Prospective study of plasma homocysteine level and risk of age-related macular degeneration in women

Association of Dietary Nitrate and a Mediterranean Diet With Age-Related Macular Degeneration Among US Adults: The Age-Related Eye Disease Study (AREDS) and AREDS2

Importance

Low dietary nitrate intake has previously been suggested to be a risk factor for age-related macular degeneration (AMD) progression; however, this finding has not been replicated in other cohorts or adjusted for dietary patterns.

Objective

To determine whether there is an association between dietary nitrate intake and AMD progression.

Design, Setting, and Participants

This cohort study analyzed data from the prospective Age-Related Eye Disease Study (AREDS) and AREDS2 randomized clinical trial cohorts and their extended follow-up studies, which were conducted in multicenter outpatient retinal practices. Participants in both trials had non-late AMD in at least 1 eye. Data were analyzed from March 1, 2020, to September 30, 2022.

Exposure

Dietary nitrate intake.

Main Outcomes and Measures

Association between dietary nitrate intake and development of late AMD (neovascular AMD [nAMD] or geographic atrophy [GA]) or large drusen. The interactions of dietary patterns, with common at-risk single-nucleotide polymorphisms, were also assessed.

Results

In the combined AREDS/AREDS2 cohort of 7788 participants (4288 AREDS participants and 3610 AREDS2 participants [110 of whom participated in both studies]), there were 13 511 eligible eyes. The combined cohort comprised 4396 women (56%) and 3392 men (44%), and the combined mean (SD) age was 71.1 (6.6) years. Dietary nitrate intake was associated with a decreased risk of progression to late AMD in the combined AREDS/AREDS2 cohort (hazard ratio [HR], 0.77 [95% CI, 0.69-0.86] for quartile 4 vs quartile 1 of intake) and a decreased risk of GA (HR, 0.71 [95% CI, 0.61-0.83]) and nAMD (HR, 0.85 [95% CI, 0.73-0.99]). In AREDS, increased nitrate intake (quartile 4 vs quartile 1) was associated with a decreased risk of late AMD (HR, 0.77 [95% CI, 0.65-0.91]) and GA (HR, 0.80 [95% CI, 0.65-0.97]) but not nAMD; in AREDS2, there was no association between nitrate intake (quartile 4 vs quartile 1) and late AMD (HR, 0.90 [95% CI, 0.80-1.02]) or nAMD (HR, 0.93 [95% CI, 0.78-1.11]). There was a correlation between Mediterranean dietary patterns and dietary nitrate intake (r = 0.52, P < .001).

Conclusions and Relevance

The findings of this cohort study suggest that dietary nitrate intake was associated with lower AMD risk. However, this association disappeared after adjusting for Mediterranean dietary patterns. These results are subject to potential bias and are hypothesis-generating in nature; therefore, they are insufficient to support new clinical recommendations. Previously described associations between dietary nitrate intake and AMD may in fact represent overall dietary patterns. Further research is needed before dietary nitrate intake can be recommended as a therapy for AMD.

Effect of long-term chronic hyperhomocysteinemia on retinal structure and function in the cystathionine-β-synthase mutant mouse

Elevated levels of the excitatory amino acid homocysteine (Hcy) have been implicated in retinal diseases in humans including glaucoma and macular degeneration. It is not clear whether elevated Hcy levels are pathogenic. Models of hyperhomocysteinemia (Hhcy) have proven useful in addressing this including mice with deficiency in the enzyme cystathionine β-synthase (CBS). Cbs^+/- mice have a ∼two-fold increase in plasma and retinal Hcy levels. Previous studies of visual function and structure in Cbs^+/- mice during the first 10 months of life revealed mild ganglion cell loss, but minimal electrophysiological alterations. It is not clear whether extended, chronic exposure to moderate Hhcy elevation will lead to visual function loss and retinal pathology. The present study addressed this by performing comprehensive analyses of retinal function/structure in 20 month Cbs^+/- and Cbs^+/+ (WT) mice including IOP, SD-OCT, scotopic and photopic ERG, pattern ERG (pERG), and visual acuity. Eyes were harvested for histology and immunohistochemical analysis of Brn3a (ganglion cells), dihydroethidium (oxidative stress) and GFAP (gliosis). The analyses revealed no difference in IOP between groups for age/strain. Visual acuity measured ∼0.36c/d for mice at 20 months in Cbs^+/- and WT mice; contrast sensitivity did not differ between groups at either age. Similarly SD-OCT, scotopic/photopic ERG and pERG revealed no differences between 20 month Cbs^+/- and WT mice. There was minimal disruption in retinal structure when eyes were examined histologically. Morphometric analysis revealed no significant differences in retinal layers. Immunohistochemistry revealed ∼5 RGCs/100 μm retinal length in both Cbs^+/- and WT mice at 20 months. While there was greater oxidative stress and gliosis in older (20 month) mice versus young (4 month) mice, there was no difference in these parameters between the 20 month Cbs^+/- and WT mice. We conclude that chronic, moderate Hhcy (at least due to deficiency of Cbs) is not accompanied by retinal structural/functional changes that differ significantly from age-matched WT littermates. Despite considerable evidence that severe Hhcy is toxic to retina, moderate Hhcy appears tolerated by retina suggesting compensatory cellular survival mechanisms.

