Amanda Warren

An international study has determined that, in line with other studies on zinc levels and age-related macular degeneration (AMD), elevated zinc may have an effect on AMD progression, but that the key to zinc's benefits may center on determining and controlling available zinc rather than increasing zinc supplementation.

Investigators, led by Po-Jung Pao, with the Department of Ocular Biology and Therapeutics and the Department of Structural and Molecular Biology at University College London, found new study results suggest that controlling levels of extracellular, biologically active, or "free" zinc could be key to harnessing zinc's benefits for AMD patients.

Zinc is the "second most abundant trace element in the human body" after iron and is present in high concentration in the human eye, Pao and colleagues noted. Ocular zinc is localized to the RPE/choroid complex, where a deficiency or overload of the element can lead to a “variety of problems."

Because zinc is often tightly bound to proteins, there is only a small amount of zinc ions that remain biologically available outside of those protein bonds.

Utilizing cultured primary human RPE cells in a zinc enriched environment, Pao and colleagues attempted to determine whether free zinc could "accelerate RPE differentiation, alter gene expression, and modify secretions of AMD-specific proteins" that reduce risk of AMD development and progression, investigators prosed. The RPE cells were differentiated into several zinc concentrations: 0, 75, 100, 125, 150, or 200 µm of zinc sulfate, for a 28-day period.

Twice weekly the researchers measured trans-epithelial resistance, toxicity, cell viability, pigmentation, coverage of pigment at different zinc concentrations, and free zinc levels. At the end of the 28-day period, the researchers performed an immunohistochemical analysis of the cells, and analyzed secreted proteins through mass spectrometry.

Pao and colleagues found a measurable difference in the maturation of RPE cells that developed in the presence of added zinc. The difference was most evident in an increase in transepithelial resistance (TER) in RPE cells exposed to 100 µm (2.7 nm free zinc)and 125 µm (3.4 nM free zinc) of added zinc, although Pao noted that TER development at 150 µm zinc (4.0 nM free zinc) and above showed no change in TER in comparison to RPE cells cultured in no additional zinc.

Study data also showed that pigmentation of RPE cells, a sign of healthy RPE cells, was more widespread in RPE cells in zinc-rich environments. Data also showed RPE cells in higher zinc environments secreted more proteins, such as apolipoprotein E (APOE), compliment factor H (CFH) and high temperature requirement serine protease A1 (HTRA1) which Pao wrote are genetically associated with AMD.

The research data revealed zinc supplements may be benefiting patients with AMD via a direct effect on RPE cells, and through affecting RPE cells zinc may influence photoreceptors and choroidal micro vessels in AMD eyes. Pao believed that changes in TER may also offer benefits related to the outer blood-retinal barrier. Zinc's effects on pigmentation of the RPE were also significant.

"Increased availability of zinc appears to be directly involved in the development and probably maintenance of a mature and healthy RPE," investigators wrote.

Pao and colleagues suggested the availability and concentration of free zinc that is contributing to RPE health, and that "the challenge for AMD research now is to determine the 'normal' free zinc concentration" in healthy eyes and help regulate zinc  to optimal healthy levels in AMD eyes.

The effects of zinc supplementation on primary human retinal pigment epithelium

Journal of Trace Elements in Medicine and Biology

Articles

Zinc is the second most abundant trace element in the human body after iron, and is present in high concentration in the human eye.

Free Zinc Regulation Could Be Key to Stopping AMD Development and Progression

Utilizing data and images gathered in the Comparison of Age-related Macular Degeneration (AMD) and Treatments Trials (CATT),  investigators have determined that certain morphological features of AMD are associated with greater risk of declining visual acuity (VA) patients over time. 

Presence, incidence, and worsening of these pathological features, according Glenn J. Jaffee, MD, with the Department of Ophthalmology at Duke University, and fellow researchers from the University of Pennsylvania and Cole Eye Institute at the Cleveland Clinic, are directly associated with greater loss of VA in patients receiving treatment with anti-vascular endothelial growth factor (anti-VEGF) agents, and suggest that there is "a significant need to develop therapies to  address these adverse pathological features."

Using data and imaging collected from 523 CATT follow-up study participants—from the two-year study which focused on the results of treatment of AMD-related choroidal neovascularization (CNV) with intraviteral anti-VEGF agents bevacizumab and ranibizumab&mdash; Jaffee and colleagues assessed the associations between macular morphology and VA and explored the retinal anatomic factors that contributed to year 5 VA. They reported that specific adverse morphological characteristics had greater association with reduced VA, including "area of CNV lesion, area of GA [geographic atrophy], new foveal GA, new foveal scar, new foveal CNV, new SHRM [subretinal hyper-reflective material] within the center 1mm, new foveal intraretinal fluid [IRF]" and new retinal thinning."

