Relationship between the concentration of copper and iron in the aqueous humour and intraocular pressure in rabbits treated with topical steroids

Novel therapeutic targets for primary open-angle glaucoma identified through multicenter proteome-wide mendelian randomization

Background

This study aimed to identify novel therapeutic targets for primary open-angle glaucoma (POAG).

Methods

The summary-data-based Mendelian randomization (SMR) method was used to evaluate the genetic association between plasma proteins and POAG. Two sets of plasma protein quantitative trait loci (pQTLs) data considered exposures were obtained from the Icelandic Decoding Genetics Study and UK Biobank Pharma Proteomics Project. The summary-level genome-wide association studies data for POAG were extracted from the latest Round 10 release of the FinnGen consortium (8,530 cases and 391,275 controls) and the UK Biobank (4,737 cases and 458,196 controls). Colocalization analysis was used to screen out pQTLs that share the same variant with POAG as drug targets identified. The two-sample Mendelian randomization, reverse causality testing and phenotype scanning were performed to further validate the main findings. Protein-protein interaction, pathway enrichment analysis and druggability assessment were conducted to determine whether the identified plasma proteins have potential as drug targets.

Results

After systematic analysis, this study identified eight circulating proteins as potential therapeutic targets for POAG. Three causal proteins with strong evidence of colocalization, ROBO1 (OR = 1.38, p = 1.48 × 10-4, PPH4 = 0.865), FOXO3 (OR = 0.35, p = 4.34 × 10-3, PPH4 = 0.796), ITIH3 (OR = 0.89, p = 2.76 × 10-4, PPH4 = 0.767), were considered tier one targets. Five proteins with medium support evidence of colocalization, NCR1 (OR = 1.25, p = 4.18 × 10-4, PPH4 = 0.682), NID1 (OR = 1.38, p = 1.54 × 10-3, PPH4 = 0.664), TIMP3 (OR = 0.91, p = 4.01 × 10-5, PPH4 = 0.659), SERPINF1 (OR = 0.81, p = 2.77 × 10-4, PPH4 = 0.59), OXT (OR = 1.17, p = 9.51 × 10-4, PPH4 = 0.526), were classified as tier two targets. Additional sensitivity analyses further validated the robustness and directionality of these findings. According to druggability assessment, Pimagedine, Resveratrol, Syringaresinol and Clozapine may potentially be important in the development of new anti-glaucoma agents.

Conclusion

Our integrated study identified eight potential associated proteins for POAG. These proteins play important roles in neuroprotection, extracellular matrix regulation and oxidative stress. Therefore, they have promising potential as therapeutic targets to combat POAG.

Role of Glucocorticoids and Glucocorticoid Receptors in Glaucoma Pathogenesis

The glucocorticoid receptor (GR), including both alternative spliced isoforms (GRα and GRβ), has been implicated in the development of primary open-angle glaucoma (POAG) and iatrogenic glucocorticoid-induced glaucoma (GIG). POAG is the most common form of glaucoma, which is the leading cause of irreversible vision loss and blindness in the world. Glucocorticoids (GCs) are commonly used therapeutically for ocular and numerous other diseases/conditions. One serious side effect of prolonged GC therapy is the development of iatrogenic secondary ocular hypertension (OHT) and OAG (i.e., GC-induced glaucoma (GIG)) that clinically and pathologically mimics POAG. GC-induced OHT is caused by pathogenic damage to the trabecular meshwork (TM), a tissue involved in regulating aqueous humor outflow and intraocular pressure. TM cells derived from POAG eyes (GTM cells) have a lower expression of GRβ, a dominant negative regulator of GC activity, compared to TM cells from age-matched control eyes. Therefore, GTM cells have a greater pathogenic response to GCs. Almost all POAG patients develop GC-OHT when treated with GCs, in contrast to a GC responder rate of 40% in the normal population. An increased expression of GRβ can block GC-induced pathogenic changes in TM cells and reverse GC-OHT in mice. The endogenous expression of GRβ in the TM may relate to differences in the development of GC-OHT in the normal population. A number of studies have suggested increased levels of endogenous cortisol in POAG patients as well as differences in cortisol metabolism, suggesting that GCs may be involved in the development of POAG. Additional studies are warranted to better understand the molecular mechanisms involved in POAG and GIG in order to develop new disease-modifying therapies to better treat these two sight threatening forms of glaucoma. The purpose of this timely review is to highlight the pathological and clinical features of GC-OHT and GIG, mechanisms responsible for GC responsiveness, potential therapeutic options, as well as to compare the similar features of GIG with POAG.

