angiogenesis.

Sulindac prevents increased mitochondrial VDAC1 expression and cell surface mistargeting induced by pathological conditions in retinal cells

Diabetic retinopathy (DR) continues to be the primary cause of vision loss in poorly controlled diabetic subjects. The molecular mechanisms underlying retinal pigment epithelium (RPE) cell dysfunction in DR still remain elusive. We investigated the role of mitochondrial volt-age-dependent anion channel 1 (VDAC1) in RPE dysfunction under glucotoxic and inflammatory conditions. Our results demonstrate that both glucotoxicity and cytokine treatment reduces cellular viability accompanied by increased VDAC1 and inducible nitric oxide synthase (iNOS) expression, concomitant with decreased expression of mitochondrial VDAC2 and constitutively ex-pressed endothelial NOS (eNOS). Increased VDAC1 expression during these conditions leads to its mistargeting to the cell surface, leading to ATP loss. Additionally, VDAC1 upregulation by glucotoxicity and inflammatory cytokines induces leakage of mitochondrial DNA (mtDNA) into the cytosol. Sulindac, a nonsteroidal anti-inflammatory agent, mitigates the adverse effects associated with increased VDAC1 level under pathophysiological conditions, by suppressing VDAC1 expression. The effect of sulindac on restoring cell viability could be comparably achieved only with VDAC1 inhibitor (VBIT-4) or VDAC1-specific antibody and not with the iNOS inhibitor aminoguanidine. Our findings suggest that sulindac's beneficial effects on ARPE-19 cell function are mediated by prevention of increased VDAC1 expression under pathological conditions, thus preventing mtDNA leakage and ATP loss, which are the key steps in induction of cellular inflammatory responses involved in the development of DR.

Research Progress on the Role of Ubiquitination in Eye Diseases

The occurrence and development of ophthalmic diseases are related to the dysfunction of eye tissues. Ubiquitin is an important form of protein post-translational modification, which plays an essential role in the occurrence and development of diseases through specific modification of target proteins. Ubiquitination governs a variety of intracellular signal transduction processes, including proteasome degradation, DNA damage repair, and cell cycle progression. Studies have found that ubiquitin can play a role in eye diseases such as cataracts, glaucoma, keratopathy, retinopathy, and eye tumors. In this paper, the role of protein ubiquitination in eye diseases was reviewed.

Impact of sarcosine on diabetic retinopathy: Findings based on weighted gene co-expression network analysis and machine learning techniques

AIM

To quantify the association between serum sarcosine and diabetic retinopathy (DR) using weighted gene co-expression network analysis (WGCNA).

METHODS

We measured serum metabolites in 69 pairs of type 2 diabetes (T2D) patients with and without DR matched by age, gender, body mass index（BMI and HbA1c, using a propensity score matching-based approach. To identify modules and metabolites linked to DR, pathway analysis was performed using WGCNA, the Kyoto Encyclopedia of Genes and Genomes and Small-Molecule Pathway Database. The association of sarcosine with DR was estimated by restricted cubic spline and conditional logistic regression models. Its joint effects with covariates on DR were also extensively examined.

RESULTS

With per interquartile range elevation of sarcosine, the adjusted odds ratio (AOR) of DR significantly decreased by 67% (AOR: 0.33, 95% confidence interval [CI]: 0.19-0.58). Similar results were also found in the tertile analysis. Compared with those in the first tertile of sarcosine, the AOR significantly decreased by 54% (AOR: 0.46, 95% CI: 0.18-1.17) and 78% (AOR: 0.22, 95% CI: 0.08-0.59) for subjects in the second and third tertiles, respectively. Compared with subjects with lower sarcosine and lower HDL-C levels, those with higher sarcosine and lower HDL-C levels had the lowest odds of DR (OR: 0.13, 95% CI: 0.04, 0.43).

CONCLUSIONS

Serum sarcosine was inversely related to DR, especially in T2D patients with insufficient HDL-C. This study provides insights on a possible novel target for DR precision prevention and control, as well as a better understanding of the DR mechanism.

Protecting the aging eye with hydrogen sulfide

Research demonstrates that senescence is associated with tissue and organ dysfunction, and the eye is no exception. Sequelae arising from aging have been well defined as distinct clinical entities and vision impairment has significant psychosocial consequences. Retina and adjacent tissues like retinal pigmented epithelium and choroid are the key structures that are required for visual perception. Any structural and functional changes in retinal layers and blood retinal barrier could lead to age-related macular degeneration, diabetic retinopathy, and glaucoma. Further, there are significant oxygen gradients in the eye that can lead to excessive reactive oxygen species, resulting in endoplasmic reticulum and mitochondrial stress response. These radicals are source of functional and morphological impairment in retinal pigmented epithelium and retinal ganglion cells. Therefore, ocular diseases could be summarized as disturbance in the redox homeostasis. Hyperhomocysteinemia is a risk factor and causes vascular occlusive disease of the retina. Interestingly, hydrogen sulfide (H2S) has been proven to be an effective antioxidant agent, and it can help treat diseases by alleviating stress and inflammation. Concurrent glutamate excitotoxicity, endoplasmic reticulum stress, and microglia activation are also linked to stress; thus, H2S may offer additional interventional strategy. A refined understanding of the aging eye along with H2S biology and pharmacology may help guide newer therapies for the eye.

NADPH Oxidase Inhibition: Preclinical and Clinical Studies in Diabetic Complications

Significance: Oxidative stress plays a critical role in the development and progression of serious micro- and macrovascular complications of diabetes. Nicotinamide adenine dinucleotide phosphate oxidase (NOX)-derived reactive oxygen species (ROS) significantly contribute to oxidative stress-associated inflammatory pathways that lead to tissue damage of different organs, including the kidneys, retina, brain, nerves, and the cardiovascular system. Recent Advances: Preclinical studies, including genetic-modified mouse models or cell culture models, have revealed the role of specific NOX isoforms in different diabetic complications, and suggested them as a promising target for the treatment of these diseases. Critical Issues: In this review, we provide an overview of the role of ROS and oxidative stress in macrovascular complications, such as stroke, myocardial infarction, coronary artery disease, and peripheral vascular disease that are all mainly driven by atherosclerosis, as well as microvascular complications, such as diabetic retinopathy, nephropathy, and neuropathy. We summarize conducted genetic deletion studies of different Nox isoforms as well as pharmacological intervention studies using NOX inhibitors in the context of preclinical as well as clinical research on diabetic complications. Future Directions: We outline the isoforms that are most promising for future clinical trials in the context of micro- and macrovascular complications of diabetes.

