Neuroprotection and other novel therapies for glaucoma

Abnormal Topological Organization of White Matter Structural Networks in Normal Tension Glaucoma Revealed via Diffusion Tensor Tractography

BACKGROUND

Normal tension glaucoma (NTG) is considered a neurodegenerative disease with glaucomatous damage extending to diffuse brain areas. Therefore, this study aims to explore the abnormalities in the NTG structural network to help in the early diagnosis and course evaluation of NTG.

METHODS

The structural networks of 46 NTG patients and 19 age- and sex-matched healthy controls were constructed using diffusion tensor imaging, followed by graph theory analysis and correlation analysis of small-world properties with glaucoma clinical indicators. In addition, the network-based statistical analysis (NBS) method was used to compare structural network connectivity differences between NTG patients and healthy controls.

RESULTS

Structural brain networks in both NTG and NC groups exhibited small-world properties. However, the small-world index in the severe NTG group was reduced and correlated with a mean deviation of the visual field (MDVF) and retinal nerve fiber layer (RNFL) thickness. When compared to healthy controls, degree centrality and nodal efficiency in visual brain areas were significantly decreased, and betweenness centrality and nodal local efficiency in both visual and nonvisual brain areas were also significantly altered in NTG patients (all p < 0.05, FDR corrected). Furthermore, NTG patients exhibited increased structural connectivity in the occipitotemporal area, with the left fusiform gyrus (FFG.L) as the hub (p < 0.05).

CONCLUSIONS

NTG exhibited altered global properties and local properties of visual and cognitive-emotional brain areas, with enhanced structural connections within the occipitotemporal area. Moreover, the disrupted small-world properties of white matter might be imaging biomarkers for assessing NTG progression.

Neurodegeneration beyond the primary visual pathways in a population with a high incidence of normal-pressure glaucoma

PURPOSE

Glaucoma is the most common age-related neurodegenerative eye disease in western society. It is an insidious disease that, when untreated or detected too late, leads inevitably to blindness. An outstanding issue is whether glaucoma should be considered exclusively an eye disease or also a brain disease. To further examine it, we used Diffusion Tensor Imaging (DTI) to study white matter integrity in a Japanese glaucoma population. This population has a very high incidence of normal-pressure glaucoma, in which optic nerve damage occurs in the absence of the elevated eye pressure that characterises the more common form of glaucoma.

METHODS

We performed DTI in 30 participants with normal-pressure glaucoma and 21 age-matched healthy controls. We used voxel-wise tract-based spatial statistics to compare fractional anisotropy and mean diffusivity of the white matter of the brain between patients and control group. Whole-brain and region of interest-based analyses served to find associations between diffusion indices and clinical measures of glaucomatous damage.

RESULTS

Fractional Anisotropy was significantly lower in glaucoma patients in a cluster in the right occipital lobe (p < 0.05; family-wise error-corrected) comprising fibres of both the optic radiation and the forceps major. Additional analysis confirmed bilateral involvement of the optic radiations and forceps major and additionally revealed damage to the corpus callosum and parietal lobe (p < 0.09; family-wise error-corrected). The region of interest-based analysis revealed a positive association between Fractional Anisotropy of the optic radiation and optic nerve damage.

CONCLUSIONS

In this specific population, glaucoma is associated with lower Fractional Anisotropy in the optic radiations, forceps major and corpus callosum. We interpret these reductions as evidence for white matter degeneration in these loci. In particular, the degeneration of the corpus callosum suggests the presence of neurodegeneration of the brain beyond what can be explained on the basis of propagated retinal and pre-geniculate damage. We discuss how this finding links to the emerging view that a brain component that is independent from the eye damage plays a role in the aetiology of glaucoma.

Inhibition on Apoptosis Induced by Elevated Hydrostatic Pressure in Retinal Ganglion Cell-5 via Laminin Upregulating β1-integrin/Focal Adhesion Kinase/Protein Kinase B Signaling Pathway

Background:

Glaucoma is a progressive optic neuropathy characterized by degeneration of neurons due to loss of retinal ganglion cells (RGCs). High intraocular pressure (HIOP), the main risk factor, causes the optic nerve damage. However, the precise mechanism of HIOP-induced RGC death is not yet completely understood. This study was conducted to determine apoptosis of RGC-5 cells induced by elevated hydrostatic pressures, explore whether laminin is associated with apoptosis under pressure, whether laminin can protect RGCs from apoptosis and affirm the mechanism that regulates the process of RGCs survival.

