Glaucoma: the retina and beyond

Oxidative Stress-Related Molecular Biomarker Candidates for Glaucoma

Purpose

Glaucoma-related molecular biomarkers can improve clinical testing to diagnose the disease early, predict its prognosis, and monitor treatment responses. Based on the evidence of increased oxidative stress in glaucomatous tissues, this study analyzed oxidative stress–related biomarker candidates in blood and aqueous humor samples with or without glaucoma.

Methods

The blood and aqueous humor samples collected from carefully selected groups of 96 patients with glaucoma and 64 healthy subjects without glaucoma were included in the study. The samples were analyzed for protein carbonyls and advanced glycation end products (AGEs) through ELISA-based quantification assays. To allow proper comparisons, the Goldmann-Witmer coefficient that reflects the ratio of aqueous humor to blood values corrected to total protein concentration in individual samples was calculated.

Results

Blood and aqueous humor levels of protein carbonyls and AGEs were found significantly higher in glaucomatous samples compared with age-matched nonglaucomatous controls (P < 0.001). The glaucoma-related increase in protein carbonyls and AGEs was more prominent in aqueous humor samples than blood samples (2.6-fold versus 1.9-fold for protein carbonyls, and 3.1-fold versus 1.9-fold for AGEs; P < 0.001). Comparison of the Goldmann-Witmer coefficients indicated greater values for protein carbonyls (1.37 ± 0.3 vs. 3.07 ± 0.8) and AGEs (1.2 ± 0.3 vs. 3.2 ± 1.1) in the glaucoma group (P < 0.001).

Conclusions

Findings of this study encourage further validation studies of oxidative stress–related biomarkers in glaucoma. Analysis of protein carbonyls and AGEs in longitudinal studies of larger and heterogeneous patient cohorts should better assess the value of these promising candidates as molecular biomarkers of glaucoma for clinical predictions.

Assessing anesthetic activity through modulation of the membrane dipole potential

There is great individual variation in response to general anesthetics (GAs) leading to difficulties in optimal dosing and sometimes even accidental awareness during general anesthesia (AAGA). AAGA is a rare, but potentially devastating, complication affecting between 0.1% and 2% of patients undergoing surgery. The development of novel personalized screening techniques to accurately predict a patient’s response to GAs and the risk of AAGA remains an unmet clinical need. In the present study, we demonstrate the principle of using a fluorescent reporter of the membrane dipole potential, di-8-ANEPPs, as a novel method to monitor anesthetic activity using a well-described inducer/noninducer pair. The membrane dipole potential has previously been suggested to contribute a novel mechanism of anesthetic action. We show that the fluorescence ratio of di-8-ANEPPs changed in response to physiological concentrations of the anesthetic, 1-chloro-1,2,2-trifluorocyclobutane (F₃), but not the structurally similar noninducer, 1,2-dichlorohexafluorocyclobutane (F₆), to artificial membranes and in vitro retinal cell systems. Modulation of the membrane dipole provides an explanation to overcome the limitations associated with the alternative membrane-mediated mechanisms of GA action. Furthermore, by combining this technique with noninvasive retinal imaging technologies, we propose that this technique could provide a novel and noninvasive technique to monitor GA susceptibility and identify patients at risk of AAGA.

Poly(ε-caprolactone) nanocapsule carriers with sustained drug release: single dose for long-term glaucoma treatment

Glaucoma is an eye-related disease accompanied by highly elevated intraocular pressure (IOP), which causes damage to the optic nerve and results in vision loss and even blindness. Although the treatment of glaucoma with eye drops may reduce the IOP, eye drops have some limitations, such as poor patient compliance and short duration. To develop drug carriers that facilitate the sustained and long-term release of drugs for glaucoma therapy, we synthesized poly(ε-caprolactone) nanoparticles (PCL NPs) capable of loading pilocarpine, a widely used drug for the treatment of dry eye and glaucoma. We prepared two types of PCL NPs, namely, nanospheres (NSs), which are solid spheres capable of harboring the drug in their solid mass, and nanocapsules (NCs), which are hollow spherical structures for encapsulating the drug. The influence of the vesicular structure of PCL NPs on the drug loading efficiencies and release was investigated. The loading of pilocarpine in the PCL NCs was approximately 3 times higher than that in the PCL NSs. In addition, pilocarpine-loaded PCL NCs (PILO-PCL NCs) exhibited a sustained drug release profile. Effective pharmacological responses (i.e., IOP reduction and pupillary constriction) were observed in rabbits intracamerally treated with pilocarpine-loaded PCL NPs. Moreover, the PILO-PCL NCs show long-term therapeutic ability in alleviating ocular hypertension-induced corneal and retinal injuries under physiological conditions, even after 42 days. The results of in vivo studies also reveal that the PCL NCs are advantageous for the treatment of chronic ocular hypertension in glaucomatous eyes.

