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1.
Pyroptosis in the Retinal Neurovascular Unit: New Insights Into Diabetic Retinopathy.
Meng, C, Gu, C, He, S, Su, T, Lhamo, T, Draga, D, Qiu, Q
Frontiers in immunology. 2021;:763092
Abstract
Diabetic retinopathy (DR) is prevalent among people with long-term diabetes mellitus (DM) and remains the leading cause of visual impairment in working-aged people. DR is related to chronic low-level inflammatory reactions. Pyroptosis is an emerging type of inflammatory cell death mediated by gasdermin D (GSDMD), NOD-like receptors and inflammatory caspases that promote interleukin-1β (IL-1β) and IL-18 release. In addition, the retinal neurovascular unit (NVU) is the functional basis of the retina. Recent studies have shown that pyroptosis may participate in the destruction of retinal NVU cells in simulated hyperglycemic DR environments. In this review, we will clarify the importance of pyroptosis in the retinal NVU during the development of DR.
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2.
Cell-Matrix Interactions in the Eye: From Cornea to Choroid.
Pouw, AE, Greiner, MA, Coussa, RG, Jiao, C, Han, IC, Skeie, JM, Fingert, JH, Mullins, RF, Sohn, EH
Cells. 2021;(3)
Abstract
The extracellular matrix (ECM) plays a crucial role in all parts of the eye, from maintaining clarity and hydration of the cornea and vitreous to regulating angiogenesis, intraocular pressure maintenance, and vascular signaling. This review focuses on the interactions of the ECM for homeostasis of normal physiologic functions of the cornea, vitreous, retina, retinal pigment epithelium, Bruch's membrane, and choroid as well as trabecular meshwork, optic nerve, conjunctiva and tenon's layer as it relates to glaucoma. A variety of pathways and key factors related to ECM in the eye are discussed, including but not limited to those related to transforming growth factor-β, vascular endothelial growth factor, basic-fibroblastic growth factor, connective tissue growth factor, matrix metalloproteinases (including MMP-2 and MMP-9, and MMP-14), collagen IV, fibronectin, elastin, canonical signaling, integrins, and endothelial morphogenesis consistent of cellular activation-tubulogenesis and cellular differentiation-stabilization. Alterations contributing to disease states such as wound healing, diabetes-related complications, Fuchs endothelial corneal dystrophy, angiogenesis, fibrosis, age-related macular degeneration, retinal detachment, and posteriorly inserted vitreous base are also reviewed.
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Baicalein, Baicalin, and Wogonin: Protective Effects against Ischemia-Induced Neurodegeneration in the Brain and Retina.
Pan, L, Cho, KS, Yi, I, To, CH, Chen, DF, Do, CW
Oxidative medicine and cellular longevity. 2021;:8377362
Abstract
Ischemia is a common pathological condition present in many neurodegenerative diseases, including ischemic stroke, retinal vascular occlusion, diabetic retinopathy, and glaucoma, threatening the sight and lives of millions of people globally. Ischemia can trigger excessive oxidative stress, inflammation, and vascular dysfunction, leading to the disruption of tissue homeostasis and, ultimately, cell death. Current therapies are very limited and have a narrow time window for effective treatment. Thus, there is an urgent need to develop more effective therapeutic options for ischemia-induced neural injuries. With emerging reports on the pharmacological properties of natural flavonoids, these compounds present potent antioxidative, anti-inflammatory, and antiapoptotic agents for the treatment of ischemic insults. Three major active flavonoids, baicalein, baicalin, and wogonin, have been extracted from Scutellaria baicalensis Georgi (S. baicalensis); all of which are reported to have low cytotoxicity. They have been demonstrated to exert promising pharmacological capabilities in preventing cell and tissue damage. This review focuses on the therapeutic potentials of these flavonoids against ischemia-induced neurotoxicity and damage in the brain and retina. The bioactivity and bioavailability of baicalein, baicalin, and wogonin are also discussed. It is with hope that the therapeutic potential of these flavonoids can be utilized and developed as natural treatments for ischemia-induced injuries of the central nervous system (CNS).
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Congenital stationary night blindness: an update and review of the disease spectrum in Saudi Arabia.
