Compound 49b Restores Retinal Thickness and Reduces Degenerate Capillaries in the Rat Retina following Ischemia/Reperfusion

EphB1 causes retinal damage through inflammatory pathways in the retina and retinal Müller cells

Purpose

To examine whether increased ephrin type-B receptor 1 (EphB1) leads to inflammatory mediators in retinal Müller cells.

Methods

Diabetic human and mouse retinal samples were examined for EphB1 protein levels. Rat Müller cells (rMC-1) were grown in culture and treated with EphB1 siRNA or ephrin B1-Fc to explore inflammatory mediators in cells grown in high glucose. An EphB1 overexpression adeno-associated virus (AAV) was used to increase EphB1 in Müller cells in vivo. Ischemia/reperfusion (I/R) was performed on mice treated with the EphB1 overexpression AAV to explore the actions of EphB1 on retinal neuronal changes in vivo.

Results

EphB1 protein levels were increased in diabetic human and mouse retinal samples. Knockdown of EphB1 reduced inflammatory mediator levels in Müller cells grown in high glucose. Ephrin B1-Fc increased inflammatory proteins in rMC-1 cells grown in normal and high glucose. Treatment of mice with I/R caused retinal thinning and loss of cell numbers in the ganglion cell layer. This was increased in mice exposed to I/R and treated with the EphB1 overexpressing AAVs.

Conclusions

EphB1 is increased in the retinas of diabetic humans and mice and in high glucose-treated Müller cells. This increase leads to inflammatory proteins. EphB1 also enhanced retinal damage in response to I/R. Taken together, inhibition of EphB1 may offer a new therapeutic option for diabetic retinopathy.

Serum levels of vasohibin-1 in type 2 diabetes mellitus patients with diabetic retinopathy

CLINICAL RELEVANCE

To determine whether Vasohibin-1 which is a potential clinical biomarker is an independent risk factor in patients with diabetic retinopathy.

BACKGROUND

Diabetic retinopathy (DR) is a common chronic microangiopathy in type 2 diabetes mellitus (T2DM). Vasohibin-1 (VASH-1) is an angiogenesis regulator that is closely related to pathological vascularization in DM. This study aimed to determine whether the serum levels of VASH-1 were related to the occurrence of DR in T2DM patients.

METHODS

T2DM patients were divided into three groups: the nondiabetic retinopathy (NDR) group (n = 41), the nonproliferative diabetic retinopathy (NPRD) group (n = 40), and the proliferative diabetic retinopathy (PDR) group (n = 41). A control (CON) group consisting of 40 healthy subjects was also recruited. The serum levels of VASH-1 were measured by enzyme-linked immunosorbent assay kits.

RESULTS

The concentration of VASH-1 in the CON groups was less significantly than that of the NDR, NPDR and PDR groups. (P < 0.05). Body mass index, fasting plasma glucose (FPG), hemoglobina1c (HbA1C), blood urea nitrogen (BUN) and diabetic durations were positively correlated with the serum concentration of VASH-1 (all P < 0.05). In univariate logistic regression analyses, the HbA1C, diabetic durations, HDL-c, eGFR and VASH1 were associated with the presence of diabetic retinopathy. Multivariate logistic regression analysis showed that duration of diabetes were significantly associated with diabetic retinopathy.

CONCLUSION

We have shown that VASH-1 is associated with an increased risk of developing diabetic retinopathy. But the serum levels of VASH-1 are not independent risk factors for DR in T2DM.

Forskolin eye drops improve retinal damage from ischemia/reperfusion

PURPOSE

To determine whether forskolin, a protein kinase A (PKA) agonist, eye drops could reduce neuronal and vascular damage after exposure to ischemia/reperfusion (I/R).

METHODS

C57BL/6J mice were exposed to the I/R protocol. A group of mice were given forskolin eye drops (10 μM) daily. Two days after I/R, neuronal measurements were performed, while vascular measurements were performed at 10 days post-I/R. Western blotting was conducted to investigate whether forskolin could increase PKA levels and reduce the levels of inflammatory mediators.