Extracellular Vesicles and MicroRNA: Putative Role in Diagnosis and Treatment of Diabetic Retinopathy

Diabetic retinopathy (DR) is a complex, progressive, and heterogenous retinal degenerative disease associated with diabetes duration. It is characterized by glial, neural, and microvascular dysfunction, being the blood-retinal barrier (BRB) breakdown a hallmark of the early stages. In advanced stages, there is formation of new blood vessels, which are fragile and prone to leaking. This disease, if left untreated, may result in severe vision loss and eventually legal blindness. Although there are some available treatment options for DR, most of them are targeted to the advanced stages of the disease, have some adverse effects, and many patients do not adequately respond to the treatment, which demands further research. Oxidative stress and low-grade inflammation are closely associated processes that play a critical role in the development of DR. Retinal cells communicate with each other or with another one, using cell junctions, adhesion contacts, and secreted soluble factors that can act in neighboring or long-distance cells. Another mechanism of cell communication is via secreted extracellular vesicles (EVs), through exchange of material. Here, we review the current knowledge on deregulation of cell-to-cell communication through EVs, discussing the changes in miRNA expression profiling in body fluids and their role in the development of DR. Thereafter, current and promising therapeutic agents for preventing the progression of DR will be discussed.

Effect of Fenofibrate on the Expression of Inflammatory Mediators in a Diabetic Rat Model

Purpose: To investigate the mechanisms of anti-inflammatory and anti-oxidative effects of fenofibrate, a peroxisome proliferator-activated receptors-α agonist, in preventing diabetic retinopathy (DR) progression via a diabetic rat model. Methods: Diabetes was induced by intraperitoneal injection of streptozotocin in 6-week-old female Wistar rats. Diabetic rats were divided into diabetes without treatment (n = 10), diabetes treated with low dose fenofibrate (30 mg/kg/day) (n = 10) and high dose fenofibrate (100 mg/kg/day) (n = 10). Serum aqueous humor (AqH) and ocular tissues were gathered after 3-month treatment. Expressions of NF-κB and inflammatory chemokines (monocyte chemoattractant protein-1, fractalkine, and intercellular adhesion molecule-1) were detected by reverse transcription-polymerase chain reaction, Western blot, enzyme-linked immunosorbent assay (ELISA), immunohistochemistry (IHC), and electrophoretic mobility shift assay. The levels of oxidative biomarkers, including acrolein, nitrotyrosine, and 8-hydroxy-2'-deoxyguanosin (8-OHdG), were determined by IHC and ELISA. The reactive oxygen species (ROS) levels in serum and AqH were measured by chemiluminescence methods. Results: After 3 months of treatment, the expressions of mRNA and protein of monocyte chemoattractant protein-1, fractalkine, and intercellular adhesion molecule-1 in the retina of diabetic rats were significantly inhibited by fenofibrate in a dose-dependent manner. These effects were mediated by inhibition of NF-κB by fenofibrate. The levels of oxidative markers, including acrolein, nitrotyrosine, and 8-OHdG, decreased in the retina of diabetic rats after fenofibrate treatment. The ROS levels in the AqH of diabetic rats also suppressed by fenofibrate. Conclusions: Fenofibrate significantly inhibited the expressions of NF-κB and inflammatory chemokines and reduced oxidative products within diabetic retina. Treatment of fenofibrate might be beneficial to preventing DR progression.

Validation of a novel diabetic retinopathy utility index using discrete choice experiments

BACKGROUND/AIMS

To validate a preference-based Diabetic Retinopathy Utility Index (DRU-I) using discrete choice experiment (DCE) methods and assess disutilities associated with vision-threatening DR (VTDR: severe non-proliferative DR, proliferative DR and clinically significant macular oedema) and associated vision impairment.

METHODS

The DRU-I comprises five quality-of-life dimensions, including Visual symptoms, Activity limitation/mobility, Lighting and glare, Socio-emotional well-being and Inconvenience, each rated as no, some, or a lot of difficulty. The DRU-I was developed using a DCE comprising six blocks of nine choice sets which, alongside the EuroQoL-5D (EQ-5D-3L) and Vision and Quality of Life (VisQoL) utility instruments, were interviewer-administered to participants. To ensure the DRU-I was sensitive to severe disease, we oversampled patients with VTDR. Data were analysed using conditional logit regression.

RESULTS

Of the 220 participants (mean±SD age 60.1±11.3 years; 70.9% men), 57 (29.1%) and 139 (70.9%) had non-VTDR and VTDR, respectively, while 157 (71.4%), 20 (9.4%) and 37 (17.3%) had no, mild or moderate/severe vision impairment, respectively. Regression coefficients for all dimensions were ordered as expected, with worsening levels in each dimension being less preferred (theoretical validity). DRU-I utilities decreased as DR severity (non-VTDR=0.87; VTDR=0.80; p=0.021) and better eye vision impairment (none=0.84; mild=0.78; moderate/severe=0.72; p=0.012) increased. DRU-I utilities had low (r=0.39) and moderate (r=0.58) correlation with EQ-5D and VisQoL utilities, respectively (convergent validity).

DISCUSSION

The DRU-I can estimate utilities associated with vision-threatening DR and associated vision impairment. It has the potential to assess the cost-effectiveness of DR interventions from a patient perspective and inform policies on resource allocation relating to DR.

Diabetic retinopathy, a vascular and inflammatory disease: Therapeutic implications

Diabetic retinopathy (DR) is the most common microvascular complication of diabetes and the leading cause of visual impairment in the working-age population in the Western world. Diabetic macular oedema (DME) is one of the major complications of DR. Therapy with intravitreal injections of anti-vascular endothelial growth factor (anti-VEGF) drugs has become the gold standard treatment for DR and its complications. However, these drugs have no effect on the pathogenesis of DR and must be administered frequently via invasive intravitreal injections over many years. Thus, there is a pressing need to develop new therapeutic strategies to improve the treatment of this devastating disease. Indeed, an increasing volume of data supports the role of the inflammatory process in the pathogenesis of DR itself and its complications, including both increased retinal vascular permeability and neovascularization. Inflammation may also contribute to retinal neurodegeneration. Evidence that low-grade inflammation plays a critical role in the pathogenesis of DME has opened up new pathways and targets for the development of improved treatments. Anti-inflammatory compounds such as intravitreal glucocorticoids, topical non-steroidal anti-inflammatory drugs (NSAIDs), antioxidants, inflammatory molecule inhibitors, renin-angiotensin system (RAS) blockers and natural anti-inflammatory therapies may all be considered to reduce the rate of administration of antineovascularization agents in the treatment of DR. This report describes the current state of knowledge of the potential role of anti-inflammatory drugs in controlling the onset and evolution of DR and DME.

