Hypothermia protects retinal ganglion cells against hypoxia-induced cell death in a retina organ culture model

Investigating retinal explant models cultured in static and perfused systems to test the performance of exosomes secreted from retinal organoids

BACKGROUND

Ex vivo cultures of retinal explants are appropriate models for translational research. However, one of the difficult problems of retinal explants ex vivo culture is that their nutrient supply needs cannot be constantly met.

NEW METHOD

This study evaluated the effect of perfused culture on the survival of retinal explants, addressing the challenge of insufficient nutrition in static culture. Furthermore, exosomes secreted from retinal organoids (RO-Exos) were stained with PKH26 to track their uptake in retinal explants to mimic the efficacy of exosomal drugs in vivo.

RESULTS

We found that the retinal explants cultured with perfusion exhibited significantly higher viability, increased NeuN+ cells, and reduced apoptosis compared to the static culture group at Days Ex Vivo (DEV) 4, 7, and 14. The perfusion-cultured retinal explants exhibited reduced mRNA markers for gliosis and microglial activation, along with lower expression of GFAP and Iba1, as revealed by immunostaining. Additionally, RNA-sequencing analysis showed that perfusion culture mainly upregulated genes associated with visual perception and photoreceptor cell maintenance while downregulating the immune system process and immune response. RO-Exos promoted the uptake of PKH26-labelled exosomes and the growth of retinal explants in perfusion culture.

COMPARISON WITH EXISTING METHODS

Our perfusion culture system can provide a continuous supply of culture medium to achieve steady-state equilibrium in retinal explant culture. Compared to traditional static culture, it better preserves the vitality, provides better neuroprotection, and reduces glial activation.

CONCLUSIONS

This study provides a promising ex vivo model for further studies on degenerative retinal diseases and drug screening.

Optimization of an Ischemic Retinopathy Mouse Model and the Consequences of Hypoxia in a Time-Dependent Manner

The retina is one of the highest metabolically active tissues with a high oxygen consumption, so insufficient blood supply leads to visual impairment. The incidence of related conditions is increasing; however, no effective treatment without side effects is available. Furthermore, the pathomechanism of these diseases is not fully understood. Our aim was to develop an optimal ischemic retinopathy mouse model to investigate the retinal damage in a time-dependent manner. Retinal ischemia was induced by bilateral common carotid artery occlusion (BCCAO) for 10, 13, 15 or 20 min, or by right permanent unilateral common carotid artery occlusion (UCCAO). Optical coherence tomography was used to follow the changes in retinal thickness 3, 7, 14, 21 and 28 days after surgery. The number of ganglion cells was evaluated in the central and peripheral regions on whole-mount retina preparations. Expression of glial fibrillary acidic protein (GFAP) was analyzed with immunohistochemistry and Western blot. Retinal degeneration and ganglion cell loss was observed in multiple groups. Our results suggest that the 20 min BCCAO is a good model to investigate the consequences of ischemia and reperfusion in the retina in a time-dependent manner, while the UCCAO causes more severe damage in a short time, so it can be used for testing new drugs.

Retinal stroke: research models, targets and experimental drugs

INTRODUCTION

Retinal artery occlusion (RAO), often caused by a microembolus and resulting in inner retinal ischemia, could be considered as the retinal analog to cerebral stroke. Although several therapeutic targets have been suggested in animal models of retinal ischemia and several potential treatments have been evaluated on small series of patients, central retinal artery occlusion (CRAO) is still rarely treatable in clinical practice.

AREAS COVERED

Here, we review several animal models of RAO, including increased intraocular pressure, laser, vasoconstriction, embolization and clamp. We also review the pathogenic mechanisms that contribute to cell death cascades during ischemia, and the therapeutic strategies targeting these events. These strategies aim to restore blood flow by fibrinolysis, increase the oxygen or glucose supply, decrease the energy demands, restrict ionic leak fluxes or reduce the detrimental effects of glutamate, calcium and free radicals. The current literature suggests that tPA treatment could be effective for CRAO.