Interaction of Wip1 and NF-κB regulates neuroinflammatory response in astrocytes

OBJECTIVE

The aims of the present study were to detect the interaction of Wip1 and NF-κB P65 in retina of an LPS-induced astrocytes activation model.

METHODS

The interaction between Wip1 and nuclear factor kappa B (NF-κB) P65 was observed in lipopolysaccharide (LPS)-stimulated primary rat astrocytes derived from retina. The expressions of Wip1 and NF-κB P65 were evaluated using Western blot and RT-PCR. Small interfering RNA (siRNA) against Wip1 was transfected into astrocytes to clarify the phosphorylation status and nuclear translocation of NF-κB P65 and expressions of these proinflammatory factors. Meanwhile, expression of Wip1 was assessed following treatment with NF-κB inhibitor.

RESULTS

Wip1 and phospho-NF-κB P65 (p-P65) expressions were significantly increased and colocalization in astrocytes after LPS treatment. The expression of p-P65 was augmented by transfected with Wip1 siRNA followed by LPS. Furthermore, pre-treatment with Wip1 siRNA further enhanced LPS-induced NF-κB P65 translocation into the nuclei and proinflammatory cytokine release. Finally, inhibition of NF-κB decreases Wip1 expression and transcription in primary astrocytes.

CONCLUSION

These data provide a mechanism for the role for a negative feedback loop of Wip1 and NF-κB in LPS-induced astrocytic activation.

Establishment and Characterization of an Acute Model of Ocular Hypertension by Laser-Induced Occlusion of Episcleral Veins

Purpose

This study was designed to develop and characterize a laser-induced model of acute intraocular hypertension that permits the study of the anterior segment of the eye.

Methods

CD1 mice aged 5 and 8 weeks were examined for elevation of IOP induced by laser photocoagulation. We compared between occlusion of episcleral veins alone and when combined with 270° limbal vessel occlusion. Anterior chamber angle, corneal thickness, and retinal nerve fiber layer (RNFL) thickness were evaluated by anterior- and posterior-segment optical coherence tomography (OCT). Additionally, at day 7 post-procedure, the anterior segment was evaluated for inflammatory cellular presentation by histologic analysis and OCT, and limbal vessels and whole-mount retina were immunostained for CD31 and Brn3a, respectively. Brn3a-positive retinal ganglion cells (RGCs) were quantified with ImageJ software.

Results

After single or combined laser treatment in mice aged 5 or 8 weeks, IOP was significantly elevated for 5 to 6 days before returning to the baseline by day 7 post-procedure. Anterior segment assessment indicated less synechiae in the anterior chamber angle and better preserved limbal vessels with single versus combined laser treatment. Corneal thickness was significantly increased after single or combined treatment. No inflammatory cells were detected in the anterior chamber. The thickness of the RNFL and the density of RGCs were both significantly reduced after single or combined treatment.

Conclusions

Laser photocoagulation of episcleral veins alone in CD1 mice aged 5 to 8 weeks may be used to induce ocular hypertension resulting in RNFL thinning and ganglion cell loss. This model permits the study of the anterior as well as the posterior segment of the eye.

Cellular Reparative Mechanisms of Mesenchymal Stem Cells for Retinal Diseases

The use of multipotent mesenchymal stem cells (MSCs) has been reported as promising for the treatment of numerous degenerative disorders including the eye. In retinal degenerative diseases, MSCs exhibit the potential to regenerate into retinal neurons and retinal pigmented epithelial cells in both in vitro and in vivo studies. Delivery of MSCs was found to improve retinal morphology and function and delay retinal degeneration. In this review, we revisit the therapeutic role of MSCs in the diseased eye. Furthermore, we reveal the possible cellular mechanisms and identify the associated signaling pathways of MSCs in reversing the pathological conditions of various ocular disorders such as age-related macular degeneration (AMD), retinitis pigmentosa, diabetic retinopathy, and glaucoma. Current stem cell treatment can be dispensed as an independent cell treatment format or with the combination of other approaches. Hence, the improvement of the treatment strategy is largely subjected by our understanding of MSCs mechanism of action.

Topical Coenzyme Q10 demonstrates mitochondrial-mediated neuroprotection in a rodent model of ocular hypertension

Coenzyme Q10 (CoQ10) is a mitochondrial-targeted antioxidant with known neuroprotective activity. Its ocular effects when co-solubilised with α-tocopherol polyethylene glycol succinate (TPGS) were evaluated. In vitro studies confirmed that CoQ10 was significantly protective in different retinal ganglion cell (RGC) models. In vivo studies in Adult Dark Agouti (DA) rats with unilateral surgically-induced ocular hypertension (OHT) treated with either CoQ10/TPGS micelles or TPGS vehicle twice daily for three weeks were performed, following which retinal cell health was assessed in vivo using DARC (Detection of Apoptotic Retinal Cells) and post-mortem with Brn3a histological assessment on whole retinal mounts. CoQ10/TPGS showed a significant neuroprotective effect compared to control with DARC (p<0.05) and Brn3 (p<0.01). Topical CoQ10 appears an effective therapy preventing RGC apoptosis and loss in glaucoma-related models.

