The role of advanced glycation in the pathogenesis of diabetic retinopathy

Advanced Glycation End Products Evolution after Pancreas-Kidney Transplantation: Plasmatic and Cutaneous Assessments

Diabetes mellitus leads to increased Advanced Glycation End Products (AGE) production, which has been associated with secondary diabetic complications. Type 1 diabetic patients undergoing pancreas-kidney transplantation (SPKT) can restore normoglycemia and renal function, eventually decreasing AGE accumulation. We aimed to prospectively study AGE evolution after SPKT. Circulating AGE were assessed in 20 patients, at time 0 (T0), 3 months (T3), 6 months (T6), and 12 months (T12) after successful SPKT. Global AGE and carboxymethyllysine (CML) were analyzed, as well as advanced oxidation protein products (AOPP). Skin biopsies were obtained at T0 and T12. Immunohistochemistry with anti-AGE antibody evaluated skin AGE deposition. AGE mean values were 16.8 ± 6.4 μg/mL at T0; 17.1 ± 3.8 μg/mL at T3; 17.5 ± 5.6 μg/mL at T6; and 16.0 ± 5.2 μg/mL at T12. CML mean values were 0.94 ± 0.36 ng/mL at T0; 1.11 ± 0.48 ng/mL at T3; 0.99 ± 0.42 ng/mL at T6; and 0.78 ± 0.38 ng/mL at T12. AOPP mean values were 130.1 ± 76.8 μMol/L at T0; 137.3 ± 110.6 μMol/L at T3; 116.4 ± 51.2 μMol/L at T6; and 106.4 ± 57.9 μMol/L at T12. CML variation was significant (P = 0.022); AOPP variation was nearly significant (P = 0.076). Skin biopsies evolved mostly from a cytoplasmic diffuse to a peripheral interkeratinocytic immunoreaction pattern; in 7 cases, a reduction in AGE immunoreaction intensity was evident at T12. In conclusion, glycoxidation markers decrease, plasmatic and on tissues, may start early after SPKT. Studies with prolonged follow-up may confirm these data.

Identification of Glucose-Binding Pockets in Human Serum Albumin Using Support Vector Machine and Molecular Dynamics Simulations

Human Serum Albumin (HSA) has been suggested to be an alternate biomarker to the existing Hemoglobin-A1c (HbA1c) marker for glycemic monitoring. Development and usage of HSA as an alternate biomarker requires the identification of glycation sites, or equivalently, glucose-binding pockets. In this work, we combine molecular dynamics simulations of HSA and the state-of-art machine learning method Support Vector Machine (SVM) to predict glucose-binding pockets in HSA. SVM uses the three dimensional arrangement of atoms and their chemical properties to predict glucose-binding ability of a pocket. Feature selection reveals that the arrangement of atoms and their chemical properties within the first 4Å from the centroid of the pocket play an important role in the binding of glucose. With a 10-fold cross validation accuracy of 84 percent, our SVM model reveals seven new potential glucose-binding sites in HSA of which two are exposed only during the dynamics of HSA. The predictions are further corroborated using docking studies. These findings can complement studies directed towards the development of HSA as an alternate biomarker for glycemic monitoring.

Non-enzymatic glycation mediated structure–function changes in proteins: case of serum albumin

Albumin, a major plasma protein with extraordinary ligand binding properties, transports various ligands ranging from drugs, hormones, fatty acids, and toxins to different tissues and organs in the body.

Oxidative stress, mitochondrial damage and diabetic retinopathy

Diabetes has emerged as an epidemic of the 21st century, and retinopathy remains the leading cause of blindness in young adults and the mechanism of this blinding disease remains evasive. Diabetes-induced metabolic abnormalities have been identified, but a causal relationship between any specific abnormality and the development of this multi-factorial disease is unclear. Reactive oxygen species (ROS) are increased and the antioxidant defense system is compromised. Increased ROS result in retinal metabolic abnormalities, and these metabolic abnormalities can also produce ROS. Sustained exposure to ROS damages the mitochondria and compromises the electron transport system (ETC), and, ultimately, the mitochondrial DNA (mtDNA) is damaged. Damaged mtDNA impairs its transcription, and the vicious cycle of ROS continues to propagate. Many genes important in generation and neutralization of ROS are also epigenetically modified further increasing ROS, and the futile cycle continues to fuel in. Antioxidants have generated beneficial effects in ameliorating retinopathy in diabetic rodents, but limited clinical studies have not been encouraging. With the ongoing use of antioxidants for other chronic diseases, there is a need for a controlled trial to recognize their potential in ameliorating the development of this devastating disease.

Oxidative stress and epigenetic modifications in the pathogenesis of diabetic retinopathy

Diabetic retinopathy remains the major cause of blindness among working age adults. Although a number of metabolic abnormalities have been associated with its development, due to complex nature of this multi-factorial disease, a link between any specific abnormality and diabetic retinopathy remains largely speculative. Diabetes increases oxidative stress in the retina and its capillary cells, and overwhelming evidence suggests a bidirectional relationship between oxidative stress and other major metabolic abnormalities implicated in the development of diabetic retinopathy. Due to increased production of cytosolic reactive oxygen species, mitochondrial membranes are damaged and their membrane potentials are impaired, and complex III of the electron transport system is compromised. Suboptimal enzymatic and nonenzymatic antioxidant defense system further aids in the accumulation of free radicals. As the duration of the disease progresses, mitochondrial DNA (mtDNA) is damaged and the DNA repair system is compromised, and due to impaired transcription of mtDNA-encoded proteins, the integrity of the electron transport system is encumbered. Due to decreased mtDNA biogenesis and impaired transcription, superoxide accumulation is further increased, and the vicious cycle of free radicals continues to self-propagate. Diabetic milieu also alters enzymes responsible for DNA and histone modifications, and various genes important for mitochondrial homeostasis, including mitochondrial biosynthesis, damage and antioxidant defense, undergo epigenetic modifications. Although antioxidant administration in animal models has yielded encouraging results in preventing diabetic retinopathy, controlled longitudinal human studies remain to be conducted. Furthermore, the role of epigenetic in mitochondrial homeostasis suggests that regulation of such modifications also has potential to inhibit/retard the development of diabetic retinopathy.

Idiopathic epiretinal membrane

BACKGROUND

Idiopathic epiretinal membrane (iERM) is a fibrocellular membrane that proliferates on the inner surface of the retina at the macular area. Membrane contraction is an important sight-threatening event and is due to fibrotic remodeling.

METHODS

Analysis of the current literature regarding the epidemiology, clinical features, and pathogenesis of iERM and fibrotic tissue contraction.

