Occlusion Of Retinal Capillaries Research Articles

R-(+)-WIN55212-2 protects pericytes from ischemic damage and restores retinal microcirculatory patency after ischemia/reperfusion injury

Background and purposeCannabinoids are vasoactive substances that act as key regulators of arterial tone in the blood vessels supplying peripheral tissues and the central nervous system. This study aimed to investigate the potential of R-(+)-WIN55212-2 (WIN), a cannabinoid receptor 1 agonist (CB1), as a treatment for retinal ischemia/reperfusion (I/R) injury. Experimental approachMale Wistar rats were subjected to retinal I/R injury by increasing intraocular pressure in the anterior chamber. The rats were randomly divided into four groups: normal control, I/R, vehicle (pre-treated with dimethyl sulfoxide [DMSO] via intraperitoneal injection), and experimental (pre-treated with WIN at a dose of 1 ml/kg via intraperitoneal injection). The rats were sacrificed at different time points of reperfusion (1 hour, 3 hours, 6 hours, and 1 day) after inducing retinal I/R injury, and their retinas were collected for analysis. Oxygen-glucose deprived/reperfusion (OGD/R) was performed by initially perfusing the retinas with oxygenated artificial cerebrospinal fluid (ACSF), then switching to an OGD solution to simulate ischemia, followed by another perfusion with ACSF. Pericyte contraction and the "no-reflow" phenomenon were observed using infrared differential interference contrast (IR-DIC) microscopy and immunohistochemistry. Western blot, enzyme-linked immunosorbent assay (ELISA), and nitric oxide (NO) detection were used to explore the potential mechanism. Key resultsIn both the OGD/R and I/R models, retinal pericytes exhibited persistent contraction even after reperfusion. The ability of WIN to regulate the tone of retinal pericytes and capillaries was specifically blocked by the BKCa inhibitor iberiotoxin (100 nM). WIN demonstrated a protective effect against retinal I/R injury by preserving blood flow in vessels containing pericytes. Pretreatment with WIN alleviated the persistent contraction and apoptosis of retinal pericytes in I/R-induced rats, accompanied by a reduction in intracellular calcium ion (Ca2+) concentration. The expression of CB1 decreased in a time-dependent manner in the I/R group. After I/R injury, endothelium-derived nitric oxide (eNOS) levels were reduced at all time points, which was successfully reversed by WIN therapy except for the 1 day group. Additionally, the downregulation of cyclic guanosine monophosphate (cGMP) and BKCa expression at 3 hours, 6 hours, and 1 day after I/R injury was restored by pretreatment of WIN. Conclusions & implicationsWIN exerted its protective effects on retinal I/R injury by inhibiting the contraction and apoptosis of pericytes through the CB1-eNOS-cGMP-BKCa signaling pathway, thus ameliorated the occlusion of retinal capillaries.

The changes of retinal capillary after anti-vascular endothelial growth factor therapy in patients with macular edema associated with retinal vein occlusion

At present, intravitreal injections of anti-VEGF agents is the main method for the treatment of macular edema secondary to retinal vein occlusion (RVO), which can significantly inhibit neovascularization, release macular edema and improve the vision of patients. However, VEGF is a survival factor of vascular endothelial cells, whether it can lead to the progress of retinal ischemia and it has an effect on retinal capillaries deserves our clinical attention. Most scholars currently think that the anti-VEGF agents will not aggravate the occlusion of retinal capillaries in the treatment of macular edema secondary to RVO from the aspects of the changes of perifoveal capillary arcade, the quantification of foveal avascular zone area, retinal nonperfusion area and retinal vascular density of the superficial and deep capillary plexus In addition, the changes of these indicators may be related to the number of times patients need treatment, visual prognosis and so on. In the future, with the gradual popularization of OCT angiography and the prolongation of the number and time of anti VEGF drug treatment, we look forward to the study of larger samples and longer follow-up time to further analyze the influence of the retinal capillary after anti-VEGF therapy in patients with macular edema associated with RVO. Key words: Retinal vein occlusion/complications; Macular edema/drug therapy; Angiogenesis inhibitors/therapeutic use; Capillaries; Review

Dietary Compound Chrysin Inhibits Retinal Neovascularization with Abnormal Capillaries in db/db Mice.