EXPERT OPINION

Eye care professionals must make a rapid and accurate diagnosis and immediately refer patients with acute retinal stroke to specialized centers. CRAO management should also be facilitated by developing local networks to encourage collaboration among ophthalmologists, retina specialists and stroke neurologists.

Combination of pigment epithelium derived factor with anti-vascular endothelial growth factor therapy protects the neuroretina from ischemic damage

Ocular ischemia is a vision-threatening disease, and is a medical condition associated with many ocular diseases. Anti-VEGF therapy has limitations related to its side effects and suppression of physiological revascularization. Pigment epithelium derived factor (PEDF) has anti-angiogenesis and neurotrophic neuroprotective functions and is a promising agent in the treatment of ischemia-induced retinal neurodegeneration. The purpose of this study is to investigate the effect of PEDF and anti-VEGF and the combined therapy on the ischemic rat eye model ex vivo. In this study, the PEDF protein, anti-VEGF drug (Avastin) or the combination of PEDF and Avastin were intravitreally injected immediately after eye enucleation. Then the eyes were incubated in Dulbecco's modified eagle medium (DMEM) at 4 ℃ for 14 h. After that the eyes were fixed immediately by formalin. VEGF, PEDF and glial fibrillary acidic protein (GFAP) were detected by immunohistochemical (IHC) staining. The IHC staining intensity was evaluated for each eye. Compared to the groups treated by vehicle, PEDF, and anti-VEGF alone, the value of staining intensity of VEGF and GFAP was significantly reduced in the retina and choroidal vessels of the PEDF/Anti-VEGF treatment group. The intravitreally injected PEDF protein can locate in the retina and the choroidal vessels. Compared to the vehicle-treatment group, both the PEDF-treatment and the PEDF/Anti-VEGF treatment groups showed significantly decreased number of TUNEL-positive nuclei, and the PEDF/Anti-VEGF treatment group had the least TUNEL-positive nuclei. Combination of PEDF and an anti-VEGF drug (Avastin) is a possible therapeutic strategy against ischemic retinal and choroidal diseases.

Cyclosporine A Protects Retinal Explants against Hypoxia

The retina is a complex neurological tissue and is extremely sensitive to an insufficient supply of oxygen. Hypoxia plays a major role in several retinal diseases, and often results in the loss of cells that are essential for vision. Cyclosporine A (CsA) is a widely used immunosuppressive drug. Furthermore, treatment with CsA has neuroprotective effects in several neurologic disorders. No data are currently available on the tolerated concentration of CsA when applied to the retina. To reveal the most effective dose, retinal explants from rat eyes were exposed to different CsA concentrations (1-9 µg/mL). Immunohistochemistry with brain-specific homeobox/POU domain protein 3a (Brn3a) and TUNEL staining was performed to determine the percentage of total and apoptotic retinal ganglion cells (RGCs), as well as the responses of micro- and macroglial cells. Furthermore, optical coherence tomography (OCT) scans were performed to measure the changes in retinal thickness, and recordings with multielectrode array (MEA) were performed to evaluate spontaneous RGC spiking. To examine the neuroprotective effects, retinas were subjected to a hypoxic insult by placing them in a nitrogen-streamed hypoxic chamber prior to CsA treatment. In the biocompatibility tests, the different CsA concentrations had no negative effect on RGCs and microglia. Neuroprotective effects after a hypoxic insult on RGCs was demonstrated at a concentration of 9 µg/mL CsA. CsA counteracted the hypoxia-induced loss of RGCs, reduced the percentage of TUNEL⁺ RGCs, and prevented a decrease in retinal thickness. Taken together, the results of this study suggest that CsA can effectively protect RGCs from hypoxia, and the administered concentrations were well tolerated. Further in vivo studies are needed to determine whether local CsA treatment may be a suitable option for hypoxic retinal diseases.

Inhibition of Protein Kinase R by C16 Protects the Retinal Ganglion Cells from Hypoxia-induced Oxidative Stress, Inflammation, and Apoptosis

AIM/PURPOSE

Individually, hypoxia and protein kinase R (PKR) induce retinal ganglion cells (RGCs) damage by aggravating reactive oxygen species (ROS), oxidative stress, inflammation, and apoptosis. However, it is still not established in hypoxia mediates such damaging effect by modulating PKR. This study investigated the expression and activation of PKR in hypoxic RGCs and tested if suppression of PKR by C16 is protective.

