Profile of lipid and protein autacoids in diabetic vitreous correlates with the progression of diabetic retinopathy

A systematic literature review of machine learning based risk prediction models for diabetic retinopathy progression

Diabetic Retinopathy (DR) is the most popular debilitating impairment of diabetes and it progresses symptom-free until a sudden loss of vision occurs. Understanding the progression of DR is a pressing issue in clinical research and practice. In this systematic review of articles on Machine Learning (ML) based risk prediction models for DR progression, ever since the use of Artificial Intelligence (AI) for DR detection, there have been more cross-sectional studies with different algorithms of use of AI, there haven't been many longitudinal studies for the AI based risk prediction models. This paper proposes a novel review to fill in the gaps identified in current reviews and facilitate other researchers with current research solutions for developing AI-based risk prediction models for DR progression and closely related problems; synthesize the current results from these studies and identify research challenges, limitations and gaps to inform the selection of machine learning techniques and predictors to build novel prediction models. Additionally, this paper suggested six (6) deep AI-related technical and critical discussion of the adopted strategies and approaches. The Systematic Literature Review (SLR) methodology was employed to gather relevant studies. We searched IEEE Xplore, PubMed, Springer Link, Google Scholar, and Science Direct electronic databases for papers published from January 2017 to 30th April 2023. Thirteen (13) studies were chosen on the basis of their relevance to the review questions and satisfying the selection criteria. However, findings from the literature review exposed some critical research gaps that need to be addressed in future research to improve on the performance of risk prediction models for DR progression.

Integration of Vitreous Lipidomics and Metabolomics for Comprehensive Understanding of the Pathogenesis of Proliferative Diabetic Retinopathy

As a vision-threatening complication of diabetes mellitus (DM), proliferative diabetic retinopathy (PDR) is associated with sustained metabolic disorders. Herein, we collected the vitreous cavity fluid of 49 patients with PDR and 23 control subjects without DM for metabolomics and lipidomics analyses. Multivariate statistical methods were performed to explore relationships between samples. For each group of metabolites, gene set variation analysis scores were generated, and we constructed a lipid network by using weighted gene co-expression network analysis. The association between lipid co-expression modules and metabolite set scores was investigated using the two-way orthogonal partial least squares (O2PLS) model. A total of 390 lipids and 314 metabolites were identified. Multivariate statistical analysis revealed significant vitreous metabolic and lipid differences between PDR and controls. Pathway analysis showed that 8 metabolic processes might be associated with the development of PDR, and 14 lipid species were found to be altered in PDR patients. Combining metabolomics and lipidomics, we identified fatty acid desaturase 2 (FADS2) as an important potential contributor to the pathogenesis of PDR. Collectively, this study integrates vitreous metabolomics and lipidomics to comprehensively unravel metabolic dysregulation and identifies genetic variants associated with altered lipid species in the mechanistic pathways for PDR.

Elucidating glial responses to products of diabetes-associated systemic dyshomeostasis

Diabetic retinopathy (DR) is a leading cause of blindness in working age adults. DR has non-proliferative stages, characterized in part by retinal neuroinflammation and ischemia, and proliferative stages, characterized by retinal angiogenesis. Several systemic factors, including poor glycemic control, hypertension, and hyperlipidemia, increase the risk of DR progression to vision-threatening stages. Identification of cellular or molecular targets in early DR events could allow more prompt interventions pre-empting DR progression to vision-threatening stages. Glia mediate homeostasis and repair. They contribute to immune surveillance and defense, cytokine and growth factor production and secretion, ion and neurotransmitter balance, neuroprotection, and, potentially, regeneration. Therefore, it is likely that glia orchestrate events throughout the development and progression of retinopathy. Understanding glial responses to products of diabetes-associated systemic dyshomeostasis may reveal novel insights into the pathophysiology of DR and guide the development of novel therapies for this potentially blinding condition. In this article, first, we review normal glial functions and their putative roles in the development of DR. We then describe glial transcriptome alterations in response to systemic circulating factors that are upregulated in patients with diabetes and diabetes-related comorbidities; namely glucose in hyperglycemia, angiotensin II in hypertension, and the free fatty acid palmitic acid in hyperlipidemia. Finally, we discuss potential benefits and challenges associated with studying glia as targets of DR therapeutic interventions. In vitro stimulation of glia with glucose, angiotensin II and palmitic acid suggests that: 1) astrocytes may be more responsive than other glia to these products of systemic dyshomeostasis; 2) the effects of hyperglycemia on glia are likely to be largely osmotic; 3) fatty acid accumulation may compound DR pathophysiology by promoting predominantly proinflammatory and proangiogenic transcriptional alterations of macro and microglia; and 4) cell-targeted therapies may offer safer and more effective avenues for DR treatment as they may circumvent the complication of pleiotropism in retinal cell responses. Although several molecules previously implicated in DR pathophysiology are validated in this review, some less explored molecules emerge as potential therapeutic targets. Whereas much is known regarding glial cell activation, future studies characterizing the role of glia in DR and how their activation is regulated and sustained (independently or as part of retinal cell networks) may help elucidate mechanisms of DR pathogenesis and identify novel drug targets for this blinding disease.

New insight of metabolomics in ocular diseases in the context of 3P medicine

Metabolomics refers to the high-through untargeted or targeted screening of metabolites in biofluids, cells, and tissues. Metabolome reflects the functional states of cells and organs of an individual, influenced by genes, RNA, proteins, and environment. Metabolomic analyses help to understand the interaction between metabolism and phenotype and reveal biomarkers for diseases. Advanced ocular diseases can lead to vision loss and blindness, reducing patients' quality of life and aggravating socio-economic burden. Contextually, the transition from reactive medicine to the predictive, preventive, and personalized (PPPM / 3P) medicine is needed. Clinicians and researchers dedicate a lot of efforts to explore effective ways for disease prevention, biomarkers for disease prediction, and personalized treatments, by taking advantages of metabolomics. In this way, metabolomics has great clinical utility in the primary and secondary care. In this review, we summarized much progress achieved by applying metabolomics to ocular diseases and pointed out potential biomarkers and metabolic pathways involved to promote 3P medicine approach in healthcare.

Interference of ALOX5 alleviates inflammation and fibrosis in high glucose‑induced renal mesangial cells

Diabetic nephropathy (DN) is the leading cause of end-stage renal disease (ESRD), seriously threatening the health of individuals. The 5-lipoxygenase (ALOX5) gene has been reported to be associated with diabetes, but whether it is involved in DN remains unclear. The present study aimed to explore the role of ALOX5 in DN and to clarify the potential mechanism. Mouse renal mesangial cells (SV40 MES-13) were treated with high glucose (HG) to mimic a DN model in vitro. The expression level of ALOX5 was assessed using reverse transcription-quantitative PCR and western blotting. Cell Counting Kit-8 and flow cytometric assays were performed to determine cell proliferation, the cell cycle and apoptosis. Immunofluorescence was carried out to detect the expression of Ki67 and proliferating cell nuclear antigen (PCNA). The inflammatory cytokines were assessed using ELISA. The expression of fibrosis- and NF-κB-related proteins was determined using western blotting. The results revealed that ALOX5 was significantly upregulated in HG-induced SV40 MES-13 cells. Interference of ALOX5 greatly hindered HG-induced cell viability loss, as well as increasing the expression of Ki67 and PCNA. In addition, HG induced cell cycle arrest in the G1 phase and cell apoptosis, which were then partly abolished by interference of ALOX5. Moreover, the elevated production of inflammatory cytokines and upregulated fibrosis-related proteins induced by HG were weakened by interference of ALOX5. Eventually, interference of ALOX5 was found to reduce the activity of NF-κB signaling in HG-induced SV40 MES-13 cells. Collectively, interference of ALOX5 serves as a protective role in HG-induced kidney cell injury, providing a potential therapeutic strategy of DN treatment.

