Total plasma homocysteine and primary open-angle glaucoma

Homocysteine and Glaucoma

Elevated levels of homocysteine (Hcy), a non-proteinogenic amino acid, may lead to a host of manifestations across the biological systems, particularly the nervous system. Defects in Hcy metabolism have been associated with many neurodegenerative diseases including glaucoma, i.e., the leading cause of blindness. However, the pathophysiology of elevated Hcy and its eligibility as a risk factor for glaucoma remain unclear. We aimed to provide a comprehensive review of the relationship between elevated Hcy levels and glaucoma. Through a systemic search of the PubMed and Google Scholar databases, we found that elevated Hcy might play an important role in the pathogenesis of glaucoma. Further research will be necessary to help clarify the specific contribution of elevated Hcy in the pathogenesis of glaucoma. A discovery and conceptual understanding of Hcy-associated glaucoma could be the keys to providing better therapeutic treatment, if not prophylactic treatment, for this disease.

Network Integration Analysis and Immune Infiltration Analysis Reveal Potential Biomarkers for Primary Open-Angle Glaucoma

Primary open-angle glaucoma (POAG) is a progressive optic neuropathy and its damage to vision is irreversible. Therefore, early diagnosis assisted by biomarkers is essential. Although there were multiple researches on the identification of POAG biomarkers, few studies systematically revealed the transcriptome dysregulation mechanism of POAG from the perspective of pre- and post-transcription of genes. Here, we have collected multiple sets of POAG's aqueous humor (AH) tissue transcription profiles covering long non-coding RNA (lncRNA), mRNA and mircoRNA (miRNA). Through differential expression analysis, we identified thousands of significant differentially expressed genes (DEGs) between the AH tissue of POAG and non-glaucoma. Further, the DEGs were used to construct a competing endogenous RNA (ceRNA) regulatory network and 1,653 qualified lncRNA-miRNA-mRNA regulatory units were identified. Two ceRNA regulatory subnets were identified based on the random walk algorithm and revealed to be involved in the regulation of multiple complex diseases. At the pre-transcriptional regulation level, a transcriptional regulatory network was constructed and three transcription factors (FOS, ATF4, and RELB) were identified to regulate the expression of multiple genes and participate in the regulation of T cells. Moreover, we revealed the immune desert status of AH tissue for POAG patients based on immune infiltration analysis and identified a specific AL590666.2-hsa-miR-339-5p-UROD axis can be used as a biomarker of POAG. Taken together, the identification of regulatory mechanisms and biomarkers will contribute to the individualized diagnosis and treatment for POAG.

Protecting the aging eye with hydrogen sulfide

Research demonstrates that senescence is associated with tissue and organ dysfunction, and the eye is no exception. Sequelae arising from aging have been well defined as distinct clinical entities and vision impairment has significant psychosocial consequences. Retina and adjacent tissues like retinal pigmented epithelium and choroid are the key structures that are required for visual perception. Any structural and functional changes in retinal layers and blood retinal barrier could lead to age-related macular degeneration, diabetic retinopathy, and glaucoma. Further, there are significant oxygen gradients in the eye that can lead to excessive reactive oxygen species, resulting in endoplasmic reticulum and mitochondrial stress response. These radicals are source of functional and morphological impairment in retinal pigmented epithelium and retinal ganglion cells. Therefore, ocular diseases could be summarized as disturbance in the redox homeostasis. Hyperhomocysteinemia is a risk factor and causes vascular occlusive disease of the retina. Interestingly, hydrogen sulfide (H2S) has been proven to be an effective antioxidant agent, and it can help treat diseases by alleviating stress and inflammation. Concurrent glutamate excitotoxicity, endoplasmic reticulum stress, and microglia activation are also linked to stress; thus, H2S may offer additional interventional strategy. A refined understanding of the aging eye along with H2S biology and pharmacology may help guide newer therapies for the eye.

