Genetic heterogeneity of primary open-angle glaucoma in Pakistan

BackgroundGlaucoma is a neurodegenerative ophthalmic disorder and is considered among the leading causes of irreversible blindness. Primary open-angle glaucoma (POAG) is the most common type of glaucoma that affects after 30 years of life, progressing slowly, and manifests as decreased visual acuity leading to blindness if not treated. POAG is genetically heterogeneous, inherited most commonly in autosomal dominant mode. Several genes have been reported for POAG with myocilin (Myoc) being most common. The present study has been conducted to screen 25 POAG families with 2 or more affected members for their association with Myoc and CYP1B1 (the most common gene in primary congenital glaucoma).MethodsAfter approval from Institutional Ethical Review Committee (ERC), 25 POAG families were enrolled from the southern province (Sindh) of Pakistan. Written informed consent was obtained from all participating individuals and diagnosis was confirmed by consultant ophthalmologists using various instruments and means. Venous blood was obtained from affected individuals and their normal family members for DNA extraction and subsequent analysis.ResultsAll samples were initially screened for the Myoc gene followed by CYP1B1. Screening for Myoc revealed one previously reported variant c.144G>T in POAG-06 whereas screening for CYP1B1 in all 25 families showed a novel variant c.649G>A in POAG-02. The pathogenicity of the novel variant was confirmed using various bioinformatics tools.ConclusionThis is the first report of any POAG family found associated with a novel variant in CYP1B1 from the southern province of Pakistan whereas one family found associated with a reported variant in Myoc. The remaining 23 POAG families did not found to be associated with either Myoc or CYP1B1 indicating genetic heterogeneity of the population in this part of the world.     

Changes of intraocular pressure in patients with open-angle glaucoma in relation to the passage of atmospheric fronts and environmental contamination

Effects of atmospheric frontal passages on intraocular pressure (IOP) in patients with open-angle glaucoma are statistically investigated to show the meteorotropism of this disease. Changes in IOP caused by frontal passages are evident; the response is not identical in all the patients near the day of the passage of a warm front, while on the third day following the passage of the front a well pronounced drop in IOP occurs. Anomalous increases of IOP over several months' duration occurred in the years 1986–7. This finding is explained in relation to the hypothesis of environmental contamination in Central Europe by radioactive cesium nuclides due to the Chernobyl accident.     

Evaluation of the intraocular pressure-reducing effect of latanoprost as monotherapy in open-angle glaucoma

Objective of this study was to evaluate the intraocular pressure-reducing effect of latanoprost as monotherapy after replacing current dual therapy in glaucoma patients. The 6-months study comprised 189 patients with primary open angle glaucoma who were treated at least 6 months with two different kind of topical medications (beta-blockers, pilocarpine, dorzolamide and brimonidine). Due to local side effects, multiple dosing regime and inadequately controlled intraocular pressure (IOP), they where switched to latanoprost 0.005% monotherapy. After switched to latanoprost, mean (IOP) was measured at baseline, after 15 days, 2 and 6 months of treatment. After six-months 178 patients had completed the study. These analyses enrolled all patients (n = 189), thus, the Intention-To-Treat (ITT) results were shown instead of the results of the reduced population. IOP was clinically importantly reduced from baseline level. Five patients had uncontrolled IOP. The difference between IOP before (21.9 +/- 2.4) and after 15 days (17.4 +/- 1.7), 2 months (16.7 +/- 1.8) and 6 months (16.6 +/- 1.4) was statistically significant (p < 0.001). 90% patients has reached target IOP < or = 18 mm. A conjunctional hyperaemia in 18 (9%), stinging and itching in 7 (4%) patients was reported. Increased iris pigmentation was seen in 3 (2%) patients. The results of this study indicate that dual therapy in open-angle glaucoma can effectively be replaced by latanoprost monotherapy in many patients.     