MATERIALS AND METHODS

Isolated RGCs were under normoxic or hypoxic conditions for 12 h. In some cases, hypoxic cells were pre-treated with C16, a PKR inhibitor, or n-acetyl cysteine (NAC) a glutathione (GSH) precursor for 1 h and then exposed to hypoxia for the next 12 h.

RESULTS

Hypoxia increased cell death, lactate dehydrogenase (LDH) levels, and levels of single-stranded DNA (ssDNA). It also increased levels of ROS, the activity of the nuclear factor-kappa beta (NF-κB), JNK, and p38 MAPK, expression of Bax, p53, and cleaved caspase-3, levels of tumor necrosis factor-α (TNF-α) and interleukin-6 (IL-6), and cytoplasmic levels of cytochrome-c. It concomitantly suppressed levels of GSH and Bcl-2. All these events were associated with increased phosphorylation (activation) of PKR and its target eukaryotic initiation factor 2 (eIF2). Pre-incubating the cells with NAC completely prevented all these effects in hypoxic cells. Similar protective effects without affecting levels of ROS and GSH levels were also seen in hypoxic cells pre-treated with C16.

CONCLUSION

Hypoxia induces oxidative stress, inflammation, and apoptosis in the RGCs mainly by ROS induced activation of PKR, whereas scavenging ROS by NAC or suppressing PKR by C16 is a novel protective mechanism.

Research Progress of the Application of Hypothermia in the Eye

Hypothermia is widely used in the medical field to protect organs or tissues from damage. Different research fields have different explanations of the protection mechanism of hypothermia. Hypothermia is also widely used in the field of ophthalmology, for example, in the eye bank, the preservation of corneal tissue and the preservation of the eyeball. Low temperature can also be applied to some ophthalmic diseases, such as allergic conjunctivitis, retinal ischemia, and retinal hypoxia. It is used to relieve eye symptoms or reduce tissue damage. Hypothermic techniques have important applications in ophthalmic surgery, such as corneal refractive surgery, vitrectomy surgery, and ciliary body cryotherapy for end-stage glaucoma. Hypothermia can reduce the inflammation of the cornea and protect the retinal tissue. The eyeball is a complex organ, including collagen tissue of the eyeball wall and retinal nerve tissue and retinal blood vessels. The mechanism of low temperature protecting eye tissue is complicated. It is important to understand the mechanism of hypothermia and its applications in ophthalmology. This review introduces the mechanism of hypothermia and its application in the eye banks, eye diseases (allergic conjunctivitis, retinal ischemia, and hypoxia), and eye surgeries (corneal transplant surgery, corneal refractive surgery, and vitrectomy).

Organ Cultures for Retinal Diseases

The successful development of novel therapies is closely linked with understanding the underlying pathomechanisms of a disease. To do so, model systems that reflect human diseases and allow for the evaluation of new therapeutic approaches are needed. Yet, preclinical animal studies often have limited success in predicting human physiology, pathology, and therapeutic responses. Moreover, animal testing is facing increasing ethical and bureaucratic hurdles, while human cell cultures are limited in their ability to represent in vivo situations due to the lack of the tissue microenvironment, which may alter cellular responses. To overcome these struggles, organ cultures, especially those of complex organs such as the retina, can be used to study physiological reactions to substances or stressors. Human and animal organ cultures are now well established and recognized. This mini-review discusses how retinal organ cultures can be used to preserve tissue architecture more realistically and therefore better represent disease-related changes. It also shows how molecular biological, biochemical, and histological techniques can be combined to investigate how anatomical localization may alter cellular responses. Examples for the use of retinal organ cultures, including models to study age-related macular degeneration (AMD), retinitis pigmentosa (RP), central artery occlusion (CRAO), and glaucoma are presented, and their advantages and disadvantages are discussed. We conclude that organ cultures significantly improve our understanding of complex retinal diseases and may advance treatment testing without the need for animal testing.