RESULTS

Epidemiologic studies report a relationship between iERM prevalence, increasing age, and posterior vitreous detachment. Clinically, iERM progresses through different stages characterized by an increased thickness and wrinkling of the membrane. Pathophysiologically, iERM formation is a fibrotic process in which myofibroblast formation and the deposition of newly formed collagens play key roles. Anomalous posterior vitreous detachment may be a key event initiating the formation of iERM. The age-related accumulation of advanced glycation end products may contribute to anomalous posterior vitreous detachment formation and may also influence the mechanical properties of the iERM.

CONCLUSION

Remodeling of the extracellular matrix at the vitreoretinal interface by aging and fibrotic changes, plays a significant role in the pathogenesis of iERM. A better understanding of molecular mechanisms underlying this process may eventually lead to the development of effective and nonsurgical approaches to treat and prevent vitreoretinal fibrotic diseases.

Oxidative stress, insulin resistance, dyslipidemia and type 2 diabetes mellitus

Oxidative stress is increased in metabolic syndrome and type 2 diabetes mellitus (T2DM) and this appears to underlie the development of cardiovascular disease, T2DM and diabetic complications. Increased oxidative stress appears to be a deleterious factor leading to insulin resistance, dyslipidemia, β-cell dysfunction, impaired glucose tolerance and ultimately leading to T2DM. Chronic oxidative stress, hyperglycemia and dyslipidemia are particularly dangerous for β-cells from lowest levels of antioxidant, have high oxidative energy requirements, decrease the gene expression of key β-cell genes and induce cell death. If β-cell functioning is impaired, it results in an under production of insulin, impairs glucose stimulated insulin secretion, fasting hyperglycemia and eventually the development of T2DM.

Ocular complications of diabetes mellitus

Diabetes mellitus (DM) is a important health problem that induces ernestful complications and it causes significant morbidity owing to specific microvascular complications such as, retinopathy, nephropathy and neuropathy, and macrovascular complications such as, ischaemic heart disease, and peripheral vasculopathy. It can affect children, young people and adults and is becoming more common. Ocular complications associated with DM are progressive and rapidly becoming the world’s most significant cause of morbidity and are preventable with early detection and timely treatment. This review provides an overview of five main ocular complications associated with DM, diabetic retinopathy and papillopathy, cataract, glaucoma, and ocular surface diseases.

Primary retinal cultures as a tool for modeling diabetic retinopathy: an overview

Experimental models of diabetic retinopathy (DR) have had a crucial role in the comprehension of the pathophysiology of the disease and the identification of new therapeutic strategies. Most of these studies have been conducted in vivo, in animal models. However, a significant contribution has also been provided by studies on retinal cultures, especially regarding the effects of the potentially toxic components of the diabetic milieu on retinal cell homeostasis, the characterization of the mechanisms on the basis of retinal damage, and the identification of potentially protective molecules. In this review, we highlight the contribution given by primary retinal cultures to the study of DR, focusing on early neuroglial impairment. We also speculate on possible themes into which studies based on retinal cell cultures could provide deeper insight.

Ocular rigidity and outflow facility in nonproliferative diabetic retinopathy

PURPOSE

To compare ocular rigidity (OR) and outflow facility (C) in patients with nonproliferative diabetic retinopathy (NPDR) and control subjects.

METHODS

Twenty-four patients with NPDR (NPDR group) and 24 controls (control group) undergoing cataract surgery were enrolled. NPDR group was further divided into patients with mild NPDR (NPDR1-group) and patients with moderate and/or severe NPDR (NPDR2-group). After cannulation of the anterior chamber, a computer-controlled device was used to infuse saline and increase the intraocular pressure (IOP) in a stepping procedure from 15 to 40 mmHg. Ocular rigidity and outflow facility coefficients were estimated from IOP and volume recordings.

RESULTS

Ocular rigidity was 0.0205 μL(-1) in NPDR group and 0.0202 μL(-1) in control group (P = 0.942). In NPDR1-group, OR was 0.017 μL(-1) and in NPDR2-group it was 0.025 μL(-1) (P = 0.192). Outflow facility was 0.120 μL/min/mmHg in NPDR-group compared to 0.153 μL/min/mmHg in the control group at an IOP of 35 mmHg (P = 0.151). There was no difference in C between NPDR1-group and NPDR2-group (P = 0.709).

CONCLUSIONS

No statistically significant differences in ocular rigidity and outflow facility could be documented between diabetic patients and controls. No difference in OR and C was detected between mild NPDR and severe NPDR.

Epigenetic Changes in Endothelial Progenitors as a Possible Cellular Basis for Glycemic Memory in Diabetic Vascular Complications

The vascular complications of diabetes significantly impact the quality of life and mortality in diabetic patients. Extensive evidence from various human clinical trials has clearly established that a period of poor glycemic control early in the disease process carries negative consequences, such as an increase in the development and progression of vascular complications that becomes evident many years later. Importantly, intensive glycemic control established later in the disease process cannot reverse or slow down the onset or progression of diabetic vasculopathy. This has been named the glycemic memory phenomenon. Scientists have successfully modelled glycemic memory using various in vitro and in vivo systems. This review emphasizes that oxidative stress and accumulation of advanced glycation end products are key factors driving glycemic memory in endothelial cells. Furthermore, various epigenetic marks have been proposed to closely associate with vascular glycemic memory. In addition, we comment on the importance of endothelial progenitors and their role as endogenous vasoreparative cells that are negatively impacted by the diabetic milieu and may constitute a "carrier" of glycemic memory. Considering the potential of endothelial progenitor-based cytotherapies, future studies on their glycemic memory are warranted to develop epigenetics-based therapeutics targeting diabetic vascular complications.

Human genetics of diabetic retinopathy

There is evidence demonstrating that genetic factors contribute to the risk of diabetic retinopathy (DR). Genetics variants, structural variants (copy number variation, CNV) and epigenetic changes play important roles in the development of DR. Genetic linkage and association studies have uncovered a number of genetic loci and common genetic variants susceptibility to DR. CNV and interactions of gene by environment have also been detected by association analysis. Apart from nucleus genome, mitochondrial DNA plays critical roles in regulation of development of DR. Epigenetic studies have indicated epigenetic changes in chromatin affecting gene transcription in response to environmental stimuli, which provided a large body of evidence of regulating development of diabetes mellitus. Identification of genetic variants and epigenetic changes contributed to risk or protection of DR will benefit uncovering the complex mechanism underlying DR. This review focused on the current knowledge of the genetic and epigenetic basis of DR.