Almutairi, F, Almeshari, N, Ahmad, K, Magliyah, MS, Schatz, P
Acta ophthalmologica. 2021;(6):581-591
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Abstract
Congenital stationary night blindness (CSNB) is a group of rare, mainly stationary disorders of the retina, resulting from dysfunction of several specific and essential visual processing mechanisms. The inheritance is often recessive and as such, CSNB may be more common among populations with a high degree of consanguinity. Here, we present a topic update and a review of the clinical and molecular genetic spectrum of CSNB in Saudi Arabia. Since a major review article on CSNB in 2015, which described 17 genes underlying CSNB, an additional four genes have been incriminated in autosomal recessive CSNB RIMS2, GNB3, GUCY2D and ABCA4. These have been associated with syndromic cone-rod synaptic disease, ON bipolar cell dysfunction with reduced cone sensitivity, CSNB with dysfunction of the phototransduction (Riggs type) and CSNB with cone-rod dystrophy, respectively. In Saudi Arabia, a total of 24 patients with CSNB were identified, using a combination of literature search and retrospective study of previously unpublished cases. Recessive mutations in TRPM1 and CABP4 accounted for the majority of cases (5 and 13 for each gene, respectively). These genes were associated with complete (cCSNB) and incomplete (icCSNB), respectively, and were associated with high myopia in the former and hyperopia in the latter. Four novel mutations were identified. For the first time, we describe the fundus albipunctatus in two patients from Saudi Arabia, caused by recessive mutation in RDH5 and RPE65, where the former in addition featured findings compatible with cone dystrophy. No cases were identified with any dominantly inherited CSNB.
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VEGFR1 signaling in retinal angiogenesis and microinflammation.
Uemura, A, Fruttiger, M, D'Amore, PA, De Falco, S, Joussen, AM, Sennlaub, F, Brunck, LR, Johnson, KT, Lambrou, GN, Rittenhouse, KD, et al
Progress in retinal and eye research. 2021;:100954
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Abstract
Five vascular endothelial growth factor receptor (VEGFR) ligands (VEGF-A, -B, -C, -D, and placental growth factor [PlGF]) constitute the VEGF family. VEGF-A binds VEGF receptors 1 and 2 (VEGFR1/2), whereas VEGF-B and PlGF only bind VEGFR1. Although much research has been conducted on VEGFR2 to elucidate its key role in retinal diseases, recent efforts have shown the importance and involvement of VEGFR1 and its family of ligands in angiogenesis, vascular permeability, and microinflammatory cascades within the retina. Expression of VEGFR1 depends on the microenvironment, is differentially regulated under hypoxic and inflammatory conditions, and it has been detected in retinal and choroidal endothelial cells, pericytes, retinal and choroidal mononuclear phagocytes (including microglia), Müller cells, photoreceptor cells, and the retinal pigment epithelium. Whilst the VEGF-A decoy function of VEGFR1 is well established, consequences of its direct signaling are less clear. VEGFR1 activation can affect vascular permeability and induce macrophage and microglia production of proinflammatory and proangiogenic mediators. However the ability of the VEGFR1 ligands (VEGF-A, PlGF, and VEGF-B) to compete against each other for receptor binding and to heterodimerize complicates our understanding of the relative contribution of VEGFR1 signaling alone toward the pathologic processes seen in diabetic retinopathy, retinal vascular occlusions, retinopathy of prematurity, and age-related macular degeneration. Clinically, anti-VEGF drugs have proven transformational in these pathologies and their impact on modulation of VEGFR1 signaling is still an opportunity-rich field for further research.
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The Role of Small Molecules and Their Effect on the Molecular Mechanisms of Early Retinal Organoid Development.
Wagstaff, EL, Heredero Berzal, A, Boon, CJF, Quinn, PMJ, Ten Asbroek, ALMA, Bergen, AA
International journal of molecular sciences. 2021;(13)
Abstract
Early in vivo embryonic retinal development is a well-documented and evolutionary conserved process. The specification towards eye development is temporally controlled by consecutive activation or inhibition of multiple key signaling pathways, such as the Wnt and hedgehog signaling pathways. Recently, with the use of retinal organoids, researchers aim to manipulate these pathways to achieve better human representative models for retinal development and disease. To achieve this, a plethora of different small molecules and signaling factors have been used at various time points and concentrations in retinal organoid differentiations, with varying success. Additions differ from protocol to protocol, but their usefulness or efficiency has not yet been systematically reviewed. Interestingly, many of these small molecules affect the same and/or multiple pathways, leading to reduced reproducibility and high variability between studies. In this review, we make an inventory of the key signaling pathways involved in early retinogenesis and their effect on the development of the early retina in vitro. Further, we provide a comprehensive overview of the small molecules and signaling factors that are added to retinal organoid differentiation protocols, documenting the molecular and functional effects of these additions. Lastly, we comparatively evaluate several of these factors using our established retinal organoid methodology.
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Management strategy and novel ophthalmological findings in neonatal severe hypertriglyceridemia: a case report and literature review.