Ganglion cell layer thickening in patients suffering from Obstructive Sleep Apnea-Hypopnea syndrome with long Mean Apnea-Hypopnea Duration during sleep

PURPOSE

To study the effects of mean apnea-hypopnea duration (MAD), a useful indicator of blood oxygenation, on peripapillary retinal nerve fiber layer (RNFL), macular ganglion cell to inner plexiform layer (GC-IPL) and macular retinal thickness in patients with obstructive sleep apnea-hypopnea syndrome (OSAHS).

METHODS

Sixty-five patients recently diagnosed with OSAHS and 35 healthy individuals were enrolled in this cross-sectional study. OSAHS patients were divided according to their MAD values into group 1 with 16 participants (MAD:10-15.5 s), group 2 with 17 participants (MAD:15.5-19 s), group 3 with 17 participants (MAD:19-30 s) and group 4 with 15 participants (MAD > 30 s). The average and sectorial values of RNFL, GC-IPL and retinal thickness were measured by SS-OCT (DRI OCT Triton, Topcon). Intraocular pressure was recorded by Goldmann Applanation and Pascal Dynamic Contour Tonometer (DCT-IOP).

RESULTS

The average RNFL and retinal thickness values were higher in group 4, but did not reach statistical significance. With the exception of the central 1 mm at the fovea, GC-IPL was always thickened in group 4, and significant differences were evident when its average value was compared with group 2 (p = 0.03), its superior and inferior-nasal values were compared with group 2 (p = 0.02, p = 0.006, respectively) and group 3 (p = 0.01, p = 0.02, respectively), its superior-temporal value was compared with group 3 (p = 0.003) and the control group (p = 0.03), and its superior-nasal value was compared with group 2 (p = 0.03), group 3 (p = 0.001) and the control group (p = 0.03). DCT-IOP was significantly positively correlated with the duration of sleep in which oxygen saturation (SaO₂ ) was decreased under 90% (r = 0.359, p = 0.01).

CONCLUSION

We report a novel observation of GC-IPL thickening in OSAHS patients experiencing long MAD, a parameter which incorporates the severity of breathing events during sleep. Higher DCT-IOP was noted with advancing hypoxemia.

Novel Porcine Retina Cultivation Techniques Provide Improved Photoreceptor Preservation

Age-related macular degeneration (AMD) is the leading cause of blindness in industrialized countries among people over 60 years. It has multiple triggers and risk factors, but despite intense research efforts, its pathomechanisms are currently not completely understood. AMD pathogenesis is characterized by soft drusen in Bruch’s membrane and involves the retinal pigment epithelium–Bruch’s membrane-choroid complex and adjacent structures, like photoreceptors. This study explores the potential of novel cultivation techniques to preserve photoreceptors in retinal explants to gain better insights in AMD pathology. The porcine retina explants were cultured for 4 and 8 days using three different explantation techniques, namely, control (photoreceptors facing down, touching the filter), filter (photoreceptors facing up, turned sample using a filter), and tweezers (photoreceptors facing up, turned sample using tweezers). Optical coherence tomography revealed that the tweezers method had the best capacity to limit thinning of the retinal explants. Both novel methods displayed advantages in maintaining outer segment thickness. Additionally, immunofluorescence evaluation revealed a better preservation of opsin⁺ cells and rhodopsin signal intensity in both novel methods, especially the tweezers method. Furthermore, RT-qPCR analysis demonstrated an upregulation of OPSIN and RHODOPSIN mRNA expression in tweezers samples at 8 days. Amacrine and bipolar cell numbers were not altered at day 4 of cultivation, while cultivation until 8 days led to reduced bipolar cell numbers. At 4 days, CALRETININ mRNA was upregulated in filter samples, but protein kinase C alpha expression was downregulated. Retinal ganglion cells were diminished in both novel techniques due to a direct physical contact with the insert. Remarkably, no difference in TUBB3 mRNA expression was detected among the techniques. Nevertheless, both novel methods exhibited an improved retention of photoreceptor cells. In conclusion, the tweezers technique was the most promising one. Due to the high homology of the porcine to the human retina, it provides a reasonable alternative to in vivo rodent models. Consequently, an adapted coculture system based on the current findings may serve as an ex vivo model suitable to analyze AMD pathomechanisms and novel therapeutic approaches.

