Protective effects of dexamethasone on hypoxia-induced retinal edema in a mouse model

Evaluation of acute effects of pulmonary involvement and hypoxia on retina and choroid in coronavirus disease 2019: An optic coherence tomography study

PURPOSE

We investigated the acute subclinical choroidal and retinal changes caused by Coronavirus Disease 2019 (COVID-19) in patients with and without pulmonary involvement, using spectral domain optic coherence tomography.

METHODS

This prospective case-control study included COVID-19 patients: 50 with pulmonary involvement and 118 with non-pulmonary involvement. All patients were examined 1 month after recovering from COVID-19. The changes were followed using optic coherence tomography parameters such as choroidal and macular thickness and retinal nerve fibre layer and ganglion cell complex measurements.

RESULTS

All choroidal thicknesses in the pulmonary involvement group were lower than in the non-pulmonary involvement group and the subfoveal choroidal thickness differed significantly (p=0.036). Although there were no significant differences between the central and average macular thicknesses in the two groups, they were slightly thicker in the pulmonary involvement group (p=0.152 and p=0.180, respectively). A significant decrease was detected in the pulmonary involvement group in all ganglion cell complex segments, except for the outer nasal inferior segment (p<0.05). In addition, a thinning tendency was observed in all retinal nerve fibre layer quadrants in the pulmonary involvement group compared to the non-pulmonary involvement group.

CONCLUSION

In COVID-19 patients with pulmonary involvement, subclinical choroidal and retinal changes may occur due to hypoxia and ischemia in the acute period. These patients may be predisposed to ischemic retinal and optic nerve diseases in the future. Therefore, COVID-19 patients with pulmonary involvement should be followed for ophthalmological diseases.

Minocycline Inhibits Microglial Activation and Improves Visual Function in a Chronic Model of Age-Related Retinal Degeneration

Age-related macular degeneration (AMD) is a chronic disease, which progresses slowly from early to late stages over many years. Inflammation critically contributes to the pathogenesis of AMD. Here, we investigated the therapeutic potential of minocycline in a chronic model of AMD (i.e., the LysMCre-Socs3^fl/flCx3cr1^gfp/gfp double knockout [DKO] mice). Five-month-old DKO and wild type (WT) (Socs3^fl/fl) mice were gavage fed with minocycline (25 mg/kg daily) or vehicle (distilled water) for 3 months. At the end of the treatment, visual function and retinal changes were examined clinically (using electroretinography, fundus photograph and optic coherence tomography) and immunohistologically. Three months of minocycline treatment did not affect the body weight, behaviour and general health of WT and DKO mice. Minocycline treatment enhanced the a-/b-wave aptitudes and increased retinal thickness in both WT and DKO. DKO mouse retina expressed higher levels of Il1b, CD68 and CD86 and had mild microglial activation, and decreased numbers of arrestin⁺ photoreceptors, PKCα⁺ and secretagogin⁺ bipolar cells compared to WT mouse retina. Minocycline treatment reduced microglial activation and rescued retinal neuronal loss in DKO mice. Our results suggest that long-term minocycline treatment is safe and effective in controlling microglial activation and preserving visual function in chronic models of AMD.

Astaxanthin Ameliorates Diabetic Retinopathy in Swiss Albino Mice via Inhibitory Processes of Neuron-Specific Enolase Activity

Retinopathy is one of the most common complications of diabetes mellitus. Diabetic retinopathy (DR) occurs due to microvascular damage in retinal tissues provoked by high blood sugar levels. The available drugs for DR are limited. Astaxanthin (AST) has anti-hypertensive, anti-obesity, and anti-diabetic properties. However, the therapeutic effect of AST on DR remains elusive. The present study is designed to investigate the effects of AST on DR via inhibition of neuron-specific enolase (NSE) activity. DR was induced by the administration of streptozotocin (STZ, 35 mg/kg: intraperitoneal; and 20 μL of STZ: intravitreal) in mice. AST (10 and 20 mg/kg) was administered orally (p.o.) for 21 days. The DR associated visual changes were assessed at different time intervals via optokinetic motor response (OMR) and penta-maze (PM) tests. Blood glucose level as well as retinal catalase, lactate dehydrogenase (LDH), & neuron-specific enolase (NSE) were estimated. The reference drug i.e., dexamethasone (DEX, 10 mg/kg; p.o.) was administered for 21 days. The administration of AST showed significant ameliorative potential in DR. Hence, AST can be used as a natural medicine for the management of DR due to its potential antioxidant, anti-diabetic, and NSE inhibitory properties.

