Reduction of Apoptosis in Ischemic Retinas of Two Mouse Models Using Hyperbaric Oxygen Treatment

Hyperbaric Oxygen Therapy in Ophthalmology: A Narrative Review

Hyperbaric oxygen therapy (HBOT) has been used for the past 50 years for conditions such as decompression disease and wound healing. It has promising effects in the treatment of vision-threatening diseases, such as retinal artery occlusion, retinal vein occlusion, diabetic macular edema, and acute optic neuropathy; however, HBOT has not been approved for use in these conditions by regulatory authorities. This paper provides an overview of the theoretical effectiveness and most recent indications for HBOT in ophthalmology. The fundamental aspects of the physiology of choroidal circulation and metabolism are provided together with the clinical aspects that should be accounted for when selecting patients for this therapy. The paper also presents case reports of when HBOT was successfully implemented. The goals of this review were to explore the indications and benefits of HBOT and to evaluate the effectiveness of HBOT as an intervention in treating ophthalmology disorders. Lastly, the paper details the side-effects and discusses the safety issues of HBOT.

Hyperbaric oxygen therapy as rescue therapy for pediatric frosted branch angiitis with Purtscher-like retinopathy: A case report

Introduction

Frosted branch angiitis (FBA) is an uncommon uveitis characterized by fulminant retinal vasculitis. Purtscher-like retinopathy (PuR) is a rare retinal angiopathy associated with a non-traumatic etiology. Both FBA and PuR can cause profound visual impairments.

Case report

We describe the case of a 10-year-old male who presented with sudden bilateral painless visual loss due to FBA with concurrent PuR, with notable viral prodrome 1 month prior to presentation. Systemic investigations revealed a recent herpes simplex virus 2 infection with a high titer of IgM, positive antinuclear antibody (ANA) (1:640), and abnormal liver function tests. After administration of systemic corticosteroids, anti-viral agents, and subsequent immunosuppressive medications, the FBA was gradually alleviated. However, fundoscopy and optical coherence tomography (OCT) revealed persistent PuR and macular ischemia. Hence, hyperbaric oxygen therapy was administered as a rescue strategy, which resulted in gradual bilateral visual acuity improvement.

Conclusion

Hyperbaric oxygen therapy may be a beneficial rescue treatment for retinal ischemia secondary to FBA with PuR.

Role of Oxidative Stress in Ocular Diseases Associated with Retinal Ganglion Cells Degeneration

Ocular diseases associated with retinal ganglion cell (RGC) degeneration is the most common neurodegenerative disorder that causes irreversible blindness worldwide. It is characterized by visual field defects and progressive optic nerve atrophy. The underlying pathophysiology and mechanisms of RGC degeneration in several ocular diseases remain largely unknown. RGCs are a population of central nervous system neurons, with their soma located in the retina and long axons that extend through the optic nerve to form distal terminals and connections in the brain. Because of this unique cytoarchitecture and highly compartmentalized energy demand, RGCs are highly mitochondrial-dependent for adenosine triphosphate (ATP) production. Recently, oxidative stress and mitochondrial dysfunction have been found to be the principal mechanisms in RGC degeneration as well as in other neurodegenerative disorders. Here, we review the role of oxidative stress in several ocular diseases associated with RGC degenerations, including glaucoma, hereditary optic atrophy, inflammatory optic neuritis, ischemic optic neuropathy, traumatic optic neuropathy, and drug toxicity. We also review experimental approaches using cell and animal models for research on the underlying mechanisms of RGC degeneration. Lastly, we discuss the application of antioxidants as a potential future therapy for the ocular diseases associated with RGC degenerations.