Analysis of Plasma Hydrogen Sulfide, Homocysteine, and L-Cysteine in Open-Angle Glaucoma Patients

Purpose: To compare the plasma levels of hydrogen sulfide (H₂S), homocysteine (Hcy), and L-cysteine (Cys) among primary open-angle glaucoma (POAG), normal tension glaucoma (NTG), ocular hypertension (OHT), and normal individuals. To explore associated factors and evaluate their diagnostic abilities in glaucoma. Methods: POAG, NTG, OHT, and normal subjects were recruited from Ruijin Hospital between December 2016 and December 2018. All subjects underwent thorough ophthalmological examinations, and fasting venous blood was taken to determine the concentrations of H₂S, Hcy, and Cys. Results: Forty-two POAG, 20 NTG, 52 OHT, and 78 controls were enrolled. The H₂S levels in POAG group were significantly lower than those in OHT group (P = 0.036) and normal group (P < 0.001), while the Hcy and Cys levels in POAG and NTG groups were significantly higher (P = 0.007-0.043). The concentrations of H₂S, Hcy, and Cys in glaucoma patients with different stages were not significantly different (all P > 0.05). POAG patients with longer duration of diagnosis had lower concentrations (P = 0.026, P = 0.001, P < 0.001), but no significant differences in NTG patients (all P > 0.05). The Hcy and Cys levels in NTG patients showed negative but weak correlations with mean deviation (r = -0.450, P = 0.047; r = -0.478, P = 0.033). All these concentrations showed significant but poor diagnostic values in POAG-Normal group [area under curve (AUC) = 0.642-0.721, P < 0.05]. The H₂S level showed poor diagnostic power in POAG-OHT group (AUC = 0.657, P < 0.01). Conclusion: Decreased levels of H₂S and increased levels of Hcy and Cys may be associated with glaucoma, especially in POAG. However, the H₂S/Hcy metabolic pathway is not sufficiently sensitive to be used as a reliable biomarker in glaucoma.

Nailfold capillary morphology in exfoliation syndrome

PurposeThe purpose of the study was to investigate nailfold microvascular morphology in exfoliation syndrome with or without glaucoma (XFS/XFG) compared with primary open-angle glaucoma (POAG) and control subjects using nailfold capillary videomicroscopy.Patients and methodsWe used a JH-1004 capillaroscope to perform nailfold capillary videomicroscopy on the fourth and fifth digit of the non-dominant hand. We enrolled 56 XFS/XFG patients, 87 POAG patients, and 75 control subjects. Masked observers graded the videos for hemorrhages, avascular zones ≥200 microns (μm), and degree of microvascular tortuosity on a four-point subjective scale. Multivariable odds ratios, 95% confidence intervals and P-for trends for assessing the relation between morphological changes and POAG or XFS/XFG were obtained from logistic regression analyses. We also assessed this relation with XFS/XFG compared with POAG in multivariable models.ResultsAfter adjusting for multiple covariates, nailfold hemorrhages, avascular zones ≥200 μm, and higher degree of vascular tortuosity were more common in XFS/XFG vs controls (P-for trend ≤0.0001) and in POAG vs controls (P-for trend ≤0.01). For each 100 capillaries, the number of hemorrhages was similar (P-for trend=0.91) between XFS/XFG and POAG patients; however, there were more avascular zones per 100 capillaries with borderline significance (P-for trend=0.04) in the XFS/XFG group. XFS/XFG patients had more tortuosity than POAG patients; specifically, having a tortuosity score ≥1.5 was associated with a 4.4-fold increased odds of XFS/XFG (95% confidence interval: 1.5-13.3) relative to a tortuosity score <1.0 (P-for trend=0.005).ConclusionA high degree of nailfold capillary tortuosity is a distinct non-ocular feature associated with XFS/XFG compared with either POAG or controls.

Homocysteine in ocular diseases

Homocysteine (Hcy) is a derived sulfur-containing and non-proteinogenic amino acid. The metabolism of Hcy occurs either through the remethylation to methionine or transsulfuration to cysteine. Studies have identified hyperhomocysteinemia (HHcy) as one of the possible risk factors for a multitude of diseases including vascular, neurodegenerative and ocular diseases. Association of HHcy with eye diseases such as retinopathy, pseudoexfoliative glaucoma maculopathy, cataract, optic atrophy and retinal vessel atherosclerosis is established. The molecular mechanism underlying these ocular diseases has been reported as impaired vascular endothelial function, apoptosis of retinal ganglion cells, extracellular matrix alterations, decreased lysyl oxidase activity and oxidative stress. The formed homocysteine-thiolactone in HHcy has stronger cytotoxicity and pro-inflammatory properties which can induce lens opacification and optic nerve damage. The metabolism of Hcy requires enzymes with vitamins such as folic acid, vitamins B12 and B6. Despite the mixed conclusion of various studies regarding the level of these vitamins in elder people, studies recommended the treatment with folate and B12 to reduce Hcy levels in subjects with or without any defect in the enzymes involved in its metabolism. The levels of Hcy, folate, B6 as well as B12 should be measured early in patients with visual impairment that would aid to screen patients for life-threatening disorders related with HHcy. Elder patients may supplement with these vitamins in order to attenuate the ocular damages. This article discusses the association of Hcy in ocular diseases and the possible mechanism in the pathogenesis.