Metabolomics in Diabetic Retinopathy: From Potential Biomarkers to Molecular Basis of Oxidative Stress

Diabetic retinopathy (DR), the leading cause of blindness in working-age adults, is one of the most common complications of diabetes mellitus (DM) featured by metabolic disorders. With the global prevalence of diabetes, the incidence of DR is expected to increase. Prompt detection and the targeting of anti-oxidative stress intervention could effectively reduce visual impairment caused by DR. However, the diagnosis and treatment of DR is often delayed due to the absence of obvious signs of retina imaging. Research progress supports that metabolomics is a powerful tool to discover potential diagnostic biomarkers and therapeutic targets for the causes of oxidative stress through profiling metabolites in diseases, which provides great opportunities for DR with metabolic heterogeneity. Thus, this review summarizes the latest advances in metabolomics in DR, as well as potential diagnostic biomarkers, and predicts molecular targets through the integration of genome-wide association studies (GWAS) with metabolomics. Metabolomics provides potential biomarkers, molecular targets and therapeutic strategies for controlling the progress of DR, especially the interventions at early stages and precise treatments based on individual patient variations.

Cytochrome P450 oxidase 2J inhibition suppresses choroidal neovascularization in mice

INTRODUCTION

Choroidal neovascularization (CNV) in age-related macular degeneration (AMD) leads to blindness. It has been widely reported that increased intake of ω-3 long-chain polyunsaturated fatty acids (LCPUFA) diets reduce CNV. Of the three major pathways metabolizing ω-3 (and ω-6 LCPUFA), the cyclooxygenase and lipoxygenase pathways generally produce pro-angiogenic metabolites from ω-6 LCPUFA and anti-angiogenic ones from ω-3 LCPUFA. Howevehr, cytochrome P450 oxidase (CPY) 2C produces pro-angiogenic metabolites from both ω-6 and ω-3 LCPUFA. The effects of CYP2J2 products on ocular neovascularization are still unknown. Understanding how each metabolic pathway affects the protective effect of ω-3 LCPUFA on retinal neovascularization may lead to therapeutic interventions.

OBJECTIVES

To investigate the effects of LCPUFA metabolites through CYP2J2 pathway and CYP2J2 regulation on CNV both in vivo and ex vivo.

METHODS

The impact of CYP2J2 overexpression and inhibition on neovascularization in the laser-induced CNV mouse model was assessed. The plasma levels of CYP2J2 metabolites were measured by liquid chromatography and tandem mass spectroscopy. The choroidal explant sprouting assay was used to investigate the effects of CYP2J2 inhibition and specific LCPUFA CYP2J2 metabolites on angiogenesis ex vivo.

RESULTS

CNV was exacerbated in Tie2-Cre CYP2J2-overexpressing mice and was associated with increased levels of plasma docosahexaenoic acids. Inhibiting CYP2J2 activity with flunarizine decreased CNV in both ω-6 and ω-3 LCPUFA-fed wild-type mice. In Tie2-Cre CYP2J2-overexpressing mice, flunarizine suppressed CNV by 33 % and 36 % in ω-6, ω-3 LCPUFA diets, respectively, and reduced plasma levels of CYP2J2 metabolites. The pro-angiogenic role of CYP2J2 was corroborated in the choroidal explant sprouting assay. Flunarizine attenuated ex vivo choroidal sprouting, and 19,20-EDP, a ω-3 LCPUFA CYP2J2 metabolite, increased sprouting. The combined inhibition of CYP2J2 with flunarizine and CYP2C8 with montelukast further enhanced CNV suppression via tumor necrosis factor-α suppression.

CONCLUSIONS

CYP2J2 inhibition augmented the inhibitory effect of ω-3 LCPUFA on CNV. Flunarizine suppressed pathological choroidal angiogenesis, and co-treatment with montelukast inhibiting CYP2C8 further enhanced the effect. CYP2 inhibition might be a viable approach to suppress CNV in AMD.

Effect of cytokine-induced alterations in extracellular matrix composition on diabetic retinopathy-relevant endothelial cell behaviors

Retinal vascular basement membrane (BM) thickening is an early structural abnormality of diabetic retinopathy (DR). Recent studies suggest that BM thickening contributes to the DR pathological cascade; however, much remains to be elucidated about the exact mechanisms by which BM thickening develops and subsequently drives other pathogenic events in DR. Therefore, we undertook a systematic analysis to understand how human retinal microvascular endothelial cells (hRMEC) and human retinal pericytes (hRP) change their expression of key extracellular matrix (ECM) constituents when treated with diabetes-relevant stimuli designed to model the three major insults of the diabetic environment: hyperglycemia, dyslipidemia, and inflammation. TNFα and IL-1β caused the most potent and consistent changes in ECM expression in both hRMEC and hRP. We also demonstrate that conditioned media from IL-1β-treated human Müller cells caused dose-dependent, significant increases in collagen IV and agrin expression in hRMEC. After narrowing our focus to inflammation-induced changes, we sought to understand how ECM deposited by hRMEC and hRP under inflammatory conditions affects the behavior of naïve hRMEC. Our data demonstrated that diabetes-relevant alterations in ECM composition alone cause both increased adhesion molecule expression by and increased peripheral blood mononuclear cell (PBMC) adhesion to naïve hRMEC. Taken together, these data demonstrate novel roles for inflammation and pericytes in driving BM pathology and suggest that inflammation-induced ECM alterations may advance other pathogenic behaviors in DR, including leukostasis.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Putative Biomarkers in Tears for Diabetic Retinopathy Diagnosis

Purpose

Tear fluid biomarkers may offer a non-invasive strategy for detecting diabetic patients with increased risk of developing diabetic retinopathy (DR) or increased disease progression, thus helping both improving diagnostic accuracy and understanding the pathophysiology of the disease. Here, we assessed the tear fluid of nondiabetic individuals, diabetic patients with no DR, and diabetic patients with nonproliferative DR (NPDR) or with proliferative DR (PDR) to find putative biomarkers for the diagnosis and staging of DR.

Methods

Tear fluid samples were collected using Schirmer test strips from a cohort with 12 controls and 54 Type 2 Diabetes (T2D) patients, and then analyzed using mass spectrometry (MS)-based shotgun proteomics and bead-based multiplex assay. Tear fluid-derived small extracellular vesicles (EVs) were analyzed by transmission electron microscopy, Western Blotting, and nano tracking.

Results

Proteomics analysis revealed that among the 682 reliably quantified proteins in tear fluid, 42 and 26 were differentially expressed in NPDR and PDR, respectively, comparing to the control group. Data are available via ProteomeXchange with identifier PXD033101. By multicomparison analyses, we also found significant changes in 32 proteins. Gene ontology (GO) annotations showed that most of these proteins are associated with oxidative stress and small EVs. Indeed, we also found that tear fluid is particularly enriched in small EVs. T2D patients with NPDR have higher IL-2/-5/-18, TNF, MMP-2/-3/-9 concentrations than the controls. In the PDR group, IL-5/-18 and MMP-3/-9 concentrations were significantly higher, whereas IL-13 was lower, compared to the controls.

Conclusions

Overall, the results show alterations in tear fluid proteins profile in diabetic patients with retinopathy. Promising candidate biomarkers identified need to be validated in a large sample cohort.

Dynamic lipid turnover in photoreceptors and retinal pigment epithelium throughout life

The retinal pigment epithelium-photoreceptor interphase is renewed each day in a stunning display of cellular interdependence. While photoreceptors use photosensitive pigments to convert light into electrical signals, the RPE supports photoreceptors in their function by phagocytizing shed photoreceptor tips, regulating the blood retina barrier, and modulating inflammatory responses, as well as regenerating the 11-cis-retinal chromophore via the classical visual cycle. These processes involve multiple protein complexes, tightly regulated ligand-receptors interactions, and a plethora of lipids and protein-lipids interactions. The role of lipids in maintaining a healthy interplay between the RPE and photoreceptors has not been fully delineated. In recent years, novel technologies have resulted in major advancements in understanding several facets of this interplay, including the involvement of lipids in phagocytosis and phagolysosome function, nutrient recycling, and the metabolic dependence between the two cell types. In this review, we aim to integrate the complex role of lipids in photoreceptor and RPE function, emphasizing the dynamic exchange between the cells as well as discuss how these processes are affected in aging and retinal diseases.

Diminished retinal complex lipid synthesis and impaired fatty acid β-oxidation associated with human diabetic retinopathy

BACKGROUND

This study systematically investigated circulating and retinal tissue lipid determinants of human diabetic retinopathy (DR) to identify underlying lipid alterations associated with severity of DR.