Influence of Trace Elements on Neurodegenerative Diseases of The Eye-The Glaucoma Model

Glaucoma is a heterogeneous group of chronic neurodegenerative disorders characterized by a relatively selective, progressive damage to the retinal ganglion cells (RGCs) and their axons, which leads to axon loss and visual field alterations. To date, many studies have shown the role of various elements, mainly metals, in maintaining the balance of prooxidative and antioxidative processes, regulation of fluid and ion flow through cell membranes of the ocular tissues. Based on the earlier and current research results, their relationship with the development and progression of glaucoma seems obvious and is increasingly appreciated. In this review, we aimed to summarize the current evidence on the role of trace elements in the pathogenesis and prevention of glaucomatous diseases. Special attention is also paid to the genetic background associated with glaucoma-related abnormalities of physiological processes that regulate or involve the ions of elements considered as trace elements necessary for the functioning of the cells.

Bioinorganic chemistry of open-angle glaucoma: A review

At present, physical methods of chemical analysis are constantly improving providing large amount of data on elemental composition of organs and tissues. However, only few works describe the correlation (or the potential connection) between the general or local bioelemental imbalances and specific biochemical reactions that are involved in pathogenesis of certain diseases. This review describes primary open-angle glaucoma (POAG) - one of the most common ophthalmic diseases - in terms of elemental chemistry. The authors look into the impact that various subgroups of elements have on passive and active processes of homeostasis regulation and hydrodynamic balance in the eye. Alkaline metals and their analogues (K, Na, Li, Rb, Cs) influence hydrostatics and hydrodynamics by means of both K-Na pumps and osmosis. Alkaline-earth elements and their analogues (Ca, Mg, Sr, Ba, Be) are involved in biomineralization and intercellular interaction in the drainage areas. Chalcophile metals and their analogues (Zn, Cu, Hg, Co, Ni, Cd, Pb, Mo, Sb) regulate redox reactions. They are the cofactors of enzymes that support structural homeostasis of the drainage area. Siderophile metals (Fe, Mn, Cr, Rh) regulate oxidation-reduction reactions, including those associated with limited nutrition of tissues in glaucoma. The role of amphoteric metals and nonmetals (Al, Si, Ga, V, TI, Sn, Ge, Zr, W) in POAG has not been described properly, but they were noted to participate in mineralization. Structure-forming non-metals and their analogues (N, S, Se, As) are directly involved in the formation of protein and non-protein aggregates that prevent aqueous humor outflow. The specific role of phosphorus in the pathogenesis of glaucoma has not been described previously. The authors analyze the involvement of phosphorus in energy-dependent processes of cellular activity, which are aimed at the reprocessing of aggregates that cause aqueous humor retention.

Relationships Between Concentrations of Biological Variables in Eye Fluids and Blood After Exercise in Lidia Cattle

Lidia cattle are a heterogeneous Iberian cattle population known for its natural aggressiveness and resistance to traditional handling procedures making in vivo blood sampling and biological fluid collections extremely difficult. Blood variables are influenced by physical exertion and stressful situations; consequently, post-mortem blood analysis does not reflect basal concentrations for this species. Nevertheless, ocular fluids (aqueous and vitreous humour) maintain their stable composition after death and maybe could be used to estimate ante-mortem blood concentrations. So, 15 bulls which had fought (for 15-20 minutes) and, subsequently after death, blood, aqueous and vitreous humour were sampled. Total protein, albumin, triglycerides, uric acid, urea, AST, ALT, GGT, AP, CK, LDH, cholesterol, creatinine, glucose and lactate were measured. Statistical analysis and correlation coefficients between the three fluids were carried out. All variables showed high plasma concentrations of glucose, uric acid, LDH and CK, compared with normal bovine concentrations. Apart from urea, all plasma concentrations were greater than those found in ocular fluids. The measured enzymes activities were higher in the vitreous than in the aqueous humour, but only marked differences in uric acid, lactate, AP and AST were found. There was a significant correlation between creatinine in the plasma and aqueous humour, and between albumin and GGT in the plasma and vitreous humour. Glucose, creatinine and urea exhibit a high correlation between ocular fluids. All plasma concentrations were clearly modified, however ocular fluids do not seem affected, thus establishing important correlations between the blood and intraocular fluids.

Inhibitory Effects of Glycyrrhiza glabra and Its Major Constituent Glycyrrhizin on Inflammation-Associated Corneal Neovascularization

Glycyrrhiza glabra L. (Leguminosae) is widely used in folk medicines. Glycyrrhizin, an active compound of G. glabra, possesses anti-inflammatory activity. This study investigates the G. glabra methanol extract and glycyrrhizin for the treatment of corneal neovascularization (CNV). G. glabra was extracted in 70% aqueous methanol. Phytochemical tests, thin layer chromatography (TLC), and high performance liquid chromatography (HPLC) were used for the analysis of chemical composition. The topical solution of G. glabra methanol extract (2% w/v) and glycyrrhizin (1% w/v) was prepared in normal saline. After corneal burn (1 N NaOH), animals were left untreated for a week so that neovascularization appears in all groups. Treatments started on day 7 and continued for next 21 consecutive days. The animals were treated with 3 drops of various topical solutions thrice a day. Digital photograph analysis and histological studies were used for the evaluation of CNV. Phytochemical analysis of the G. glabra methanol extract showed the presence of saponins, phenols, carbohydrates, flavonoids, and proteins. TLC and HPLC confirmed the presence of glycyrrhizin. Photograph analysis of the extract and glycyrrhizin treated group showed a considerable decrease in CNV. Histological study of G. glabra and glycyrrhizin treated groups showed no blood vessels with properly arranged collagen fibers. This study showed that G. glabra and glycyrrhizin can be used for the treatment of CNV. Bioassay guided isolation can lead to preparation of ophthalmic solutions for the treatment of CNV.