Eyes with more macular fluid saw slightly greater mean reduction in GA (VA = 63 letters) compared to those without macular fluid (VA = 59), but that the mean VA differed "depending on the specific type of fluid." Investigators noted that, relative to the mean VA in eyes with no IRF (68 letters), mean VA was worse for eyes with extrafoveal IRF (VA = 5) and worse for those with foveal IRF (VA= 44). Data also revealed trends towards better VA in eyes with no SHRM (VA= 72, p<0.001) in comparison to eyes without foveal SHRM or with extrafoveal SHRM (VA= 41; 63, respectively), and better VA in eyes without outer retinal tubulations (ORTs) (VA= 63) in comparison to eyes with ORTs (VA= 52, All 

Thickness of certain morphological features recorded by optical coherence tomography (OCT) also revealed associations with better or worse VA over time. Jaffee wrote that at year 5, eyes with total thickness >550 μm had “markedly worse mean VA (46 letters) than the 192 eyes with < 550 μm (mean 61-65 letters) (all 

Other morphological features which were associated with worsening VA were neovascular lesions of greater than 20 mm

(mean VA = 49), presence of GA or scarring (fibrotic and non fibrotic) in the foveal center (mean VA = 46).

Study eyes with 2 or more of the features Jaffee and colleagues labeled "adverse morphological features" saw a greater mean decrease in VA than those eyes with only one or none of these features.

“The mean VA declined more between year 2 to year 5 when there were abnormal features, but the average VA at each time point was worse from year 1 to year 5, as the number of adverse features increased," Jaffee wrote. Even with anti-VEGF treatment, the data showed that VA tended to worsen below baseline by year 5, dependent on associated adverse pathological features.

Jaffee and colleagues believed their findings reveal a significant unmet need to develop treatments that limit or protect against scar formation, GA development, retinal thinning, fluid increase, and lesions, as an accompaniment to anti-VEGF treatments.

Understanding how these morphological features are connected to AMD disease progression and changes in VA even in patients treated with anti-VEGF agents, could lead to the development of alternative or complementary AMD treatment and save patient sight.

Macular Morphology and Visual Acuity in Year Five of the Comparison of Age-related Macular Degeneration Treatments Trials (CATT)

There is a found significant unmet need to develop treatments that limit or protect against scar formation, GA development, retinal thinning, fluid increase, and lesions, as an accompaniment to anti-VEGF therapy.

New Therapies Needed to Address Key Contributors to AMD Vision Loss

A new study determined that, although imaging methods like fundus autoflorescence (FAF) and optical coherence tomography (OCT) can determine characteristics of disease presence and progression in age-related macular degeneration (AMD) by identifying signs of macular atrophy (MA), there may be signs of AMD development occurring prior to evidence of MA that are detectable on the cellular level.

Led by Rosa Dolz-Marco, MD, PhD, of the Vitreous Retina Macula Consultants, investigators found that MA may be evidence of late-stage disease progression, and that more research is needed into earlier anatomic endpoints.

Although investigators noted that detailed outer retinal morphology is "readily visible on high-quality OCT" there is still a large range of retinal pigment epithelium (RPE) morphology in patients with advanced AMD.

“The termination of the continuous RPE layer provides an inexact boundary for analyzing atrophy progression,” Dolz-Marco and colleagues wrote.

A more concise measure of atrophy progression could be found in the curved line formed by the descent of the external limiting membrane (ELM) toward the Bruch membrane (BrM), according to the study, which could provide a clearer delimitation of RPE and photoreceptor atrophy on the histological level.

The case study focused on the right eye of a 98 year old female patient with advanced MA caused by AMD and related open-angle glaucoma who was treated over an 11-year period at the Vitreous Retina Macula Consultants of New York. Investigators compared in vivo eye-tracked cross-sectional OCT scans of the study eye performed 8 and 13 months prior to the patient's death and to cellular postmortem analysis of  the study eye in order to determine the effectiveness of OCT in determining retinal thickness and extent of retinal damage in comparison to OCT-tracked histology for subcellular resolution across the macula.

Dolz-Marco and colleagues report that the studied eye exhibited a “collapsed acquired vitelliform deposit and, seen only upon histology, a type 1 neovascularization, sub-RPE hematoma, and intraretinal fluid.”

The researchers also found basal linear deposit, basal laminar deposit ( BLamD), and subretinal drusenoid deposits which supported the diagnosis of macular atrophy secondary to AMD and exhibited multiple AMD features not explained by normal aging.

Investigators noted there was evidence of AMD progression to macular atrophy observed between the  8- and 13- month visits with disruption or disappearance of the RPE layer and persistence of BLamD across the atrophic area. They added that ELM was not visible in areas of atrophy, but was throughout non-atrophic areas.