Osteopontin-induced vascular hyperpermeability through tight junction disruption in diabetic retina

Diabetic retinopathy is a major cause of blindness in developed countries, and is characterized by deterioration of barrier function causing vascular hyperpermeability and retinal edema. Vascular endothelial growth factor (VEGF) is a major mediator of diabetic macular edema. Although anti-VEGF drugs are the first-line treatment for diabetic macular edema, some cases are refractory to anti-VEGF therapy. Osteopontin (OPN) is a phosphoglycoprotein with diverse functions and expressed in various cells and tissues. Elevated OPN level has been implicated in diabetic retinopathy, but whether OPN is involved in hyperpermeability remains unclear. Using streptozotocin-induced diabetic mice (STZ mice) and human retinal endothelial cells (HRECs), we tested the hypothesis that up-regulated OPN causes tight junction disruption, leading to vascular hyperpermeability. The serum and retinal OPN concentrations were elevated in STZ mice compared to controls. Intravitreal injection of anti-OPN neutralizing antibody (anti-OPN Ab) suppressed vascular hyperpermeability and prevented decreases in claudin-5 and ZO-1 gene expression levels in the retina of STZ mice. Immunohistochemical staining of retinal vessels in STZ mice revealed claudin-5 immunoreactivity with punctate distribution and attenuated ZO-1 immunoreactivity, and these changes were prevented by anti-OPN Ab. Intravitreal injection of anti-OPN Ab did not change VEGF gene expression or protein concentration in retina of STZ mice. In an in vitro study, HRECs were exposed to normal glucose or high glucose with or without OPN for 48 h, and barrier function was evaluated by transendothelial electrical resistance and Evans blue permeation. Barrier function deteriorated under high glucose condition, and was further exacerbated by the addition of OPN. Immunofluorescence localization of claudin-5 and ZO-1 demonstrated punctate appearance with discontinuous junction in HRECs exposed to high glucose and OPN. There were no changes in VEGF and VEGF receptor-2 expression levels in HRECs by exposure to OPN. Our results suggest that OPN induces tight junction disruption and vascular hyperpermeability under diabetic conditions. Targeting OPN may be an effective approach to manage diabetic retinopathy.

Pharmacological torpor prolongs rat survival in lethal normobaric hypoxia

Resistance to hypoxia is one of the most prominent features of natural hibernation and is expected to be present in the pharmacological torpor (PT) that simulates hibernation. We studied resistance to lethal hypoxia (3.5% oxygen content) in rats under PT. To initiate PT, we used the previously developed pharmacological composition (PC) which, after a single intravenous injection, can induce a daily decrease in Tb by 7 °C-8 °C at the environmental temperature of 22 °C-23 °C. Half-survival (median) time of rats in lethal hypoxia was found to increase from 5 ± 0.8 min in anesthetized control rats to 150 ± 12 min in rats injected with PC, which is a 30-fold increase. Behavioral tests after PT and hypoxia, including the traveling distance, the number of rearing and grooming episodes, revealed that animal responses are significantly restored within a week. It is assumed that the discovered unprecedented resistance of artificially torpid rats to lethal hypoxia may open up broad prospects for the therapeutic use of PT for preconditioning to various damaging factors, treatment of diseases, and extend the so-called "golden hour" for lifesaving interventions.

Hypoxia-induced inflammation: Profiling the first 24-hour posthypoxic plasma and central nervous system changes

Central nervous system and visual dysfunction is an unfortunate consequence of systemic hypoxia in the setting of cardiopulmonary disease, including infection with SARS-CoV-2, high-altitude cerebral edema and retinopathy and other conditions. Hypoxia-induced inflammatory signaling may lead to retinal inflammation, gliosis and visual disturbances. We investigated the consequences of systemic hypoxia using serial retinal optical coherence tomography and by assessing the earliest changes within 24h after hypoxia by measuring a proteomics panel of 39 cytokines, chemokines and growth factors in the plasma and retina, as well as using retinal histology. We induced severe systemic hypoxia in adult C57BL/6 mice using a hypoxia chamber (10% O2) for 1 week and rapidly assessed measurements within 1h compared with 18h after hypoxia. Optical coherence tomography revealed retinal tissue edema at 18h after hypoxia. Hierarchical clustering of plasma and retinal immune molecules revealed obvious segregation of the 1h posthypoxia group away from that of controls. One hour after hypoxia, there were 10 significantly increased molecules in plasma and 4 in retina. Interleukin-1β and vascular endothelial growth factor were increased in both tissues. Concomitantly, there was significantly increased aquaporin-4, decreased Kir4.1, and increased gliosis in retinal histology. In summary, the immediate posthypoxic period is characterized by molecular changes consistent with systemic and retinal inflammation and retinal glial changes important in water transport, leading to tissue edema. This posthypoxic inflammation rapidly improves within 24h, consistent with the typically mild and transient visual disturbance in hypoxia, such as in high-altitude retinopathy. Given hypoxia increases risk of vision loss, more studies in at-risk patients, such as plasma immune profiling and in vivo retinal imaging, are needed in order to identify novel diagnostic or prognostic biomarkers of visual impairment in systemic hypoxia.