Plasma homocysteine and genetic variants of homocysteine metabolism enzymes in patients from central Greece with primary open-angle glaucoma and pseudoexfoliation glaucoma

BACKGROUND

The purpose of this study was to investigate plasma homocysteine levels and polymorphisms in genes encoding enzymes in the metabolic pathway of homocysteine in association with primary open-angle glaucoma (POAG) and pseudoexfoliation glaucoma (PXFG).

METHODS

A total of 156 glaucoma patients (76 with POAG and 80 with PXFG) and 135 controls matched for age and sex were enrolled in this study. Plasma homocysteine levels were measured using a commercially available enzyme-linked immunosorbent assay kit. DNA was extracted from peripheral blood leukocytes and real-time polymerase chain reaction was performed for genotyping of the samples. Patients were genotyped using predesigned TaqMan(®) single nucleotide polymorphism genotyping assays for two exon variations (rs1801131, rs1801133) in the 5,10-methylenetetrahydrofolate reductase (MTHFR) gene and one intron variation (rs8006686) in the methylenetetrahydrofolate dehydrogenase (MTHFD1) gene.

RESULTS

Homocysteine levels were slightly higher in the patient group (POAG and PXFG) compared with controls, but the difference did not reach statistical significance. The minor alleles of the MTHFR single nucleotide polymorphisms showed a protective effect for POAG and showed an increased risk for PXFG, but none of these associations reached statistical significance (P>0.05). The minor allele of MTHFD1 rs8006686 showed a trend for increased risk of both POAG and PXFG (P>0.05). No statistically significant interaction was seen between the genetic variants and homocysteine levels (P>0.05).

CONCLUSION

Our results show that neither the examined single nucleotide polymorphisms from genes involved in the pathway of homocysteine metabolism nor the measured homocysteine levels were associated with POAG or PXFG in our study cohort.

Levels of circulating homocysteine, vitamin B6, vitamin B12, and folate in different types of open-angle glaucoma

OBJECTIVE

To compare the levels of plasma homocysteine (Hcy), vitamin B6 (vit-B6), serum vitamin B12 (vit-B12), and folate in healthy individuals and in patients with normal tension glaucoma (NTG), pseudoexfoliative glaucoma (PXG), or primary open-angle glaucoma (POAG).

STUDY DESIGN

A prospective controlled trial.

PARTICIPANTS AND METHODS

Forty healthy subjects, 48 patients with NTG, 38 patients with PXG, and 34 patients with POAG were included in the study. Those who used vitamin supplements or medications affecting Hcy and vitamin levels were excluded from the study. The levels of Hcy and vit-B6 were measured by High Performance Liquid Chromatography (HPLC). The levels of serum vit-B12 and folic acid were measured by competitive chemiluminescent enzyme immunoassay (CEI). One-way analysis if variance (ANOVA), analysis of covariance (ANCOVA), and the Tukey honestly significant difference test were used for statistical analysis.

RESULTS

The mean Hcy level of the PXG group was 15.46+/-9.27 micromol/L which was significantly higher (P=0.03) than that of the control group. There were no statistical differences in serum vit-B12 and folate levels among control subjects and NTG, PXG and POAG groups (P>0.05). It was found that the mean plasma vit-B6 level was significantly higher in subjects with NTG (P=0.03) and POAG (P=0.025) versus controls. Mean vit-B6 levels in NTG and POAG were 30.50+/-11.29 microg/L and 30+/-12.15 microg/L, respectively.

CONCLUSIONS

The plasma level of Hcy was found to be increased only in PXG patients and the plasma levels of vit-B6 were found to increase in the NTG and POAG sample groups. Using homocysteine and vit-B6 levels as the determinants of hyperhomocysteinemia still needs further research.