Dolz-Marco and colleagues wrote that their data suggested that RPE and ELM morphology may have prognostic value, and that detection of the ELM descent to determine shape and thickening of BLamD toward the ELM descent may serve as an earlier sign of macular degeneration than atrophy itself.

“How atrophy is detected impacts its clinical relevance, and diagnostic technologies to date have revealed only some of the challenges to treatments targeting atrophy in AMD," investigators wrote.

The Border of Macular Atrophy in Age-Related Macular Degeneration: A Clinicopathologic Correlation

The findings lend to investigators believe that earlier endpoints for AMD diagnosis are needed.

Macular Atrophy Occurs Late in AMD Progression, Study Suggests

It's often difficult for healthcare researchers and epidemiologists to obtain accurate data on disease prevalence, particularly among underserved, and hard-to-reach populations.

 has outlined the use of a new approach to estimating disease prevalence of hepatitis C virus (HCV) in New York City (NYC), which takes into account the limitations of existing methods. The new Bayesian evidence synthesis model, according to researchers, accounts for bias in data sources.

Use of this new approach suggests that HCV infection burden in NYC has been underestimated in populations considered high-risk for HCV, and that HCV transmission has increased among young adults in NYC.

Lead author of the study and PhD candidate Sarah Tan, of Cornell University's Department of Statistical Science, noted that estimating the prevalence of chronic hepatitis C (HCV) in the general population presents “numerous challenges" due to the asymptomatic nature of the disease, and the sub-demographics of those populations at greatest risk for HCV infection including current injection drug users (IDUs), the incarcerated, and the homeless."

Alternative sampling strategies in use to capture data on HCV burden in correctional facilities, and among IDUs, those approaches invite additional challenge, as some subpopulation sizes are “not easily measured, and estimates, when available, are subject to considerable uncertainty.”

Other approaches to estimating HCV prevalence use nationwide data, but fail to capture the inherent spatial-temporal aspects of disease transmission which underserves populations in large cities where estimates for HCV prevalence is greater, Tan noted.

The approach designed by Tan and colleagues uses a Bayesian evidence synthesis model (BESM) to improve estimates of HCV prevalence. Tan wrote that their model utilized 10 sources of data on IDU and HCV. Among the data sources, investigators gathered from the US Census Bureau, the New York Metropolitan Statistical Area (NYMSA), the National Survey of Substance Abuse Treatment Services, and Health and Nutrition Examination Survey (HANES) household surveys.

The BESM, according to the investigators, "falls under the broader category of static, non-mechanistic models of infectious diseases" which works in contrast to traditionally employed models by culling data from multiple sources of partial information. Applying BESM to different data sources covering a range of NYC subpopulations, recognizing the biases inherent in those data sources, and adjusting for that bias creates a clearer picture of HCV burden as a whole.

Tan wrote that drug use history variables can help relate "data-scarce quantities to data-rich quantities" to estimate factors like proportion of current IDUs to ex-IDUs, which can affect accuracy of estimations.

The new approach stratifies the NYC population first into 3 IDU risk groups (current, ex, non-IDU), and then further stratifies those groups into 4 age level groups (20-29, 30-39, 40-49, 50-59 years of age). Tan writes that the two-level stratification creates 12 groups in total with varying levels of risk, since "both injection drug use and HCV prevalence vary by age."

HCV relevance, Tan wrote, can be estimated as a weighted average of 2 factor: HCV prevalence among age and type of IDU, and the proportion of type of IDU by age, weighted by the population size of those age groups in NYC.

The BESM-based estimates showed that "an estimated 0.29% (13,000 individuals) of the NYC population aged 20-59 are currently injection drug users and are HCV positive." Tan wrote that these individuals make up 50.2% (95% CI; 47.9%-53.4%) of the 27,600 current IDUs in NYC and that the group most affected by HCV burden is ex-IDUs aged 50-59, with 29,100 individuals.

The BESM-based model revealed that the HCV prevalence in NYC is currently underestimated by existing models, particularly in current- and ex-IDU populations.  The BESM-based estimates also suggest that HCV transmission has increased in specific populations, primarily among young IDUs in NYC.

Tan and colleagues wrote that local prevalence estimates of HCV are “increasingly important" in order to better allocate funding for treatments, interventions, educational programs, and services. Researchers warn that underestimates of HCV burden could affect treatment of individuals and even lead to increases in HCV.

A Bayesian evidence synthesis approach to estimate disease prevalence in hard-to-reach populations: hepatitis C in New York City

Use of this new approach suggests that HCV infection burden in New York City has been underestimated in populations considered high-risk for HCV, and that HCV transmission has increased among young adults in the city. 