Treatments for dry age-related macular degeneration and Stargardt disease: a systematic review

BACKGROUND

Age-related macular degeneration (AMD) is the leading cause of visual loss in older people. Advanced AMD takes two forms, neovascular (wet) and atrophic (dry). Stargardt disease (STGD) is the commonest form of inherited macular dystrophy.

OBJECTIVE

To carry out a systematic review of treatments for dry AMD and STGD, and to identify emerging treatments where future NIHR research might be commissioned.

DESIGN

Systematic review.

METHODS

We searched MEDLINE, EMBASE, Web of Science and The Cochrane Library from 2005 to 13 July 2017 for reviews, journal articles and meeting abstracts. We looked for studies of interventions that aim to preserve or restore vision in people with dry AMD or STGD. The most important outcomes are those that matter to patients: visual acuity (VA), contrast sensitivity, reading speed, ability to drive, adverse effects of treatment, quality of life, progression of disease and patient preference. However, visual loss is a late event and intermediate predictors of future decline were accepted if there was good evidence that they are strong predictors of subsequent visual outcomes. These include changes detectable by investigation, but not necessarily noticed by people with AMD or STGD. ClinicalTrials.gov, the World Health Organization search portal and the UK Clinical Trials gateway were searched for ongoing and recently completed clinical trials.

RESULTS

The titles and abstracts of 7948 articles were screened for inclusion. The full text of 398 articles were obtained for further screening and checking of references and 112 articles were included in the final report. Overall, there were disappointingly few good-quality studies (including of sufficient size and duration) reporting useful outcomes, particularly in STGD. However we did identify a number of promising research topics, including drug treatments, stem cells, new forms of laser treatment, and implantable intraocular lens telescopes. In many cases, research is already under way, funded by industry or governments.

LIMITATIONS

In AMD, the main limitation came from the poor quality of much of the evidence. Many studies used VA as their main outcome despite not having sufficient duration to observe changes. The evidence on treatments for STGD is sparse. Most studies tested interventions with no comparison group, were far too short term, and the quality of some studies was poor.

FUTURE WORK

We think that the topics on which the Health Technology Assessment (HTA) and Efficacy Mechanism and Evaluation (EME) programmes might consider commissioning primary research are in STGD, a HTA trial of fenretinide (ReVision Therapeutics, San Diego, CA, USA), a visual cycle inhibitor, and EME research into the value of lutein and zeaxanthin supplements, using short-term measures of retinal function. In AMD, we suggest trials of fenretinide and of a potent statin. There is epidemiological evidence from the USA that the drug, levodopa, used for treating Parkinson's disease, may reduce the incidence of AMD. We suggest that similar research should be carried out using the large general practice databases in the UK. Ideally, future research should be at earlier stages in both diseases, before vision is impaired, using sensitive measures of macular function. This may require early detection of AMD by screening.

STUDY REGISTRATION

This study is registered as PROSPERO CRD42016038708.

FUNDING

The National Institute for Health Research HTA programme.