METHODS

Retinal tissues were retrieved from postmortem human eyes, including 19 individuals without diabetes, 20 with diabetes but without DR, and 20 with diabetes and DR, for lipidomic study. In a parallel study, serum samples from 28 American Indians with type 2 diabetes from the Gila River Indian Community, including 12 without DR, 7 with mild nonproliferative DR (NPDR), and 9 with moderate NPDR, were selected. A mass-spectrometry–based lipidomic platform was used to measure serum and tissue lipids.

RESULTS

In the postmortem retinas, we found a graded decrease of long-chain acylcarnitines and longer-chain fatty acid ester of hydroxyl fatty acids, diacylglycerols, triacylglycerols, phosphatidylcholines, and ceramide(NS) in central retina from individuals with no diabetes to those with diabetes with DR. The American Indians’ sera also exhibited a graded decrease in circulating long-chain acylcarnitines and a graded increase in the intermediate-length saturated and monounsaturated triacylglycerols from no DR to moderate NPDR.

CONCLUSION

These findings suggest diminished synthesis of complex lipids and impaired mitochondrial β-oxidation of fatty acids in retinal DR, with parallel changes in circulating lipids.

TRIAL REGISTRATION

ClinicalTrials.gov NCT00340678.

FUNDING

This work was supported by NIH grants R24 DK082841, K08DK106523, R03DK121941, P30DK089503, P30DK081943, P30DK020572, P30 EY007003; The Thomas Beatson Foundation; and JDRF Center for Excellence (5-COE-2019-861-S-B).

Metabolomics in Retinal Diseases: An Update

Retinal diseases are a leading cause of visual loss and blindness, affecting a significant proportion of the population worldwide and having a detrimental impact on quality of life, with consequent economic burden. The retina is highly metabolically active, and a number of retinal diseases are associated with metabolic dysfunction. To better understand the pathogenesis underlying such retinopathies, new technology has been developed to elucidate the mechanism behind retinal diseases. Metabolomics is a relatively new "omics" technology, which has developed subsequent to genomics, transcriptomics, and proteomics. This new technology can provide qualitative and quantitative information about low-molecular-weight metabolites (M.W. < 1500 Da) in a given biological system, which shed light on the physiological or pathological state of a cell or tissue sample at a particular time point. In this article we provide an extensive review of the application of metabolomics to retinal diseases, with focus on age-related macular degeneration (AMD), diabetic retinopathy (DR), retinopathy of prematurity (ROP), glaucoma, and retinitis pigmentosa (RP).

Nuclear factor of activated T-cells (NFAT) regulation of IL-1β-induced retinal vascular inflammation

Chronic low-grade retinal inflammation is an essential contributor to the pathogenesis of diabetic retinopathy (DR). It is characterized by increased retinal cell expression and secretion of a variety of inflammatory cytokines; among these, IL-1β has the reputation of being a major driver of cytokine-induced inflammation. IL-1β and other cytokines drive inflammatory changes that cause damage to retinal cells, leading to the hallmark vascular lesions of DR; these include increased leukocyte adherence, vascular permeability, and capillary cell death. Nuclear factor of activated T-cells (NFAT) is a transcriptional regulator of inflammatory cytokines and adhesion molecules and is expressed in retinal cells. Consequently, it may influence multiple pathogenic steps early in DR. We investigated the NFAT-dependency of IL-1β-induced inflammation in human Müller cells (hMC) and human retinal microvascular endothelial cells (hRMEC). Our results show that an NFAT inhibitor, Inhibitor of NFAT-Calcineurin Association-6 (INCA-6), decreased IL-1β-induced expression of IL-1β and TNFα in hMC, while having no effect on VEGF, CCL2, or CCL5 expression. We also demonstrate that INCA-6 attenuated IL-1β-induced increases of IL-1β, TNFα, IL-6, CCL2, and CCL5 (inflammatory cytokines and chemokines), and ICAM-1 and E-selectin (leukocyte adhesion molecules) expression in hRMEC. INCA-6 similarly inhibited IL-1β-induced increases in leukocyte adhesion in both hRMEC monolayers in vitro and an acute model of retinal inflammation in vivo. Finally, INCA-6 rescued IL-1β-induced permeability in both hRMEC monolayers in vitro and an acute model of retinal inflammation in vivo. Taken together, these data demonstrate the potential of NFAT inhibition to mitigate retinal inflammation secondary to diabetes.

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

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

Cytochrome P450-epoxygenated fatty acids inhibit Müller glial inflammation

Free fatty acid dysregulation in diabetics may elicit the release of inflammatory cytokines from Müller cells (MC), promoting the onset and progression of diabetic retinopathy (DR). Palmitic acid (PA) is elevated in the sera of diabetics and stimulates the production of the DR-relevant cytokines by MC, including IL-1β, which induces the production of itself and other inflammatory cytokines in the retina as well. In this study we propose that experimental elevation of cytochrome P450 epoxygenase (CYP)-derived epoxygenated fatty acids, epoxyeicosatrienoic acid (EET) and epoxydocosapentaenoic acid (EDP), will reduce PA- and IL-1β-induced MC inflammation. Broad-spectrum CYP inhibition by SKF-525a increased MC expression of inflammatory cytokines. Exogenous 11,12-EET and 19,20-EDP significantly decreased PA- and IL-1β-induced MC expression of IL-1β and IL-6. Both epoxygenated fatty acids significantly decreased IL-8 expression in IL-1β-induced MC and TNFα in PA-induced MC. Interestingly, 11,12-EET and 19,20-EDP significantly increased TNFα in IL-1β-treated MC. GSK2256294, a soluble epoxide hydrolase (sEH) inhibitor, significantly reduced PA- and IL-1β-stimulated MC cytokine expression. 11,12-EET and 19,20-EDP were also found to decrease PA- and IL-1β-induced NFκB-dependent transcriptional activity. These data suggest that experimental elevation of 11,12-EET and 19,20-EDP decreases MC inflammation in part by blocking NFκB-dependent transcription and may represent a viable therapeutic strategy for inhibition of early retinal inflammation in DR.

Vitreous composition modification after transpalpebral electrical stimulation of the eye: Biochemical analysis

Electrical stimulation (ES) of the eye represents a therapeutic approach in various clinical applications ranging from retinal dystrophies, age-related macular degeneration, retinal artery occlusion and nonarteritic ischemic optic neuropathy. In clinical practice, ES of the eye is mainly performed with a transcorneal or transpalpebral approach. These procedures are non-invasive and well-tolerated by the patients, reporting only minimal and transient adverse events, while serious adverse effects were not observed. Despite the growing literature on animal models, only clinical parameters have been investigated in humans and few data are available about biochemical changes induced by ES of the eye. The purpose of this study is to investigate the possible mechanism that regulates the beneficial effects of ES on retinal cells function and survival in humans. 28 patients undergoing pars plana vitrectomy (PPV) for idiopathic epiretinal membrane (iERM) were randomly divided in two groups: 13 patients were treated with transpalpebral ES before surgery and 15 underwent surgery with no prior treatment. Vitreous samples were collected for biochemical analysis during PPV. ES treatment leads to a reduction in the vitreous expression of both proinflammatory cytokines, namely IL-6 and IL-8, and proinflammatory lipid mediators, such as lysophosphatidylcholine. Indeed, we observed a 70% decrease of lysophosphatidylcholine 18:0, which has been proven to exert the greatest proinflammatory activities among the lysophosphatidylcholine class. The content of triglycerides is also affected and significantly decreased following ES application. The vitreous composition of patients undergoing PPV for iERM displays significant changes following ES treatment. Proinflammatory cytokines and bioactive lipid mediators expression decreases, suggesting an overall anti-inflammatory potential of ES. The investigation of the mechanism by which this treatment alters the retinal neurons leading to good outcomes is essential for supporting ES therapeutic application in various types of retinal diseases.