Diabetic retinopathy (DR) develops in a significant proportion of patients with chronic diabetes, characterized by retinal macular edema and abnormal retinal vessel outgrowth leading to vision loss. Chrysin, a naturally-occurring flavonoid found in herb and honeycomb, has anti-inflammatory, antioxidant, and anti-cancer properties. This study sought to determine the protective effects of chrysin on retinal neovascularization with abnormal vessels and blood-retinal barrier (BRB) breakdown in 33 mM glucose-exposed human retinal endothelial cells and in db/db mouse eyes. High glucose caused retinal endothelial apoptotic injury, which was inhibited by submicromolar chrysin. This compound diminished the enhanced induction of HIF-1α, vascular endothelial growth factor (VEGF), and VEGF receptor-2 (VEGFR2) in high glucose-exposed retinal endothelial cells. Consistently, oral administration of 10 mg/kg chrysin reduced the induction of these proteins in db/db mouse eye tissues. In addition, chrysin restored the decrement of VE-cadherin and ZO-1 junction proteins and PECAM-1 in hyperglycemia-stimulated retinal endothelial cells and diabetic mouse retina, possibly maintaining tight cell-cell interactions of endothelial cells and pericytes. Anti-apoptotic chrysin reduced the up-regulation of Ang-1, Ang-2, and Tie-2 crucial to retinal capillary occlusion and BRB permeability. Furthermore, orally treating chrysin inhibited acellular capillary formation, neovascularization, and vascular leakage observed in diabetic retinas. These observations demonstrate, for the first time, that chrysin had a capability to encumber diabetes-associated retinal neovascularization with microvascular abnormalities and BRB breakdown.

Occlusion of retinal capillaries caused by glial cell proliferation in chronic ocular inflammation.

The inner blood-retinal barrier is a gliovascular unit in which glial cells surround capillary endothelial cells and regulate retinal capillaries by paracrine interactions. During chronic ocular inflammation, microvascular complications can give rise to vascular proliferative lesions, which compromise visual acuity. This pathologic remodelling caused by proliferating Müller cells determines occlusion of retinal capillaries. The aim of the present study was to identify qualitative and quantitative alterations in the retinal capillaries in patients with post-traumatic chronic ocular inflammation or post-thrombotic vascular glaucoma. Moreover, we investigated the potential role of vascular endothelial growth factor (VEGF) and pro-inflammatory cytokines in retinal inflammation. Our electron microscopy findings demonstrated that during chronic ocular inflammation, thickening of the basement membrane, loss of pericytes and endothelial cells and proliferation of Müller cells occur with irreversible occlusion of retinal capillaries. Angiogenesis takes place as part of a regenerative reaction that results in fibrosis. We believe that VEGF and pro-inflammatory cytokines may be potential therapeutic targets in the treatment of this disease although further studies are required to confirm these findings.

Intravitreal autologous bone marrow‐derived mononuclear cell transplantation: a feasibility report

To report on the feasibility and safety of an intravitreal injection of mononuclear cells derived from autologous bone marrow. A 43-year-old patient with very advanced atrophy of the retina and optic nerve caused by diabetic retinopathy had undergone pars plana vitrectomy with silicone oil endotamponade. Despite complete retinal attachment, vision was limited to defective light perception as a result of retinal capillary occlusion. As an ultima ratio, the patient underwent an intravitreal injection of autologous bone marrow-derived stem cells obtained by isolating mononuclear cells from 100 ml of bone marrow. On postoperative day 1, a cluster of injected cells was observed on the retinal surface in the inferior fundus periphery. The anterior chamber was completely filled with silicone oil, which was released transcorneally. Subsequently, intraocular pressure remained normal and the anterior chamber was free of inflammatory cells or flare. Within 1 week of the injection, visual acuity remained at light perception. There were no signs of any side-effects of the therapy, such as inflammation or infection. Intravitreal autologous bone marrow mononuclear cell transplantation is technically feasible.