Microglia increase tight-junction permeability in coordination with Müller cells under hypoxic condition in an in vitro model of inner blood-retinal barrier

Microglia and Müller cells (MCs) are believed to be critically involved in hypoxia-induced blood-retinal barrier (BRB) disruption, which is a major pathogenic factor of various retinopathies. However, the underlying mechanism remains poorly defined. The inner BRB (iBRB) is primarily formed of microvascular endothelial cells (ECs) with tight junction (TJ), which are surrounded and supported by retinal glial cells. We developed a novel in vitro iBRB model sheet by sandwiching Transwell membrane with layered mouse brain microvascular ECs (bEnd.3) and mouse retinal MCs (QMMuC-1) on each side of the membrane. Using this model, we tested the hypothesis that under hypoxic condition, activated microglia produce inflammatory cytokines such as interleukin (IL)-1β, which may promote vascular endothelial growth factor (VEGF) production from MCs, leading to TJ disruption. The iBRB model cell sheets were exposed to 1% oxygen for 6 h with or without mouse brain microglia (BV2) or IL-1β. TJ structure and function were examined by zonula occludens (ZO)-1 immunostaining and fluorescein isothiocyanate permeability assay, respectively. Relative gene expression of IL-1β in BV2 under normoxic and hypoxic conditions was examined by real-time reverse transcription-polymerase chain reaction. VEGF protein concentration in QMMuC-1 supernatants was measured by enzyme-linked immunosorbent assay. The bEnd.3 cell sheet incubated with BV2 in hypoxic condition or with IL-1β in normoxic condition showed abnormal localization of ZO-1 and aberrated barrier function. Under normoxic condition, EC-MC iBRB model cell sheet showed lower permeability than bEnd.3 cell sheet. Under hypoxic conditions, the barrier function of EC-MC iBRB model cell sheet was more deteriorated compared to bEnd.3 cell sheet. Under hypoxic condition, incubation of EC-MC iBRB model cell sheet with BV2 cells or IL-1β significantly increased barrier permeability, and hypoxia-treated BV2 cells expressed significantly higher levels of IL-1β mRNA. Incubation of QMMuC-1 with IL-1β increased VEGF production. These results suggest that under hypoxic condition, microglia are activated to release proinflammatory cytokines such as IL-1β that promote VEGF production from MCs, leading to disruption of iBRB function. Modulating microglia and MCs function may be a novel approach to treat hypoxia-induced retinal BRB dysfunction.

Retinal changes in mice spontaneously developing diabetes by Th17-cell deviation

Elevated level of interleukin (IL)-17, predominantly produced by T helper (Th) 17 cells, has been implicated in diabetic retinopathy (DR), but it remains unclear whether IL-17 is involved in the pathogenesis of DR. Ins2^Akita (Akita) mice spontaneously develop diabetes, and show early pathophysiological changes in diabetic complications. On the other hand, interferon-γ knock out (GKO) mice exhibit high differentiation and activation of Th2 and Th17 cells as a result of Th1 cell inhibition. In this study, Ins2^Akita IFN-γ-deficient (Akita-GKO) mice were established by crossbreeding Akita mice with GKO mice, and Th17-mediated immune responses on DR were investigated. Blood glucose levels (BGL) of Akita mice and Akita-GKO mice were significantly higher than those of age-matched wild type (WT) or GKO mice, and there was no significant difference in BGL between Akita and Akita-GKO mice. Relative mRNA expression of ROR-γt that is a transcriptional factor of Th17 cells but not GATA-3 that is for Th2 cells was significantly upregulated only in Akita-GKO mice compared with WT mice, and the proportions of IL-17 and IL-22-producing splenic CD4⁺ cells were significantly higher in Akita-GKO mice than in wild type (WT), Akita, or GKO mice. In the retina, mRNA expression of vascular endothelial growth factor (VEGF) and intercellular adhesion molecule-1 (ICAM-1) were increased in Akita-GKO mice more than in Akita or GKO mice, and statistically significant differences were observed between Akita-GKO mice and WT mice. Leukostasis in retinal vessels and ocular level of VEGF protein increased significantly in Akita-GKO mice compared with the other groups. Edematous change in the retinal surface layer, retinal exudative lesions depicted as areas of hyperfluorescence in fluorescein angiography (FA), and vascular basement membrane thickening in all layers of the retina were also observed in Akita-GKO mice at 9-week-old but not in age-matched Akita or GKO mice. These results suggested that Th17 cell-mediated immune responses might be involved in promotion of functional and morphological changes in the retina of mice spontaneously developing diabetes.