Pemafibrate, A Novel Selective Peroxisome Proliferator-Activated Receptor α Modulator, Reduces Plasma Eicosanoid Levels and Ameliorates Endothelial Dysfunction in Diabetic Mice

Aims: Various pathological processes related to diabetes cause endothelial dysfunction. Eicosanoids derived from arachidonic acid (AA) have roles in vascular regulation. Fibrates have recently been shown to attenuate vascular complications in diabetics. Here we examined the effects of pemafibrate, a selective peroxisome proliferator-activated receptor α modulator, on plasma eicosanoid levels and endothelial function in diabetic mice.

Methods: Diabetes was induced in 7-week-old male wild-type mice by a single injection of streptozotocin (150 mg/kg). Pemafibrate (0.3 mg/kg/day) was administered orally for 3 weeks. Untreated mice received vehicle. Circulating levels of eicosanoids and free fatty acids were measured using both gas and liquid chromatography-mass spectrometry. Endothelium-dependent and endothelium-independent vascular responses to acetylcholine and sodium nitroprusside, respectively, were analyzed.

Results: Pemafibrate reduced both triglyceride and non-high-density lipoprotein-cholesterol levels ( P ＜0.01), without affecting body weight. It also decreased circulating levels of AA ( P ＜0.001), thromboxane B ₂ ( P ＜0.001), prostaglandin E ₂ , leukotriene B ₄ ( P ＜0.05), and 5-hydroxyeicosatetraenoic acid ( P ＜0.001), all of which were elevated by the induction of diabetes. In contrast, the plasma levels of 15-deoxy-Δ ^12,14 -prostaglandin J ₂ , which declined following diabetes induction, remained unaffected by pemafibrate treatment. In diabetic mice, pemafibrate decreased palmitic acid (PA) and stearic acid concentrations ( P ＜0.05). Diabetes induction impaired endothelial function, whereas pemafibrate ameliorated it ( P ＜0.001). The results of ex vivo experiments indicated that eicosanoids or PA impaired endothelial function.

Conclusion: Pemafibrate diminished the levels of vasoconstrictive eicosanoids and free fatty acids accompanied by a reduction of triglyceride. These effects may be associated with the improvement of endothelial function by pemafibrate in diabetic mice.

Eicosanoid Profiles in the Vitreous Humor of Patients with Proliferative Diabetic Retinopathy

Proliferative diabetic retinopathy is a potentially blinding sequela of uncontrolled diabetes that involves a complex interaction of pro-angiogenic and inflammatory pathways. In this study, we compared the levels of pro-angiogenic arachidonic acid-derived mediators in human vitreous humor obtained from eyes with high-risk proliferative diabetic retinopathy versus controls. The results indicated that lipoxygenase and cytochrome P450-derived eicosanoids were elevated (5-HETE, 12-HETE, 20-HETE, and 20-COOH-AA), and there appeared to be no differences in levels measured in eyes with tractional retinal detachments versus those without. These results provide further insight into the pathogenesis of this disease and for the development of future potential therapeutic agents that target arachidonic acid metabolites to treat diabetic retinopathy.

Circulating Metabolites and Lipids Are Associated to Diabetic Retinopathy in Individuals With Type 1 Diabetes

Omics-based methods may provide new markers associated to diabetic retinopathy (DR). We investigated a wide omics panel of metabolites and lipids related to DR in type 1 diabetes. Metabolomic analyses were performed using two-dimensional gas chromatography with time-of-flight mass spectrometry and lipidomic analyses using an ultra-high-performance liquid chromatography quadruple time-of-flight mass spectrometry method in 648 individuals with type 1 diabetes. Subjects were subdivided into no DR, mild nonproliferative DR (NPDR), moderate NPDR, proliferative DR, and proliferative DR with fibrosis. End points were any progression of DR, onset of DR, and progression from mild to severe DR tracked from standard ambulatory care and investigated using Cox models. The cohort consisted of 648 participants aged a mean of 54.4 ± 12.8 years, 55.5% were men, and follow-up was 5.1-5.5 years. Cross-sectionally, 2,4-dihydroxybutyric acid (DHBA), 3,4-DHBA, ribonic acid, ribitol, and the triglycerides 50:1 and 50:2 significantly correlated (P < 0.042) to DR stage. Longitudinally, higher 3,4-DHBA was a risk marker for progression of DR (n = 133) after adjustment (P = 0.033). We demonstrated multiple metabolites being positively correlated to a higher grade of DR in type 1 diabetes and several triglycerides being negatively correlated. Furthermore, higher 3,4-DHBA was an independent risk marker for progression of DR; however, confirmation is required.

Eicosanoids and Oxidative Stress in Diabetic Retinopathy

Oxidative stress is an important factor to cause the pathogenesis of diabetic retinopathy (DR) because the retina has high vascularization and long-time light exposition. Cyclooxygenase (COX), lipoxygenase (LOX), and cytochrome P450 (CYP) enzymes can convert arachidonic acid (AA) into eicosanoids, which are important lipid mediators to regulate DR development. COX-derived metabolites appear to be significant factors causative to oxidative stress and retinal microvascular dysfunction. Several elegant studies have unraveled the importance of LOX-derived eicosanoids, including LTs and HETEs, to oxidative stress and retinal microvascular dysfunction. The role of CYP eicosanoids in DR is yet to be explored. There is clear evidence that CYP-derived epoxyeicosatrienoic acids (EETs) have detrimental effects on the retina. Our recent study showed that the renin-angiotensin system (RAS) activation augments retinal soluble epoxide hydrolase (sEH), a crucial enzyme degrading EETs. Our findings suggest that EETs blockade can enhance the ability of RAS blockade to prevent or mitigate microvascular damage in DR. This review will focus on the critical information related the function of these eicosanoids in the retina, the interaction between eicosanoids and reactive oxygen species (ROS), and the involvement of eicosanoids in DR. We also identify potential targets for the treatment of DR.

The association between the rs4987105 of 5-lipoxygenase (ALOX5) gene and gestational glucose metabolism in Chinese population

Objective

The arachidonate 5-lipoxygenase (ALOX5) pathway has been investigated in diverse chronic inflammatory diseases including metabolic disorders. Recently, the ALOX5 polymorphism rs4987105 was identified to confer susceptibility to type 2 diabetes mellitus (T2DM), implicating its role in regulating glucose homeostasis. Gestational diabetes mellitus (GDM) shares similar pathogenic mechanism with T2DM. Thus, we aimed to evaluate the association between rs4987105 and gestational glucose metabolism in Chinese pregnant women.

Results

A total of 380 unrelated Chinese pregnant women including 241 GDM patients and 139 controls were included in this study. The genotypes of rs4987105 were examined by the Agena MassARRAY iPLEX platform, the association between rs4987105 and fasting plasma glucose (FPG) levels at 24–28 gestational weeks was evaluated using different statistical methods. We found that carriers of rs4987105 CT/TT genotypes exhibited significantly lower FPG levels (P = 0.011). In addition, we observed a significant association between rs4987105 and FPG levels after adjusting confounding variables in the linear regression analysis using dominant genetic model (b = − 0.218; P = 0.01). The present study for the first time reported that the rs4987105 of 5-lipoxygenase (ALOX5) gene was associated with gestational glucose metabolism in Chinese pregnant women.

Fair-Weather Friends: Evidence of Lipoxin Dysregulation in Neurodegeneration

Lipoxins (LXs) are autacoids, specialized proresolving lipid mediators (SPMs) acting locally in a paracrine or autocrine fashion. They belong to a complex superfamily of dietary small polyunsaturated fatty acid (PUFA)-metabolites, which direct potent cellular responses to resolve inflammation and restore tissue homeostasis. Together, these SPM activities have been intensely studied in systemic inflammation and acute injury or infection, but less is known about LX signaling and activities in the central nervous system. LXs are derived from arachidonic acid, an omega-6 PUFA. In addition to well-established roles in systemic inflammation resolution, they have increasingly become implicated in regulating neuroinflammatory and neurodegenerative processes. In particular, chronic inflammation plays a central role in Alzheimer's disease (AD) etiology, and dysregulated LX production and activities have been reported in a variety of AD rodent models and clinical tissue samples, yet with complex and sometimes conflicting results. In addition, reduced LX production following retinal injury has been reported recently by the authors, and an intriguing direct neuronal activity promoting survival and homeostasis in retinal and cortical neurons is demonstrated. Here, the authors review and clarify this growing literature and suggest new research directions to further elaborate the role of lipoxins in neurodegeneration.