Methods:

RGC-5 cells were exposed to 0, 20, 40, and 60 mmHg in a pressurized incubator for 6, 12, and 24 h, respectively. The effect of elevated hydrostatic pressure on RGC-5 cells was measured by Annexin V-fluorescein isothiocyanate/propidium iodide staining, 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay, and Western blotting of cleaved caspase-3 protein. Location and expression of laminin were detected by immunofluorescence. The expression of β1-integrin, phosphorylation of focal adhesion kinase (FAK) and protein kinase B (PKB, or AKT) were investigated with real-time polymerase chain reaction and Western blotting analysis.

Results:

Elevated hydrostatic pressure induced apoptosis in cultured RGC-5 cells. Pressure with 40 mmHg for 24 h induced a maximum apoptosis. Laminin was declined in RGC-5 cells after exposing to 40 mmHg for 24 h. After pretreating with laminin, RGC-5 cells survived from elevated pressure. Furthermore, β1-integrin and phosphorylation of FAK and AKT were increased compared to 40 mmHg group.

Conclusions:

The data show apoptosis tendency of RGC-5 cells with elevated hydrostatic pressure. Laminin can protect RGC-5 cells against high pressure via β1-integrin/FAK/AKT signaling pathway. These results suggest that the decreased laminin of RGC-5 cells might be responsible for apoptosis induced by elevated hydrostatic pressure, and laminin or activating β1-integrin/FAK/AKT pathway might be potential treatments to prevent RGC loss in glaucomatous optic neuropathy.

Structural brain MRI studies in eye diseases: are they clinically relevant? A review of current findings

Many eye diseases reduce visual acuity or are associated with visual field defects. Because of the well-defined retinotopic organization of the connections of the visual pathways, this may affect specific parts of the visual pathways and cortex, as a result of either deprivation or transsynaptic degeneration. For this reason, over the past several years, numerous structural magnetic resonance imaging (MRI) studies have examined the association of eye diseases with pathway and brain changes. Here, we review structural MRI studies performed in human patients with the eye diseases albinism, amblyopia, hereditary retinal dystrophies, age-related macular degeneration (AMD) and glaucoma. We focus on two main questions. First, what have these studies revealed? Second, what is the potential clinical relevance of their findings? We find that all the aforementioned eye diseases are indeed associated with structural changes in the visual pathways and brain. As such changes have been described in very different eye diseases, in our view the most parsimonious explanation is that these are caused by the loss of visual input and the subsequent deprivation of the visual pathways and brain regions, rather than by transsynaptic degeneration. Moreover, and of clinical relevance, for some of the diseases - in particular glaucoma and AMD - present results are compatible with the view that the eye disease is part of a more general neurological or neurodegenerative disorder that also affects the brain. Finally, establishing structural changes of the visual pathways has been relevant in the context of new therapeutic strategies to restore retinal function: it implies that restoring retinal function may not suffice to also effectively restore vision. Future structural MRI studies can contribute to (i) further establish relationships between ocular and neurological neurodegenerative disorders, (ii) investigate whether brain degeneration in eye diseases is reversible, (iii) evaluate the use of neuroprotective medication in ocular disease, (iv) determine optimal timing for retinal implant insertion and (v) establish structural MRI examination as a diagnostic tool in ophthalmology.

Retinal neurodegeneration in experimental glaucoma

In rats and mice, limbar tissues of the left eye were laser-photocoagulated (LP) and ocular hypertension (OHT) effects were investigated 1 week to 6 months later. To investigate the innermost layers, retinas were examined in wholemounts using tracing from the superior colliculi to identify retinal ganglion cells (RGCs) with intact retrograde axonal transport, melanopsin immunodetection to identify intrinsically photosensitive RGCs (m(+)RGC), Brn3a immunodetection to identify most RGCs but not m(+)RGCs, RECA1 immunodetection to examine the inner retinal vessels, and DAPI staining to detect all nuclei in the GC layer. The outer retinal layers (ORLs) were examined in cross sections analyzed morphometrically or in wholemounts to study S- and L-cones. Innervation of the superior colliculi was examined 10 days to 14 weeks after LP with orthogradely transported cholera toxin subunit B. By 2 weeks, OHT resulted in pie-shaped sectors devoid of FG(+)RGCs or Brn3a(+)RGCs but with large numbers of DAPI(+)nuclei. Brn3a(+)RGCs were significantly greater than FG(+)RGCs, indicating the survival of large numbers of RGCs with their axonal transport impaired. The inner retinal vasculature showed no abnormalities that could account for the sectorial loss of RGCs. m(+)RGCs decreased to approximately 50-51% in a diffuse loss across the retina. Cross sections showed focal areas of degeneration in the ORLs. RGC loss at 1m diminished to 20-25% and did not progress further with time, whereas the S- and L-cone populations diminished progressively up to 6m. The retinotectal projection was reduced by 10 days and did not progress further. LP-induced OHT results in retrograde degeneration of RGCs and m(+)RGCs, severe damage to the ORL, and loss of retinotectal terminals.