Glycation and HMG-CoA Reductase Inhibitors: Implication in Diabetes and Associated Complications

INTRODUCTION

Diabetes Mellitus (DM) acts as an absolute mediator of cardiovascular risk, prompting the prolonged occurrence, size and intricacy of atherosclerotic plaques via enhanced Advanced Glycation Endproducts (AGEs) formation. Moreover, hyperglycemia is associated with enhanced glyco-oxidized and oxidized Low-Density Lipoprotein (LDL) possessing greater atherogenicity and decreased the ability to regulate HMG-CoA reductase (HMG-R). Although aminoguanidine (AG) prevents the AGE-induced protein cross-linking due to its anti-glycation potential, it exerts several unusual pharmaco-toxicological effects thus restraining its desirable therapeutic effects. HMG-R inhibitors/ statins exhibit a variety of beneficial impacts in addition to the cholesterol-lowering effects.

OBJECTIVE

Inhibition of AGEs interaction with receptor for AGEs (RAGE) and glyco-oxidized-LDL by HMG-R inhibitors could decrease LDL uptake by LDL-receptor (LDL-R), regulate cholesterol synthesis via HMG-R, decrease oxidative and inflammatory stress to improve the diabetes-associated complications.

CONCLUSION

Current article appraises the pathological AGE-RAGE concerns in diabetes and its associated complications, mainly focusing on the phenomenon of both circulatory AGEs and those accumulating in tissues in diabetic nephropathy, diabetic neuropathy, and diabetic retinopathy, discussing the potential protective role of HMG-R inhibitors against diabetic complications.

Activation of the Notch‑Nox4‑reactive oxygen species signaling pathway induces cell death in high glucose‑treated human retinal endothelial cells

Diabetic retinopathy (DR) occurs in almost all patients with diabetes and remains as one of the major causes of vision loss worldwide. Nevertheless, the molecular mechanisms underlying the pathogenesis of DR remain elusive. The present study aimed to investigate the role and association of Notch signaling and NADPH oxidase 4 (Nox4)‑mediated oxidative stress in high glucose (HG)‑treated retinal cells. Human retinal endothelial cells were cultured for various durations in RPMI‑1640 medium containing 30 mM glucose (HG) or 30 mM mannitol (MN) as an osmotic control; apoptotic cell death and reactive oxygen species (ROS) levels were assessed, respectively. Alterations in the expression profiles of Nox and Notch proteins were evaluated using reverse transcription‑quantitative polymerase chain reaction and western blot analysis. Knockdown of Nox4 and recombination signal‑binding protein J (RBPj) was generated by transfection with specific small interfering (siRNA). Persistent activation of Notch signaling was induced via the overexpression of Notch intracellular domain (NICD). In the present study, time‑dependent increases in ROS production and cell death were detected in HG‑treated cells. Depletion of ROS by diphenyleneiodonium decreased HG‑induced cell death, and suppressed increases in caspase 3 activity and B‑cell lymphoma 2‑associated X protein levels. In HG‑treated cells, Nox4 expression was upregulated at the mRNA and protein levels, and inhibition of Nox4 by GKT137831 or knockdown of expression by siRNA Nox4 significantly reduced ROS levels and cell death. In the presence of HG, Notch1 expression levels were elevated, and increased NICD abundance was detected in whole cell lysates and nuclear fractions. Additionally, HG‑induced cell death was decreased by treatment with γ‑secretase inhibitor (GSI), but increased via the overexpression of NICD. The application of GSI or knockdown of RBPj by siRNA RBPj prevented increases in Nox4 expression within HG‑treated cells. The findings of the present study demonstrated that Nox4‑mediated ROS serves an important role in HG‑induced retinal cell damage, in which the activation of Notch signaling may be responsible for Nox4 upregulation. Therefore, inhibition of Notch signaling or Nox4 expression may be considered as potential therapeutic targets in patients with DR.

A non-invasive, multi-target approach to treat diabetic retinopathy

Hyperglycemia invoke number of pathways resulting in development of diabetic retinopathy (DR), including protein kinase C activation, increased expression of VEGF, advanced glycation end product (AGEs) formation and activation of polyol pathway, among which the pathophysiology of aldose reductase (ALR2) of the polyol pathway is evident by more than a decade of research. Subtle involvement of ALR2 in invoking various pathways of diabetic complications has caused an increase in attention towards the identification of novel aldose reductase inhibitors (ARIs). Numerous ARIs of different classes were employed in the treatment of diabetic complications initially, but few came into light as drugs. Though no ALR2 inhibitor has been used for the treatment or control of DR, Epalrestat has been used worldwide for treating diabetic neuropathy. This review critically analyses different treatments available for diabetic retinopathy, their limitations and the importance of the development of novel inhibitors of ALR2 that could prevent progression of DR, by causing a direct or indirect effect on controlling factors associated with DR.

STAT3-mediated activation of miR-21 is involved in down-regulation of TIMP3 and neovascularization in the ischemic retina

Retinal neovascularization (RNV) is a sight threatening complication of ischemic retinopathies with limited therapeutic options. The transcription factor signal transducer and activator of transcription 3 (STAT3) has been shown to play a crucial role in promoting RNV. However, manipulating of STAT3 activity can cause significant adverse side effects due to its neurotrophic properties. In this study, we identified microRNA-21 (miR-21) as a downstream effector of STAT3 activity in the ischemic retinas and determined its role in promoting RNV through inhibition of its molecular target, the tissue inhibitor of matrix metalloproteinases 3 (TIMP3). Using human retinal endothelial cells (HREC) exposed to hypoxia and a mouse model of oxygen-induced retinopathy (OIR), we found that TIMP3 expression was significantly decreased at both mRNA and protein levels and this paralleled the activation of STAT3 and up-regulation of miR-21. Moreover, TIMP3 expression was restored by knockdown of STAT3 or blocking of miR-21 in HREC, thus, confirming TIMP3 as a downstream target of STAT3/miR-21 pathway. Finally, in a mouse model of OIR, blockade of miR-21 by a specific antisense (a.miR-21), halted RNV and this effect was associated with rescuing of TIMP3 expression. Our data show that miR-21 mediates STAT3 pro-angiogenic effects in the ischemic retina, thus suggesting its blockade as a potential therapy to prevent/halt RNV.