Hyperbaric Oxygen Therapy for Central Retinal Artery Occlusion: Patient Selection and Perspectives

The central retinal artery occlusion (CRAO) is a rare ophthalmological emergency that can occur in the eye. CRAO can affect persons of any age, however it is most common in people over the age of 60. CRAO is associated with a number of risk factors, including giant cell arteritis, carotid artery atherosclerosis, cardiogenic emboli, hypertension, smoking, diabetes, and thromboembolic disease. The chance of each of these etiologies being present is assessed during the course of the investigation. Hyperbaric oxygen treatment (HBOT) is classified by the American Heart Association for CRAO at level IIb. In accordance with that, HBOT might be considered for the treatment of such a severe condition. HBOT can maintain retinal oxygenation during ischemic events by allowing oxygen to diffuse through choroidal capillaries that have been exposed to elevated partial pressures of oxygen. As a result, ischemia-related damage is reversed if applied within proper time frame. The amount of time that has passed prior to initiation of HBOT is considered to be the most critical factor in determining the best visual prognosis. According to the Undersea and Hyperbaric Medical Society, patients who are identified with CRAO after the onset of symptoms should be evaluated for HBOT within 24 hours. HBOT has the advantage of having a low risk profile, and it can be utilized to improve visual outcomes in proper patients.

Hyperbaric Oxygen Therapy for Mumps-Associated Outer Retinitis with Frosted Branch Angiitis

PURPOSE

To describe a case of outer retinitis with frosted branch angiitis associated with mumps infection treated with hyperbaric oxygen (HBO) therapy.

METHODS

Observational case report.

CASE REPORT

A four-year-old boy with bilateral blindness was diagnosed with necrotizing outer retinitis with frosted branch angiitis associated with serologically confirmed mumps virus infection. He was treated with HBO therapy. Visual acuity subsequently improved to 20/40 in the right eye and to 20/320 in the left eye. Sequential follow-up optical coherence tomography examinations showed progressive recovery of the outer retinal layers in the right eye.

CONCLUSION

HBO therapy appears to be a feasible and safe treatment that might improve the anatomical and functional outcome in patients with mumps retinitis.

Protective effect of hyperbaric oxygen treatment on rat intestinal mucosa after mesenteric ischaemia and reperfusion

INTRODUCTION

Mesenteric ischaemia results from a lack of adequate blood flow to and oxygenation of the mesentery and intestines. The aim of the present study was to evaluate the effect of hyperbaric oxygen treatment (HBOT) on the healing process in intestinal mucosa of rats undergoing mesenteric ischaemia and reperfusion.

METHODS

Thirty-two Wistar-Albino rats were divided into four groups of eight: 1) ischaemia/reperfusion (I/R); 2) sham operation; 3) I/R+HBOT started 6 hours after reperfusion; 4) I/R+HBOT started 12 hours after reperfusion. In the I/R groups, a vascular clamp was placed across the superior mesenteric artery to occlude arterial circulation for 60 minutes, followed by reperfusion. A dose of HBOT consisted of 100% oxygen breathing for 90 minutes at 2.5 atmospheres absolute pressure. Thirteen doses of HBOT were administered after ischaemia. The rats were sacrificed on the eighth day, and their intestinal tissues were harvested for histopathologic analysis. The tissue levels of catalase, malondialdehyde, and glutathione were determined.

RESULTS

The histopathological scores (HSCORE) were consistent with macroscopic examinations. The scores were significantly higher (worse) in Group 1 compared to Group 2, Group 3, and Group 4 (for all comparisons, P < 0.05). Group 4's HSCORE was significantly higher than those of Group 2 and Group 3 (for both comparisons P < 0.05). Group 3's HSCOREs were only marginally higher than Group 2. Group 3 exhibited higher glutathione levels than Group 1 (P < 0.05). There were no significant differences across the groups with respect to malondialdehyde and catalase levels.

CONCLUSION

A beneficial effect of HBOT was observed on oxidative stress and inflammation in acute mesenteric ischaemia-reperfusion.