New Insights into the Connection Between Histone Deacetylases, Cell Metabolism, and Cancer

SIGNIFICANCE

Histone deacetylases (HDACs) activity and cell metabolism are considered important targets for cancer therapy, as both are deregulated and associated with the onset and maintenance of tumors.

RECENT ADVANCES

Besides the classical function of HDACs as HDAC enzymes controlling the transcription, it is becoming increasingly evident that these proteins are involved in the regulation of several other cellular processes by their ability to deacetylate hundreds of proteins with different functions in both the cytoplasm and the nucleus. Importantly, recent high-throughput studies have identified as important target proteins several enzymes involved in different metabolic pathways. Conversely, it has been also shown that metabolic intermediates may control HDACs activity. Consequently, the acetylation/deacetylation of metabolic enzymes and the ability of metabolic intermediates to modulate HDACs may represent a cross-talk connecting cell metabolism, transcription, and other HDACs-controlled processes in physiological and pathological conditions.

CRITICAL ISSUES

Since metabolic alterations and HDACs deregulation are important cancer hallmarks, disclosing connections among them may improve our understanding on cancer mechanisms and reveal novel therapeutic protocols against this disease.

FUTURE DIRECTIONS

High-throughput metabolic studies performed by using more sophisticated technologies applied to the available models of conditional deletion of HDACs in cell lines or in mice will fill the gap in the current understanding and open directions for future research.

Altered Expression Levels of MMP1, MMP9, MMP12, TIMP1, and IL-1β as a Risk Factor for the Elevated IOP and Optic Nerve Head Damage in the Primary Open-Angle Glaucoma Patients

The aim of presented work was to analyze the impact of particular polymorphic changes in the promoter regions of the -1607 1G/2G MMP1, -1562 C/T MMP9, -82 A/G MMP12, -511 C/T IL-1β, and 372 T/C TIMP1 genes on their expression level in POAG patients. Blood and aqueous humor samples acquired from 50 patients with POAG and 50 control subjects were used for QPCR and protein levels analysis by ELISA. In vivo promoter activity assays were carried on HTM cells using dual luciferase assay. All studied subjects underwent ophthalmic examination, including BCVA, intraocular pressure, slit-lamp examination, gonioscopy, HRT, and OCT scans. Patients with POAG are characterized by an increased mRNA expression of MMP1, MMP9, MMP12, and IL-1β genes as compared to the control group (P < 0.001). Aqueous humor acquired from patients with POAG displayed increased protein expression of MMP1, MMP9, MMP12, and IL-1β compared to the control group (P < 0.001). Allele -1607 1G of MMP1 gene possesses only 42,91% of the -1607 2G allele transcriptional activity and allele -1562 C of MMP9 gene possesses only 21,86% of the -1562 T allele. Increased expression levels of metalloproteinases can be considered as a risk factor for the development of POAG.

Neuroprotection of a novel cyclopeptide C*HSDGIC* from the cyclization of PACAP (1-5) in cellular and rodent models of retinal ganglion cell apoptosis

Purpose

To investigate the protective effects of a novel cyclopeptide C*HSDGIC* (CHC) from the cyclization of Pituitary adenylate cyclase-activating polypeptide (PACAP) (1–5) in cellular and rodent models of retinal ganglion cell apoptosis.

Methodology/Principal Findings

Double-labeling immunohistochemistry was used to detect the expression of Thy-1 and PACAP receptor type 1 in a retinal ganglion cell line RGC-5. The apoptosis of RGC-5 cells was induced by 0.02 J/cm² Ultraviolet B irradiation. MTT assay, flow cytometry, fluorescence microscopy were used to investigate the viability, the level of reactive oxygen species (ROS) and apoptosis of RGC-5 cells respectively. CHC attenuated apoptotic cell death induced by Ultraviolet B irradiation and inhibited the excessive generation of ROS. Moreover, CHC treatment resulted in decreased expression of Bax and concomitant increase of Bcl-2, as was revealed by western-blot analysis. The in vivo apoptosis of retinal ganglion cells was induced by injecting 50 mM N-methyl-D-aspartate (NMDA) (100 nmol in a 2 µL saline solution) intravitreally, and different dosages of CHC were administered. At day 7, rats in CHC+ NMDA-treated groups showed obvious aversion to light when compared to NMDA rats. Electroretinogram recordings revealed a marked decrease in the amplitudes of a-wave, b-wave, and photopic negative response due to NMDA damage. In retina receiving intravitreal NMDA and CHC co-treatment, these values were significantly increased. CHC treatment also resulted in less NMDA-induced cell loss and a decrease in the proportion of dUTP end-labeling-positive cells in ganglion cell line.