RESULTS

Forskolin statistically significantly increased PKA levels, but not exchange protein activated by cAMP 1 (Epac1). The forskolin eye drops also reduced neuronal and vascular damage compared to I/R alone. Tumor necrosis factor alpha (TNF-α) and interleukin-1-β (IL-1β) levels were statistically significantly reduced after administration of forskolin eye drops compared to I/R alone.

CONCLUSIONS

Forskolin eye drops were protective against I/R. The findings offer a new therapeutic for local delivery.

Glycyrrhizin protects IGFBP-3 knockout mice from retinal damage

We previously reported that insulin-like growth factor binding protein 3 (IGFBP-3) knockout (KO) mice have neuronal and vascular damage to the retina. We also reported that glycyrrhizin, a high mobility growth factor binding protein 1 (HMGB1) inhibitor, is protective to the diabetic retina. In this study, we investigated whether glycyrrhizin could reduce neuronal and vascular damage in the IGFBP-3 KO mouse retina. We used measurements of retinal thickness, cell number in the ganglion cell layer, degenerate capillaries, reactive oxygen species (ROS) and protein levels of HMGB1, tumor necrosis factor alpha (TNFα), interleukin-1-beta (IL-1β) and sirtuin 1 (SIRT1) to determine whether glycyrrhizin could protect the retina. Data show that glycyrrhizin in the drinking water was effective in reducing neuronal damage at 2 months and vascular damage at 6 months. Glycyrrhizin reduced ROS levels at 6 months, and reduced levels of HMGB1, TNFα, and IL-1β at both 2 and 6 months. Taken together, the data suggest that glycyrrhizin is protective to the retina of IGFBP-3 KO mice through anti-inflammatory mechanisms.

Glycyrrhizin Protects the Diabetic Retina against Permeability, Neuronal, and Vascular Damage through Anti-Inflammatory Mechanisms

Damage associated molecular pattern (DAMPs), such as high mobility group box 1 (HMGB1), may be involved in retinal inflammation in response to high glucose. To test whether HMGB1 inhibition could protect the diabetic retina, C57BL/6J mice were made diabetic and treated with glycyrrhizin, a HMGB1 inhibitor, for up to six months. Measurements of permeability, neuronal, and vascular changes were done, as well as assessments of HMGB1, tumor necrosis factor alpha (TNFα), and interleukin-1-beta (IL1β) levels. Retinal endothelial cells (REC) treated with glycyrrhizin had reduced IL1β and cleaved caspase 3 levels. Data also demonstrate that glycyrrhizin effectively reduced HMGB1 levels throughout the retina, as well as maintained normal retinal permeability and retinal capillary coverage. Glycyrrhizin maintained normal cell numbers in the ganglion cell layer and prevented thinning of the retina at two months. These histological changes were associated with reduced reactive oxygen species, as well as reduced HMGB1, TNFα, and IL1β levels. The data strongly imply that HMGB1 inhibition prevented diabetic retinal changes through anti-inflammatory pathways.

Epac1 and Glycyrrhizin Both Inhibit HMGB1 Levels to Reduce Diabetes-Induced Neuronal and Vascular Damage in the Mouse Retina