Lipidomic methodologies for biomarkers of chronic inflammation in nutritional research: ω-3 and ω-6 lipid mediators

The evolutionary history of hominins has been characterized by significant dietary changes, which include the introduction of meat eating, cooking, and the changes associated with plant and animal domestication. The Western pattern diet has been linked with the onset of chronic inflammation, and serious health problems including obesity, metabolic syndrome, and cardiovascular diseases. Diets enriched with ω-3 marine PUFAs have revealed additional improvements in health status associated to a reduction of proinflammatory ω-3 and ω-6 lipid mediators. Lipid mediators are produced from enzymatic and non-enzymatic oxidation of PUFAs. Interest in better understanding the occurrence of these metabolites has increased exponentially as a result of the growing evidence of their role on inflammatory processes, control of the immune system, cell signaling, onset of metabolic diseases, or even cancer. The scope of this review has been to highlight the recent findings on: a) the formation of lipid mediators and their role in different inflammatory and metabolic conditions, b) the direct use of lipid mediators as antiinflammatory drugs or the potential of new drugs as a new therapeutic option for the synthesis of antiinflammatory or resolving lipid mediators and c) the impact of nutritional interventions to modulate lipid mediators synthesis towards antiinflammatory conditions. In a second part, we have summarized methodological approaches (Lipidomics) for the accurate analysis of lipid mediators. Although several techniques have been used, most authors preferred the combination of SPE with LC-MS. Advantages and disadvantages of each method are herein addressed, as well as the main LC-MS difficulties and challenges for the establishment of new biomarkers and standardization of experimental designs, and finally to deepen the study of mechanisms involved on the inflammatory response.

TRActional DIabetic reTInal detachment surgery with co-adjuvant intravitreal dexamethasONe implant: the TRADITION STUDY

AIM

Main failure of diabetic tractional retinal detachment (TRD) surgery is the development of proliferative vitreoretinopathy (PVR), causing higher re-detachment rates. We investigated whether the use of dexamethasone (DEX) implant at the end of pars plana vitrectomy (PPV) with silicone oil tamponade might have an impact on these outcomes.

DESIGN

Comparative, nonrandomized, retrospective study.

PARTICIPANTS

A total of 148 eyes from 148 patients that underwent PPV with silicone oil tamponade for diabetic TRD (with DEX implant, n = 52; without DEX implant, n = 96).

METHODS

Consecutive patients' records were reviewed for time between TRD diagnosis and surgery; lens status before surgery and after 6, 12, and 24 months; retina attachment rate after primary PPV; change in postoperative PVR severity; rate of re-detachment at 6, 12, and 24 months; use of IOP lowering treatment after 6, 12, and 24 months; surgery details; intra- and postoperative complications. Correlations between outcome measures, postoperative PVR severity, and re-detachment rates were analyzed.

MAIN OUTCOME MEASURES

Change in postoperative PVR severity and retinal re-detachment rates with and without the adjuvant use of DEX implant.

RESULTS

Retinal re-detachment rates were significantly higher in the group of patients that did not receive DEX implant [11/96 (11.5%) vs. 0/52 (0%), p = 0.049; 11/84 (12.9%) vs. 4/52 (7.7%), p = 0.007; 14/71 (19.7%) vs. 5/52 (10%) p < 0.001 at 6, 12, and 24 months, respectively]. PVR severity correlated with retinal status at 12 and 24 months (p = 0.018 and p = 0.027, respectively). The difference in PVR severity between the two groups was statistically significant at 6, 12, and 24 months (p < 0.001).

CONCLUSIONS

DEX implant at the end of PPV in patients with diabetic TRD improves PVR severity and decreases re-detachment rates. This should be considered as an option in the customized treatment of TRD.

Montelukast Prevents Early Diabetic Retinopathy in Mice

Chronic inflammation and oxidative stress are critical components in the pathogenic cascade of early diabetic retinopathy, characterized by neuronal and vascular degeneration. We investigated pharmacologic inhibition of the proinflammatory leukotriene cascade for therapeutic benefit in early diabetic retinopathy. Using the streptozotocin-induced diabetes mouse model, we administered montelukast, a leukotriene receptor antagonist, and diabetes-related retinal pathology was assessed. Early biochemical and cellular function measures were evaluated at 3 months' diabetes duration and included vascular permeability, superoxide production, leukotriene generation, leukocyte-induced microvascular endothelial cell death, and retinal function by electroretinography. Histopathology assessments at 9 months' diabetes duration included capillary degeneration and retinal ganglion cell loss. Leukotriene receptor antagonism resulted in a significant reduction of early, diabetes-induced retinal capillary leakage, superoxide generation, leukocyte adherence, and leukotriene generation. After 9 months of diabetes, the retinal microvasculature from untreated diabetic mice demonstrated a nearly threefold increase in capillary degeneration compared with nondiabetic mice. Montelukast inhibited the diabetes-induced capillary and neuronal degeneration, whether administered as a prevention strategy, immediately after induction of diabetes, or as an intervention strategy starting at 4.5 months after confirmation of diabetes. Pharmacologic blockade of the leukotriene pathway holds potential as a novel therapy to prevent or slow the development of diabetic retinopathy.

New Lipid Mediators in Retinal Angiogenesis and Retinopathy

Retinal diseases associated with vascular destabilization and the inappropriate proliferation of retinal endothelial cells have major consequences on the retinal vascular network. In extreme cases, the development of hypoxia, the upregulation of growth factors, and the hyper-proliferation of unstable capillaries can result in bleeding and vision loss. While anti-vascular endothelial growth factor therapy and laser retinal photocoagulation can be used to treat the symptoms of late stage disease, there is currently no treatment available that can prevent disease progression. Cytochrome P450 enzymes metabolize endogenous substrates (polyunsaturated fatty acids) to bioactive fatty acid epoxides that demonstrate biological activity with generally protective/anti-inflammatory and insulin-sensitizing effects. These epoxides are further metabolized by the soluble epoxide hydrolase (sEH) to fatty acid diols, high concentrations of which have vascular destabilizing effects. Recent studies have identified increased sEH expression and activity and the subsequent generation of the docosahexaenoic acid-derived diol; 19,20-dihydroxydocosapentaenoic acid, as playing a major role in the development of diabetic retinopathy. This review summarizes current understanding of the roles of cytochrome P450 enzyme and sEH–derived PUFA mediators in retinal disease.

Human vitreous in proliferative diabetic retinopathy: Characterization and translational implications

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

Analysis of sphingolipid composition in human vitreous from control and diabetic individuals

OBJECTIVE

Sphingolipids have a fundamental role in many cellular processes, and they have been implicated in insulin resistance and Diabetes Mellitus (DM) and its complications, including diabetic retinopathy (DR). Little is known about how bioactive sphingolipids relate to retinopathies in human DM. In this study, we analyzed the sphingolipid composition of type 2 diabetic (T2DM) and non-diabetic human vitreous samples.

METHODS

We conducted an observational study on post-mortem human vitreous samples from non-diabetic (Controls; n = 4; age: 71.6 ± 11.0 years, mean ± SD) and type 2 diabetic (T2DM; n = 9; age: 67.0 ± 9.2 years) donors to identify changes in sphingolipid composition. Samples were analyzed by a triple quadrupole mass spectrometer and individual sphingolipid species were identified and quantified using established protocols.

RESULTS

The total quantity (pmol/mg) of ceramide (Cer), lactosylceramide (Lac-Cer), and sphingomyelin (SM) were increased in type 2 diabetic vitreous samples. Among individual species, we found a general trend of increase in the longer chain species of ceramides, hexosylceramides (Hex-Cer), Lac-Cer, and SM.

CONCLUSIONS

This study shows the presence of measurable levels of sphingolipids in human vitreous. The results indicate changes in sphingolipid composition in the vitreous due to type 2 diabetes, which could be connected to the disease pathologies of the retina, retinal vessels, vitreous and the surrounding tissues.