Conclusions

C*HSDGIC*, a novel cyclopeptide from PACAP (1–5) attenuates apoptosis in RGC-5 cells and inhibits NMDA-induced retinal neuronal death. The beneficial effects may occur via the mitochondria pathway. PACAP derivatives like CHC may serve as a promising candidate for neuroprotection in glaucoma.

Activation of muscarinic receptors protects against retinal neurons damage and optic nerve degeneration in vitro and in vivo models

AIMS

Muscarinic acetylcholine receptor agonist pilocarpine reduces intraocular pressure (IOP) of glaucoma mainly by stimulating ciliary muscle contraction and then increasing aqueous outflow. It is of our great interest to know whether pilocarpine has the additional properties of retinal neuroprotection independent of IOP lowering in vitro and in vivo models.

METHODS

In rat primary retinal cultures, cell viability was measured using an MTT assay and the trypan blue exclusion method, respectively. Retinal ganglion cells (RGCs) were identified by immunofluorescence and quantified by flow cytometry. For the in vivo study, the retinal damage after retinal ischemia/reperfusion injury in rats was evaluated by histopathological study using hematoxylin and eosin staining, transmission electron microscopy, and immunohistochemical study on cleaved caspase-3, caspase-3, and ChAT.

RESULTS

Pretreatment of pilocarpine attenuated glutamate-induced neurotoxicity of primary retinal neurons in a dose-dependent manner. Protection of pilocarpine in both retinal neurons and RGCs was largely abolished by the nonselective muscarinic receptor antagonist atropine and the M1-selective muscarinic receptor antagonist pirenzepine. After ischemia/reperfusion injury in retina, the inner retinal degeneration occurred including ganglion cell layer thinning and neuron lost, and the optic nerve underwent vacuolar changes. These degenerative changes were significantly lessened by topical application of 2% pilocarpine. In addition, the protective effect of pilocarpine on the ischemic rat retina was favorably reflected by downregulating the expression of activated apoptosis marker cleaved caspase-3 and caspase-3 and upregulating the expression of cholinergic cell marker ChAT.

CONCLUSIONS

Taken together, this highlights pilocarpine through the activation of muscarinic receptors appear to afford significant protection against retinal neurons damage and optic nerve degeneration at clinically relevant concentrations. These data also further support muscarinic receptors as potential therapeutic neuroprotective targets in glaucoma.

One Year of Glaucoma Research in Review: 2012 to 2013

PURPOSE

The objective of this study was to provide the practicing clinical ophthalmologist with an update of pertinent glaucoma literature published from 2012 to 2013.

DESIGN

Literature review.

METHODS

The authors conducted a 1-year (July 1, 2012, to September 30, 2013) English-language glaucoma literature search on PubMed using the following terms: glaucoma, automated perimetry, optic nerve imaging, optical coherence tomography, glaucoma structure and function, intraocular pressure, central corneal thickness, glaucoma medical therapy, neuroprotection, glaucoma laser treatment, secondary glaucoma, glaucoma surgery, and miscellaneous topics in glaucoma.

RESULTS

Of 2659 articles on glaucoma published during our time frame, this review selected original and review articles that reflect novel aspects and updates in the field of glaucoma, while excluding letters to the editor, unpublished works, and abstracts. Preference was given to human research.

CONCLUSIONS

This review focuses on literature that is applicable to ophthalmologists in practice and also highlights studies that may enhance the diagnosis and management of glaucoma.

Magnetic resonance diffusion tensor imaging of optic nerve and optic radiation in healthy adults at 3T

AIM

To investigate the diffusion characteristics of water of optic nerve and optic radiation in healthy adults and its related factors by diffusion tensor imaging (DTI) at 3T.

METHODS

A total of 107 healthy volunteers performed head conventional MRI and bilateral optic nerve and optic radiation DTI. The primary data of DTI was processed by post-processing software of DTI studio 2.3, obtaining fractional anisotropy value, mean diffusivity value, principal engine value, orthogonal engine value by measuring, and analyzed by the SPSS13.0 statistical software.