Homocysteine and risk of age-related macular degeneration: a systematic review and meta-analysis

There is still no agreement on total plasma homocysteine (tHcy) role in age-related macular degeneration (AMD), the leading cause of new blindness in industrialized countries. We performed a systematic review and meta-analysis of the published data on the correlation between tHcy and AMD. MEDLINE/PubMed and ISI Web of Sciences searches were performed according to MOOSE guidelines. Case-control studies were eligible for inclusion. Participants and controls were AMD patients and subjects without AMD. The main outcome measure was wet AMD. Homocysteine level was the main exposure variable. Data were pooled using a random-effects model. Twelve case-control studies were identified: 10 assessed wet AMD, four dry AMD, one early AMD, one late AMD, and one any AMD. As for wet AMD, there was a total of 453 cases and 514 controls. Mean tHcy was on average 1.1 μmol/l (95% confidence interval [CI] = 0.96-1.25) greater in wet AMD cases, but there was evidence of extreme between-study heterogeneity (p < 0.001, I²  = 91.8%). In a model homogenous for age, including six wet AMD studies (214 cases, 274 controls), mean tHcy was on average 0.58 μmol/l (95% CI = 0.35-0.73) greater in the case group, a not statistically significant result (p = 0.144) associated with moderate heterogeneity (I²  = 39.2%). Our meta-analysis indicates that there is some weak evidence that increased tHcy might be associated with wet AMD; however, this result should be interpreted cautiously, because of a marked between-study heterogeneity and the possible effect of publication bias. Future studies, preferably of cohort design, are necessary before any firm conclusions on the putative role of increased tHcy on AMD can be drawn.

Epigenetic modifications in hyperhomocysteinemia: potential role in diabetic retinopathy and age-related macular degeneration

To study Hyperhomocysteinemia (HHcy)-induced epigenetic modifications as potential mechanisms of blood retinal barrier (BRB) dysfunction, retinas isolated from three- week-old mice with elevated level of Homocysteine (Hcy) due to lack of the enzyme cystathionine β-synthase (cbs^-/- , cbs^+/- and cbs^+/+ ), human retinal endothelial cells (HRECs), and human retinal pigmented epithelial cells (ARPE-19) treated with or without Hcy were evaluated for (1) histone deacetylases (HDAC), (2) DNA methylation (DNMT), and (3) miRNA analysis. Differentially expressed miRNAs in mice with HHcy were further compared with miRNA analysis of diabetic mice retinas (STZ) and miRNAs within the exosomes released from Hcy-treated RPEs. Differentially expressed miRNAs were further evaluated for predicted target genes and associated pathways using Ingenuity Pathway Analysis. HHcy significantly increased HDAC and DNMT activity in HRECs, ARPE-19, and cbs mice retinas, whereas inhibition of HDAC and DNMT decreased Hcy-induced BRB dysfunction. MiRNA profiling detected 127 miRNAs in cbs^+/- and 39 miRNAs in cbs^-/- mice retinas, which were significantly differentially expressed compared to cbs^+/+ . MiRNA pathway analysis showed their involvement in HDAC and DNMT activation, endoplasmic reticulum (ER), and oxidative stresses, inflammation, hypoxia, and angiogenesis pathways. Hcy-induced epigenetic modifications may be involved in retinopathies associated with HHcy, such as age-related macular degeneration and diabetic retinopathy.

Prospective study of plasma homocysteine, its dietary determinants, and risk of age-related macular degeneration in men

PURPOSE

Cross-sectional and case-control studies generally support a direct association between elevated plasma homocysteine and age-related macular degeneration (AMD), but data from prospective studies are limited. We examined the prospective relation of plasma homocysteine level, its dietary determinants, and risk of AMD in a large cohort of apparently healthy male physicians.

METHODS

During a mean follow-up of 11.2 years, we identified 146 incident cases of visually significant AMD (responsible for a reduction of visual acuity to 20/30 or worse), and 146 controls matched for age, smoking status, and time of blood draw. We measured concentration of homocysteine in blood samples collected at baseline using an enzymatic assay. and we assessed dietary intake of B vitamins and related compounds betaine and choline with a food frequency questionnaire administered at baseline.

RESULTS

AMD was not associated with plasma level of homocysteine; the multivariable-adjusted odds ratio (OR) of AMD comparing the highest and lowest quartile of homocysteine was 1.09 (95% confidence interval [95% CI]: 0.52-2.31; p for trend = 0.99). However, AMD was inversely associated with quartile of intake of total folate (OR: 0.55; 95% CI: 0.24-1.23; p for trend = 0.08), vitamin B₆ from food (OR: 0.39; 95% CI: 0.17-0.88; p for trend = 0.01), and betaine (OR: 0.53; 95% CI: 0.22-1.27; p for trend = 0.048).