Retinal Microvascular Patency in the Diabetic Rat

To study whether the patency to erythrocytes in retinal microvessels of diabetic rats is reduced or blocked before the vessels lose their patency to plasma flow. We used recognized techniques to induce diabetic and galactose related microvascular retinal lesions in rats: (1) alloxan induction (2) streptozotocin induction (3) galactose-containing diet. The rats were followed up to 17 months. We used our vascular trichrome technique to observe the effects of the ongoing diabetes on the retinal microcirculation. A focal leakage of a plasma-borne fluorescent dye was noted around the junction of the deep retinal capillaries and the ascending venules to the superficial retinal circulation in the streptozotocin and alloxan diabetic rats by the 14th month, and, by the 16th month, retinal capillary non-perfusion and retinal vascular malformations were present. The affected vessels showed patency to microspheres (0.2 microm in diameter) but no perfusion of erythrocytes. No such changes were seen in the galactose-fed rats. (1) The location between the deep retinal capillary net and the ascending venules may be the site of early vascular leakage in the diabetic rat model, (2) the erythrocytes' passage in the affected retinal microcirculation was blocked before the development of complete blockage to plasma in diabetic rats. The logical assumption that during the development stage of retinal capillary occlusion there may be a transient stage of microvascular insufficiency was examined. The lathyrogen, imino-diproprionitrile (IDPN), had previously been effective for creating a fast-developing model of retinal vasculopathy. Using that model, we demonstrated a stage in which the retinal microvasculature was blocked to erythrocytes but not to plasma [1]. However, we questioned the applicability of our findings to more slowly developing microvasculopathies, such as diabetic retinopathy. We designed the current study to examine the presence of such stage in slowly developing microvasculopathy. Animal models that are known to induce "diabetic retinopathy-like" changes used [2-4]. The diabetic animals were followed for a period of 17 months. Starting at the 12th month, a few animals of each group were killed and the retains were examined with our trichrome method [1] for relative capillary patency to erythrocytes and plasma, for functionality of endothelial cells, and for disturbances in the blood-retinal barrier. The results of this study support the hypothesis that retinal microvascular insufficiency does exist as a temporary stage that precedes the development of complete capillary blockage in long-term developing rat models of diabetic retinopathy.

Ocular Manifestations in Dengue Fever

Purpose: To report a case of Dengue fever resulting in permanent visual loss in both eyes due to retinal capillary occlusion. Methods: Case report. Results: Severe permanent visual loss occurred in a patient with Dengue fever. Dilated fundus exam showed vascular sheathing with associated retinal hemorrhages at the equator and cotton wool spots in the maculae of both eyes. Fluorescein angiography revealed areas of capillary nonperfusion at the equator and in the macula. The diagnosis of Dengue fever was confirmed by serology detecting IgM antibodies to the Dengue virus. Conclusion: Ocular abnormalities may be seen in patients with Dengue fever, therefore ophthalmoscopy should be performed in patients presenting with severe forms of the disease.

Indocyanine green-mediated photothrombosis as a new technique of treatment for persistent central serous chorioretinopathy

Purpose. To evaluate the potential benefit and complications of indocyanine green-mediated photothrombosis (IMP) in the management of patients with persistent central serous chorioretinopathy (CSC). Methods. Interventional noncomparative case series. Eleven patients with CSC presenting with persistent subretinal fluid in optical coherence tomography (OCT) four months after presentation and decrease in visual acuity (VA) were submitted to a single IMP session with 2 mg/kg body weight ICG and application of 5.6 W/cm 2 light at 810 nm. A continuous follow-up was provided with best-corrected ETDRS VA assessment, and angiographic and OCT documentation 72 hours before and at 2 days, 1 and 2 weeks, 1, 3, 6, and 12 months after treatment. Results. Pretreatment VA levels ranged from 20/32 - 1 to 20/100 (mean, 20/63 + 2 [logMAR equivalent, 0.460 ±0.155]); post treatment levels ranged from 20/25 - 2 to 20/20 (mean, 20/20 - 2 [logMAR equivalent, 0.038 ± 0.048]). Ten out of eleven patients presented with VA levels of =20/25 2 weeks after treatment; the mean logMAR VA change of 0.345 at that time was statistically significant (p < 0.05, Friedman test). OCT disclosed resolution of persistent subretinal fluid in all eyes. No recurrence was observed after 12 months of follow-up. Complications included transient retinal whitening in two patients, and associated occlusion of retinal capillaries in one. Conclusions. Photothrombosis using low-intensity 810 nm light to direct laser energy continuously at the active leakage sites after intravenous ICG infusion induced rapid VA recovery in patients with persistent CSC; accordingly, restoration of the macular architecture was evidenced on OCT, and no recurrence was noted 12 months after IMP.