Lycium barbarum polysaccharides protects retinal ganglion cells against oxidative stress injury

The accumulation of excessive reactive oxygen species can exacerbate any injury of retinal tissue because free radicals can trigger lipid peroxidation, protein damage and DNA fragmentation. Increased oxidative stress is associated with the common pathological process of many eye diseases, such as glaucoma, diabetic retinopathy and ischemic optic neuropathy. Many studies have demonstrated that Lycium barbarum polysaccharides (LBP) protects against oxidative injury in numerous cells and tissues. For the model of hypoxia we used cultured retinal ganglion cells and induced hypoxia by incubating with 200 µM cobalt chloride (CoCl₂) for 24 hours. To investigate the protective effect of LBP and its mechanism of action against oxidative stress injury, the retinal tissue was pretreated with 0.5 mg/mL LBP for 24 hours. The results of flow cytometric analysis showed LBP could effectively reduce the CoCl₂-induced retinal ganglion cell apoptosis, inhibited the generation of reactive oxygen species and the reduction of mitochondrial membrane potential. These findings suggested that LBP could protect retinal ganglion cells from CoCl₂-induced apoptosis by reducing mitochondrial membrane potential and reactive oxygen species.

Hyperbaric Oxygen Therapy in Retinal Arterial Occlusion: Epidemiology, Clinical Approach, and Visual Outcomes

Purpose

To evaluate the efficacy and safety of hyperbaric oxygen therapy (HBOT) in patients with acute retinal artery occlusion (RAO). Secondarily, to analyse the epidemiology and the clinical approach.

Methods

Retrospective study of 13 patients submitted to HBOT between 2013 and 2018. The analysed parameters consisted of: systemic history, time between symptoms onset and treatment, initial approach, number of HBOT sessions, complications of HBOT and best corrected visual acuity—BCVA (of the total sample, central RAO—CRAO—group, and branch RAO—BRAO group).

Results

Arterial hypertension was the most prevalent systemic risk factor (53.8%). Initial therapies were 100% normobaric oxygen administration, topical and oral hypotensive medication, eye massage and aspirin. CRAO was observed in 69.2% and BRAO in 30.8% of the cases, with clinically significant visual improvement (a decrease in logMAR of 0.3) in 55.5% and 75%, respectively. Time between symptoms onset and treatment had a median of 9 hours. The median number of HBOT sessions was 7, without complications.

Conclusions

HBOT provide BCVA improvement in patients with RAO, when it is performed in an early time after the symptom onset. It seems to be an effective and safe therapeutic option for a pathology that still remains without approved treatment.

Development of visual acuity under hyperbaric oxygen treatment (HBO) in non arteritic retinal branch artery occlusion

PURPOSE

Nonperfusion of retinal tissue due to arterial occlusion leads inevitably to mostly irreversible retinal damage. Until today no evidence-based treatment exists. Inhalation of 100% oxygen at high atmospheric pressure causes an increased solubility of oxygen in the blood that helps the retinal tissue to survive through diffusion in case of an artery occlusion till vascular recanalization occurs. Hence the purpose of this study is to compare the visual outcome in patients with retinal branch artery obstruction treated with hyperbaric oxygen versus patients treated with hemodilution only.

METHODS

Non-randomized, monocentric, retrospective study. Patients with diagnosis of non-arteritic retinal branch artery occlusion (BRAO) treated with hyperbaric oxygen therapy between 1997 and 2017. Exclusion criteria were central retinal artery occlusion, presence of a cilioretinal artery and arteritic cases. The control group was matched based on visual acuity (VA) at admission, age, and delay between symptoms and beginning of clinical care.

RESULTS

The control group and the matching oxygen group contained 14 patients each. Initial VA in the matched HBO group was 0.18 ± 0.19 and 0.23 ± 0.19 in the control group (p = 0.57). Final VA at discharge was 0.69 ± 0.29 in the matched oxygen group and 0.32 ± 0.23 in the control group (p = 0.0009). HBO-treated patients had a significant visual increase compared with the control group. The most common comorbidities were arterial hypertension and vascular sclerosis.

CONCLUSION

HBO treatment appears to have a beneficial effect on visual outcome in patients with retinal branch artery occlusion. HBO treatment could be a rescue therapy at an early stage of BRAO, especially to bridge the time of a potential reperfusion. However, further, prospective, randomized clinical trials are required to verify this assumption.