Retina in a dish: Cell cultures, retinal explants and animal models for common diseases of the retina

For many retinal diseases, including age-related macular degeneration (AMD), glaucoma, and diabetic retinopathy (DR), the exact pathogenesis is still unclear. Moreover, the currently available therapeutic options are often unsatisfactory. Research designed to remedy this situation heavily relies on experimental animals. However, animal models often do not faithfully reproduce human disease and, currently, there is strong pressure from society to reduce animal research. Overall, this creates a need for improved disease models to understand pathologies and develop treatment options that, at the same time, require fewer or no experimental animals. Here, we review recent advances in the field of in vitro and ex vivo models for AMD, glaucoma, and DR. We highlight the difficulties associated with studies on complex diseases, in which both the initial trigger and the ensuing pathomechanisms are unclear, and then delineate which model systems are optimal for disease modelling. To this end, we present a variety of model systems, ranging from primary cell cultures, over organotypic cultures and whole eye cultures, to animal models. Specific advantages and disadvantages of such models are discussed, with a special focus on their relevance to putative in vivo disease mechanisms. In many cases, a replacement of in vivo research will mean that several different in vitro models are used in conjunction, for instance to analyze and validate causative molecular pathways. Finally, we argue that the analytical decomposition into appropriate cell and tissue model systems will allow making significant progress in our understanding of complex retinal diseases and may furthermore advance the treatment testing.

Effect of hypothermic perfusion on phacoemulsification in cataract patients complicated with uveitis: a randomised trial

Background

To evaluate the effectiveness and safety of hypothermic perfusion in the phacoemulsification of cataract caused by uveitis.

Methods

This was a prospective, single-masked, randomised, controlled clinical trial. One hundred and six patients with uveitis-associated cataract underwent phacoemulsification with perfusion fluid temperature at 4 °C (treatment group) or 24 °C (control group). Anterior chamber inflammation grade, corneal endothelial cell count, corneal thickness, macular fovea thickness, and intraocular pressure (IOP) were observed on the 1st day and 7th day after operation.

Results

The aqueous flare score was 0.83 ± 0.76 in the 4 °C group, which was lower than that in the 24 °C group (1.51 ± 1.02, p = 0.006) on the first day after operation. The aqueous cells score was lower in the 4 °C group (0.17 ± 0.38) than that in the 24 °C group (0.62 ± 0.94, p = 0.025). The mean corneal thickness of incision in the 4 °C group (907.66 ± 85.37 μm) was thinner than that in the 24 °C group (963.75 ± 103.81 μm, p = 0.005). Corneal endothelial cells density, macular fovea thickness, or percentage of transiently increased IOP showed no difference between the two groups (p > 0.05). There was no significant difference in all the main outcome parameters between the two groups on the 7th day after operation (p > 0.05).

Conclusions

Hypothermic perfusion in the phacoemulsification of uveitis-associated cataract is safe, and it can effectively inhibit anterior chamber inflammation and reduce the incisional corneal edema in the early postoperative stage.

Trial registration

The study was registered with the Chinese Clinical Trial Registry. (http://www.chictr.org.cn/, Registration Number: ChiCTR1800016145).

Mouth breathing impairs the development of temporomandibular joint at a very early stage

OBJECTIVES

The study aimed to explore the effects of mouth breathing and hypoxia on the condyle of temporomandibular joint (TMJ) via two animal models.

METHODS

24 four-week-old rats were randomly separated into three groups, consisting of eight control rats, eight intermittent hypoxia (IH) rats, and eight intermittent nasal obstruction (INO) rats. We use the IH model and the INO model to simulate children suffering from hypoxia and mouth breathing. After 16 days, the condyle of TMJ and surrounding white adipose tissue (WAT) and skeletal muscle tissue were obtained for further staining and qRT-PCR. Finally, RNA-seq was used to verify the results.

RESULTS

The intermittent hypoxia cannot significantly change the overall structure in the cause of short-term hypoxia stimulation, but the intermittent nasal obstruction can alter the condyle, WAT, and muscle, while also introducing noticeable structural changes in tissue hypoxia and macrophage infiltration. Sequencing data verified these findings and also suggested that this process might involve the Hif-1α/Vegf axis.