RESULTS

The bilateral optic nerve and optic radiation fibers presented green color in directional encoded color (DEC) maps and presented high signal in fractional anisotropy (FA) maps. The FA value of the left optic nerve was 0.598±0.069 and the right was 0.593±0.065; the mean diffusivity (MD) value of the left optic nerve was (1.324±0.349)×10(-3)mm(2)/s and the right was (1.312±0.350)×10(-3)mm(2)/s; the principal engine value (λ‖) of the left optic nerve was (2.297±0.522)×10(-3)mm(2)/s and the right was (2.277±0.526)×10(-3)mm(2)/s; the orthogonal engine value (λ⊥) of the left optic nerve was (0.838±0.285)×10(-3)mm(2)/s and the right was (0.830±0.280)×10(-3)mm(2)/s; the FA value of the left optic radiation was 0.636±0.057 and the right was 0.628±0.056; the mean diffusivity (MD) value of the left optic radiation was (0.907±0.103)×10(-3)mm(2)/s and the right was (0.889±0.125)×10(-3)mm(2)/s; the principal eigenvalue (λ‖) of the left optic radiation was (1.655±0.210)×10(-3)mm(2)/s and the right was (1.614±0.171)×10(-3)mm(2)/s; the orthogonal enginvalue (λ⊥) of the left optic radiation was (0.531±0.103)×10(-3)mm(2)/s and the right was (0.524±0.152)×10(-3)mm(2)/s. There was no obvious difference between the FA, MD, λ‖, λ⊥ of the bilateral optic radiation and the bilateral optic nerve (P>0.05) and no obvious difference between male and female group. The FA, MD, λ‖, λ⊥ of the bilateral optic radiation and the bilateral optic nerve had no obvious correlations to the age.

CONCLUSION

DTI is sensitive to the optic nerve and radiation and the relevant DTI parameters of the optic nerve and radiation are established preliminarily in this study.

Proton magnetic resonance spectroscopy ((1)H-MRS) reveals geniculocalcarine and striate area degeneration in primary glaucoma

BACKGROUND

Glaucoma is a collection of neurodegenerative diseases that affect both the retina and the central visual pathway. We investigated whether metabolites' concentrations changed in the geniculocalcarine (GCT) and the striate area of occipital lobe by proton magnetic resonance spectroscopy ((1)H-MRS), suggesting neurodegeneration of the central visual pathway in primary glaucoma.

METHODOLOGY/PRINCIPAL FINDINGS

20 patients with glaucoma in both eyes were paired with 20 healthy volunteers in same gender and an age difference less than 3 years. All the participants were examined by MR imaging including T1 Flair, T2 FSE and (1)H-MRS. The T1 intensity and T2 intensity of their GCTs and striate areas were measured. The ratio of N-acetylaspartate (NAA)/Creatine (Cr), Choline (Cho)/Cr, glutamine and glutamate (Glx)/Cr were derived by multi-voxels (1)H-MRS in the GCT and the striate area of each brain hemisphere. The T1 intensity and T2 intensity had no difference between the groups. Significant decreases in NAA/Cr and Cho/Cr but no difference in Glx/Cr was found between the groups in both the GCT and the striate area.

CONCLUSIONS/SIGNIFICANCE

Primary glaucoma affects metabolites' concentrations in the GCT and the striate area suggesting there is ongoing neurodegenerative process.

Oral janus kinase inhibitor for the treatment of rheumatoid arthritis: tofacitinib

Since the introduction of immune modulators in the treatment of rheumatoid arthritis (RA), there has been hope that orally effective biologic agents would be developed. Tofacitinib, a Janus kinase inhibitor, has become the first oral biologic to receive approval for use in active RA patients. This paper reviews the efficacy and safety profile of Tofacitinib at dosages of 5 mg and 10 mg twice daily. Remarkable improvement in terms of ACR 20 response and HAQ-DI score was noted at month 3 and month 6. DAS 28-4 ESR < 2.6 achievement was noticeably obvious at month 6 for both dosages. No significant serious adverse events, serious infections, neutropenia, or anaemia were observed compared to placebo. In fact, Tofacitinib 5 mg was even found to have significant protective effect of anaemia in the meta-analysis (P = 0.004). Tofacitinib has a noticeable efficacy in controlling disease activity in RA with a manageable safety profile. However, longer studies are needed for its long-term safety profile.