RNA sequencing reveals retinal transcriptome changes in STZ-induced diabetic rats

The present study aimed to investigate changes in retinal gene expression in streptozotocin (STZ)‑induced diabetic rats using next‑generation sequencing, utilize transcriptome signatures to investigate the molecular mechanisms of diabetic retinopathy (DR), and identify novel strategies for the treatment of DR. Diabetes was chemically induced in 10‑week‑old male Sprague‑Dawley rats using STZ. Flash‑electroretinography (F‑ERG) was performed to evaluate the visual function of the rats. The retinas of the rats were removed to perform high throughput RNA sequence (RNA‑seq) analysis. The a‑wave, b‑wave, oscillatory potential 1 (OP1), OP2 and ∑OP amplitudes were significantly reduced in the diabetic group, compared with those of the control group (P<0.05). Furthermore, the implicit b‑wave duration 16 weeks post‑STZ induction were significantly longer in the diabetic rats, compared with the control rats (P<0.001). A total of 868 genes were identified, of which 565 were upregulated and 303 were downregulated. Among the differentially expressed genes (DEGs), 94 apoptotic genes and apoptosis regulatory genes, and 19 inflammatory genes were detected. The results of the KEGG pathway significant enrichment analysis revealed enrichment in cell adhesion molecules, complement and coagulation cascades, and antigen processing and presentation. Diabetes alters several transcripts in the retina, and RNA‑seq provides novel insights into the molecular mechanisms underlying DR.

Imbalance of the Nerve Growth Factor and Its Precursor: Implication in Diabetic Retinopathy

Diabetic retinopathy is the leading cause of blindness in working age in US and worldwide. Neurotrophins including nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), neurotrophin-3 (NT-3) and neurotrophin-4 (NT-4) are known to be essential for growth, differentiation and survival of neurons in the developing and mature retina. Nevertheless, a growing body of evidence supports an emerging role of neurotrophins in retinal diseases and in particular, diabetic retinopathy. Neurotrophins are initially synthesized in a pro-form and undergo proteolytic cleavage to produce the mature form that activates two distinctive receptors, the tyrosine kinase tropomycin receptor (Trk) and, to lesser extent, the common low affinity p75 neurotrophin receptor (p75^NTR). Despite tight glycemic and metabolic control, many diabetic patients continue to experience progressive retinal damage. Understanding the molecular events involved in diabetic retinopathy is extremely important to identify novel therapeutic strategies to halt the disease progression. Diabetes induces imbalance in neurotrophins by increasing its proform, which is associated with upregulation of the p75^NTR receptor in the retina. A growing body of evidence supports a link between the imbalance of pro-neurotrophins and early retinal inflammation, neuro-and microvascular degeneration. Therefore, examining changes in the levels of neurotrophins and its receptors might provide a therapeutically beneficial target to combat disease progression in diabetic patients. This commentary aims to highlight the impact of diabetes-impaired balance of neurotrophins and in particular, the NGF and its receptors; TrkA and p75^NTR in the pathology of DR.

Molecular mechanisms of diabetic retinopathy: potential therapeutic targets

Diabetic retinopathy (DR) is the leading cause of blindness in working-age adults in United States. Research indicates an association between oxidative stress and the development of diabetes complications. However, clinical trials with general antioxidants have failed to prove effective in diabetic patients. Mounting evidence from experimental studies that continue to elucidate the damaging effects of oxidative stress and inflammation in both vascular and neural retina suggest its critical role in the pathogenesis of DR. This review will outline the current management of DR as well as present potential experimental therapeutic interventions, focusing on molecules that link oxidative stress to inflammation to provide potential therapeutic targets for treatment or prevention of DR. Understanding the biochemical changes and the molecular events under diabetic conditions could provide new effective therapeutic tools to combat the disease.

Treatment with hydrogen sulfide alleviates streptozotocin-induced diabetic retinopathy in rats

BACKGROUND AND PURPOSE

Retinopathy, as a common complication of diabetes, is a leading cause of reduced visual acuity and acquired blindness in the adult population. The aim of present study was to investigate the therapeutic effect of hydrogen sulfide on streptozotocin (STZ)-induced diabetic retinopathy in rats.

EXPERIMENTAL APPROACH

Rats were injected with a single i.p. injection of STZ (60 mg·kg⁻¹) to induce diabetic retinopathy. Two weeks later, the rats were treated with NaHS (i.p. injection of 0.1 mL·kg⁻¹·d⁻¹ of 0.28 mol·L⁻¹ NaHS, a donor of H₂S) for 14 weeks.

KEY RESULTS

Treatment with H₂S had no significant effect on blood glucose in STZ-induced diabetic rats. Treatment with exogenous H₂S enhanced H₂S levels in both plasma and retinas of STZ-induced diabetic rats. Treatment with H₂S in STZ-treated rats improved the retinal neuronal dysfunction marked by enhanced amplitudes of b-waves and oscillatory potentials and expression of synaptophysin and brain-derived neurotrophic factor, alleviated retinal vascular abnormalities marked by reduced retinal vascular permeability and acellular capillary formation, decreased vitreous VEGF content, down-regulated expressions of HIF-1α and VEGFR2, and enhanced occludin expression, and attenuated retinal thickening and suppressed expression of extracellular matrix molecules including laminin β1 and collagen IVα3 expression in retinas of STZ-induced diabetic rats. Treatment with H₂S in retinas of STZ-induced diabetic rats abated oxidative stress, alleviated mitochondrial dysfunction, suppressed NF-κB activation and attenuated inflammation.

CONCLUSIONS AND IMPLICATIONS

Treatment with H₂S alleviates STZ-induced diabetic retinopathy in rats possibly through abating oxidative stress and suppressing inflammation.

Cerebral neovascularization in diabetes: implications for stroke recovery and beyond

Neovascularization is an innate physiologic response by which tissues respond to various stimuli through collateral remodeling (arteriogenesis) and new vessel formation from existing vessels (angiogenesis) or from endothelial progenitor cells (vasculogenesis). Diabetes has a major impact on the neovascularization process but the response varies between different organ systems. While excessive angiogenesis complicates diabetic retinopathy, impaired neovascularization contributes to coronary and peripheral complications of diabetes. How diabetes influences cerebral neovascularization remained unresolved until recently. Diabetes is also a major risk factor for stroke and poor recovery after stroke. In this review, we discuss the impact of diabetes, stroke, and diabetic stroke on cerebral neovascularization, explore potential mechanisms involved in diabetes-mediated neovascularization as well as the effects of the diabetic milieu on poststroke neovascularization and recovery, and finally discuss the clinical implications of these effects.

Role of dietary and endogenous antioxidants in diabetes

Diabetes affects different people of all ages, race, and sex. This is a condition characterized by a state of chronic hyperglycaemia that leads to an increase of intracellular oxidative stress linked to the overproduction of free radicals. In the present review, we focus our attention on the molecular mechanisms leading to oxidative stress-mediates complications with particular regard to central nervous system (CNS). Furthermore, the present review reports the effects of different kind of antioxidants with enzymatic and nonenzymatic action that may significantly decrease the intracellular free radicals' overproduction and prevents the hyperglycaemia-mediated complications.