Animal Models Used to Simulate Retinal Artery Occlusion: A Comprehensive Review

Purpose

To present an overview of animal models of retinal artery occlusion (RAO).

Methods

Through a systematic literature search in PubMed and Embase, papers describing methods of inducing RAO in animal models were included. The identified methodologic approaches were presented in a narrative synthesis and compared with RAO in humans.

Results

In total, 83 papers reporting on 88 experiments were included. Six different species were used with rodents and monkeys being the most common, and a minority were performed using cats, dogs, rabbits, or pigs. The anatomy of pigs and monkeys resemble that of humans most closely. The two most frequently used methods were laser-induced occlusion or ligation of the arteries. Other methods included raised intraocular pressure, arterial clamping, administration of vasoconstricting agents, the use of an occluder, embolization, and endovascular approaches to induce occlusion. In general, occlusions lasted for only 30 to 90 minutes, often followed by reperfusion.

Conclusions

Although a broad range of methods have previously been used, they all have limitations. Preferably, the methods should imitate the human disease as closely as possible and avoid damaging other structures. Therefore, monkeys followed by pigs are to be preferred and ligation or clamping may be a suitable model in larger animals as there is a potential to isolate and occlude the retinal artery only. Being less invasive, laser-induced occlusion is another suitable approach.

Translational Relevance

This review aims at assisting researchers in deciding on the most ideal experimental setting, and thereby increase the translational value to human disease.

The novel chalcone analog L2H17 protects retinal ganglion cells from oxidative stress-induced apoptosis

Chalcone is a plant metabolite widely found in fruits, vegetables, spices and tea, and has anti-tumor, anti-inflammation, immunomodulation, antibacterial and anti-oxidation activities, as well as many other pharmacological and biological effects. Our team has shown that its analogs have antioxidant activity, and oxidative stress is a pathological hallmark of retinal ischemia/reperfusion injury that can lead to retinal damage and visual loss. This investigation aims to identify a chalcone that protects retinal ganglion cells in vitro from the effects of oxidative stress and examine its mechanism. Rat retinal ganglion cell-5 cells were pretreated with chalcones and then exposed to tert-butyl hydroperoxide that causes oxidative damage. Controls received dimethyl sulfoxide only or tert-butyl hydroperoxide in dimethyl sulfoxide. Only (E)-3,4-dihydroxy-2'-methylether ketone (L2H17), of the five chalcone analogs, markedly increased the survival rate of oxidatively injured RGC-5 cells. Thus, subsequent experiments only analyzed the results of the L2H17 intervention. Cell viability and apoptosis were measured. Intracellular superoxide dismutase and reactive oxygen species levels were used to assess induced oxidative stress. The mechanism of action by L2H17 was explored by measuring the ER stress/UPR pathway and the expression and localization of Nrf2. All results demonstrated that L2H17 could reduce the apoptosis of oxidatively injured cells, inhibit caspase-3 activity, increase Bcl-2 expression, decrease Bad expression, increase the activity of superoxide dismutase, inhibit the production of reactive oxygen species, increase Nrf2 immunoreactivity, and reduce the activating transcription factor 4, phospho-eukaryotic initiation factor 2 and CHOP expression. L2H17 protects retinal ganglion cells induced by oxidative stress by regulating Nrf2, which indicates that it has the potential to become a drug for retinal ischemia/reperfusion.

Oxygen therapy in patients with retinal artery occlusion: A meta-analysis

BACKGROUND

Oxygen therapy has been widely used for RAO (retinal artery occlusion) patients; however, inconsistent results have been reported.

METHODS

PubMed, Web of Science, EMBASE, Medline (OvidSP), Cochrane, China National Knowledge Infrastructure (CNKI), and Wanfang Database were examined. The primary endpoint was visual acuity (VA), and RevMan software 5.3 was used to statistically analyze the outcomes.