CONCLUSIONS

These prospective data from a cohort of apparently healthy men do not support a major role for homocysteine in AMD occurrence, but do suggest a possible beneficial role for higher intake of several nutrients involved in homocysteine metabolism.

Systemic and ocular fluid compounds as potential biomarkers in age-related macular degeneration

Biomarkers can help unravel mechanisms of disease and identify new targets for therapy. They can also be useful in clinical practice for monitoring disease progression, evaluation of treatment efficacy, and risk assessment in multifactorial diseases, such as age-related macular degeneration (AMD). AMD is a highly prevalent progressive retinal disorder for which multiple genetic and environmental risk factors have been described, but the exact etiology is not yet fully understood. Many compounds have been evaluated for their association with AMD. We performed an extensive literature review of all compounds measured in serum, plasma, vitreous, aqueous humor, and urine of AMD patients. Over 3600 articles were screened, resulting in more than 100 different compounds analyzed in AMD studies, involved in neovascularization, immunity, lipid metabolism, extracellular matrix, oxidative stress, diet, hormones, and comorbidities (such as kidney disease). For each compound, we provide a short description of its function and discuss the results of the studies in relation to its usefulness as AMD biomarker. In addition, biomarkers identified by hypothesis-free techniques, including metabolomics, proteomics, and epigenomics, are covered. In summary, compounds belonging to the oxidative stress pathway, the complement system, and lipid metabolism are the most promising biomarker candidates for AMD. We hope that this comprehensive survey of the literature on systemic and ocular fluid compounds as potential biomarkers in AMD will provide a stepping stone for future research and possible implementation in clinical practice.

Risk factors and biomarkers of age-related macular degeneration

A biomarker can be a substance or structure measured in body parts, fluids or products that can affect or predict disease incidence. As age-related macular degeneration (AMD) is the leading cause of blindness in the developed world, much research and effort has been invested in the identification of different biomarkers to predict disease incidence, identify at risk individuals, elucidate causative pathophysiological etiologies, guide screening, monitoring and treatment parameters, and predict disease outcomes. To date, a host of genetic, environmental, proteomic, and cellular targets have been identified as both risk factors and potential biomarkers for AMD. Despite this, their use has been confined to research settings and has not yet crossed into the clinical arena. A greater understanding of these factors and their use as potential biomarkers for AMD can guide future research and clinical practice. This article will discuss known risk factors and novel, potential biomarkers of AMD in addition to their application in both academic and clinical settings.

Mining for genes related to choroidal neovascularization based on the shortest path algorithm and protein interaction information

BACKGROUND

Choroidal neovascularization (CNV) is a serious eye disease that may cause visual loss, especially for older people. Many factors have been proven to induce this disease including age, gender, obesity, and so on. However, until now, we have had limited knowledge on CNV's pathogenic mechanism. Discovering the genes that underlie this disease and performing extensive studies on them can help us to understand how CNV occurs and design effective treatments.

METHODS

In this study, we designed a computational method to identify novel CNV-related genes in a large protein network constructed using the protein-protein interaction information in STRING. The candidate genes were first extracted from the shortest paths connecting any two known CNV-related genes and then filtered by a permutation test and using knowledge of their linkages to known CNV-related genes.

RESULTS

A list of putative CNV-related candidate genes was accessed by our method. These genes are deemed to have strong relationships with CNV.

CONCLUSIONS

Extensive analyses of several of the putative genes such as ANK1, ITGA4, CD44 and others indicate that they are related to specific biological processes involved in CNV, implying they may be novel CNV-related genes.

GENERAL SIGNIFICANCE

The newfound putative CNV-related genes may provide new insights into CNV and help design more effective treatments. This article is part of a Special Issue entitled "System Genetics" Guest Editor: Dr. Yudong Cai and Dr. Tao Huang.

Antioxidant supplements for prevention of mortality in healthy participants and patients with various diseases

BACKGROUND

Our systematic review has demonstrated that antioxidant supplements may increase mortality. We have now updated this review.