The role of high mobility group box 1 (HMGB1) in acute diabetic retinal damage has been demonstrated. We recently reported that glycyrrhizin, a HMGB1 inhibitor, protected the diabetic retina against neuronal, vascular, and permeability changes. In this study, we wanted to investigate the role of exchange protein for cAMP 1 (Epac1) on HMGB1 and the actions of glycyrrhizin. Using endothelial cell specific knockout mice for Epac1, we made some mice diabetic using streptozotocin, and treated some with glycyrrhizin for up to 6 months. We measured permeability, neuronal, and vascular changes in the Epac1 floxed and knockout mice. We also investigated whether Epac1 and glycyrrhizin work synergistically to reduce the retinal inflammatory mediators, tumor necrosis factor alpha (TNFα) and interleukin-1-beta (IL1β), as well as sirtuin 1 (SIRT1) levels. Epac1 and glycyrrhizin reduced inflammatory mediators with synergistic actions. Glycyrrhizin also increased SIRT1 levels in the Epac1 mice. Overall, these studies demonstrate that glycyrrhizin and Epac1 can work together to protect the retina. Finally, glycyrrhizin may regulate HMGB1 through increased SIRT1 actions.

Vagal Nerve Stimulation Attenuates Ischemia-Reperfusion Induced Retina Dysfunction in Acute Ocular Hypertension

Purpose: The present study aimed to investigate whether cervical vagal nerve stimulation (VNS) could prevent retinal ganglion cell (RGC) loss and retinal dysfunction after ischemia/reperfusion (I/R) injury.

Methods: First, rats were randomly divided into sham group (n = 4) and VNS group (n = 12). Activation of the nodose ganglia (NOG), nucleus of the solitary tract (NTS), superior salivatory nucleus (SSN), and pterygopalatine ganglion (PPG) neural circuit were evaluated by c-fos expression at 0 h after sham VNS and at 0 h (n = 4), 6 h (n = 4), 72 h (n = 4) after VNS. Secondly, rats were randomly assigned to I/R group (pressure-induced retinal ischemia for 1 h and reperfusion for 1 h in the right eye, n = 16) and I/R+VNS group (right cervical VNS for 2 h during the I/R period, n = 16). The left eye of each rat served as a control. Electroretinogram (ERG), RGC numbers, tumor necrosis factor-α (TNF-α) and vasoactive intestinal polypeptide (VIP) levels in retina were determined. Additionally, the level of VIP in PPG was evaluated.

Results: In the first part of the study, compared with the sham group, the VNS group exhibited significantly increased expression of c-fos in NOG, NTS, SSN, and PPG tissues at 0, 6, and 72 h. In the second part of the study, compared with left eyes, retinal function in right eyes (as assessed by the a-wave, b-wave and the oscillatory potential amplitudes of ERG and RGC data) was significantly decreased by I/R. The decreased retinal function was attenuated by VNS. In addition, I/R induced an increase in inflammation, which was reflected by elevated TNF-α expression in the retina. VNS significantly attenuated the increase in I/R-induced inflammation. Moreover, VIP expression in the retina and PPG, which may contribute to the inhibition of the inflammatory response, was significantly increased after VNS.

Conclusion: VNS could protect against retinal I/R injury by downregulating TNF-α. Upregulation of VIP expression due to activation of the NOG-NTS-SSN-PPG neural circuit may underlie to the protective effects of VNS.

Propranolol 0.2% Eye Micro-Drops for Retinopathy of Prematurity: A Prospective Phase IIB Study

Background: Oral propranolol reduces retinopathy of prematurity (ROP) progression, although not safely. Propranolol 0.1% eye micro-drops administered to newborns with stage 2 ROP are well-tolerated, but not sufficiently effective. Methods: A multi-center open-label trial was conducted to assess the safety and efficacy of propranolol 0.2% eye micro-drops in newborns with stage 1 ROP. The progression of the disease was evaluated with serial ophthalmologic examinations. Hemodynamic, respiratory, biochemical parameters, and propranolol plasma levels were monitored. Demographic and perinatal characteristics, co-morbidities and co-intervention incidences, together with ROP progression, were compared with a historical control group in the same centers participating in the trial. Results: Ninety-eight newborns were enrolled and compared with the historical control group. Populations were not perfectly homogeneous (as demonstrated by the differences in the Apgar score and the different incidence rate in surfactant administration and oxygen exposure). The progression to ROP stage 2 or 3 plus was significantly lower than the incidence expected on the basis of historical data (Risk Ratio 0.521, 95% CI 0.297- 0.916). No adverse effects related to propranolol were observed and the mean propranolol plasma level was significantly lower than the safety cut-off of 20 ng/mL. Unexpectedly, three newborns treated with oral propranolol before the appearance of ROP, showed a ROP that was unresponsive to propranolol eye micro-drops and required laser photocoagulation treatment. Conclusion: Propranolol 0.2% eye micro-drops were well-tolerated and appeared to reduce the ROP progression expected on the basis of a comparison with a historical control group. Propranolol administered too early appears to favor a more aggressive ROP, suggesting that a β-adrenoreceptor blockade is only useful during the proliferative phase. Further randomized placebo-controlled trials are required to confirm the current results. Clinical Trial Registration  The trial was registered at ClinicalTrials.gov with Identifier NCT02504944 and with EudraCT Number 2014-005472-29.