Effects of diabetes on retinal pigment epithelial cell proliferation and mitogen-activated protein kinase signaling in dark Agouti rats

Although diabetes induces retinopathy its effects on retinal pigment epithelium (RPE) are not clearly known. The present study investigated the effects of streptozotocin-induced diabetes on RPE cell proliferation and the expression of extracellular signal-regulated kinases 1 and 2 (ERK1/2), and c-Jun N-terminal kinases (JNKs) in rats. The bromodeoxyuridine immunohistochemistry revealed diabetes induced RPE cell proliferation at the end of first and second weeks in dark Agouti rats and at the end of first week in Wistar rats, but it inhibited the proliferation in both strains at the end of fifth week (P<0.05). A further analysis at the end of second week in the dark Agouti rats showed the cell proliferation, but not apoptosis, in association with an increase in ERK1/2 expression (P<0.05). However, the increased ERK level did not affect the expression of one of its substrates, the transcription factor c-Fos, suggesting that this protein has no role in the induction of the RPE cell proliferation. On the other hand, although total JNKs showed a decrease in the diabetic group (P<0.05), the JNKp46 isoform was increased and the JNKp54 isoform was decreased, but without any effects on one of their substrates, the transcription factor, c-Myc. Our results indicate that the RPE cell proliferation in diabetic rats may be mediated through mitogen-activated protein kinases. Thus, modulation of mitogen-activated protein kinases signaling may be a putative therapeutic option to alleviate the genesis of diabetes-induced retinal disruptions including retinopathy.

Glycated serum albumin: a potential disease marker and an intermediate index of diabetes control

Glycation is a non-enzymatic spontaneous process in proteins which has remarkable impact on its physical and functional aspect. This alteration with addition of carbohydrate residue to human serum albumin leads to several pathological events such as diabetic nephropathy, neuropathy, retinopathy and cardiovascular complications. Human serum albumin is the major protein and is most susceptible to non-enzymatic glycation. Structural and biological properties of functional albumin alter due to the addition of reducing carbohydrate to free amino terminal residues vivo. These irreversible changes in functional albumin are stable which makes this modified albumin as new gold standard future diagnostic marker in diabetes associated complications. Glycated albumin can be used to determine the glycemic control due to short half life than erythrocytes which makes it an alternate reliable disease marker in diabetes. In this review, Human serum albumin glycation has been overviewed, stating concept of glycation and sites that are prone to this modifications. Impact of non-enzymatic addition of carbohydrate to albumin's structural and biological properties has also been elaborated. Accurate measurements of glycated albumin with implications of new highly sensitive techniques have also been described briefly. Interestingly human serum albumin imposed glycation can serve as future tool not for diagnosing diabetes but also its potential in assessment of diabetes associated complications.

Role of epigenetic mechanisms in the development of chronic complications of diabetes

There is growing evidence that epigenetic regulation of gene expression including post-translational histone modifications (PTHMs), DNA methylation and microRNA (miRNA)-regulation of mRNA translation could play a crucial role in the development of chronic, diabetic complications. Hyperglycemia can induce an abnormal action of PTHMs and DNA methyltransferases as well as alter the levels of numerous miRNAs in endothelial cells, vascular smooth muscle cells, cardiomyocytes, retina, and renal cells. These epigenetic abnormalities result in changes in the expression of numerous genes contributing to effects such as development of chronic inflammation, impaired clearance of reactive oxygen species (ROS), endothelial cell dysfunction and/or the accumulation of extracellular matrix in the kidney, which causing the development of retinopathy, nephropathy or cardiomyopathy. Some epigenetic modifications, for example PTHMs and DNA methylation, become irreversible over time. Therefore, these processes have gained much attention in explaining the long-lasting detrimental consequences of hyperglycaemia causing the development of chronic complications even after improved glycaemic control is achieved. Our review suggests that the treatment of chronic complications should focus on erasing metabolic memory by targeting chromatin modification enzymes and by restoring miRNA levels.

Advanced glycation end products and diabetic complications

During long standing hyperglycaemic state in diabetes mellitus, glucose forms covalent adducts with the plasma proteins through a non-enzymatic process known as glycation. Protein glycation and formation of advanced glycation end products (AGEs) play an important role in the pathogenesis of diabetic complications like retinopathy, nephropathy, neuropathy, cardiomyopathy along with some other diseases such as rheumatoid arthritis, osteoporosis and aging. Glycation of proteins interferes with their normal functions by disrupting molecular conformation, altering enzymatic activity, and interfering with receptor functioning. AGEs form intra- and extracellular cross linking not only with proteins, but with some other endogenous key molecules including lipids and nucleic acids to contribute in the development of diabetic complications. Recent studies suggest that AGEs interact with plasma membrane localized receptors for AGEs (RAGE) to alter intracellular signaling, gene expression, release of pro-inflammatory molecules and free radicals. The present review discusses the glycation of plasma proteins such as albumin, fibrinogen, globulins and collagen to form different types of AGEs. Furthermore, the role of AGEs in the pathogenesis of diabetic complications including retinopathy, cataract, neuropathy, nephropathy and cardiomyopathy is also discussed.

Advanced glycation end products and diabetic complications

During long standing hyperglycaemic state in diabetes mellitus, glucose forms covalent adducts with the plasma proteins through a non-enzymatic process known as glycation. Protein glycation and formation of advanced glycation end products (AGEs) play an important role in the pathogenesis of diabetic complications like retinopathy, nephropathy, neuropathy, cardiomyopathy along with some other diseases such as rheumatoid arthritis, osteoporosis and aging. Glycation of proteins interferes with their normal functions by disrupting molecular conformation, altering enzymatic activity, and interfering with receptor functioning. AGEs form intra- and extracellular cross linking not only with proteins, but with some other endogenous key molecules including lipids and nucleic acids to contribute in the development of diabetic complications. Recent studies suggest that AGEs interact with plasma membrane localized receptors for AGEs (RAGE) to alter intracellular signaling, gene expression, release of pro-inflammatory molecules and free radicals. The present review discusses the glycation of plasma proteins such as albumin, fibrinogen, globulins and collagen to form different types of AGEs. Furthermore, the role of AGEs in the pathogenesis of diabetic complications including retinopathy, cataract, neuropathy, nephropathy and cardiomyopathy is also discussed.

Targeting Neovascularization in Ischemic Retinopathy: Recent Advances

Pathological retinal neovascularization (RNV) is a common micro-vascular complication in several retinal diseases including retinopathy of prematurity, diabetic retinopathy, age-related macular degeneration and central vein occlusion. The current therapeutic modalities of RNV are invasive and although they may slow or halt the progression of the disease they are unlikely to restore normal acuity. Therefore, there is an urgent need to develop treatment modalities, which are less invasive and therefore associated with fewer procedural complications and systemic side effects. This review article summarizes our understanding of the pathophysiology and current treatment of RNV in ischemic retinopathies; lists potential therapeutic targets; and provides a framework for the development of future treatment modalities.