5-Lipoxygenase (ALOX5): Genetic susceptibility to type 2 diabetes and vitamin D effects on monocytes

The arachidonate 5-lipoxygenase (ALOX5) pathway has been implicated in chronic inflammatory disease which may be influenced by vitamin D due to vitamin D response elements (VDRE). We investigated an ALOX5 polymorphism (rs4987105) in patients with type 2 diabetes (T2D) and the in vitro effects of calcitriol (1,25(OH)₂D₃) on ALOX5 metabolism in monocytes of T2D patients and healthy controls (HC). 533 T2D and 473 HC were genotyped for the rs4987105 polymorphism. In addition, the 25(OH)D₃ and 1,25(OH)₂D₃ plasma levels were measured in both cohorts. Further C-reactive protein (CRP) was determined in T2D patients. Our results demonstrate, that genotype CC and the allele C of ALOX5 rs4987105 polymorphism were more frequent in T2D compared to HC (OR = 1.44; 95% CI: 1.12-1.84; p < 0.05). Lower levels of both vitamin D metabolites (p < 0.0001 respectively) were found in the CC genotyped T2D patients compared to CC genotyped HC. In addition, CC genotyped T2D patients had higher levels of CRP compared to CT and TT genotyped T2D patients, (p < 0.01). In order to evaluate the impact of calcitriol in primary isolated monocytes, we isolated monocytes of 20 T2D patients and 20 HC. The cells were treated with 1,25(OH)₂D₃ and interleukin-1beta (IL-1β) for 24 h. The following genes were analysed for expression changes: ALOX5, leukotriene A4 hydrolase (LTA4H), leukotriene B4 receptor type 1 (LTB4R1) and CD14. Treatment with IL-1β+1,25(OH)₂D₃ increased ALOX5, LTA4H and LTB4R1 and CD14 mRNA in both T2D patients and HC (p < 0.0001, respectively). In addition, IL-1β+1,25(OH)₂D₃ treatment led to higher ALOX5, LTA4H and CD14 mRNA levels in T2D patients compared to HC (p < 0.001, p < 0.05, p ≤ 0.05, respectively). In conclusion, ALOX5 rs4987105 allele C confers susceptibility to T2D, lower vitamin D metabolites and higher CRP levels complement this association. Additionally, IL-1β+1,25(OH)₂D₃ treatment on, ALOX5, LTA4H and CD14 mRNA indicate a diabetes specific modulation. These findings identify a novel pathway in T2D potentially amenable for individualized therapeutic targeting.

Emerging role of 12/15-Lipoxygenase (ALOX15) in human pathologies

12/15-lipoxygenase (12/15-LOX) is an enzyme, which oxidizes polyunsaturated fatty acids, particularly omega-6 and -3 fatty acids, to generate a number of bioactive lipid metabolites. A large number of studies have revealed the importance of 12/15-LOX role in oxidative and inflammatory responses. The in vitro studies have demonstrated the ability of 12/15-LOX metabolites in the expression of various genes and production of cytokine related to inflammation and resolution of inflammation. The studies with the use of knockout and transgenic animals for 12/15-LOX have further shown its involvement in the pathogenesis of a variety of human diseases, including cardiovascular, renal, neurological and metabolic disorders. This review summarizes our current knowledge on the role of 12/15-LOX in inflammation and various human diseases.

Metabolomics and Age-Related Macular Degeneration

Age-related macular degeneration (AMD) leads to irreversible visual loss, therefore, early intervention is desirable, but due to its multifactorial nature, diagnosis of early disease might be challenging. Identification of early markers for disease development and progression is key for disease diagnosis. Suitable biomarkers can potentially provide opportunities for clinical intervention at a stage of the disease when irreversible changes are yet to take place. One of the most metabolically active tissues in the human body is the retina, making the use of hypothesis-free techniques, like metabolomics, to measure molecular changes in AMD appealing. Indeed, there is increasing evidence that metabolic dysfunction has an important role in the development and progression of AMD. Therefore, metabolomics appears to be an appropriate platform to investigate disease-associated biomarkers. In this review, we explored what is known about metabolic changes in the retina, in conjunction with the emerging literature in AMD metabolomics research. Methods for metabolic biomarker identification in the eye have also been discussed, including the use of tears, vitreous, and aqueous humor, as well as imaging methods, like fluorescence lifetime imaging, that could be translated into a clinical diagnostic tool with molecular level resolution.

Exenatide modulates expression of metalloproteinases and their tissue inhibitors in TNF-α stimulated human retinal pigment epithelial cells

BACKGROUND

Diabetic retinopathy (DR) is one of the most common complications of diabetes and the leading cause of acquired blindness in adults. In diabetic patients hyperglycemia induces complex metabolic abnormalities affecting retinal homeostasis, and promotes retinal inflammation and angiogenesis. Incretin mimetic drugs such exenatide, are a relatively new group of drugs used in the treatment of diabetes. We investigated the potential direct effects of exenatide on human retinal pigment epithelium (HRPE).

METHODS

cAMP production was measured after stimulation of HRPE cells with GLP-1 and exenatide. Intracellular signaling pathways were also examined. HRPE cells were stimulated with TNF-α and subsequently incubated with exenatide. The concentration of metalloproteinases, MMP-1, MMP-2 and MMP-9, and tissue inhibitors of metalloproteinases, TIMP-1, TIMP-2, and TIMP-3 were evaluated. Viability, cytotoxicity and caspase 3/7 activation were determined. Activity of dipeptidyl peptidase-4 (DPP-4), an enzyme involved in GLP-1 inactivation, was also determined.

RESULTS

Both GLP-1 and exenatide stimulation in HRPE cells caused no effect in cAMP levels suggesting alternative signaling pathways. Signaling pathway analysis showed that exenatide reduced phosphorylation of Akt-Ser473, PRAS40, SAPK/JNK, Bad, and S6 proteins but not Akt-Thr308. Exenatide also decreased MMP-1, MMP-9, and TIMP-2 protein levels whereas MMP-2 level in HRPE cells was increased. Finally, we show that exenatide decreased the activity of DPP-4 in TNF-α stimulated HRPE cells.

CONCLUSIONS

These findings indicate that exenatide modulates regulation of extracellular matrix components involved in retinal remodeling.

Assessment of association between lipoxygenase genes variants in elderly Greek population and type 2 diabetes mellitus

BACKGROUND

Inflammation plays a pivotal role in the pathogenesis of diabetes and its complications. Arachidonic acid lipoxygenases have been intensively studied in their role in inflammation in metabolic pathways. Thus, we aimed to explore variants of lipoxygenase genes (arachidonate lipoxygenase genes) in a diabetes adult population using a case-control study design.

METHODS

Study population consisted of 1285 elderly participants, 716 of whom had type 2 diabetes mellitus. The control group consisted of non-diabetes individuals with no history of diabetes history and with a glycated haemoglobin <6.5% (<48 mmol/mol)] and fasting plasma glucose levels <126 mg/dL. Blood samples were genotyped on Illumina Infinium PsychArray. Variants of ALOX5, ALOX5AP, ALOX12, ALOX15 were selected. All statistical analyses were undertaken within PLINK and SPSS packages utilising permutation analysis tests.

RESULTS

Our findings showed an association of rs9669952 (odds ratio = 0.738, p = 0.013) and rs1132340 (odds ratio = 0.652, p = 0.008) in ALOX5AP and rs11239524 in ALOX5 gene with disease (odds ratio = 0.808, p = 0.038). Rs9315029 which is located near arachidonate ALOX5AP also associated with type 2 diabetes mellitus ( p = 0.025). No variant of ALOX12 and ALOX15 genes associated with disease.

CONCLUSION

These results indicate a potential protective role of ALOX5AP and 5-arachidonate lipoxygenase gene in diabetes pathogenesis, indicating further the importance of the relationship between diabetes and inflammation. Larger population studies are required to replicate our findings.

Progression of diabetic retinopathy severity after treatment with dexamethasone implant: a 24-month cohort study the 'DR-Pro-DEX Study'

PURPOSE

Intravitreal anti-vascular endothelial growth factor agents have been shown to reduce diabetic retinopathy (DR) progression; data on the effects of intravitreal corticosteroids on modifying disease severity are limited. This study evaluates the long-term effect of intravitreal dexamethasone implant (DEX) on the severity and progression of non-proliferative DR (NPDR).