Plasma homocysteine, MTHFR gene mutation, and open-angle glaucoma

OBJECTIVE

Elevated plasma homocysteine has been associated with an increased risk of cardiovascular disease. The association between open-angle glaucoma and cardiovascular disease has recently stimulated interest in the role of homocysteine in the pathogenesis of glaucoma. Some studies report elevated plasma homocysteine in patients with pseudoexfoliation syndrome and pseudoexfoliation glaucoma (PXFG), but have not found this association consistently in other types of open-angle glaucoma. In this study, we have measured plasma homocysteine and C677T methylenetetrahydrofolate reductase (MTHFR) mutation, the commonest genetic cause of elevated plasma homocysteine, in patients with PXFG, primary open-angle glaucoma (POAG), and normal tension glaucoma (NTG).

DESIGN

Prospective cross-sectional cohort study.

PARTICIPANTS

Forty-eight patients with PXFG, 36 patients with POAG, 34 patients with NTG, and 42 controls without glaucoma.

METHODS

Fasting venous blood samples from each participant were analyzed for plasma homocysteine and the C677T MTHFR gene mutation. MAIN OUTCOME OF INTEREST: Mean plasma homocysteine levels, number of individuals with homocysteine above the reference range, and percentage of individuals with heterozygous or homozygous C677T MTHFR gene mutations.

RESULTS

Mean plasma homocysteine was significantly higher in PXFG (11.77+/-4.18 micromol/L), POAG (11.21+/-2.84 micromol/L), and NTG (11.74+/-3.79 micromol/L) compared with control (9.82+/-1.75 micromol/L). Hyperhomocysteinemia was found in 27.1% of PXFG patients, 30.6% of POAG patients, and 29.4% of NTG patients. There was no significant difference in frequency of MTHFR C677T gene mutation between groups.

CONCLUSIONS

Plasma homocysteine was elevated in PXFG, POAG, and NTG. Elevated plasma homocysteine seems to be associated with glaucoma in these patients.

Homocysteine, folates, and the eye

Plasma homocysteine has been identified as a risk factor for arterial disease, retinal artery and vein occlusions, and other common eye diseases. The value of treating an elevated plasma homocysteine with folic acid for preventing further vascular disease has not been proven. Although secondary prevention of coronary artery disease using this approach has been unsuccessful, trials on primary prevention of stroke and loss of cognitive function with folic acid supplementation appear to be successful. Further trial data are awaited. In patients with premature retinovascular disease, the measurement of plasma homocysteine is suggested and reduction of elevated homocysteine with folic acid for secondary prevention of retinal arterial and venous occlusion. Meanwhile, the debate on fortification of flour for primary prevention of neural tube defects, which has already taken place in North America, continues in European countries. Such fortification could have an impact on primary and secondary prevention of vascular disease.

Investigation of the association between 677C>T and 1298A>C 5,10-methylenetetra- hydrofolate reductase gene polymorphisms and normal-tension glaucoma

PURPOSE

Homozygous polymorphism of the 5,10-methylenetetrahydrofolate reductase (MTHFR) gene and resultant hyperhomocysteinaemia have been established as an independent risk factor for vascular diseases. There are evidences that vascular abnormalities are involved in the pathogenesis and progression of normal-tension glaucoma (NTG). In the present study, we were to find out the associations between 677C>T and 1298A>C polymorphisms of the MTHFR gene and NTG.

METHODS

This was a retrospective, case-controlled study enrolling 78 NTG patients and 100 controls. DNA from peripheral blood lymphocytes was extracted and the genotypes of polymorphisms (677C>T and 1298A>C) in the MTHFR gene were determined using PCR followed by restriction enzyme digestion. The frequencies of the polymorphic genotypes in the patients with NTG and controls were compared.

RESULTS

The frequencies of the polymorphisms of the MTHFR gene (677C>T and 1298A>C) in the NTG patients were not significantly different from those of controls. But the younger NTG patients (age at diagnosis < or = 45 years) showed significantly higher prevalence of 677C>T polymorphism than the older NTG patients (age at diagnosis > 45 years) (TT genotype, 38.9 vs 11.9%, P=0.006, OR=4.71, 95% CI=1.49-14.9) and than the younger control subgroup (TT genotype, 38.9 vs 6.1%, P=0.001, OR=9.86, 95% CI=2.23-42.4).

CONCLUSIONS

The 677C>T polymorphism was significantly associated with NTG in the younger patients, while 1298A>C polymorphism was not. This suggests that 677C>T polymorphism of the MTHFR gene can be a genetic risk factor of NTG in Korean population.