Genetics in diabetic retinopathy: current concepts and new insights

There is emerging evidence which indicates the essential role of genetic factors in the development of diabetic retinopathy (DR). In this regard it should be highlighted that genetic factors account for 25-50% of the risk of developing DR. Therefore, the use of genetic analysis to identify those diabetic patients most prone to developing DR might be useful in designing a more individualized treatment. In this regard, there are three main research strategies: candidate gene studies, linkage studies and Genome-Wide Association Studies (GWAS). In the candidate gene approach, several genes encoding proteins closely related to DR development have been analyzed. The linkage studies analyze shared alleles among family members with DR under the assumption that these predispose to a more aggressive development of DR. Finally, Genome-Wide Association Studies (GWAS) are a new tool involving a massive evaluation of single nucleotide polymorphisms (SNP) in large samples. In this review the available information using these three methodologies is critically analyzed. A genetic approach in order to identify new candidates in the pathogenesis of DR would permit us to design more targeted therapeutic strategies in order to decrease this devastating complication of diabetes. Basic researchers, ophthalmologists, diabetologists and geneticists should work together in order to gain new insights into this issue.

Antioxidants and diabetic retinopathy

The biochemical perturbations in diabetes mellitus (DM) create the conditions for the production of free radicals, the consequence of which is increased oxidative stress. Evidence has accrued over the past 2 decades that suggests that oxidative stress is an important pathogenetic factor in the development of diabetic retinopathy (DR). Experimental data show that the use of strategies that ameliorate oxidative stress can prevent and retard the development of DR in the animal model. Clinical observations also suggest that reducing oxidative stress may help to reverse pathological manifestations of DR. The present article constitutes an examination of the role of antioxidants in the management of DR and the current state of clinically relevant knowledge.

Advanced glycation end products and diabetic retinopathy

Retinopathy is a serious microvascular complication of diabetes and a major cause of blindness in young adults, worldwide. Early diabetic retinopathy is characterized by a loss of pericytes from retinal capillaries, the appearance of acellular capillaries and microaneurysms, and a breakdown of the blood-retinal barrier. In later stages, this can evolve into the proliferative phase in which there is neovascularization of the retina, which greatly increases the probability of vision loss. Advanced glycation end products (AGEs) which accumulate under hyperglycemic conditions are thought to play an important role in the pathogenesis of diabetic retinopathy. AGEs arise primarily by the modification of amine groups of proteins by reactive dicarbonyls such as methylglyoxal. Intracellular proteins including anti-oxidant enzymes, transcription factors and mitochondrial proteins are targets of dicarbonyl modification and this can modify their functional properties and thus compromise cellular physiology. Likewise, modification of extracellular proteins by dicarbonyls can impair cell adhesion and can generate ligands that can potentially bind to cell surface AGE receptors that activate pro-inflammatory signaling pathways. AGE inhibitors have been shown to provide protection in animal models of diabetic retinopathy and currently are being evaluated in clinical trials.

Hyperglycemia and vascular metabolic memory: truth or fiction?

Prevention of long-term complications remains the main challenge in the treatment of diabetes. A strong relationship between glucose control and development of complications is apparent in all epidemiologic studies. Yet, intervention trials have yielded questionable results, particularly when intensive treatment was introduced in patients with long-standing diabetes. It has been postulated that in these subjects, prior exposure to chronic hyperglycemia may have generated a negative "metabolic memory," preventing full exertion of the beneficial effects of any subsequent improvement of glucose control. This phenomenon has been replicated in animal models and it recognizes a molecular basis in the role of oxidative stress, advanced glycation processes, and epigenetic mechanisms accounting for self-perpetuating modifications of gene expression. Conversely, early intervention in both type 1 and type 2 diabetes has proven that good glycemic control reduces the risk of development and progression of complications with a beneficial effect that extends well beyond the duration of near-normoglycemia. This has brought up the concept of "metabolic legacy," an advantage handed down by early and effective implementation of treatments designed to reduce blood glucose levels as safely as possible along with multifactorial intervention of all cardiovascular risk factors. The evidence, nature, and clinical implication of these concepts are reviewed.

Ethyl pyruvate prevents methyglyoxal-induced retinal vascular injury in rats

Pyruvate is an endogenous antioxidant substance. The aim of this study was to investigate the protective effects of ethyl pyruvate (EP) on retinal vascular injury in diabetic retinopathy. To investigate the protective effect of EP on vascular cell apoptosis and blood-retinal barrier (BRB) breakage, we have used intravitreally methylglyoxal-(MGO-) injected rat eyes. Apoptosis of the retinal vascular cell that was stimulated by the intravitreal injection of MGO was evidently attenuated by the EP treatment. EP exerts inhibitory effect on MGO-induced vascular cell apoptosis by blocking oxidative injury. In addition, EP treatment prevented MGO-induced BRB breakage and the degradation of occludin, an important tight junction protein. These observations suggest that EP acts through an antioxidant mechanism to protect against oxidative stress-induced apoptosis in retinal vessels.

Triple therapy: Phaco-vitrectomy with ILM peeling, retinal endophotocoagulation, and intraoperative use of bevacizumab for diffuse diabetic macular edema

BACKGROUND

The aim of this study was to evaluate the visual acuity and structural outcomes of combined phacovitrectomy with ILM peeling, retinal endophotocoagulation and use of bevacizumab in patients with diffuse diabetic macular edema (DDME).

MATERIAL/METHODS

In this prospective, nonrandomized, interventional study we included 29 eyes of 26 patients with DDME. The best-corrected visual acuity (BCVA) and central retinal thickness and volume (CRT and CRV) were recorded at 4, 8, 12, and 16 months after surgery.

RESULTS

The mean preoperative BCVA was 0.74±0.36 logMAR (0.3-1.5) and improved finally to 0.4±0.24 logMAR (-0.1-1.0) p=0.000006. The mean preoperative CRT in the 1mm zone was 516±184 microm (256-950) and decreased postoperatively at the last control to 237±75 microm (117-489) p=0.000003. The mean preoperative CRV in the 1mm zone was 0.39±0.14 microL (0.19-0.74) and decreased postoperatively at the last control to 0.17±0.06 microL (0.09-0.36) p=0.000003. The mean preoperative CRT in the 6 mm zone was 407±105 microm (279-640) and decreased postoperatively at the last control to 282±40 µm (212-380) p=0.000004. The mean preoperative CRV in the 6 mm zone was 11.4±2.9 microL (7.85-17.93) and decreased postoperatively at the last control to 7.92±1.0 microL (5.62-10.97) p=0.000003. The 23 (79.3%) eyes showed improvement in BCVA ≥0.2 logMAR, 5 (17.2%) eyes improvement or stabilization of BCVA and 1(3.5%) eye deterioration. Preoperative BCVA was a positive factor for prognosis of BCVA at 12th month follow-up (b=0.42; p=0.006), while the negative factors were: previous panretinal photocoagulation (b=-0.24; p=0.04), presence of vitreomacular traction (b=-0.29; p=0.02) and preoperative CRT in the 1000 microm zone (b=-0.24; p=0.07). A greater visual acuity improvement occurred in eyes with worse baseline visual acuity (b=-1.01; p=0.00001). The presentation of vitreomacular traction (b=-0.38; p=0.02), previous panretinal photocoagulation (b=-0.31, p=0.04) and greater preoperative CRT in the 1000 µm zone (b=-0.31; p=0.07) were negative factors for visual improvement.