Extraction of Iron from the Rabbit Anterior Chamber with Reverse Iontophoresis

Ocular siderosis is a common eye disease caused by retention of an iron-containing intraocular foreign body in the eye. Iron-containing intraocular foreign bodies may cause severe inflammatory reaction and affect visual function. Currently the optimal treatment method of ocular siderosis is a moot point. This study used the reverse iontophoresis technique to noninvasively extract iron from the rabbit anterior chamber. By slit lamp observation and histological examination, reverse iontophoresis treatment has a good effect on ocular siderosis. Reverse iontophoresis seems to be a noninvasive and promising approach to extract iron from the anterior chamber to treat ocular siderosis.

Abnormal metal levels in the primary visual pathway of the DBA/2J mouse model of glaucoma

The purpose of this study was to determine metal ion levels in central visual system structures of the DBA/2J mouse model of glaucoma. We used inductively coupled plasma mass spectrometry (ICP-MS) to measure levels of iron (Fe), copper (Cu), zinc (Zn), magnesium (Mg), manganese (Mn), and calcium (Ca) in the retina and retinal projection of 5-month (pre-glaucomatous) and 10-month (glaucomatous) old DBA/2J mice and age-matched C57BL/6J controls. We used microbeam X-ray fluorescence (μ-XRF) spectrometry to determine the spatial distribution of Fe, Zn, and Cu in the superior colliculus (SC), which is the major retinal target in rodents and one of the earliest sites of pathology in the DBA/2J mouse. Our ICP-MS experiments showed that glaucomatous DBA/2J had lower retinal Fe concentrations than pre-glaucomatous DBA/2J and age-matched C57BL/6J mice. Pre-glaucomatous DBA/2J retina had greater Mg, Ca, and Zn concentrations than glaucomatous DBA/2J and greater Mg and Ca than age-matched controls. Retinal Mn levels were significantly deficient in glaucomatous DBA/2J mice compared to aged-matched C57BL/6J and pre-glaucomatous DBA/2J mice. Regardless of age, the SC of C57BL/6J mice contained greater Fe, Mg, Mn, and Zn concentrations than the SC of DBA/2J mice. Greater Fe concentrations were measured by μ-XRF in both the superficial and deep SC of C57BL/6J mice than in DBA/2J mice. For the first time, we show direct measurement of metal concentrations in central visual system structures affected in glaucoma and present evidence for strain-related differences in metal content that may be specific to glaucomatous pathology.

Long-term outcome of iron-endocytosing cultured corneal endothelial cell transplantation with magnetic attraction

The long-term efficacy and safety of transplanting iron-endocytosing cultured corneal endothelial cells (CECs) with magnetic attraction were evaluated. Rabbit corneas were subjected to cryo-injury to detach CECs. Cultured rabbit CECs (RCEC) were exposed to spherical iron powder and then injected into the anterior chamber, after which a neogium magnet was fixed on the eyelid for 24 hr to attract the cells to Descemet's membrane (RCEC-iron group, n=4). An RCEC group (cryo-injury and injection of normal cultured RCEC, n=4) and a Cryo group (cryo-injury without injection of RCEC, n=4) served as controls. Intraocular pressure was measured for 12 months after surgery. Corneal findings on slit lamp biomicroscopy, RCEC density, the electro-retinogram (ERG), and residual iron in the ocular tissues were evaluated at final assessment. Intraocular pressure did not increase in any group throughout 12 months of observation. At the final assessment, the average corneal edema score of the RCEC-iron group was significantly lower than that of the RCEC or Cryo groups (p=0.021). The average CEC density of the RCEC-iron group was 2581+/-230 cells mm(-2) (mean+/-SD), whereas no CECs were observed on the inner surface of the central cornea in the RCEC and Cryo groups. No significant differences of the ERG (a- and b-wave amplitudes, and b-wave/a-wave ratio) were detected among the groups. Iron powder was not detected by Berlin blue staining in the ocular tissues of the RCEC-iron group. Apoptotic cells were not observed in the endothelium by terminal transferase-mediated nick-end labeling. Transplanted iron-endocytosing RCEC remained viable for 12 months after surgery. There were no detectable ocular complications after the transplantation of iron-endocytosing cultured RCEC. Magnetic attachment of iron-endocytosing CECs can be an effective and safe method for corneal endothelial repair.