Homocysteine levels in aqueous humor and plasma of patients with primary open-angle glaucoma

We determined homocysteine (Hcy) levels in aqueous humor (AH) and plasma and their association with B-vitamin levels in patients with primary open-angle glaucoma (POAG) and controls. Both AH Hcy and plasma Hcy levels were significantly increased in POAG, and elevation of AH Hcy and plasma Hcy was a significant risk factor for POAG. In contrast to controls, neither plasma nor AH Hcy of POAG patients demonstrated a significant association with important non-genetic determinants of elevated Hcy such as low B-vitamin levels, increasing age and caffeine consumption. Considering that Hcy is a neurotoxin that induces apoptotic retinal ganglion cell death via stimulation of the N-methyl-D-asparate (NMDA) receptor, increased Hcy concentrations in AH and plasma might contribute to the optic nerve damage in POAG.

Serum homocysteine, vitamin B 12 and folic acid levels in different types of glaucoma

Background

This study was performed to compare levels of serum homocysteine (Hcy), vitamin B12 and folic acid in patients with primary open-angle glaucoma (POAG), pseudoexfoliative glaucoma (PEXG), normotensive glaucoma (NTG) and healthy controls.

Methods

Twentyfive patients with POAG, 24 with PEXG, and 18 with NTG, along with 19 control healthy subjects were included this prospective study. Levels of serum Hcy were measured using immunoassay, and those of serum vitamin B12 and folic acid were measured using competitive chemiluminescent enzyme immunoassay.

Results

The mean Hcy concentration in the PEXG group was significantly higher (P < 0.001) as compared to the other groups. There were no significant differences with respect to the mean Hcy concentrations among other groups (P > 0.05). There were no statistical differences in serum vitamin B12 levels among POAG, PEXG, NTG and control subjects (P > 0.05).

The mean serum folic acid level was significantly lower in the subjects with PEXG (P < 0.009). However, the mean folic acid concentrations among the other groups did not differ significantly (P > 0.05).

Conclusion

Elevated levels of Hcy in PEXG may explain the role of endothelial dysfunction among patients with PEXG.

Homocysteine and nitric oxide levels in plasma of patients with pseudoexfoliation syndrome, pseudoexfoliation glaucoma, and primary open-angle glaucoma

PURPOSE

To evaluate plasma total homocysteine (tHcy) and nitric oxide (NO) marker levels in patients with pseudoexfoliation syndrome (PXS), pseudoexfoliation glaucoma (PXG), primary open-angle glaucoma (POAG), and normal controls.

METHODS

This cross-sectional, prospective study involved 19 patients with POAG, 18 with PXS, 22 with PXG, and 20 control subjects. Fasting tHcy levels of all study participants were determined using a fluorescence polarization immunoassay method. Quantitation of total nitrate was based on the Griess reaction, in which a chromophore with a strong absorbance at 545 nm is formed by reaction of nitrite with a mixture of naphthylethylenediamine and sulphanilamide.

RESULTS

The mean plasma homocysteine level was statistically significantly elevated in the PXS (p=0.033) and the PXG (p=0.023) groups but not in the POAG group (p=0.996) when compared with the control group. Multiple logistic regression analyses comparing the various patient groups with the single control group indicated that elevation in plasma homocysteine concentration was a significant risk factor for PXS (odds ratio per 1 micromol/l increase in homocysteine concentration=2.05, 95% CI=1.19-3.52) and PXG (odds ratio per 1 micromol/l increase in homocysteine concentration=1.36, 95% CI=1.00-1.85) but was not a significant risk factor for POAG (odds ratio per 1 micromol/l increase in homocysteine concentration=0.99, 95% CI=0.78-1.26). NO markers levels were found to be slightly higher in PXS and PXG patients than control and POAG patients but the differences were not statistically significant (p=0.151). Multiple logistic regression analyses comparing the various patient groups with the single control group indicated that elevation in NO marker concentration was not a significant risk factor for PXS (odds ratio per 1 micromol/l increase in NO concentration=1.00, 95% CI=0.99-1.01), PXG (odds ratio per 1 micromol/l increase in NO concentration=1.00, 95% CI=0.99-1.00) and POAG (odds ratio per 1 micromol/l increase in NO concentration=0.99, 95% CI=0.99-1.00). No statistically significant correlations were observed between plasma tHcy and NO markers in study groups (p>0.05).

CONCLUSION

Elevated levels of homocysteine in pseudoexfoliation patients with and without glaucoma may partly explain the increased risk of vascular disease among patients with pseudoexfoliation. No significant difference was found in plasma NO markers among the POAG, PXS, PXG, and the control subjects.