CONCLUSIONS

This combined treatment resulted in improvement or stabilization of BCVA and decrease of CRT and CRV. Larger comparative studies are necessary to establish the real impact of this therapeutic approach.

Diabetic retinopathy and signaling mechanism for activation of matrix metalloproteinase-9

In the pathogenesis of diabetic retinopathy, H-Ras (a small molecular weight G-protein) and matrix metalloproteinase-9 (MMP9) act as pro-apoptotic, accelerating the apoptosis of retinal capillary cells, a phenomenon that predicts its development and the activation of MMP9 is under the control of H-Ras. The goal of this study is to elucidate the cellular mechanism by which H-Ras activates MMP9 culminating in the development of diabetic retinopathy. Using isolated retinal endothelial cells, the effect of regulation of H-Ras downstream signaling cascade, Raf-1, MEK, and ERK, was investigated on glucose-induced activation of MMP9. In vitro results were confirmed in the retina obtained from diabetic mice manipulated for MMP9 gene, and also in the retinal microvasculature obtained from human donors with diabetic retinopathy. Regulation of Raf-1/MEK/ERK by their specific siRNAs and pharmacologic inhibitors prevented glucose-induced activation of MMP9 in retinal endothelial cells. In MMP9-KO mice, diabetes had no effect on retinal MMP9 activation, and H-Ras/Raf-1/MEK signaling cascade remained normal. Similarly, donors with diabetic retinopathy had increased MMP9 activity in their retinal microvessels, the site of histopathology associated with diabetic retinopathy, and this was accompanied by activated H-Ras signaling pathway (Raf-1/ERK). Collectively, these results suggest that Ras/Raf-1/MEK/ERK cascade has an important role in the activation of retinal MMP9 resulting in the apoptosis of its capillary cells. Understanding the upstream mechanism responsible for the activation of MMP9 should help identify novel molecular targets for future pharmacological interventions to inhibit the development/progression of diabetic retinopathy.

PEDF in diabetic retinopathy: a protective effect of oxidative stress

Diabetic retinopathy (DR) is a major cause of blindness in working age adults, and oxidative stress plays a vital role in the pathogenesis of DR. Pigment-epithelium-derived factor (PEDF), a multifunctional protein, has shown to inhibit the development of DR by accumulating evidence. This paper highlights the current understanding of probable mechanism about how PEDF blocks the deterioration of DR through its antioxidative properties and application prospects of PEDF as a novel therapeutic target in DR. Gene therapy of PEDF is becoming more and more acceptable and will widely be applied to the actual treatment in the near future.

Blockade of early and late retinal biochemical alterations associated with diabetes development by the selective bradykinin B1 receptor antagonist R-954

The chronic hyperglycemia measured alongside diabetes development is associated with significant long-term damage and failure of various organs. In the present study it was shown that hyperglycemia induced early and long term increases in nitric oxide (NO) levels, kallikrein activity and vascular capillary permeability measured as plasma extravasation, and decreases of Na/K ATPase activity in diabetic rat retina 4 and 12 weeks after streptozotocin (STZ) injection. Treatment of the animals for 5 consecutive days with a novel selective bradykinin B(1) receptor (BKB(1)-R) antagonist R-954 (2mg/kg s.c) at the end of the 4 and 12 week periods highly reduced NO, kallikrein and capillary permeability and increased Na/K ATPase activity in the retina. These results suggest that the BKB(1)-R receptor subtype is over-expressed during the streptozotocin-induced development of diabetes in rat retina as evidenced by the inhibitory effects of the BKB(1)-R antagonist R-954 on NO, kallikrein and vascular permeability increases as well as Na/K ATPase decreases. The beneficial role of the BKB(1)-R antagonist R-954 for the treatment of the diabetic retinopathy is also suggested.

Effect of advanced glycation end products on oxidative stress and senescence of trabecular meshwork cells

Purpose

To investigate the effect of advanced glycation end products (AGE) on oxidative stress and cellular senescence in cultured human trabecular meshwork cells (HTMC).

Methods

Primarily cultured HTMC were exposed to 0, 10, 50, 100, 200 µg/mL of glycated bovine serum albumin (G-BSA) for 5 days. Also co-exposed were L-arginine, sepiapterin, and antioxidant N-acetylcysteine (NAC). Cellular survival and production of nitric oxide (NO), superoxide, and reactive oxygen species were assessed by 3-[4, 5-dimethylthiazol-2-yl]-2, 5-diphenyltetrazolium bromide assay, Griess assay, cytochrome c assay, and dichlorofluorescin diacetate assay, respectively. Senescence-associated β-galactosidase staining was performed to quantify the degree of cellular senescence.

Results

G-BSA decreased cellular survival, NO production, and increased superoxide production significantly in a dose-dependent manner. The effects of G-BSA were abolished with co-exposure of L-arginine, sepiapterin, and NAC. G-BSA enhanced cellular senescence accompanied by increased production of reactive oxygen species. G-BSA-induced cellular senescence was suppressed by application of L-arginine, sepiapterin, and NAC.

Conclusions

AGE enhances cellular senescence of HTMC accompanied with increased oxidative stress. AGE-induced oxidative stress and cellular senescence could be delayed by application of anti-oxidants.

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.

Interocular symmetry of abnormal multifocal electroretinograms in adolescents with diabetes and no retinopathy

PURPOSE

To investigate, in adolescents with type 1 diabetes and no retinopathy, the spatial correspondence between abnormal multifocal electroretinogram (mfERG) responses in the two eyes.

METHODS

mfERG and fundus photographs were measured in both eyes of 68 adolescents with type 1 diabetes and no retinopathy (13 to 19 years old; best corrected visual acuity ≥ 20/20), and 30 age-matched controls. The mfERG stimulus was comprised of 103 hexagons, and subtended 45°. mfERG implicit times (IT) and amplitudes (AMP) were derived. Fifteen patients for IT, and five for AMP with at least one eye defined as abnormal (six or more locations with abnormal Z-scores; P < 0.03) were analyzed.