O-GlcNAcylation under hypoxic conditions and its effects on the blood-retinal barrier in diabetic retinopathy

An increase in O-linked N-acetylglucosamine (O-GlcNAc) protein modifications has been observerd in db/db mouse retinas. O-GlcNAc-modified proteins in the db/db mouse retina have been shown to be localized in the ganglion cell layer, the inner nuclear layer, the retina pigment epithelium (RPE) layer and the inner plexiform layer, in which hypoxia-inducible factor 1α (HIF1α) has also been shown to be localized. In the current study, we examined whether hypoxia increases O-GlcNAcylation in retinal vascular cells under high glucose conditions and whether HIF1α activation is consistent with the response to and activation of O-GlcNAcylation in retinal lesions in diabetic retinopathy. In addition, the effects of O-GlcNAcylation on the blood-retinal barrier were verified in vitro by the inhibition of O-GlcNAcylation. A time-dependent increase in the O-GlcNAcylation in bovine retinal vascular endothelial cells (BRVECs) was observed following incubation of the cells with high glucose medium (glucose 4.5 g/l) under hypoxic (1-3% O2) conditions. Hypoxia-induced BRVEC O-GlcNAcylation was not observed when the BRVECs were transfected with siRNA targeting O-GlcNAc transferase (OGT) or treated with alloxan (an OGT inhibitor) prior to exposure to high glucose. The increase in BRVEC O-GlcNAcylation induced by high glucose, as well as by thiamet G [an O-GlcNAcase (OGA) inhibitor] led to a reduction in occludin expression levels in vitro, which was prevented by treatment with OGT siRNA and alloxan. In conclusion, the current study demonstrates the relationship between O-GlcNAc glycosylation and hypoxia during diabetic retinopathy and that hyperglycemia induced O2 consumption activates HIF1α and O-GlcNAc modification protein in the same retinal layer. The reduced protein BRVEC O-GlcNAcylation levels exert protective effects on the blood-retinal barrier and thus represent a potential therapeutic target for the treatment of diabetic retinopathy.

Angiogenesis inhibitors in cancer therapy: mechanistic perspective on classification and treatment rationales

Angiogenesis, a process of new blood vessel formation, is a prerequisite for tumour growth to supply the proliferating tumour with oxygen and nutrients. The angiogenic process may contribute to tumour progression, invasion and metastasis, and is generally accepted as an indicator of tumour prognosis. Therefore, targeting tumour angiogenesis has become of high clinical relevance. The current review aimed to highlight mechanistic details of anti-angiogenic therapies and how they relate to classification and treatment rationales. Angiogenesis inhibitors are classified into either direct inhibitors that target endothelial cells in the growing vasculature or indirect inhibitors that prevent the expression or block the activity of angiogenesis inducers. The latter class extends to include targeted therapy against oncogenes, conventional chemotherapeutic agents and drugs targeting other cells of the tumour micro-environment. Angiogenesis inhibitors may be used as either monotherapy or in combination with other anticancer drugs. In this context, many preclinical and clinical studies revealed higher therapeutic effectiveness of the combined treatments compared with individual treatments. The proper understanding of synergistic treatment modalities of angiogenesis inhibitors as well as their wide range of cellular targets could provide effective tools for future therapies of many types of cancer.

Modulation of p75(NTR) prevents diabetes- and proNGF-induced retinal inflammation and blood-retina barrier breakdown in mice and rats

AIMS/HYPOTHESIS

Diabetic retinopathy is characterised by early blood-retina barrier (BRB) breakdown and neurodegeneration. Diabetes causes imbalance of nerve growth factor (NGF), leading to accumulation of the NGF precursor (proNGF), as well as the NGF receptor, p75 neurotrophin receptor (p75(NTR)), suggesting a possible pathological role of the proNGF-p75(NTR) axis in the diabetic retina. To date, the role of this axis in diabetes-induced retinal inflammation and BRB breakdown has not been explored. We hypothesised that modulating p75(NTR) would prevent diabetes- and proNGF-induced retinal inflammation and BRB breakdown.

METHODS

Diabetes was induced by streptozotocin in wild-type and p75(NTR) knockout (p75KO) mice. After 5 weeks, the expression of inflammatory mediators, ganglion cell loss and BRB breakdown were determined. Cleavage-resistant proNGF was overexpressed in rodent retinas with and without p75(NTR) short hairpin RNA or with pharmacological inhibitors. In vitro, the effects of proNGF were investigated in retinal Müller glial cell line (rMC-1) and primary Müller cells.

RESULTS

Deletion of p75(NTR) blunted the diabetes-induced decrease in retinal NGF expression and increases in proNGF, nuclear factor κB (NFκB), p-NFκB and TNF-α. Deletion of p75(NTR) also abrogated diabetes-induced glial fibrillary acidic protein expression, ganglion cell loss and vascular permeability. Inhibited expression or cleavage of p75(NTR) blunted proNGF-induced retinal inflammation and vascular permeability. In vitro, proNGF induced p75(NTR)-dependent production of inflammatory mediators in primary wild-type Müller and rMC-1 cultures, but not in p75KO Müller cells.

CONCLUSIONS/INTERPRETATION

The proNGF-p75(NTR) axis contributes to retinal inflammation and vascular dysfunction in the rodent diabetic retina. These findings underscore the importance of p75(NTR) as a novel regulator of inflammation and potential therapeutic target in diabetic retinopathy.

Diabetes-induced superoxide anion and breakdown of the blood-retinal barrier: role of the VEGF/uPAR pathway

Diabetes-induced breakdown of the blood-retinal barrier (BRB) has been linked to hyperglycemia-induced expression of vascular endothelial growth factor (VEGF) and is likely mediated by an increase in oxidative stress. We have shown that VEGF increases permeability of retinal endothelial cells (REC) by inducing expression of urokinase plasminogen activator receptor (uPAR). The purpose of this study was to define the role of superoxide anion in VEGF/uPAR expression and BRB breakdown in diabetes. Studies were performed in streptozotocin diabetic rats and mice and high glucose (HG) treated REC. The superoxide dismutase (SOD) mimetic tempol blocked diabetes-induced permeability and uPAR expression in rats and the cell permeable SOD inhibited HG-induced expression of uPAR and VEGF in REC. Inhibiting VEGFR blocked HG-induced expression of VEGF and uPAR and GSK-3β phosphorylation in REC. HG caused β-catenin translocation from the plasma membrane into the cytosol and nucleus. Treatment with HG-conditioned media increased REC paracellular permeability that was blocked by anti-uPA or anti-uPAR antibodies. Moreover, deletion of uPAR blocked diabetes-induced BRB breakdown and activation of MMP-9 in mice. Together, these data indicate that diabetes-induced oxidative stress triggers BRB breakdown by a mechanism involving uPAR expression through VEGF-induced activation of the GSK3β/β-catenin signaling pathway.