METHODS

This was a retrospective cohort study. Sixty eyes from 60 consecutive patients with NPDR and diabetic macular edema (DME) treated with dexamethasone implant (DEX group) and 49 eyes from consecutive 49 patients without DME requiring observation only. Fundus angiography images from baseline and after 24 months were graded by two masked assessors into mild, moderate and severe NPDR and PDR, according to the ETDRS classification. Patients were followed up 1-3 and 4-6 months after each DEX implant. Re-treatment with DEX implant was on a pro re nata basis. Records were reviewed for performance of panretinal photocoagulation. Main outcome was as follows: change of DR ≥ 1 grade and progression to proliferative diabetic retinopathy (PDR).

RESULTS

Three eyes (5%) in the DEX group and 43 (87.8%) eyes in the control group progressed to PDR (P < 0.0001). Twenty-five eyes (41.7%) in the DEX group but none in the control group demonstrated an improvement in DR severity (P < 0.0001).

CONCLUSION

This study provides the first long-term evidence that DEX implant has the potential to not only delay progression of DR and PDR development, but may also improve DR severity over 24 months. Better understanding of the effects of corticosteroids will help guide its use in the treatment pathway of DR.

The dipeptidyl peptidase-4 (DPP-4) inhibitor sitagliptin ameliorates retinal endothelial cell dysfunction triggered by inflammation

Diabetic retinopathy is considered a low-grade chronic inflammatory disease and several inflammatory molecules, including tumor necrosis factor (TNF)-α, are known to play a major role in the degeneration of retinal capillaries. Previous studies have reported that sitagliptin, a DPP-4 inhibitor, prevents the increase in blood-retinal barrier (BRB) permeability and inhibits the tight junction disassembly induced by diabetes.

AIM

Our goal was to investigate whether sitagliptin is able to prevent retinal endothelial cells (EC) dysfunction triggered by the pro-inflammatory cytokine TNF-α.

MAIN METHODS

The effects of TNF-α and/or sitagliptin on primary cultures of bovine retinal EC were tested. The EC monolayer permeability was analyzed by using 70 kDa rhodamine isothiocyanate (RITC) dextran. The cellular distribution profile of claudin-5 was examined by immunofluorescence staining, and DPP-4 activity was evaluated by using a fluorogenic substrate. Cell viability was assessed by MTT assay, and cell proliferation by the BrdU incorporation assay. Retinal EC migration and angiogenesis were evaluated by a scratch assay and a capillary tube formation in matrigel assay, respectively.

KEY FINDINGS

TNF-α increased the permeability of EC monolayer and induced the loss of claudin-5 immunostaining at the cell borders. This impairment was associated with decreased migration and capillary morphogenesis of retinal EC. Sitagliptin was unable to prevent the effect of TNF-α on EC permeability. However, it decreased DPP-4 activity in bovine retinal EC exposed to TNF-α, without affecting cell viability. Moreover, sitagliptin enhanced the migration and capillary morphogenesis in bovine retinal EC challenged with TNF-α.

SIGNIFICANCE

These results suggest that sitagliptin is able to positively modulate vascular EC function under conditions of retinal inflammation.

Recent advances in the applications of metabolomics in eye research

Metabolomics, the identification and quantitation of metabolites in a system, have been applied to identify new biomarkers or elucidate disease mechanism. In this review, we discussed the application of metabolomics in several ocular diseases and recent developments in metabolomics regarding tear fluids analysis, data acquisition and processing.

ω-3 and ω-6 long-chain PUFAs and their enzymatic metabolites in neovascular eye diseases

Neovascular eye diseases, including retinopathy of prematurity, diabetic retinopathy, and age-related macular degeneration, threaten the visual health of children and adults. Current treatment options, including anti-vascular endothelial growth factor therapy and laser retinal photocoagulation, have limitations and are associated with adverse effects; therefore, the identification of additional therapies is highly desirable. Both clinical and experimental studies show that dietary ω-3 (n-3) long-chain polyunsaturated fatty acids (LC-PUFAs) reduce retinal and choroidal angiogenesis. The ω-3 LC-PUFA metabolites from 2 groups of enzymes, cyclooxygenases and lipoxygenases, inhibit [and the ω-6 (n-6) LC-PUFA metabolites promote] inflammation and angiogenesis. However, both of the ω-3 and the ω-6 lipid products of cytochrome P450 oxidase 2C promote neovascularization in both the retina and choroid, which suggests that inhibition of this pathway might be beneficial. This review summarizes our current understanding of the roles of ω-3 and ω-6 LC-PUFAs and their enzymatic metabolites in neovascular eye diseases.

Safety and Feasibility of Quantitative Multiplexed Cytokine Analysis From Office-Based Vitreous Aspiration

Purpose

The goals of this study were to evaluate the safety of office-based vitreous sampling, and determine the utility of these samples with multiplex cytokine analysis.

Methods

Vitreous samples were collected from office-based needle aspiration and the rate of adverse events during follow-up was reviewed. The vitreous cytokine concentrations in a subset of patients with diabetic macular edema (DME) were analyzed using a 42 plex-cytokine bead array. These results were compared with vitreous cytokine concentrations in proliferative diabetic retinopathy (PDR) and controls (macular hole, epiretinal membrane, symptomatic vitreous floaters) from pars plana vitrectomy.

Results

An adequate volume of vitreous fluid (100–200 μL) was obtained in 52 (88%) of 59 office-based sampling attempts. The average length of follow-up was 300 days (range, 42–926 days). There were no complications, including cataract, retinal tear or detachment, and endophthalmitis. Two patients (3%) had posterior vitreous detachments within 3 months. Vitreous cytokine concentrations were measured in 44 patients: 14 controls, 13 with DME, and 17 with PDR. The concentration of ADAM11, CXCL-10, IL-8, and PDGF-A were higher in PDR compared with controls and DME. The concentration of IL-6 was higher in PDR compared with controls, but not compared with DME.

Conclusions

Office-based vitreous aspiration is safe and yields high-quality samples for multiplex vitreous cytokine analysis. Significant elevations of vitreous cytokines were found in PDR compared with DME and controls, including the novel finding of elevated ADAM11. As such, office-based aspiration is a safe and effective means to identify vitreous factors associated with vitreoretinal disease.

Protective Effect of a GLP-1 Analog on Ischemia-Reperfusion Induced Blood-Retinal Barrier Breakdown and Inflammation

Purpose

Inflammation associated with blood–retinal barrier (BRB) breakdown is a common feature of several retinal diseases. Therefore, the development of novel nonsteroidal anti-inflammatory approaches may provide important therapeutic options. Previous studies demonstrated that inhibition of dipeptidyl peptidase-IV, the enzyme responsible for the degradation of glucagon-like peptide-1 (GLP-1), led to insulin-independent prevention of diabetes-induced increases in BRB permeability, suggesting that incretin-based drugs may have beneficial pleiotropic effects in the retina. In the current study, the barrier protective and anti-inflammatory properties of exendin-4 (Ex-4), an analog of GLP-1, after ischemia-reperfusion (IR) injury were examined.

Methods

Ischemia-reperfusion injury was induced in rat retinas by increasing the intraocular pressure for 45 minutes followed by 48 hours of reperfusion. Rats were treated with Ex-4 prior to and following IR. Blood–retinal barrier permeability was assessed by Evans blue dye leakage. Retinal inflammatory gene expression and leukocytic infiltration were measured by qRT-PCR and immunofluorescence, respectively. A microglial cell line was used to determine the effects of Ex-4 on lipopolysaccharide (LPS)-induced inflammatory response.

Results

Exendin-4 dramatically reduced the BRB permeability induced by IR injury, which was associated with suppression of inflammatory gene expression. Moreover, in vitro studies showed that Ex-4 also reduced the inflammatory response to LPS and inhibited NF-κB activation.

Conclusions

The present work suggests that Ex-4 can prevent IR injury–induced BRB breakdown and inflammation through inhibition of inflammatory cytokine production by activated microglia and may provide a novel option for therapeutic intervention in diseases involving retinal inflammation.