OBJECTIVES

To assess the beneficial and harmful effects of antioxidant supplements for prevention of mortality in adults.

SEARCH METHODS

We searched The Cochrane Library, MEDLINE, EMBASE, LILACS, the Science Citation Index Expanded, and Conference Proceedings Citation Index-Science to February 2011. We scanned bibliographies of relevant publications and asked pharmaceutical companies for additional trials.

SELECTION CRITERIA

We included all primary and secondary prevention randomised clinical trials on antioxidant supplements (beta-carotene, vitamin A, vitamin C, vitamin E, and selenium) versus placebo or no intervention.

DATA COLLECTION AND ANALYSIS

Three authors extracted data. Random-effects and fixed-effect model meta-analyses were conducted. Risk of bias was considered in order to minimise the risk of systematic errors. Trial sequential analyses were conducted to minimise the risk of random errors. Random-effects model meta-regression analyses were performed to assess sources of intertrial heterogeneity.

MAIN RESULTS

Seventy-eight randomised trials with 296,707 participants were included. Fifty-six trials including 244,056 participants had low risk of bias. Twenty-six trials included 215,900 healthy participants. Fifty-two trials included 80,807 participants with various diseases in a stable phase. The mean age was 63 years (range 18 to 103 years). The mean proportion of women was 46%. Of the 78 trials, 46 used the parallel-group design, 30 the factorial design, and 2 the cross-over design. All antioxidants were administered orally, either alone or in combination with vitamins, minerals, or other interventions. The duration of supplementation varied from 28 days to 12 years (mean duration 3 years; median duration 2 years). Overall, the antioxidant supplements had no significant effect on mortality in a random-effects model meta-analysis (21,484 dead/183,749 (11.7%) versus 11,479 dead/112,958 (10.2%); 78 trials, relative risk (RR) 1.02, 95% confidence interval (CI) 0.98 to 1.05) but significantly increased mortality in a fixed-effect model (RR 1.03, 95% CI 1.01 to 1.05). Heterogeneity was low with an I(2)- of 12%. In meta-regression analysis, the risk of bias and type of antioxidant supplement were the only significant predictors of intertrial heterogeneity. Meta-regression analysis did not find a significant difference in the estimated intervention effect in the primary prevention and the secondary prevention trials. In the 56 trials with a low risk of bias, the antioxidant supplements significantly increased mortality (18,833 dead/146,320 (12.9%) versus 10,320 dead/97,736 (10.6%); RR 1.04, 95% CI 1.01 to 1.07). This effect was confirmed by trial sequential analysis. Excluding factorial trials with potential confounding showed that 38 trials with low risk of bias demonstrated a significant increase in mortality (2822 dead/26,903 (10.5%) versus 2473 dead/26,052 (9.5%); RR 1.10, 95% CI 1.05 to 1.15). In trials with low risk of bias, beta-carotene (13,202 dead/96,003 (13.8%) versus 8556 dead/77,003 (11.1%); 26 trials, RR 1.05, 95% CI 1.01 to 1.09) and vitamin E (11,689 dead/97,523 (12.0%) versus 7561 dead/73,721 (10.3%); 46 trials, RR 1.03, 95% CI 1.00 to 1.05) significantly increased mortality, whereas vitamin A (3444 dead/24,596 (14.0%) versus 2249 dead/16,548 (13.6%); 12 trials, RR 1.07, 95% CI 0.97 to 1.18), vitamin C (3637 dead/36,659 (9.9%) versus 2717 dead/29,283 (9.3%); 29 trials, RR 1.02, 95% CI 0.98 to 1.07), and selenium (2670 dead/39,779 (6.7%) versus 1468 dead/22,961 (6.4%); 17 trials, RR 0.97, 95% CI 0.91 to 1.03) did not significantly affect mortality. In univariate meta-regression analysis, the dose of vitamin A was significantly associated with increased mortality (RR 1.0006, 95% CI 1.0002 to 1.001, P = 0.002).

AUTHORS' CONCLUSIONS

We found no evidence to support antioxidant supplements for primary or secondary prevention. Beta-carotene and vitamin E seem to increase mortality, and so may higher doses of vitamin A. Antioxidant supplements need to be considered as medicinal products and should undergo sufficient evaluation before marketing.