Long-term effectiveness of photodynamic therapy by using a hydrophilic photosensitizer ATX-S10(Na) against experimental choroidal neovascularization in rats.

We previously demonstrated that a hydrophilic photosensitizer ATX-S10 had a potent photodynamic effect. This study was designed to reveal the long-term effectiveness of photodynamic therapy (PDT) with this agent in occluding choroidal neovascularization (CNV) and its selectivity in the neovascular tissue. Experimental CNV was induced by intense photocoagulation in rat eyes. Immediately or 2 hours after intravenous injection of 8 mg/kg body weight of ATX-S10(Na), a cis isomer of ATX-S10, eyes were irradiated by a diode laser at the radiance of 3.25-65.3 J/cm(2) Vascular occlusion was identified by fundus photography, fluorescein angiography, and histology at 1, 3, 7, 14, and 28 days after PDT. As controls, non-neovascular eyes were subjected to PDT and similarly analyzed. By using the following treatment parameters, PDT with ATX-S10(Na) successfully occluded CNV without causing occlusion of retinal capillaries for 28 days; 7.4 and 19.6 J/cm(2) immediately after dye injection and 36.7 and 65.3 J/cm(2) 2 hours after injection. Although these conditions also caused occlusion of normal choriocapillaries and mild injuries of retinal vessels, retinal pigment epithelium, and photoreceptors at 1 day, retinal vessels and pigment epithelial cells recovered from damages by 28 days. No injuries were found in the inner retina. In optimal treatment conditions, PDT with ATX-S10(Na) can induce long-term, selective occlusion of CNV without causing irreversible damages in the inner retina.

Neutrophils in Galactose-Fed Dogs: Suppressed Apoptosis and Increased Adhesion to Retinal Capillary Endothelial Cells

Dogs fed a diet containing 30% galactose develop diabetes-like retinal capillary changes. As retinal capillary occlusion is commonly observed in diabetic retinopathy, neutrophil apoptosis and the interaction of neutrophils with retinal capillary endothelial cells were investigated. Neutrophils were isolated with Ficoll-Hypaque centrifugation from dogs fed a 30% galactose diet and dogs fed a normal, control diet containing 30% non-nutrient filler. Apoptosis of neutrophils was microscopically examined after incubation at 37°C for 3 hours with either 100 U/mL tumor necrosis factor α (TNF-α), 2 μg/mL cycloheximide or 50 ng/mL phorbol 12-myristate 13-acetate (PMA). Neutrophil adhesion to dog retinal capillary endothelial cells was examined by counting the cells attached to the surface of endothelial cells after the incubation in the presence of either 100 U/mL TNF-α or 5 μg/mL lipopolysaccharides (LPS) at 37°C for 3 hours. With all three stimulants TNF-α, cycloheximide and PMA, the rate of apoptosis was significantly lower for neutrophils isolated from galactose-fed dogs compared to control dogs fed a normal diet. Preincubation of neutrophils from control dogs in medium containing 30% galactose for 3 hours did not affect the rate of apoptosis. Neutrophil adhesion to retinal capillary endothelial cells induced by incubation in the presence of either 100 U/mL TNF-α or 5 μg/ml LPS was significantly higher with neutrophils isolated from galactose-fed dogs than those from control dogs. The data indicate that long-term galactose feeding is essential with development of various neutrophil dysfunctions. These neutrophil changes may contribute to the development of retinal microangiopathy associated with diabetes and galactosemia.

Abnormalities of the foveal avascular zone in diabetic retinopathy.

The dimensions of the foveal avascular zone (FAZ) were measured in fluorescein angiograms from 36 diabetic patients and 20 nondiabetic controls. The median values for longest diameter, mean diameter, and circumference were significantly greater in the diabetic group than in the control group. Longest diameters greater than 1.0 mm were found almost exclusively in eyes with proliferative diabetic retinopathy. The FAZ dimensions were strongly positively correlated with the severity of capillary nonperfusion in the posterior retina, but not with fluorescein leakage. The presence of proliferative diabetic retinopathy was also strongly correlated with capillary nonperfusion. Retinal capillary occlusion as the cause of FAZ enlargement in diabetic retinopathy is supported by these findings.