Collagen peptide modified carboxymethyl cellulose as both antioxidant drug and carrier for drug delivery against retinal ischaemia/reperfusion injury

Oxidative stress can cause injury in retinal endothelial cells. Carboxymethyl cellulose modified with collagen peptide (CMCC) is of a distinct antioxidant capacity and potentially a good drug carrier. In this study, the protective effects of CMCC against H2 O2 -induced injury of primary retinal endothelial cells were investigated. In vitro, we demonstrated that CMCC significantly promoted viability of H2 O2 -treated cells, efficiently restrained cellular reactive oxygen species (ROS) production and cell apoptosis. Then, the CMCC was employed as both drug and anti-inflammatory drug carrier for treatment of retinal ischaemia/reperfusion (I/R) in rats. Animals were treated with CMCC or interleukin-10-loaded CMCC (IL-10@CMCC), respectively. In comparisons, the IL-10@CMCC treatment exhibited superior therapeutic effects, including better restoration of retinal structural thickness and less retinal apoptosis. Also, chemiluminescence demonstrated that transplantation of IL-10@CMCC markedly reduced the retinal oxidative stress level compared with CMCC alone and potently recovered the activities of typical antioxidant enzymes, SOD and CAT. Therefore, it could be concluded that CMCC provides a promising platform to enhance the drug-based therapy for I/R-related retinal injury.

Epac1 protects the retina against ischemia/reperfusion-induced neuronal and vascular damage

We had previously reported that exchange protein for cAMP 1 (Epac1) reduced inflammatory mediators in the retina of mice and in retinal endothelial cells (REC). Since ischemia can induce retinal damage potentially through activation of inflammatory cascades, we hypothesized that Epac1 would protect the retina against neuronal and vascular damage after exposure to ischemia/reperfusion (I/R). We used Epac1 floxed and endothelial cell specific Epac1 knockout mice for this work. We exposed them to ischemia for 90 minutes followed by reperfusion. One day after I/R, some mice were used for fluorescein angiography imaging or Evan’s blue measurements of permeability. Mice were sacrificed at 2 days for neuronal measurements and at 10 days for measurements of degenerate capillaries. Data show increased leakage in the Epac1 Cre-Lox (Epac1 EC-KO) mice exposed to I/R when compared to Epac1 floxed mice with the same treatment. I/R also increased numbers of degenerate capillaries and cell loss in all retinal layers of Epac1 EC-KO mice. Retinal thickness was reduced more significantly in the Epac1 EC-KO mice compared to Epac1 floxed mice after I/R. Taken together, the data suggest that Epac1 is protective against both neuronal and vascular damage to the retina after exposure to I/R.

Long non-coding RNA nuclear paraspeckle assembly transcript 1 inhibits the apoptosis of retina Müller cells after diabetic retinopathy through regulating miR-497/brain-derived neurotrophic factor axis

BACKGROUND

The role of long non-coding RNA in diabetic retinopathy, a serious complication of diabetes mellitus, has attracted increasing attention in recent years. The purpose of this study was to explore whether long non-coding RNA nuclear paraspeckle assembly transcript 1 was involved in the context of diabetic retinopathy and its underlying mechanisms.

