Immune-Based Therapy With Glatiramer Acetate for Dry AMD
Immune-Based Therapy With Glatiramer Acetate for Dry AMD
GENNADY LANDA, MD · OLEG BUTOVSKY, PhD · JOHAI SHOSHANI, MD · MICHAL SCHWARTZ, PhD · AYALA POLLACK, MD
Age-related macular degeneration (AMD) and Alzheimer's disease (AD) are chronic neurodegenerative diseases that are strongly associated with advancing age. AD is the most common cause of dementia, afflicting 24 million people worldwide. In its most common form, it occurs in people over 65 years old, although a less prevalent early-onset form also exists.1 The cause and progression of AD is not well understood, but it is associated with plaques and tangles in the brain.2
There is a similarity between AMD and AD. Both diseases are characterized by deposit formation, where amyloid beta (Aβ) is one of the main components in the plaques of AD and in drusen of AMD. In 1991, the amyloid hypothesis was proposed.3 This hypothesis stated that Aβ deposits are the causative factor in AD.4 The amyloid hypothesis is compelling because the gene for the Aβ precursor is located on chromosome 21, and patients with trisomy 21 (Down syndrome), who thus have an extra gene copy, almost universally exhibit AD-like disorders by 40 years of age.5,6 The traditional formulation of the amyloid hypothesis points to the cytotoxicity of mature aggregated amyloid fibrils, which are believed to be the toxic form of the protein responsible for disrupting the cell's calcium ion homeostasis and thus inducing apoptosis.7 It should be noted further that apolipoprotein E, the major genetic risk factor for AD, leads to excess amyloid buildup in the brain before AD symptoms arise. Thus, Aβ deposition precedes clinical AD.8 Another strong support for the amyloid hypothesis, which looks at Aβ as the common initiating factor for AD, is that transgenic mice solely expressing a mutant human amyloid precursor protein gene develop fibrillar amyloid plaques.9
|Gennady Landa, MD, is an ophthalmologist at Kaplan Medical Center in Rehovot, Israel, and at the Retina Center of the Department of Ophthalmology at the New York Eye and Ear Infirmary. Oleg Butovsky, PhD, is in the department of neurobiology at the Weizmann Institute of Science in Rehovot and at the Center for Neurologic Diseases in the department of neurology at the Harvard Medical School in Boston. Johai Shoshani, MD, is in the department of ophthalmology at Kaplan. Michal Schwartz, PhD, is in the department of neurobiology at the Weizmann Institute. Ayala Pollack, MD, is in the department of ophthalmology at Kaplan. The authors report no financial interests in the products discussed in this article. Dr. Landa can be reached via e-mail at doctor. firstname.lastname@example.org.|
One biochemical study of drusen composition found that up to 65% of the proteins identified in drusen are present in drusen derived from patients with AMD, as well as from healthy, age-matched donors.10 However, approximately 33% of the drusen-derived proteins from AMD-patient donors were not observed in healthy-donor drusen. These findings may imply that, although there is some degree of continuity between aging changes in the Bruch's membrane and aging changes associated with AMD, there are also distinct differences leading to development of the disease. Bruch's membrane thickness increases with aging.11 Advanced glycation end products accumulate in the Bruch's membrane during aging.12 Aging is also associated with increased oxidative damage.13 Plasma glutathione, vitamin C, and vitamin E levels decrease, and oxidized glutathione levels increase, for example, with age.13-16 Lipid peroxidation seems to increase with aging as well.17-18 The susceptibility of retinal pigment epithelium (RPE) cells to oxidative damage increases with aging. In addition, RPE cells that experience phototoxicity exhibit membrane blebbing,19 a phenomenon observed in aging and in the eyes of patients with AMD.
Alzheimer's disease, like AMD, is also strongly associated with aging. There are additional similarities between AMD and AD. Both are chronic neurodegenerative diseases and both are characterized by deposit formation. The formation of insoluble extracellular deposits consisting of misfolded, aggregated protein is a hallmark of many neurodegenerative diseases. Recent evidence suggests that drusen formation and AMD share some similarities with amyloid-associated AD.19-21 In addition, inflammatory mediators and, in particular, activated microglia are present in amyloid deposits, as well as in drusen, suggesting a possible common role for the inflammatory pathway in AMD and amyloid diseases.22 Moreover, Ambati and colleagues described a new model of AMD in transgenic mice when an absence of normally functioning macrophages led to the development of clinical AMD.23
Recent evidence suggests that Aβ could be a therapeutic target for both AD and AMD. In AD, it was shown that when anti-Aβ antibodies were directed toward the specific region of Alzheimer's amyloid protein in transgenic AD mouse models and were delivered to the central nervous system (CNS), they could prevent formation of Aβ and dissolve real plaques.24 In AMD, anti-Aβ antibodies administered systemically in a mouse model of AMD led to decreased amounts of Aβ in the retina and brain and also to attenuation of the electroretinogram deficits in the retina.25 In most chronic neurodegenerative diseases, a local immune response takes place.