RESULTS

Nasal retina had significantly more abnormal IT locations compared with temporal retina (P = 0.015), and the opposite was true with regard to abnormal AMP (P < 0.001). The proportion of abnormal responses in the superior retina was not significantly different from that in the inferior retina (P > 0.1 for IT and AMP). Interocular correspondence of locations with abnormal mfERG IT was significant for all 15 patients (P values <0.0001-0.012), and agreement between eyes was 68% to 94% (AC1 agreement coefficient: 0.48-0.94). Overall interocular correspondence was also significant (P < 0.0002), with 86% agreement (AC1 = 0.76). Overall interocular correspondence of locations with abnormal mfERG AMP was also significant (P < 0.0002).

CONCLUSIONS

Interocular spatial correspondence of abnormal mfERG responses exists in adolescents with type 1 diabetes and no retinopathy. This is most apparent for IT abnormalities. This correspondence could be used in clinical trials, and raises the possibility of initiating treatment in both eyes at early disease stages as new topical treatments emerge.

Evaluation of indoleamine 2,3-dioxygenase expression and kynurenine pathway metabolites levels in serum samples of diabetic retinopathy patients

CONTEXT

Diabetic retinopathy (DR) is the leading cause of acquired blindness. The involvement of indoleamine 2, 3-dioxygenase (IDO) and kynurenines, the products of tryptophan degradation in various pathological conditions was well documented.

OBJECTIVE

The aim of the present study was to determine the expression of IDO and levels of tryptophan metabolites in serum samples of DR patients.

MATERIALS AND METHODS

Tryptophan and its metabolites, i.e. kynurenine, kynurenic acid and 3-hydroxy kynurenine were measured by HPLC in serum of normal subjects as well as non-proliferative (NPDR) and proliferative DR (PDR) patients. The expression of IDO was measured using semi-quantitative reverse transcriptase polymerase chain reaction.

RESULTS

Elevated expression of IDO and levels of kynurenine, kynurenic acid and 3-hydroxykynurenine were observed in NPDR and a higher expression was observed in PDR. No significant change was noticed in levels of tryptophan.

CONCLUSION

An elevation in the concentrations of tryptophan metabolites and IDO expression was evident in diabetic retinopathy patients. The results indicate probable association of IDO and tryptophan metabolites with DR.

Metabolic memory and individual treatment aims in type 2 diabetes--outcome-lessons learned from large clinical trials

Reducing the burden of long-term complications in type 2 diabetic patients remains a major task, and represents a huge challenge. Whilst tight glycemic control has been shown to reduce the risk of microvascular complications, controversy remains regarding the benefit of intensive treatment in relation to the prevention of cardiovascular events. Recent large trials (including ACCORD, ADVANCE, and VADT) were unable to show a significant impact of glycemic control on cardiovascular events. Also, it has been argued that these trials included patients with a long duration of the disease, and with previous unsatisfactory glycemic control. Chronic exposure to hyperglycemia may cause a kind of negative metabolic memory, and thereby reduce the potential impact of good glycemic control. This concept has been corroborated by the UKPDS which recruited only subjects with newly diagnosed diabetes and without prior cardiovascular events. In these patients, early achievement of glycemic control translated into a long-term reduction of the risk of micro- and macrovascular complications. This observation prompted the UKPDS investigators to propose a positive "glycemic legacy", supporting the need for early and appropriate treatment of hyperglycemia and associated metabolic disturbances. This should be feasible now through the selection of individual targets and personalized pharmacologic treatments. In doing so, the potential risks of intensive treatment might then be avoided.

Beyond AREDS: is there a place for antioxidant therapy in the prevention/treatment of eye disease?

Age-related macular degeneration (AMD), the major cause of blindness in adults (65 years of age and older), and diabetic retinopathy, the major cause of blindness in working adults, are chronic, progressive diseases with multifaceted etiologies that are not fully understood. Progression and lack of treatment of both diseases may lead to the advanced stage with neovascularization. Although the detailed cellular mechanisms leading to the development of AMD and diabetic retinopathy remain elusive, oxidative damage to the retina and its pigment epithelium are considered to be involved. Clinical studies have shown that the progression of AMD can be slowed down by nutritional antioxidants, but trials with antioxidants for diabetic retinopathy (very limited in number) have been inconclusive. Long-term administration of the AREDS antioxidants, the same nutritional antioxidants that have been demonstrated to slow the progression of AMD, have yielded exciting results in preventing the pathogenesis of retinopathy in diabetic rodents. These results suggest the merit of testing the AREDS antioxidants in a clinical trial to prevent the development and/or progression of diabetic retinopathy, with the possibility of reducing the impact of this common vision-threatening disease.

Diabetic retinopathy: pathogenic mechanisms and current treatments

Since diabetes is now a global epidemic, the incidence of retinopathy, a leading cause of blindness in patients aged 20-74 years, is also expected to rise to alarming levels. The risk of development and progression of diabetic retinopathy is closely associated with the type and duration of diabetes, blood glucose, blood pressure and possibly lipids. It is an unmet medical need that can lead to severe and irreversible loss of vision in people of working age worldwide. The aim of this review is to give an overview of the clinical and anatomical changes during the progression of retinopathy, the underlying pathogenic mechanisms that link hyperglycemia with retinal tissue damage, current treatments, and the emerging pharmacological therapies for this sight-threatening complication of diabetes.

Naturally occurring inhibitors against the formation of advanced glycation end-products

Advanced glycation end-products (AGEs) are the final products of the non-enzymatic reaction between reducing sugars and amino groups in proteins, lipids and nucleic acids. Recently, the accumulation of AGEs in vivo has been implicated as a major pathogenic process in diabetic complications, atherosclerosis, Alzheimer's disease and normal aging. The early recognition of AGEs can ascend to the late 1960s when a non-enzymatic glycation process was found in human body which is similar to the Maillard reaction. To some extent, AGEs can be regarded as products of the Maillard reaction. This review firstly introduces the Maillard reaction, the formation process of AGEs and harmful effects of AGEs to human health. As AGEs can cause undesirable diseases or disorders, it is necessary to investigate AGE inhibitors to offer a potential therapeutic approach for the prevention of diabetic or other pathogenic complications induced by AGEs. Typical effective AGE inhibitors with different inhibition mechanisms are also reviewed in this paper. Both synthetic compounds and natural products have been evaluated as inhibitors against the formation of AGEs. However, considering toxic or side effects of synthetic molecules present in clinical trials, natural products are more promising to be developed as potent AGE inhibitors.

Decreased cerebrovascular brain-derived neurotrophic factor-mediated neuroprotection in the diabetic brain

OBJECTIVE

Diabetes is an independent risk factor for stroke. However, the underlying mechanism of how diabetes confers that this risk is not fully understood. We hypothesize that secretion of neurotrophic factors by the cerebral endothelium, such as brain-derived neurotrophic factor (BDNF), is suppressed in diabetes. Consequently, such accrued neuroprotective deficits make neurons more vulnerable to injury.