RESULTS

Seven randomized controlled trials (RCTs) met the inclusion criteria. Patients who received oxygen therapy exhibited probability of visual improvement about 5.61 times compared with the control group who did not receive oxygen therapy (OR = 5.61; 95% CI, 3.60-8.73; p < 0.01). No statistically significant difference was observed between oxygen inhalation methods (Chi2 = 0.18, df = 1, p = 0.67), combined therapy (Chi2 = 0.21, df = 1, p = 0.64), or RAO type (Chi2 = 0.06, df = 1, p = 0.81). Conversely, 100% oxygen (Chi2 = 4.55, df = 1, p < 0.05) and hyperbaric oxygen (Chi2 = 4.55, df = 1, p < 0.05) significantly improved VA in RAO patients. Better effect was showed in period within 3 months (Chi2 = 5.76, df = 1, p < 0.05). The most effective treatment length was over 9 hours (Chi2 = 6.58, df = 1, p < 0.05).

CONCLUSION

Oxygen therapy demonstrated beneficial effects in improving VA in RAO patients, particularly when patients were treated with 100% hyperbaric oxygen and for over 9 hours.

[Retinal artery occlusion]

Retinal artery occlusion leads to profound visual impairment in the affected eye. It is rarely caused by local ophthalmic pathologies. Most patients present with a large number of cardio- and cerebrovascular risk factors. Visual loss is the leading symptom in central retinal artery occlusion (CRAO), whereas a circumscribed visual field defect is claimed in branch retinal artery occlusion (BRAO). Although many attempts have been made to improve the course of the disease, no effective therapy is available. There is some hope that intravenous fibrinolysis could influence the natural course but the therapeutic window is small (ca. 4.5 h), and treatment efficacy is still not proven. It is important for ophthalmologists to guide the patients to a comprehensive and prompt neurological and cardiological diagnostic work-up.

Early Onset of Ocular Neovascularization After Hyperbaric Oxygen Therapy in a Patient With Central Retinal Artery Occlusion

Central retinal artery occlusion (CRAO) is an infarction to the retina that results in acute, frequently severe vision loss. Long-term complications such as ocular neovascularization (ONV) can occur and result in neovascular glaucoma and vitreous hemorrhage. Recent studies have explored acute hyperbaric oxygen (HBO) therapy as a promising treatment for CRAO to improve long-term vision potential; however, its effects on CRAO complications have not been well characterized. This study was conducted to better characterize the effects of HBO therapy on complications from CRAO. We present a unique case of ONV in an eye within 1 month after successfully completing acute HBO therapy for a CRAO, highlighting the importance of routine monitoring in this unique population.

Comparison of hyperbaric oxygen versus iloprost treatment in an experimental rat central retinal artery occlusion model

PURPOSE

Central retinal artery occlusion (CRAO) is one of the serious ophthalmological emergencies with poor visual prognosis. Iloprost is a stable prostacyclin analogue and has prominent anti-edema, anti-inflammatory, vasodilatory, and antiagregant effects. The main objective of this work was to investigate iloprost as an alternative agent versus hyperbaric oxygen (HBO) in the treatment of CRAO.

METHODS

Twenty-eight healthy Wistar albino male rats were randomly assigned into control (n = 7, sham operation), HBO (n = 7), iloprost (n = 7), and sham groups (n = 7). CRAO model was created through optic nerve exploration and ligation. Full-thickness retina (FTR), outer nuclear layer (ONL), inner nuclear layer (INL) and ganglion cell layer (GCL) thickness were measured on Hematoxylin/Eosin (H&E) stained retinal sections and immunohistochemical analysis including terminal deoxynucleotidyl transferase-mediated biotindeoxyuridine triphosphate nick-end labeling (TUNEL) assay was performed to determine the apoptotic index (AI).