Pronerve growth factor induces angiogenesis via activation of TrkA: possible role in proliferative diabetic retinopathy

Proliferative diabetic retinopathy (PDR) is the leading cause of blindness in working age Americans. We demonstrated that diabetes disturbs the homeostasis of nerve growth factor (NGF) resulting in accumulation of its precursor proNGF. Increases in proNGF were positively correlated with progression of diabetic retinopathy, having the highest level in ocular fluids from PDR patients compared to nondiabetic patients. Here, we attempted to evaluate the contribution and the possible mechanism of proNGF to PDR. The angiogenic response of aqueous humor samples from PDR patients was examined in human retinal endothelial cells in the presence or absence of anti-proNGF antibody. Additional cultures were treated with mutant-proNGF in the presence of specific pharmacological inhibitors of TrkA and p75(NTR) receptors. PDR-aqueous humor samples exerted significant angiogenic response including cell proliferation, migration, and alignment into tube-like structures. These effects were significantly reduced by anti-proNGF antibody but not by IgG. Treatment of retinal endothelial cells with mutant-proNGF activated phosphorylation of TrkA and p38MAPK; however, it did not alter p75(NTR) expression. Inhibition of TrkA but not p75(NTR) significantly reduced mutant-proNGF-induced cell proliferation, cell migration, and tube formation. Taken together, these results provide evidence that proNGF can contribute to PDR at least in part via activation of TrkA.

Anemia as a factor related to the progression of proliferative diabetic retinopathy after photocoagulation

OBJECTIVE

This study aimed to investigate factors that could be related to the progression of proliferative diabetic retinopathy in patients treated with photocoagulation.

METHODS

In this case-control study, a total of 106 patients with diabetic retinopathy participated who were treated with photocoagulation. We analyzed glycaemia, serum cholesterol, triglycerides, hemoglobin, platelet levels, blood pressure measurement, diabetes duration, diabetes and hypertension treatment, sex, and age. The statistical analysis was done with t test, χ² test, odds ratio (OR), and simple linear regression.

RESULTS

We found statistical significance in blood glucose level(P=.038), cholesterol level (P<.001), and hemoglobin level (P<.001). The simple linear regression was significant with blood glucose level (P<.05) and hemoglobin level (P=.001). Hemoglobin had a significant result: OR=2.432, 95% CI 1.902-3.115; Pearson χ²=16.812; P<.001.

CONCLUSIONS

Anemia is an important finding in diabetic patients. Anemia is a relevant factor related to the progression of proliferative diabetic retinopathy, which can be treated with photocoagulation.

S-glutathionylation of LMW-PTP regulates VEGF-mediated FAK activation and endothelial cell migration

Although promising, the ability to regulate angiogenesis through delivery of VEGF remains an unrealized goal. We have shown previously that physiological levels of peroxynitrite (1 µM) are required for a VEGF-mediated angiogenic response, yet the redox-regulated mechanisms that govern the VEGF signal remain unexplored. We assessed the impact of VEGF and peroxynitrite on modifying redox-state, the level of reduced-glutathione (GSH) and S-glutathionylation on regulation of the low molecular weight protein tyrosine phosphatase (LMW-PTP) and focal adhesion kinase (FAK), which are key mediators of VEGF-mediated cell migration. Stimulation of human microvascular endothelial (HME) cells with VEGF (20 ng/ml) or peroxynitrite (1 µM) caused an immediate and reversible negative-shift in the cellular redox-state and thiol oxidation of LMW-PTP, which culminated in cell migration. VEGF causes reversible S-glutathionylation of LMW-PTP, which inhibits its phosphorylation and activity, and causes the transient activation of FAK. Modulating the redox-state using decomposing peroxynitrite (FeTPPS, 2.5 µM) or the GSH-precursor [N-acetylcysteine (NAC), 1 mM] caused a positive-shift of the redox-state and prevented VEGF-mediated S-glutathionylation and oxidative inhibition of LMW-PTP. NAC and FeTPPS prevented the activation of FAK, its association with LMW-PTP and cell migration. Inhibiting LMW-PTP expression markedly enhanced FAK activation and cell migration. Although mild oxidative stress achieved by combining VEGF with 0.1-0.2 mM peroxynitrite augmented cell migration, an acute shift to oxidative stress achieved by combining VEGF with 0.5 mM peroxynitrite induced and sustained FAK activation, and LMW-PTP S-glutathionylation, resulting in LMW-PTP inactivation and inhibited cell migration. In conclusion, our findings demonstrate that a balanced redox-state is required for VEGF to facilitate reversible S-glutathionylation of LMW-PTP, FAK activation and endothelial cell migration. Shifting the redox-state to reductive stress or oxidative stress inhibited the VEGF-mediated angiogenic response.

Prevalence and risk factors of diabetic retinopathy in Chongqing pre-diabetes patients

PURPOSE

To investigate the prevalence of diabetic retinopathy (DR) and relative risk factors among Chongqing pre-diabetes patients.

METHODS

A total of 750 participants were recruited in this cross-sectional study. All participants underwent a complete physical examination and an oral glucose-tolerance test. In all, 110 of the 125 newly diagnosed pre-diabetics and their healthy spouses as controls were examined with fluorescence fundus angiographies, and their blood with biochemical analyses. All the pre-diabetics with DR (23 subjects), 23 normal controls and 23 pre-diabetics without DR were compared for serum concentrations of regulated upon activation, normal T-expressed and secreted (RANTES). Student's t-test was used to compare continuous variables, and χ (2) test and analysis of variance to compare proportions among groups. Multiple logistic regression models were used to determine the risk factors for DR in pre-diabetics.

RESULTS

In all, 20.91% of the 110 pre-diabetics showed mild non-proliferative DR (NPDR). There was a statistically significant difference in serum concentrations of RANTES between pre-diabetics with and without DR (P<0.01), and also between pre-diabetics with DR and normal controls (P<0.01). However, age, body mass index, waist-hip ratio, triacylglycerol (TG), total cholesterol (TC), high-density lipoprotein-C, low-density lipoprotein-C, blood urea nitrogen, blood creatinine, and urine albumin excretion rate seemed to have no reliable relationship with DR in pre-diabetics (P>0.05).