CONCLUSIONS

Our findings reveal the very early structural impact of mouth breathing on condyle reconstruction in rat models, and hypoxia does not induce evident alteration on condyle. However, since these results are mainly focused on rats, further studies are needed to understand its effects on humans.

Melatonin Relations with Energy Metabolism as Possibly Involved in Fatal Mountain Road Traffic Accidents

Previous results evidenced acute exposure to high altitude (HA) weakening the relation between daily melatonin cycle and the respiratory quotient. This review deals with the threat extreme environments pose on body time order, particularly concerning energy metabolism. Working at HA, at poles, or in space challenge our ancestral inborn body timing system. This conflict may also mark many aspects of our current lifestyle, involving shift work, rapid time zone crossing, and even prolonged office work in closed buildings. Misalignments between external and internal rhythms, in the short term, traduce into risk of mental and physical performance shortfalls, mood changes, quarrels, drug and alcohol abuse, failure to accomplish with the mission and, finally, high rates of fatal accidents. Relations of melatonin with energy metabolism being altered under a condition of hypoxia focused our attention on interactions of the indoleamine with redox state, as well as, with autonomic regulations. Individual tolerance/susceptibility to such interactions may hint at adequately dealing with body timing disorders under extreme conditions.

Oxidative stress-induced retinal damage is prevented by mild hypothermia in an ex vivo model of cultivated porcine retinas

BACKGROUND

Hydrogen peroxide (H₂ O₂ ) can be used in vitro to simulate oxidative stress. In retinal organ cultures, H₂ O₂ induces strong neurodegeneration of the retina. It is known that oxidative stress plays a role in the development of several retinal diseases including glaucoma and ischemia. Thus, we investigated whether processes underlying oxidative stress can be prevented by hypothermia using an ex vivo organ culture model of porcine retinas.

METHODS

Porcine retinal explants were cultivated for 5 and 8 days. Oxidative stress was induced via 300 μM H₂ O₂ on day 1 for 3 hours. Hypothermia treatment at 30°C was applied simultaneously with H₂ O₂ , for 3 hours. Retinal ganglion cells (RGCs), apoptosis, bipolar and cholinergic amacrine cells, microglia and macroglia were evaluated immunohistologically. Apoptosis rate was additionally analysed via western blot.

RESULTS

Reduced apoptosis rates through hypothermia led to a preservation of RGCs (P < .001). Amacrine cells were rescued after hypothermia treatment (P = .17), whereas bipolar cells were only protected partly. Additionally, at 8 days, microglial response due to oxidative stress was completely counteracted via hypothermia (P < .001).

CONCLUSIONS

H₂ O₂ induced strong degenerative processes in porcine retinas. The role of oxidative stress in the progression of retinal diseases makes this ex vivo organ culture model suitable to investigate new therapeutic approaches. In the present study, the damaging effect of H₂ O₂ to several retinal cell types was counteracted or strongly alleviated through hypothermia treatment. Especially RGCs, which are affected in glaucoma disease, were protected due to a reduced apoptosis rate through hypothermia.

Species Differences in the Nutrition of Retinal Ganglion Cells among Mammals Frequently Used as Animal Models

The diffusion rate for proper nutrition of the inner retina depends mainly on four factors which are discussed in this review: 1. The diffusion distance between blood and retinal ganglion cells shows morphological variants in different mammalian species, namely a choroidal nutrition type, a retinal nutrition type, and a mixture of both types. 2. Low oxygen concentration levels in the inner retina force the diffusion of oxygen especially in the choroidal nutrition type. Other nutrients might be supplied by surrounding cells, mainly Müller cells. 3. Diffusion in the eye is influenced by the intraocular pressure, which is vital for the retinal ganglion cells but might also influence their proper function. Again, the nutrition types established might explain the differences in normal intraocular pressure levels among different species. 4. Temperature is a critical feature in the eye which has to be buffered to avoid neuronal damage. The most effective buffer system is the increased blood turnover in the choroid which has to be established in all species.