RESULTS

AI values of HBO (0.204 ± 0.067) and iloprost (0.197 ± 0.052) groups were significantly lower than sham (0.487 ± 0.046) group (p < 0.001). Any significant difference was found between the HBO and iloprost groups in terms of AI (p = 0.514). A statistically significant increase in thickness of FTR, ONL, INL and GCL was detected in HBO, iloprost and sham groups compared to the control group (p = 0.002). FTR, ONL, INL and GCL thickness were significantly thinner in HBO and iloprost groups than in the sham group (p = 0.002). A significant lesser increase was observed in all the retinal layers thickness in iloprost group versus HBO group (p = 0.002) except for INL (p = 0.665).

CONCLUSIONS

The study results demonstrated anti-edema, neuroprotective, and anti-apoptotic effects of iloprost quantitatively; thus, iloprost may be a beneficial alternative agent in the treatment of CRAO.

Inhibiting Matrix Metalloproteinase 3 Ameliorates Neuronal Loss in the Ganglion Cell Layer of Rats in Retinal Ischemia/Reperfusion

It has been demonstrated that matrix metalloproteinase 3 (MMP3) is integrally involved in the neuronal degeneration of the central nervous system by promoting glial activation, neuronal apoptosis and damage to the brain-blood barrier. However, whether MMP3 also contributes to the neuronal degeneration induced by retinal ischemia/reperfusion is still uncertain. In the present study, we detected the cellular localization of MMP3 in adult rat retinae and explored the relationship of its expression with neuronal loss in the ganglion cell layer (GCL) in retinal ischemia/reperfusion. We found that MMP3 was widely expressed in many cells throughout the layers of the rat retinae, including Vertebrate neuron-specific nuclear protein (NeuN)-, parvalbumin-, calbindin-, protein kinase C-α-, glial fibrillary acidic protein-, glutamine synthetase- and CD11b-positive cells. Furthermore, all rats were treated with high intraocular pressure (HIOP) for 1 h (h) and sacrificed at 6 h, 1 day (d), 3 d, and 7 d after HIOP. Compared to the normal control, the expression of both proenzyme MMP3 and active MMP3 were significantly up-regulated after HIOP treatment without alteration of the laminar distribution pattern. Moreover, inhibiting MMP3 ameliorated the loss of NeuN-positive cells in the GCL following HIOP. In summary, our data demonstrates that MMP3 is expressed in multiple types of neurons and glial cells in normal rat retinae. Simultaneously, the up-regulation of its expression and activity are closely involved in neuronal loss in the GCL in retinal ischemia/reperfusion.

Peptide-binding GRP78 protects neurons from hypoxia-induced apoptosis

Brain ischemia has major consequences leading to the apoptosis of astrocytes and neurons. Glucose-regulated protein 78 (GRP78) known for its role in endoplasmic reticulum stress alleviation was discovered on several cell surfaces acting as a receptor for signaling pathways. We have previously described peptides that bind cell surface GRP78 on endothelial cells to induce angiogenesis. We have also reported that ADoPep1 binds cardiomyocytes to prevent apoptosis of ischemic heart cells. In this study we describe the effect of hypoxia on astrocytes and neurons cell surface GRP78. Under hypoxic conditions, there was an increase of more than fivefold in GRP78 on cell surface of neurons while astrocytes were not affected. The addition of the GRP78 binding peptide, ADoPep1, to neurons decreased the percentage of GRP78 positive cells and did not change the percent of astrocytes. However, a significant increase in early and late apoptosis of both astrocytes and neurons under hypoxia was attenuated in the presence of ADoPep1. Intravitreal administration of ADoPep1 to mice in a model of optic nerve crush significantly reduced retinal cell loss after 21 days compared to the crush-damaged eyes without treatment or by control saline vehicle injection. Histological staining demonstrated reduced GRP78 after ADoPep1 treatment. The mechanism of peptide neuroprotection was demonstrated by the inhibition of hypoxia induced caspase 3/7 activity, cytochrome c release and p38 phosphorylation. This study is the first report on hypoxic neuronal and astrocyte cell surface GRP78 and suggests a potential therapeutic target for neuroprotection.