CONCLUSION

The prevalence of DR in Chongqing pre-diabetes patients in the study was about 20.91% and only mild NPDR was found. It seems that RANTES is one possible risk factor associated with DR in pre-diabetics, not age, TG and TC, and others.

Reversal of the Caspase-Dependent Apoptotic Cytotoxicity Pathway by Taurine from Lycium barbarum (Goji Berry) in Human Retinal Pigment Epithelial Cells: Potential Benefit in Diabetic Retinopathy

Diabetic retinopathy is a preventable microvascular diabetic complication and a leading cause of vision loss. Retinal pigment epithelial cell apoptosis is an early event in diabetic retinopathy. Taurine is reportedly beneficial for diabetic retinopathy and is abundant in the fruit of Lycium barbarum (LB). We have investigated the effect of pure taurine and an extract of LB rich in taurine on a model of diabetic retinopathy, the retinal ARPE-19 cell line exposed to high glucose. We demonstrate for the first time that LB extract and the active ligand, taurine, dose dependently enhance cell viability following high glucose treatment in the ARPE-19 retinal epithelial cell line. This cytoprotective effect was associated with the attenuation of high glucose-induced apoptosis, which was shown by characteristic morphological staining and the dose-dependent decrease in the number of apoptotic cells, determined by flow cytometry. Moreover, we have shown that LB extract and taurine dose dependently downregulate caspase-3 protein expression and the enzymatic activity of caspase-3. We conclude that taurine, a major component of LB, and the LB extract, have a cytoprotective effect against glucose exposure in a human retinal epithelial cell line and may provide useful approaches to delaying diabetic retinopathy progression.

Oxidative stress in preretinopathic diabetes subjects and antioxidants

BACKGROUND

This study assessed the effect of a systemic oral treatment with antioxidants (AOs) in preretinopathic diabetes (PRD) patients, through the evaluation of oxidative stress in plasma and changes in the full-field electroretinogram (ERG).

METHODS

Thirty-two PRD subjects with good metabolic control were recruited. Patients were randomized in two groups, one of which received oral AO treatment with α-lipoic acid at 400 mg/day in association with genistein and vitamins, whereas the other group received a placebo. Free radicals and the AO barrier were evaluated in plasma with the Free Radical Analytical System 4 instrument (H&D srl, Parma, Italy), and the same day the electrophysiological response was measured by ERG. These analyses were performed at enrollment and after 30 days of treatment.

RESULTS

Statistically significant increases of plasma AO levels and ERG oscillatory potential values were observed in the group treated with AO, but not in the control group.

CONCLUSIONS

Results of this preliminary study suggest that an oral treatment with AOs in PRD subjects may have a protective effect on retinal cells, as detected by ERG analysis, through the strengthening of the plasma AO barrier.

Anti-inflammatory therapy for diabetic retinopathy

Diabetic retinopathy (DR) is one of the most common complications of diabetes. This devastating disease is a leading cause of blindness in people of working age in industrialized countries and affects the daily lives of millions of people. Despite tight glycemic control, blood pressure control and lipid-lowering therapy, the number of DR patients keeps growing and therapeutic approaches are limited. Moreover, there are significant limitations and side effects associated with the current therapies. Thus, there is a great need for development of new strategies for prevention and treatment of DR. Studies have shown that DR has prominent features of chronic, subclinical inflammation. This article focuses on the role of inflammation in DR and summarizes the progress of studies of anti-inflammatory strategies for DR.

Diabetes-induced peroxynitrite impairs the balance of pro-nerve growth factor and nerve growth factor, and causes neurovascular injury

AIMS/HYPOTHESIS

Diabetic retinopathy, the leading cause of blindness in working-age Americans, is characterised by reduced neurotrophic support and increased proinflammatory cytokines, resulting in neurotoxicity and vascular permeability. We sought to elucidate how oxidative stress impairs homeostasis of nerve growth factor (NGF) and its precursor, proform of NGF (proNGF), to cause neurovascular dysfunction in the eye of diabetic patients.

METHODS

Levels of NGF and proNGF were examined in samples from human patients, from retinal Müller glial cell line culture cells and from streptozotocin-induced diabetic animals treated with and without atorvastatin (10 mg/kg daily, per os) or 5,10,15,20-tetrakis (4-sulfonatophenyl)porphyrinato iron (III) chloride (FeTPPs) (15 mg/kg daily, i.p.) for 4 weeks. Neuronal death and vascular permeability were assessed by TUNEL and extravasation of BSA-fluorescein.

RESULTS

Diabetes-induced peroxynitrite formation impaired production and activity of matrix metalloproteinase-7 (MMP-7), which cleaves proNGF extracellularly, leading to accumulation of proNGF and reducing NGF in samples from diabetic retinopathy patients and experimental models. Treatment of diabetic animals with atorvastatin exerted similar protective effects that blocked peroxynitrite using FeTPPs, restoring activity of MMP-7 and hence the balance between proNGF and NGF. These effects were associated with preservation of blood-retinal barrier integrity, preventing neuronal cell death and blocking activation of RhoA and p38 mitogen-activated protein kinase (p38MAPK) in experimental and human samples.

CONCLUSIONS/INTERPRETATION

Oxidative stress plays an unrecognised role in causing accumulation of proNGF, which can activate a common pathway, RhoA/p38MAPK, to mediate neurovascular injury. Oral statin therapy shows promise for treatment of diabetic retinopathy.

Epicatechin blocks pro-nerve growth factor (proNGF)-mediated retinal neurodegeneration via inhibition of p75 neurotrophin receptor expression in a rat model of diabetes [corrected]

AIMS/HYPOTHESIS

Accumulation of pro-nerve growth factor (NGF), the pro form of NGF, has been detected in neurodegenerative diseases. However, the role of proNGF in the diabetic retina and the molecular mechanisms by which proNGF causes retinal neurodegeneration remain unknown. The aim of this study was to elucidate the role of proNGF in neuroglial activation and to examine the neuroprotective effects of epicatechin, a selective inhibitor of tyrosine nitration, in an experimental rat model of diabetes.

METHODS

Expression of proNGF and its receptors was examined in retinas from streptozotocin-induced diabetic rats, and in retinal Müller and retinal ganglion cells (RGCs). RGC death was assessed by TUNEL and 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assays in diabetic retinas and cell culture. Nitrotyrosine was determined using Slot-blot. Activation of the tyrosine kinase A (TrkA) receptor and p38 mitogen-activated protein kinase (p38MAPK) was assessed by western blot.