RESULTS

Our results revealed that nuclear paraspeckle assembly transcript 1 was significantly downregulated in the retina of diabetes mellitus rats. Meanwhile, miR-497 was significantly increased in diabetes mellitus rats' retina and high glucose-treated Müller cells, but brain-derived neurotrophic factor was increased. We also found that high glucose-induced apoptosis of Müller cells was accompanied by the significant downregulation of nuclear paraspeckle assembly transcript 1 in vitro. Further study demonstrated that high glucose-promoted Müller cells apoptosis through downregulating nuclear paraspeckle assembly transcript 1 and downregulated nuclear paraspeckle assembly transcript 1 mediated this effect via negative regulating miR-497. Moreover, brain-derived neurotrophic factor was negatively regulated by miR-497 and associated with the apoptosis of Müller cells under high glucose.

CONCLUSION

Our results suggested that under diabetic conditions, downregulated nuclear paraspeckle assembly transcript 1 decreased the expression of brain-derived neurotrophic factor through elevating miR-497, thereby promoting Müller cells apoptosis and aggravating diabetic retinopathy.

Toll-Like Receptor 4 Reduces Occludin and Zonula Occludens 1 to Increase Retinal Permeability Both in vitro and in vivo

We reported that β-adrenergic receptors regulate toll-like receptor 4 (TLR4) signaling in the retina of diabetic mice and in retinal endothelial cells (REC) and Müller cells. We hypothesized that TLR4 regulates retinal permeability both in vitro and in vivo in the retinal vasculature. We used REC cultured in normal and high-glucose conditions and TLR4 siRNA treatments for cell culture studies of permeability and protein analyses of tumor necrosis factor α, occludin, and zonula occludens 1 (ZO-1). We used endothelial cell (EC)-specific Cre-Lox TLR4 knockout mice to study retinal permeability and neuronal and vascular changes following exposure to ocular ischemia/reperfusion (I/R) used as a retinal stressor. We found that the loss of TLR4 in the EC led to the reduced permeability following I/R and fewer degenerate capillaries. Retinal permeability was increased in REC grown in high-glucose conditions but was inhibited by TLR4 siRNA treatment. High-glucose culture conditions significantly reduced occludin and ZO-1 levels in REC, and TLR4 siRNA treatment restored levels to baseline. In conclusion, these studies demonstrate that TLR4 in EC strongly regulates retinal permeability and neuronal and vascular changes following exposure to stressors such as I/R.

Clinical significance of mechanical ventilation on ischemic-reperfusion injury caused by lung chest trauma and VEGF expression levels in peripheral blood

We investigated the clinical significance of mechanical ventilation on ischemic-reperfusion injury caused by lung chest trauma as well as vascular endothelial growth factor (VEGF) expression levels in peripheral blood. Sixty-eight patients with severe chest trauma complicated with acute respiratory distress syndrome that were treated at our Tianjin Hospital from September 2013 to July 2016 were recruited. These patients were randomly and evenly divided into two groups, the research group and the control group. Thirty-four age and gender matched healthy people were selected as the normal group. Routine treatment was given to both the research and control groups, but mechanical ventilation was used in the research group. We detected pulmonary vascular resistance (PVR) and alveolar-arterial oxygen difference (AaDO₂) for patients in both groups before treatment, and after treatment for 1, 3, 6 and 12 h. We also tested PMN, superoxide dismutase (SOD), malondialdehyde (MDA), NO and Ang II value 30 min before and after treatment. We used the ELISA-test to detect VEGF expression levels in peripheral blood, followed by a statistical analysis. PVR levels of different time points in the research group were significantly lower than control group after treatment. The AaDO₂ value of the control group is much smaller than research group (P<0.5) after treatment for 1, 3 or 6 h. PMN count difference and MDA level in the research group is significantly lower than the control group after treatment for 30 min, but SOD and NO levels are much higher. Ang II levels of the research group in left atrial blood is significantly lower than control group (P<0.05). By comparing the hospitalization times, we found that patients in the research group have a shorter duration in hospital than the control group; differences are statistically significant (P<0.05). Additionally, compared to control group, research group VEGF expression levels in peripheral blood are significantly lower (P<0.05). Therefore, mechanical ventilation can reduce the high VEGF expression levels in serum caused by ischemic-reperfusion and can be used for clinical application.