RESEARCH DESIGN AND METHODS

We examined BDNF protein levels in a streptozotocin-induced rat model of diabetes by Western blotting and immunohistochemistry. Levels of total and secreted BDNF protein were quantified in human brain microvascular endothelial cells after exposure to advanced glycation end product (AGE)-BSA by enzyme-linked immunosorbent assay and immunocytochemistry. In media transfer experiments, the neuroprotective efficacy of conditioned media from normal healthy endothelial cells was compared with AGE-treated endothelial cells in an in vitro hypoxic injury model.

RESULTS

Cerebrovascular BDNF protein was reduced in the cortical endothelium in 6-month diabetic rats. Immunohistochemical analysis of 6-week diabetic brain sections showed that the reduction of BDNF occurs early after induction of diabetes. Treatment of brain microvascular endothelial cells with AGE caused a similar reduction in BDNF protein and secretion in an extracellular signal-related kinase-dependent manner. In media transfer experiments, conditioned media from AGE-treated endothelial cells were less neuroprotective against hypoxic injury because of a decrease in secreted BDNF.

CONCLUSIONS

Taken together, our findings suggest that a progressive depletion of microvascular neuroprotection in diabetes elevates the risk of neuronal injury for a variety of central nervous system diseases, including stroke and neurodegeneration.

Diabetic retinopathy, superoxide damage and antioxidants

Retinopathy, the leading cause of acquired blindness in young adults, is one of the most feared complications of diabetes, and hyperglycemia is considered as the major trigger for its development. The microvasculature of the retina is constantly bombarded by high glucose, and this insult results in many metabolic, structural and functional changes. Retinal mitochondria become dysfunctional, its DNA is damaged and proteins encoded by its DNA are decreased. The electron transport chain system becomes compromised, further producing superoxide and providing no relief to the retina from a continuous cycle of damage. Although the retina attempts to initiate repair mechanisms by inducing gene expressions of the repair enzymes, their mitochondrial accumulation remains deficient. Understanding the molecular mechanism of mitochondrial damage should help identify therapies to treat/retard this sight threatening complication of diabetes. Our hope is that if the retinal mitochondria are maintained healthy with adjunct therapies, the development and progression of diabetic retinopathy can be inhibited.

Retinal redox stress and remodeling in cardiometabolic syndrome and diabetes

Diabetic retinopathy (DR) is a significant cause of global blindness; a major cause of blindness in the United States in people aged between 20–74. There is emerging evidence that retinopathy is initiated and propagated by multiple metabolic toxicities associated with excess production of reactive oxygen species (ROS). The four traditional metabolic pathways involved in the development of DR include: increased polyol pathway flux, advanced glycation end-product formation, activation of protein kinase Cisoforms and hexosamine pathway flux. These pathways individually and synergisticallycontribute to redox stress with excess ROS resulting in retinal tissue injury resulting in significant microvascular blood retinal barrier remodeling. The toxicity of hyperinsulinemia, hyperglycemia, hypertension, dyslipidemia, increased cytokines and growth factors, in conjunction with redox stress, contribute to the development and progression of DR. Redox stress contributes to the development and progression of abnormalities of endothelial cells and pericytes in DR. This review focuses on the ultrastructural observations of the blood retinal barrier including the relationship between the endothelial cell and pericyte remodeling in young nine week old Zucker obese (fa/ fa) rat model of obesity; cardiometabolic syndrome, and the 20 week old alloxan induced diabetic porcine model. Preventing or delaying the blindness associated with these intersecting abnormal metabolic pathways may be approached through strategies targeted to reduction of tissue inflammation and oxidative—redox stress. Understanding these abnormal metabolic pathways and the accompanying redox stress and remodeling mayprovide both the clinician and researcher a new concept of approaching this complicated disease process

Medical-grade honey enriched with antimicrobial peptides has enhanced activity against antibiotic-resistant pathogens

Honey has potent activity against both antibiotic-sensitive and -resistant bacteria, and is an interesting agent for topical antimicrobial application to wounds. As honey is diluted by wound exudate, rapid bactericidal activity up to high dilution is a prerequisite for its successful application. We investigated the kinetics of the killing of antibiotic-resistant bacteria by RS honey, the source for the production of Revamil® medical-grade honey, and we aimed to enhance the rapid bactericidal activity of RS honey by enrichment with its endogenous compounds or the addition of antimicrobial peptides (AMPs). RS honey killed antibiotic-resistant isolates of Pseudomonas aeruginosa, Staphylococcus epidermidis, Enterococcus faecium, and Burkholderia cepacia within 2 h, but lacked such rapid activity against methicillin-resistant S. aureus (MRSA) and extended-spectrum beta-lactamase (ESBL)-producing Escherichia coli. It was not feasible to enhance the rapid activity of RS honey by enrichment with endogenous compounds, but RS honey enriched with 75 μM of the synthetic peptide Bactericidal Peptide 2 (BP2) showed rapid bactericidal activity against all species tested, including MRSA and ESBL E. coli, at up to 10–20-fold dilution. RS honey enriched with BP2 rapidly killed all bacteria tested and had a broader spectrum of bactericidal activity than either BP2 or honey alone.

Nocturnal intermittent serious hypoxia and reoxygenation in proliferative diabetic retinopathy cases

PURPOSE

To clarify the relationship between evaluation items of sleep-disordered breathing and diabetic retinopathy in detail.

DESIGN

Cross-sectional comparative study.

METHODS

Sixty-eight consecutive nonproliferative diabetic retinopathy and 151 proliferative diabetic retinopathy (PDR) cases who had undergone surgeries in our department were included in this study. Pulse oximetry was conducted overnight and mean oxygen saturation by pulse oximeter (SpO(2); %), the sleeping 4% oxygen desaturation index (4% ODI times/hour), lowest SpO(2) (%), and the cumulative percent time spent at SpO(2) < 90% (CT 90%) were calculated. The results were evaluated and compared between the 2 groups. In addition, these results and preoperative patient background factors were analyzed using logistic regression analysis to clarify risk factor of PDR.

RESULTS

4% ODI and CT 90% in the PDR group were significantly higher than in the nonproliferative diabetic retinopathy group (4% ODI, 7.8 vs. 4.9; P = .007; CT 90%, 2.2 vs 0.8; P = .0006). Lowest SpO(2) was significantly lower in the PDR group than in the nonproliferative diabetic retinopathy groups (82.4 vs 87.0; P = .0006). Logistic regression analysis identified being younger, having a lower value for the lowest SpO(2), and a high hemoglobin A1c value to be risk factors for PDR (age: odds ratio, 0.90; 95% confidence interval, -0.86 to -0.94; P < .0001; lowest SpO(2): odds ratio, 0.93; 95% confidence interval, 0.88 to 0.99; P = .02; hemoglobin A1c: odds ratio, 1.00 to 1.69; P = .047).