RESULTS

Diabetes-induced peroxynitrite impaired phosphorylation of TrkA-Y490 via tyrosine nitration, activated glial cells and increased expression of proNGF and its receptor, p75 neurotrophin receptor (p75(NTR)), in vivo and in Müller cells. These effects were associated with activation of p38MAPK, cleaved poly-(ADP-ribose) polymerase and RGC death. Treatment of diabetic animals with epicatechin (100 mg kg(-1) day(-1), orally) blocked these effects and restored neuronal survival. Co-cultures of RGCs with conditioned medium of activated Müller cells significantly reduced RGC viability (44%). Silencing expression of p75(NTR) by use of small interfering RNA protected against high glucose- and proNGF-induced apoptosis in RGC cultures.

CONCLUSIONS/INTERPRETATION

Diabetes-induced peroxynitrite stimulates p75(NTR) and proNGF expression in Müller cells. It also impairs TrkA receptor phosphorylation and activates the p75(NTR) apoptotic pathway in RGCs, leading to neuronal cell death. These effects were blocked by epicatechin, a safe dietary supplement, suggesting its potential therapeutic use in diabetic patients.

[Diabetic maculopathy and retinopathy. Functional and sociomedical significance]

OBJECTIVE

The incidence of diabetic microvascular complications is expected to increase by 20-50% in the coming years. Diabetic macular edema (DME) is already a leading cause of blindness in the working-age population in developed countries, and its impact is expected to increase dramatically.

METHODS

Recent literature on the epidemiology and impact of diabetic microangiopathy (maculopathy) on visual function was reviewed to provide a comprehensive overview of the functional and socioeconomic consequences of diabetic retinal microangiopathy and new therapeutic strategies.

RESULTS

The first changes indicating diabetic microangiopathy are detectable shortly after the development of hyperglycemia, and in the long term they induce severe organ damage. More resources are used for this condition's treatment than for the treatment of hyperglycemia, corresponding to an enormous sociomedical burden of disease. Early detection of increased retinal vascular permeability may help control treatment effects. The control of recognized risk factors for the development and progression of DME, namely hyperglycemia and hyperlipidemia, as well as of hypertension has remained the cornerstone of therapy and serves as the basis for preserving visual function.

CONCLUSIONS

Modern treatment options, begun early, may result in a remarkably delayed occurrence of irreversible diabetic microvascular pathologies, particularly diabetic retinopathy and maculopathy. Ophthalmological screening nowadays aims at earlier recognition of at-risk individuals to optimize the therapeutic strategy--that is, before visual impairment is imminent. Close interdisciplinary medical cooperation and implementation of new therapeutic options may provide the foundation for success in terms of maintaining visual function.

Diverse effects of statins on angiogenesis: new therapeutic avenues

Angiogenesis is an important process for a variety of physiologic and pathologic conditions. Different angiogenic modulating targets are under extensive investigation both experimentally and clinically. The 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors (statins) are the first-line agents used in hypercholesterolemia. They are also characterized by having other benefits apart from their lipid-lowering effects. Among these pleiotropic effects are the pro- and antiangiogenic properties of statins. The pleiotropic effects of statins and how they modulate new blood vessel formation are discussed in this review. The currently available data from both animal and human studies regarding the effects of statins on angiogenesis in ischemic heart disease, stroke, ocular diseases, and cancer are also reviewed. Statins are safe, orally available agents that may acquire novel therapeutic indications through their angiogenic modulating effects.

Early intervention of tyrosine nitration prevents vaso-obliteration and neovascularization in ischemic retinopathy

Diabetic retinopathy and retinopathy of prematurity are blinding disorders that follow a pathological pattern of ischemic retinopathy and affect premature infants and working-age adults. Yet, the treatment options are limited to laser photocoagulation. The goal of this study is to elucidate the molecular mechanism and examine the therapeutic effects of inhibiting tyrosine nitration on protecting early retinal vascular cell death and late neovascularization in the ischemic retinopathy model. Ischemic retinopathy was developed by exposing neonatal mice to 75% oxygen [postnatal day (p) 7-p12] followed by normoxia (21% oxygen) (p12-p17). Peroxynitrite decomposition catalyst 5,10,15,20-tetrakis(4-sulfonatophenyl)porphyrinato iron III chloride (FeTPPS) (1 mg/kg), the nitration inhibitor epicatechin (10 mg/kg) or the thiol donor N-acetylcysteine (NAC, 150 mg/kg) were administered (p7-p12) or (p7-p17). Vascular endothelial cells were incubated at hyperoxia (40% oxygen) or normoxia (21% oxygen) for 48 h. Vascular density was determined in retinal flat mounts labeled with isolectin B4. Expression of vascular endothelial growth factor, caspase-3, and poly(ADP ribose) polymerase (PARP), activation of Akt and p38 mitogen-activated protein kinase (MAPK), and tyrosine nitration of the phosphatidylinositol (PI) 3-kinase p85 subunit were analyzed by Western blot. Hyperoxia-induced peroxynitrite caused endothelial cell apoptosis as indicated by expression of cleaved caspase-3 and PARP leading to vaso-obliteration. These effects were associated with significant tyrosine nitration of the p85 subunit of PI 3-kinase, decreased Akt activation, and enhanced p38 MAPK activation. Blocking tyrosine nitration of PI 3-kinase with epicatechin or NAC restored Akt phosphorylation, and inhibited vaso-obliteration at p12 and neovascularization at p17 comparable with FeTPPS. Early inhibition of tyrosine nitration with use of epicatechin or NAC can represent safe and effective vascular-protective agents in ischemic retinopathy.

Activation of the Wnt pathway plays a pathogenic role in diabetic retinopathy in humans and animal models

Although Wnt signaling is known to mediate multiple biological and pathological processes, its association with diabetic retinopathy (DR) has not been established. Here we show that retinal levels and nuclear translocation of beta-catenin, a key effector in the canonical Wnt pathway, were increased in humans with DR and in three DR models. Retinal levels of low-density lipoprotein receptor-related proteins 5 and 6, coreceptors of Wnts, were also elevated in the DR models. The high glucose-induced activation of beta-catenin was attenuated by aminoguanidine, suggesting that oxidative stress is a direct cause for the Wnt pathway activation in diabetes. Indeed, Dickkopf homolog 1, a specific inhibitor of the Wnt pathway, ameliorated retinal inflammation, vascular leakage, and retinal neovascularization in the DR models. Dickkopf homolog 1 also blocked the generation of reactive oxygen species induced by high glucose, suggesting that Wnt signaling contributes to the oxidative stress in diabetes. These observations indicate that the Wnt pathway plays a pathogenic role in DR and represents a novel therapeutic target.