Target intraocular pressure in the management of glaucoma

Achievement of target intraocular pressure is the goal of every efficient antiglaucoma therapy. Target intraocular pressure is the level of intraocular pressure which is associated with minimal likelihood of visual field or optic nerve lesion, or an existing lesion progression due to elevated intraocular pressure. Results of large clinical studies which have offered some new concepts on target intraocular pressure in the management of glaucoma are reviewed. An association between the curve of intraocular pressure decrease and glaucoma progression was demonstrated in these studies. Generally, a lower value of target intraocular pressure implies better protection from the loss of vision and visual field impairment in glaucoma patients. In advanced glaucoma, the greatest possible reduction from the initial intraocular pressure should be attempted. A 20% reduction from the initial intraocular pressure or decrease to < 18 mmHg in advanced glaucoma has been recognized as a favorable strategy to reach target intraocular pressure. In normal tension glaucoma, a lower value of target intraocular pressure is associated with a slower disease progression. In patients with initial glaucoma, 25% reduction from the initial intraocular pressure will slow down the disease progression by 45%. The value of target intraocular pressure depends on the pretreatment level of intraocular pressure, optic nerve condition, glaucoma disease state, rate of glaucoma progression, patient's age, and other risk factors for the development of glaucoma.     

The association between Japanese primary open-angle glaucoma and normal tension glaucoma patients and the optineurin gene

Glaucoma represents one of the most common eye diseases and is characterized by progressive loss of visual fields. In the more advanced stages bilateral blindness may result, due to optic nerve atrophy and an excavated optic nerve head. Open-angle glaucoma is one of the main disease subsets, which may be further divided into high tension primary open-angle glaucoma (POAG) and normal tension glaucoma (NTG). Recently, the optineurin (OPTN) gene was identified as a causative factor for NTG. Alterations in this gene were found in Caucasian families with NTG. In particular, c.458G>A, c.691-692insAG and c.1944G>A were shown to be risk factors. Since NTG is reported to be the most common form of glaucoma in Japan, and to identify if the OPTN gene plays a role in POAG, the DNAs from 148 unrelated Japanese patients with NTG, 165 patients with POAG and 196 unrelated controls who were not suffering glaucoma were investigated by appropriate genotyping techniques. No glaucoma-specific mutations were found in the OPTN gene in Japanese glaucoma patients. However, some novel single-nucleotide polymorphisms (SNPs) in the exons and introns are reported in this paper for the first time.S. Tang and Y. Toda contributed to the same degree for this study     

Mitochondrial damage in the trabecular meshwork occurs only in primary open-angle glaucoma and in pseudoexfoliative glaucoma

Background

Open-angle glaucoma appears to be induced by the malfunction of the trabecular meshwork cells due to injury induced by oxidative damage and mitochondrial impairment. Here, we report that, in fact, we have detected mitochondrial damage only in primary open-angle glaucoma and pseudo-exfoliation glaucoma, among several glaucoma types compared.

Methodology/Principal Findings

Mitochondrial damage was evaluated by analyzing the common mitochondrial DNA deletion by real-time PCR in trabecular meshwork specimens collected at surgery from glaucomatous patients and controls. Glaucomatous patients included 38 patients affected by various glaucoma types: primary open-angle, pigmented, juvenile, congenital, pseudoexfoliative, acute, neovascular, and chronic closed-angle glaucoma. As control samples, we used 16 specimens collected from glaucoma-free corneal donors. Only primary open-angle glaucoma (3.0-fold) and pseudoexfoliative glaucoma (6.3-fold) showed significant increases in the amount of mitochondrial DNA deletion. In all other cases, deletion was similar to controls.

Conclusions/Significance

Despite the fact that the trabecular meshwork is the most important tissue in the physiopathology of aqueous humor outflow in all glaucoma types, the present study provides new information regarding basic physiopathology of this tissue: only in primary open-angle and pseudoexfoliative glaucomas oxidative damage arising from mitochondrial failure play a role in the functional decay of trabecular meshwork.     