Management of glaucoma as a neurodegenerative disease

Glaucoma is a neurodegenerative disease with an estimated prevalence of 60 million people, and the most common cause of irreversible blindness worldwide. The mainstay of treatment has been aimed at lowering intraocular pressure, currently the only modifiable risk factor. Unfortunately, despite adequate pressure control, many patients go on to suffer irreversible visual loss. We first briefly examine currently established intraocular pressure lowering-treatments, with a discussion of their roles in neuroprotection as demonstrated by both animal and clinical studies. The review then examines currently available intraocular pressure independent agents that have shown promise for possessing neuroprotective effects in the management of glaucoma. Finally, we explore potential future treatments such as immune-modulation, stem cell therapy and neural regeneration as they may provide further protection against the neurodegenerative processes involved in glaucomatous optic neuropathy.

Stem cell therapies for retinal diseases: recapitulating development to replace degenerated cells

Retinal degenerative diseases are the leading causes of blindness worldwide. Replacing lost retinal cells via stem cell-based therapies is an exciting, rapidly advancing area of translational research that has already entered the clinic. Here, we review the status of these clinical efforts for several significant retinal diseases, describe the challenges involved and discuss how basic developmental studies have contributed to and are needed to advance clinical goals.

[Clinical, morphological and molecular biological characteristics of the aging eye]

BACKGROUND

The physiological aging of the eye is associated with loss of visual function. Age-related changes of the eye can result in ophthalmological diseases. The aim of this article is to display morphological, histological and molecular biological alterations of the aging eye.

MATERIAL AND METHODS

A web-based search and review of the literature for aging of the visual system including cornea, lens, vitreous humor, retina, retinal pigment epithelium (RPE), choroidea and optic nerve were carried out. The most important results related to morphological, histological and molecular biological changes are summarized.

RESULTS

Age-related, morphological alterations can be found in preretinal structures, e. g. cornea, lens and vitreous humor, as well as neuronal structures, such as the retina. In addition to negligible clinical signs of the aging eye, there are clinically relevant changes which can develop into pathological ophthalmological diseases. These transitions from age-related alterations to relevant ophthalmological diseases, e. g. age-related macular degeneration and glaucoma are continuous.

CONCLUSION

An understanding of aging could provide predictive factors to detect the conversion of physiological aging into pathological conditions. The derivation of physiological markers or new approaches to detection and treatment of disease-related entities associated with the risk factor aging are desirable. Translational approaches in clinical and basic science are necessary to provide new therapeutic options for relevant ophthalmological diseases in the future.

Ocular indicators of Alzheimer's: exploring disease in the retina

Although historically perceived as a disorder confined to the brain, our understanding of Alzheimer's disease (AD) has expanded to include extra-cerebral manifestation, with mounting evidence of abnormalities in the eye. Among ocular tissues, the retina, a developmental outgrowth of the brain, is marked by an array of pathologies in patients suffering from AD, including nerve fiber layer thinning, degeneration of retinal ganglion cells, and changes to vascular parameters. While the hallmark pathological signs of AD, amyloid β-protein (Aβ) plaques and neurofibrillary tangles (NFT) comprising hyperphosphorylated tau (pTau) protein, have long been described in the brain, identification of these characteristic biomarkers in the retina has only recently been reported. In particular, Aβ deposits were discovered in post-mortem retinas of advanced and early stage cases of AD, in stark contrast to non-AD controls. Subsequent studies have reported elevated Aβ42/40 peptides, morphologically diverse Aβ plaques, and pTau in the retina. In line with the above findings, animal model studies have reported retinal Aβ deposits and tauopathy, often correlated with local inflammation, retinal ganglion cell degeneration, and functional deficits. This review highlights the converging evidence that AD manifests in the eye, especially in the retina, which can be imaged directly and non-invasively. Visual dysfunction in AD patients, traditionally attributed to well-documented cerebral pathology, can now be reexamined as a direct outcome of retinal abnormalities. As we continue to study the disease in the brain, the emerging field of ocular AD warrants further investigation of how the retina may faithfully reflect the neurological disease. Indeed, detection of retinal AD pathology, particularly the early presenting amyloid biomarkers, using advanced high-resolution imaging techniques may allow large-scale screening and monitoring of at-risk populations.