Epoxygenated Fatty Acids Inhibit Retinal Vascular Inflammation

The objective of the present study was to assess the effect of elevating epoxygenated fatty acids on retinal vascular inflammation. To stimulate inflammation we utilized TNFα, a potent pro-inflammatory mediator that is elevated in the serum and vitreous of diabetic patients. In TNFα-stimulated primary human retinal microvascular endothelial cells, total levels of epoxyeicosatrienoic acids (EETs), but not epoxydocosapentaenoic acids (EDPs), were significantly decreased. Exogenous addition of 11,12-EET or 19,20-EDP when combined with 12-(3-adamantane-1-yl-ureido)-dodecanoic acid (AUDA), an inhibitor of epoxide hydrolysis, inhibited VCAM-1 and ICAM-1 expression and protein levels; conversely the diol product of 19,20-EDP hydrolysis, 19,20-DHDP, induced VCAM1 and ICAM1 expression. 11,12-EET and 19,20-EDP also inhibited leukocyte adherence to human retinal microvascular endothelial cell monolayers and leukostasis in an acute mouse model of retinal inflammation. Our results indicate that this inhibition may be mediated through an indirect effect on NFκB activation. This is the first study demonstrating a direct comparison of EET and EDP on vascular inflammatory endpoints, and we have confirmed a comparable efficacy from each isomer, suggesting a similar mechanism of action. Taken together, these data establish that epoxygenated fatty acid elevation will inhibit early pathology related to TNFα-induced inflammation in retinal vascular diseases.

Application of multiplex immunoassay technology to investigations of ocular disease

Eye-derived fluids, including tears, aqueous humour and vitreous humour often contain molecular signatures of ocular disease states. These signatures can be composed of cytokines, chemokines, growth factors, proteases and soluble receptors. However, the small quantities (<10 µl) of these fluids severely limit the detection of these proteins by traditional enzyme-linked immunosorbent assay or Western blot. To maximise the amount of information generated from the analysis of these specimens, many researchers have employed multiplex immunoassay technologies for profiling the expression or modification of multiple proteins from minute sample volumes.

Targeting Imbalance between IL-1β and IL-1 Receptor Antagonist Ameliorates Delayed Epithelium Wound Healing in Diabetic Mouse Corneas

Patients with diabetes mellitus often develop corneal complications and delayed wound healing. How diabetes might alter acute inflammatory responses to tissue injury, leading to delayed wound healing, remains mostly elusive. Using a streptozotocin-induced type I diabetes mellitus mice and corneal epithelium-debridement wound model, we discovered that although wounding induced marked expression of IL-1β and the secreted form of IL-1 receptor antagonist (sIL-1Ra), diabetes suppressed the expressions of sIL-1Ra but not IL-1β in healing epithelia and both in whole cornea. In normoglycemic mice, IL-1β or sIL-1Ra blockade delayed wound healing and influenced each other's expression. In diabetic mice, in addition to delayed reepithelization, diabetes weakened phosphatidylinositol 3-kinase-Akt signaling, caused cell apoptosis, diminished cell proliferation, suppressed neutrophil and natural killer cell infiltrations, and impaired sensory nerve reinnervation in healing mouse corneas. Local administration of recombinant IL-1Ra partially, but significantly, reversed these pathological changes in the diabetic corneas. CXCL10 was a downstream chemokine of IL-1β-IL-1Ra, and exogenous CXCL10 alleviated delayed wound healing in the diabetic, but attenuated it in the normal corneas. In conclusion, the suppressed early innate/inflammatory responses instigated by the imbalance between IL-1β and IL-1Ra is an underlying cause for delayed wound healing in the diabetic corneas. Local application of IL-1Ra accelerates reepithelialization and may be used to treat chronic corneal and potential skin wounds of diabetic patients.

Plasma eicosanoid profiles determined by high-performance liquid chromatography coupled with tandem mass spectrometry in stimulated peripheral blood from healthy individuals and sickle cell anemia patients in treatment

Eicosanoids play an important role in homeostasis and in the pathogenesis of various human diseases. Pharmacological agents such as Ca(2+) ionophores and Ca(2+)-ATPase inhibitors, as well as natural agonists such as formylmethionine-leucyl-phenylalanine (fMLP), can stimulate eicosanoid biosynthesis. The aims of this work were to develop a method to determine the eicosanoid profile of human plasma samples after whole blood stimulation and to assess differences between healthy and sick individuals. For this purpose, a liquid chromatography-tandem mass spectrometry (LC-MS/MS) method was partially validated for the quantification of 22 eicosanoids using human plasma from healthy volunteers. In addition, we optimized a method for the stimulation of eicosanoids in human whole blood. LC-MS/MS analyses were performed by negative electrospray ionization and multiple reaction monitoring. An assumption of linearity resulted in a regression coefficient ≥0.98 for all eicosanoids tested. The mean intra-assay and inter-assay accuracy and precision values had relative standard deviations and relative errors of ≤15%, except for the lower limit of quantification, where these values were ≤20%. For whole blood stimulation, four stimuli (fMLP, ionomycin, A23187, and thapsigargin) were tested. Results of the statistical analysis showed that A23187 and thapsigargin were potent stimuli for the production or liberation of eicosanoids. We next compared the eicosanoid profiles of stimulated whole blood samples of healthy volunteers to those of patients with sickle cell anemia (SCA) under treatment with hydroxyurea (HU) or after chronic red blood cell (RBC) transfusion. The results indicate that the method was sufficient to find a difference between lipid mediators released in whole blood of SCA patients and those of healthy subjects, mainly for 5-HETE, 12-HETE, LTB4, LTE4, TXB2, and PGE2. In conclusion, our analytical method can detect significant changes in eicosanoid profiles in stimulated whole blood, which will contribute to establishing the eicosanoid profiles associated with different inflammatory and infectious diseases.

ANGPTL-4 correlates with vascular endothelial growth factor in patients with proliferative diabetic retinopathy

PURPOSE

To investigate the relationship between angiopoietin-like protein 4 (ANGPTL-4) and vascular endothelial growth factor (VEGF) in the serum and vitreous of eyes in patients with proliferative diabetic retinopathy (PDR).

METHODS

Thirty-five eyes of 35 patients with PDR, 20 eyes of 20 patients with non-proliferative diabetic retinopathy, 20 eyes of 20 patients with diabetes but no diabetic retinopathy, and 14 eyes of 14 nondiabetic patients with an idiopathic macular hole (IMH) were recruited from Shanghai First People's Hospital. The ANGPTL-4 and VEGF concentrations were determined using enzyme-linked immunosorbent assays. Group means were compared using one-way analysis of variance with GraphPad Prism 4.0 and SPSS ver. 17.0. The research followed the tenets of the Declaration of Helsinki.

RESULTS

The ANGPTL-4 and VEGF levels were significantly higher in the vitreous and serum of patients with PDR compared with patients with IMH. There were significant correlations between the ANGPTL-4 and VEGF levels in the vitreous and serum of patients with PDR. The vitreous and serum ANGPTL-4 levels were also significantly correlated in patients with PDR. The ANGPTL-4 in both the vitreous and serum correlated with the serum triglyceride and high-density lipoprotein cholesterol levels.

CONCLUSIONS

The ANGPTL-4 levels were markedly elevated and the ANGPTL-4 expression was directly correlated with the VEGF expression in the vitreous and serum of patients with PDR. The vitreous and serum ANGPTL-4 levels were also significantly correlated with serum lipids in patients with PDR. Our results suggest that the ANGPTL-4 may be used as a new therapeutic target for the treatment of PDR.

Lipidomics to Assess Omega 3 Bioactivity

How can we resolve the conflict between the strong epidemiological evidence pointing to the usefulness of fish—and, thus, omega 3—consumption with the debacle of supplementation trials? One potential explanation is that the null results obtained thus far are the consequences of ill-contrived investigations that do not allow us to conclude on the effects (or lack thereof) of omega 3 fatty acid supplementation. One potential solution is through the use of lipidomics, which should prove very useful to screen suitable patients and to correlate plasma (or red blood cells, or whole blood, or phospholipid) fatty acid profile with outcomes. This has never been done in omega 3 trials. The wise use of lipidomics should be essential part of future omega 3 trials and would help in untangling this current riddle.