Changes of nitric oxide level at different stages of primary open-angle glaucoma

The contents of NO stable metabolites in tears, and blood serum of the patients with different stages of open-angle glaucoma have been studied. The increasing of NO stable metabolite contents was found in tears, aqueous humor and blood serum during glaucoma progression. The depletion of glaucoma pathogenesis oxidative link was found at the terminal stage of the disease. The results of our investigation are proposed to be used for glaucoma diagnostic.     

Senescent phenotype of trabecular meshwork cells displays biomarkers in primary open-angle glaucoma

Glaucoma is a major cause of irreversible blindness, affecting more than 70 million individuals worldwide. Elevated intraocular pressure (IOP) is a major risk factor in the development of glaucoma and in the progression of glaucomatous damage. High IOP usually occurs as a result of an increase in aqueous humor outflow resistance in trabecular meshwork (TM). Primary open angle glaucoma (POAG) is characterized by quantifiable parameters including the IOP, the aqueous outflow facility, and geometric measurements of the optic disc and visual defects. Morphological and biochemical analyses of the TM of POAG patients revealed loss of cells, increased accumulation of extracellular matrix (ECM), changes in the cytoskeleton, cellular senescence and the process of subclinical inflammation. Various biochemical and molecular biology biomarkers of TM cells senescence are considered in the article. Oxidative stress is becoming an important factor more likely to be involved in the pathogenesis of POAG. Treatment of TM cells with oxidative stress induced POAG-typical changes like ECM accumulation, cell death, disarrangement of the cytoskeleton, advanced senescence and the release of inflammatory markers. Oxidative stress is able to induce characteristic glaucomatous TM changes and these oxidative stress-induced TM changes can be minimized by the use of antioxidants, such as carnosine-related analogues and IOP-lowering substances. There is evidence demonstrating that carnosine related analogues may have antioxidative capacities, can prevent cellular senescence and the attrition of telomeres during the action of oxidative stress. Prevention of oxidative stress exposure to the TM with N-acetylcarnosine ophthalmic prodrug of carnosine and oral formulation of non-hydrolized carnosine may help to reduce the progression of POAG. The previous work has demonstrated that carnosine is able to reach the TM directly via the transcorneal and systemic pathways of administration with N-acetylcarnosine ophthalmic prodrug and oral formulation of non-hydrolized carnosine. We suggest in this article that dual therapy with N-acetylcarnosine lubricant eye drops, oral formulation of non-hydrolized carnosine combined with anti-glaucoma adrenergic drug may become the first-line therapy in glaucoma due to their efficiency in reducing IOP, prevention and reversal of oxidative stress-induced damages in TM and the low rate of severe side effects during combined treatment.     

Association between MTHFR C677T polymorphism and primary open-angle glaucoma: A meta-analysis

Epidemiological studies have evaluated the association between methylenetetrahydrofolate reductase (MTHFR) C677T polymorphism and primary open-angle glaucoma (POAG) risk. However, the results remain conflicting. The aim of this study was to investigate the association between MTHFRC677T polymorphism and POAG risk. All genetic association studies on MTHFR C677T polymorphism and POAG were systematically searched by the electronic databases PubMed, Embase and Web of Science. Study selection, data abstraction and study quality evaluation were conducted in duplicate independently. The strength of association between MTHFR C677T polymorphism and POAG was measured by odds ratios (ORs) and 95% confidence intervals (CIs). Publication bias was tested by Begg's funnel plot and Egger's regression test. A total of 10 studies including 1224 cases and 1105 controls were included in our final meta-analysis. There was no evidence of significant association of the overall population (for allelic model: OR = 1.17, 95% CI = 0.94–1.46; for additive model: OR = 1.15, 95% CI = 0.85–1.57; for dominant model: OR = 1.19, 95% CI = 0.92–1.55 and for recessive model: OR = 1.11, 95% CI = 0.83–1.49). Significant associations were found between MTHFR C677T polymorphisms and POAG in allelic model (OR = 1.39, 95% CI = 1.05–1.83) and additive model (OR = 1.88, 95% CI = 1.04–3.43) for population-based (PB) subgroup. This meta-analysis suggested that there were significant associations between MTHFR C677T polymorphism and POAG in allelic model and additive model for PB subgroup which indicated that the T allele or TT genotype might increase the risk of POAG, whereas no evidence of significant association was shown of the overall studied population. However, this conclusion should be interpreted cautiously. More large sample-size and multi-ethnicity studies with well-defined POAG patients and well-study design are needed in the future study.     