Dexmedetomidine preconditioning protects against retinal ischemia/reperfusion injury and inhibits inflammation response via toll-like receptor 4 (TLR4) pathway

BACKGROUND

Retinal ischemia/reperfusion (I/R) injury is one of significant cause of visual dysopia and causes inflammatory response. Dexmedetomidine is widely applied to general/local anaesthesia and has been reported to have extensive anti-inflammatory effect. However, the role of dexmedetomidine in retinal I/R injury is currently unknown. This study investigates the effect of dexmedetomidine preconditioning on retinal I/R injury and explore the related signal mechanism toll-like receptor 4 (TLR4) pathway.

METHODS

Retinal I/R injury model were established with SD rats through periocular injection. Retinal damage was quantified by measuring the thickness of retinal layers, cell counts of retinal ganglion cells (RGCs) and electroretinography (ERG). Apoptosis of retinal cell was detected by TUNEL assay. Protein and mRNA expression of glial fibrillary acidic protein (GFAP) were measured by western blot and real-time quantitate PCR. Bax, Bcl-2 and nuclear factor-κB (NF-κB) in retinas were detected by western blot.

RESULTS

ERG and HE staining showed that dexmedetomidine preconditioning significantly inhibited the histologic damage induced by I/R injury, which expresses apparent concentration dependent. TUNEL demonstrated that apoptosis of retinal cells were reduced by dexmedetomidine. The expression of NF-κB and GFAP were decreased compared I/R blank group.

CONCLUSION

Dexmedetomidine preconditioning suppresses retinal I/R injury and shows effective anti-inflammatory effect by inhibiting TLR4/NF-κB expression.

Inhibition of HMGB1 protects the retina from ischemia-reperfusion, as well as reduces insulin resistance proteins

The role of inflammation in diabetic retinal amage is well accepted. While a number of cytokines and inflammatory mediators are responsible for these changes, upstream regulators are less well studied. Additionally, the role for these upstream mediators in retinal health is unclear. In this study, we hypothesized that inhibition of high mobility group box 1 (HMGB1) could restore normal insulin signaling in retinal endothelial cells (REC) grown in high glucose, as well as protect the retina against ischemia/reperfusion (I/R)-induced retinal damage. REC were grown in normal (5mM) or high glucose (25mM) and treated with Box A or glycyrrhizin, two different HMGB1 inhibitors. Western blotting was done for HMGB1, toll-like receptor 4 (TLR4), insulin receptor, insulin receptor substrate-1 (IRS-1), and Akt. ELISA analyses were done for tumor necrosis factor alpha (TNFα) and cleaved caspase 3. In addition, C57/B6 mice were treated with glycyrrhizin, both before and after ocular I/R. Two days following I/R, retinal sections were processed for neuronal changes, while vascular damage was measured at 10 days post-I/R. Results demonstrate that both Box A and glycyrrhizin reduced HMGB1, TLR4, and TNFα levels in REC grown in high glucose. This led to reduced cleavage of caspase 3 and IRS-1^Ser307 phosphorylation, and increased insulin receptor and Akt phosphorylation. Glycyrrhizin treatment significantly reduced loss of retinal thickness and degenerate capillary numbers in mice exposed to I/R. Taken together, these results suggest that inhibition of HMGB1 can reduce retinal insulin resistance, as well as protect the retina against I/R-induced damage.