CONCLUSIONS

This study indicated that PDR cases had episodes of nocturnal intermittent hypoxia and reoxygenation as a result of sleep-disordered breathing and that low-value lowest SpO(2) were the risk factors for PDR development.

Expression of advanced glycation end products and related molecules in diabetic fibrovascular epiretinal membranes

PURPOSE

To investigate associations between expressions of advanced glycation end products (AGEs), transforming growth factor-beta (TGF-beta), tumour necrosis factor-alpha (TNF-alpha) and integrins and correlations between their expression and level of vascularization and proliferative activity in diabetic fibrovascular epiretinal membranes.

METHODS

Membranes from eight patients with active proliferative diabetic retinopathy and nine patients with inactive proliferative diabetic retinopathy were studied by immunohistochemistry.

RESULTS

Blood vessels expressed AGEs, TGF-beta, TNF-alpha and alpha(v)beta(3) integrin in 5, 13, 8 and 8 membranes, respectively. Stromal cells expressed AGEs, TNF-alpha and alpha(v)beta(3) integrin in 15, 13 and 3 membranes, respectively. There was no immunoreactivity for alpha(v)beta(5), alpha(5)beta(1) and alpha(2)beta(1) integrins. There were significant correlations between number of blood vessels expressing CD34 and number of blood vessels expressing AGEs (r(s) = 0.496; P = 0.043), TGF-beta (r(s) = 0.777; P < 0.001) and TNF-alpha (r(s) = 0.699; P = 0.002). There were significant correlations between number of blood vessels expressing AGEs and number of blood vessels expressing TGF-beta (r(s) = 0.532; P = 0.028) and TNF-alpha (r(s) = 0.626; P = 0.007). The correlation between number of blood vessels expressing TNF-alpha and alpha(v)beta(3) integrin was significant (r(s) = 0.617; P = 0.008). Number of blood vessels expressing CD34 (P = 0.001), TGF-beta (P = 0.006) and TNF-alpha (P = 0.002) and stromal cells expressing AGEs (P = 0.001) and TNF-alpha (P = 0.004) were significantly higher in active membranes than in inactive membranes.

CONCLUSION

Interactions of AGEs, TGF-beta, TNF-alpha and alpha(v)beta(3) integrin might be involved in pathogenesis of proliferative diabetic retinopathy fibrovascular proliferation.

Prediction of diabetic retinopathy: role of oxidative stress and relevance of apoptotic biomarkers

Diabetic retinopathy (DR) is the foremost cause of blindness in working-aged worldwide; it is characterized by vascular and neuronal degeneration. Features of DR include leukocyte adhesion, increased vascular permeability, neovascularization and neuronal cell death. Early diagnosis and intervention are important to prevent or at least ameliorate the development of DR. Recent reports indicate that pathophysiological mechanisms leading to diabetic retinopathy include oxidative stress and retinal cell death cascades. Circulating biomarkers of oxidative stress such as malondialdehyde (MDA), thiobarbituric acid reacting substances (TBARS), conjugated diene (CD), advanced oxidation protein products (AOPP), protein carbonyl, 8-hydroxydeoxyguanosin (8-OHdG), nitrotyrosine, and F(2) isoprostanes and pro-apoptosis molecules (caspase-3, Fas, and Bax) are associated with increased susceptibility to develop DR in diabetic subjects. Thus, identification of oxidative stress and cell death biomarkers in diabetic patients could be in favor of predicting, diagnosis, and prevention of DR, and to target for novel therapeutic interventions.

Molecular spectral imaging system for quantitative immunohistochemical analysis of early diabetic retinopathy

A molecular spectral imaging system has been developed based on microscopy and spectral imaging technology. The system is capable of acquiring molecular spectral images from 400 nm to 800 nm with 2 nm wavelength increments. The basic principles, instrumental systems, and system calibration method as well as its applications for the calculation of the stain-uptake by tissues are introduced. As a case study, the system is used for determining the pathogenesis of diabetic retinopathy and evaluating the therapeutic effects of erythropoietin. Some molecular spectral images of retinal sections of normal, diabetic, and treated rats were collected and analyzed. The typical transmittance curves of positive spots stained for albumin and advanced glycation end products are retrieved from molecular spectral data with the spectral response calibration algorithm. To explore and evaluate the protective effect of erythropoietin (EPO) on retinal albumin leakage of streptozotocin-induced diabetic rats, an algorithm based on Beer-Lambert's law is presented. The algorithm can assess the uptake by histologic retinal sections of stains used in quantitative pathology to label albumin leakage and advanced glycation end products formation. Experimental results show that the system is helpful for the ophthalmologist to reveal the pathogenesis of diabetic retinopathy and explore the protective effect of erythropoietin on retinal cells of diabetic rats. It also highlights the potential of molecular spectral imaging technology to provide more effective and reliable diagnostic criteria in pathology.

Glyceraldehyde-3-phosphate dehydrogenase in retinal microvasculature: implications for the development and progression of diabetic retinopathy

PURPOSE

Glyceraldehyde-3-phosphate dehydrogenase (GAPDH) has been hypothesized as a mediator in the activation of multiple pathways implicated in the pathogenesis of diabetic retinopathy. The objective of this study was to understand the mechanism by which high glucose inactivates GAPDH in retinal microvascular cells.

METHODS

Bovine retinal endothelial cells (BRECs), transfected with GAPDH, were incubated in 20 mM glucose. The effect of the overexpression of GAPDH on its activity, apoptosis, and upstream signaling pathways, protein kinase C, and hexosamine pathways was determined. The effect of the inhibitors of nitration and ribosylation on GAPDH activity, its nuclear translocation and reversal of glucose insult was also evaluated.

RESULTS

High glucose decreased GAPDH activity, expression, and nuclear translocation. Overexpression of GAPDH prevented glucose-induced inhibition of its activity, nuclear translocation, apoptosis, and activation of protein kinase C and hexosamine pathways. Inhibitors of nitration and ribosylation ameliorated glucose-induced inhibition of GAPDH, and their addition during the normal glucose exposure that followed high glucose levels had a beneficial effect on GAPDH activity and the degree of nitration and ribosylation.

CONCLUSIONS

In hyperglycemia, GAPDH in retinal microvascular cells is inhibited by its covalent modifications, and this activates multiple pathways implicated in the pathogenesis of diabetic retinopathy. The agents that can directly target modification of GAPDH have potential in inhibiting the development and in arresting the progression of diabetic retinopathy.