Common genetic determinants of uveitis shared with other autoimmune disorders

Uveitis is a complex multifactorial autoimmune disease of the eye characterized by inflammation of the uvea and retina, degeneration of the retina, and blindness in genetically predisposed patients. Using the rat model of experimental autoimmune uveitis (EAU), we previously identified three quantitative trait loci (QTL) associated with EAU on rat chromosomes 4, 12, and 10 (Eau1, Eau2, and Eau3). The primary goal of the current study is to delineate additional non-MHC chromosomal regions that control susceptibility to EAU, and to identify any QTLs that overlap with the QTLs of other autoimmune diseases. Using a set of informative microsatellite markers and F(2) generations of resistant and susceptible MHC class II-matched rat strains (F344 and LEW), we have identified several new significant or suggestive QTLs on rat chromosomes 2, 3, 7, 10, and 19 that control susceptibility to EAU. A protective allele was identified in the susceptible LEW strain in the Eau5 locus at D7Wox18, and epistatic interactions between QTLs were found to influence the severity of disease. The newly identified regions (Eau4 through Eau9) colocalize with the genetic determinants of other autoimmune disease models, and to disease-regulating syntenic regions identified in autoimmune patients on human chromosomes 4q21-31, 5q31-33, 16q22-24, 17p11-q12, 20q11-13, and 22q12-13. Our results suggest that uveitis shares some of the pathogenic mechanisms associated with other autoimmune diseases, and lends support to the "common gene, common pathway" hypothesis for autoimmune disorders.     

Mapping a gene for adult-onset primary open-angle glaucoma to chromosome 3q.

Glaucoma is the third-leading cause of blindness in the world, affecting >13.5 million people. Adult-onset primary open-angle glaucoma (POAG) is the most common form of glaucoma in the United States. We present a family in which adult-onset POAG is inherited as an autosomal dominant trait. Twelve affected family members were identified from 44 at-risk individuals. The disease-causing gene was mapped to chromosome 3q21-24, with analysis of recombinant haplotypes suggesting a total inclusion region of 11.1 cM between markers D3S3637 and D3S1744. This is the first report of mapping of an adult-onset POAG gene to chromosome 3q, gene symbol GLC1C.     

Low expression of GSTP1 in the aqueous humour of patients with primary open-angle glaucoma

Primary open-angle glaucoma (POAG) is characterized by irreversible neurodegeneration accompanied by visual field defects and high intraocular pressure. Currently, an effective treatment is not available to prevent the progression of POAG, other than treatments to decrease the high intraocular pressure. We performed proteomic analysis of aqueous humour (AH) samples from patients with POAG combined with cataract and patients with cataract to obtain a better understanding of the pathogenesis of POAG and explore potential treatment targets for this condition. Samples were collected from 10 patients with POAG combined with cataract and 10 patients with cataract. Samples from each group were pooled. A high-resolution, label-free, liquid chromatography-tandem mass spectrometry-based quantitative proteomic analysis was performed. In total, 610 proteins were identified in human AH samples from the two groups. A total of 48 up-regulated proteins and 49 down-regulated proteins were identified in the POAG combined with cataract group compared with the control group. Gene Ontology (GO) analysis revealed key roles for these proteins in inflammation, immune responses, growth and development, cellular movement and vesicle-mediated transport in the biological process category. Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis indicated the down-regulated expression of glutathione S-transferase P (GSTP1) in the glutathione metabolism signalling pathway in the POAG combined with cataract group. Additionally, certain significantly differentially expressed proteins in the proteomic profile were verified by enzyme-linked immunosorbent assay (ELISA). GSTP1 levels were reduced in the human AH samples from the POAG combined with cataract group, based on the results of ELISA and proteomic profiling. Therefore, GSTP1, a redox-related marker, may be involved in the pathological process of POAG and may become a treatment target in the future.     