El-Koofy, NM, Abdo, YA, El-Fayoumi, D, Esmael, AF, Elmonem, MA, Ezzeldin, Z
Lipids in health and disease. 2021;(1):38
Abstract
BACKGROUND Neonatal severe hypertriglyceridemia is rarely reported in the literature and there is no consensus for hypertriglyceridemia management at this age group. METHODS The index case is a 4-week-old male infant with severe hypertriglyceridemia accidentally discovered during a circumcision surgery. His clinical and genetic characteristics and his successful management strategy are described. Furthermore, a detailed ophthalmological examination of the proband was conducted at 3 and 6 months of age using Fourier-domain-optical coherence tomography. RESULTS Triglycerides level at presentation was extremely high 33,727 mg/dL (380.8 mmol/L). Two sessions of exchange blood transfusion on two consecutive days successfully reduced triglycerides to 382 mg/dL (4.3 mmol/L) with no adverse effects. The infant was discharged 3 days later. At discharge, the mother was advised to continue breastfeeding together with a medium-chain triglycerides formula. Satisfactory growth parameters and lipid profile values were obtained for a follow-up duration of 5 months with no reported attacks of acute pancreatitis. Lipoprotein lipase deficiency was confirmed by the detection of the LPL homozygous pathogenic variant c.805G > A; p.(Glu269Lys). Early corneal and macular lesions were detected and persisted on follow-up despite relatively good lipemic control. CONCLUSION This case highlights the importance of the early discovery of severe hypertriglyceridemia during the neonatal period, which is needed for prompt management and prevention of severe complications. Rationalized breastfeeding can be tolerated within the diet plan of the disease with satisfactory outcomes. To our knowledge, it is the first study reporting early corneal and macular affection by severe hypertriglyceridemia in a neonate. Prolonged follow-up is needed to determine the extent of ophthalmological lesions.
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The Diabetic Retinopathy Clinical Research Network (DRCR.net) and Its Contributions to the Treatment of Diabetic Retinopathy.
Sun, JK, Jampol, LM
Ophthalmic research. 2019;(4):225-230
Abstract
Over the past two decades, the Diabetic Retinopathy Clinical Research Network (now known as the DRCR Retina Network) has contributed to multiple and substantial advances in the clinical care of diabetic eye disease. Network studies helped establish anti-vascular endothelial growth factor (VEGF) agents as an effective alternative to panretinal photocoagulation for eyes with proliferative diabetic retinopathy (PDR) and as first-line therapy for eyes with visual impairment for diabetic macular edema (DME), defined treatment algorithms for the use of intravitreal medications in these conditions, and provided critical data to understand how to better evaluate the diabetic eye using optical coherence tomography and other imaging modalities. Ongoing DRCR.net studies will address whether anti-VEGF therapy is effective at preventing vision-threatening complications in eyes with severe non-proliferative diabetic retinopathy, if photobiomodulation has a beneficial effect in eyes with DME, and whether initiation of DME treatment with bevacizumab and rescue with aflibercept can provide visual outcomes as good as those achieved with aflibercept alone. Future plans for the Network also include the expansion into non-diabetic eye disease in areas such as age-related macular degeneration.
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Mechanisms enhancing the protective functions of macular xanthophylls in the retina during oxidative stress.
Widomska, J, Subczynski, WK
Experimental eye research. 2019;:238-246
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Abstract
Macular xanthophylls (MXs) are distinguished from other dietary carotenoids by their high membrane solubility and preferential transmembrane orientation. Additionally, these properties enhance the chemical and physical stability of MXs in the eye retina, and maximize their protective activities. The effectiveness of MXs' protection is also enhanced by their selective accumulation in the most vulnerable domains of retinal membranes. The retina is protected by MXs mainly through blue-light filtration, quenching of the excited triplet states of potent photosensitizers, and physical quenching of singlet oxygen. To perform these physical, photo-related actions, the structure of MXs should remain intact. However, the conjugated double-bond structure of MXs makes them highly chemically reactive and susceptible to oxidation. Chemical quenching of singlet oxygen and scavenging of free radicals destroy their intact structure and consume MXs. Consequently, their physical actions, which are critical to the protection of retina, are diminished. Thus, it is timely and important to identify mechanisms whereby the chemical destruction (bleaching) of MXs in retinal membranes can be reduced. It was shown that nitroxide free radicals (spin labels) located in membranes protect MXs against destruction, and their effect is especially pronounced during the light-induced formation of singlet oxygen. That should extend and enhance their positive action in the retina through physical processes. In this review, we will discuss possible applications of this new strategy during ophthalmological procedures, which can cause acute bleaching of MXs and damage the retina through oxidative processes.
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Update on Screening for Sight-Threatening Diabetic Retinopathy.
Scanlon, PH
Ophthalmic research. 2019;(4):218-224
Abstract
PURPOSE The aim of this article was to describe recent advances in the use of new technology in diabetic retinopathy screening by looking at studies that assessed the effectiveness and cost-effectiveness of these technologies. METHODS The author conducts an ongoing search for articles relating to screening or management of diabetic retinopathy utilising Zetoc with keywords and contents page lists from relevant journals. RESULTS The areas discussed in this article are reference standards, alternatives to digital photography, area of retina covered by the screening method, size of the device and hand-held cameras, mydriasis versus non-mydriasis or a combination, measurement of distance visual acuity, grading of images, use of automated grading analysis and cost-effectiveness of the new technologies. CONCLUSIONS There have been many recent advances in technology that may be adopted in the future by screening programmes for sight-threatening diabetic retinopathy but each device will need to demonstrate effectiveness and cost-effectiveness before more widespread adoption.