Gender-specific genetic determinants of blood pressure and organ weight: pharmacogenetic approach

A total genome scan and pharmacogenetic study were designed to search for genetic determinants of blood pressure (BP) as well as heart and kidney weights. Genome scanning was carried out in 266 F(2) intercrosses from Prague hypertensive hypertriglyceridemic rats for phenotypes of organ weights, baseline BP, BP after blockade of the renin-angiotensin system (RAS) by losartan, of the sympathetic nervous system (SNS) by pentolinium, and of the nitric oxide (NO) synthase by N(G)-nitro-L-arginine methyl ester. Pharmacogenetic analysis showed that, in males, BP was controlled by two loci on chromosomes 1 and 5 (Chr1, Chr5) through the SNS, and these loci showed a positive contribution for relative kidney weight (KW/BW). On the other hand, baseline BP in females was controlled by two loci on Chr3 and Chr7. The effect of these loci was not mediated by the RAS, SNS or NO system. These loci did not show any effect for KW/BW. Negatively-linked loci for KW/BW and relative heart weight (HW/BW) were identified on Chr2 in both genders. Another negatively-linked locus for KW/BW, located on Chr8 in males, affected BP through the SNS. This locus on Chr8 overlapped with a previously-reported modifier locus for polycystic kidney disease (PKD). In conclusion, this pharmacogenetic study determined two loci for BP and relative organ mass implicating sympathetic overactivity. Concordance of the identified locus for KW/BW and BP through the SNS on Chr8 with the PKD locus revealed the importance of this region for renal complications in various diseases.     

Cannabinol modulates neuroprotection and intraocular pressure: A potential multi-target therapeutic intervention for glaucoma

ObjectivesGlaucoma is characterized by progressive damage of the retinal ganglion cells (RGCs), resulting in irreversible vision loss. Cannabinoids (CBs) ameliorate several factors that contribute to the progression of glaucoma, including increased intraocular pressure (IOP), degeneration of RGC and optical nerve (ON) damage. However, a direct correlation of specific CBs with the molecular events pertaining to glaucoma pathology is not well established. Therefore, this study aims to evaluate the role of cannabinol (CBN) on RGC protection, modulation of IOP, and its effects on the level of extracellular matrix (ECM) proteins using both in vitro and in vivo models of glaucoma.Methods and resultsWhen exposed to elevated hydrostatic pressure, CBN, in a dose-dependent manner, protected differentiated mouse 661W retinal ganglion precursor-like cells from pressure-induced toxicity. In human trabecular meshwork cells (hTM), CBN attenuated changes in the ECM proteins, including fibronectin and α-smooth muscle actin (α-SMA), as well as mitogen-activated protein kinases (phospho-ERK1/2) in the presence or absence of transforming growth factor-beta 2 (TGF-β₂) induced stress. Ocular pharmacokinetic parameters were evaluated post-intravitreal (IVT) CBN delivery in vivo. Furthermore, we demonstrated that IVT-administered CBN improved pattern electroretinogram (pERG) amplitudes and reduced IOP in a rat episcleral vein laser photocoagulation model of glaucoma.ConclusionCBN promotes neuroprotection, abrogates changes in ECM protein, and normalizes the IOP levels in the eye. Therefore, our observations in the present study indicate a therapeutic potential for CBN in the treatment of glaucoma.