Microglia and T cells are the main cells participating in local immune response. Microglia cells are immune-resident cells and play a crucial role in inflammation and in local immune response. T cells are focused in CNS-damaged sites and can "shape" activated microglial phenotypes.26-28 Activated microglia cells also are needed for tissue defense.29,30 According to this hypothesis, resting microglia can adopt 1 of 2 phenotypes, depending on the manner of activation. When resting microglia are activated by the innate immunity activators, such as lipopolysaccharide or Aβ, they are transformed to a phagocytic phenotype that is characterized by production of various inflammatory mediators. These activated microglia cells become cytotoxic and can kill and remove microorganisms. Conversely, when an activation of microglia is caused by adaptive immunity mediators, such as T-cell–derived cytokines (interleukin [IL]-4 or interferon-gamma), a neuroprotective phenotype of microglia develops.27,31,32 This phenotype is characterized by an expression of major histocompatibility complex class 2 and CD11c and enables microglia to act as antigen presenting cells.32
Researchers recently demonstrated that aggregated Aβ-induced microglia become cytotoxic27 and block neurogenesis from adult rodent neural progenitor cells.8,32 IL-4 reversed the impediment, attenuated tumor necrosis factor α production, and overcame blockage of insulin-like growth factor (IGF)-I production caused by Aβ.27,32 The significance of microglia for in vivo neural-cell renewal was demonstrated by enhanced neurogenesis in the rat dentate gyrus after injection of IL-4-activated microglia intracerebroventricularly and by the presence of IGF-I–expressing microglia in the dentate gyrus of rats kept in an enriched environment34 or in the animal model of multiple sclerosis (MS).31 Using double-transgenic mice expressing mutant human genes encoding presenilin 1 and chimeric mouse/human amyloid precursor protein (mouse AD model), it was shown that modulation of microglia into dendritic-like cells, achieved by a T-cell–based vaccination with Copolymer-1 (glatiramer acetate; Copaxone, Teva Pharmaceuticals), resulted in reduction of cognitive decline, elimination of plaque formation, and induction of neuronal survival and neurogenesis.33 Glatiramer was identified as an agent that could direct the immune response safely. Glatiramer is a drug approved by the US Food and Drug Administration to treat MS and is a weak agonist of self-antigens. It has the ability to modulate T cells to produce IL-4,35 which activates resting microglia cells to become neuroprotective. Vaccination with glatiramer, which cross-reacts with T cells recognizing brain or eye proteins,36,37 can be used for boosting the level of T cells needed to shape microglia/monocytes in AD and perhaps in AMD.
STUDIES UNDER WAY
These results introduce new microglia phenotypes as necessary players in fighting off neurodegenerative conditions, such as AD and AMD. To summarize: There is a common inflammatory pathway for both AMD and AD. Aβ is one of the main proteins present both in drusen of AMD and in the deposits of AD. An accumulation of extracellular amyloid in plaques or in drusen triggers a local toxic chronic inflammatory response whereby cytotoxic microglia produce neurotoxins causing neurodegeneration. Accumulation of these deposits is associated with loss of photoreceptors and deterioration of macular function in AMD, analogous to neuronal loss and cognitive decline in AD. These implications made us think that in AD and in AMD, an immune response should be modulated rather than suppressed, and "the perfect microglia/macrophages" could remove plaque/drusen without cytotoxicity, and support repair.
In light of the similarity in the deposition and the inflammatory response between AD and AMD, we decided to investigate whether the effect of glatiramer on drusen in dry AMD is similar to that on deposits of other age-related chronic neurodegenerative diseases such as AD. The working hypothesis of the current study is that weekly treatment with glatiramer might lead to the clearing of drusen in dry AMD, which could delay or inhibit disease progression. Based on the studies in a mouse AD model,27,30 it was decided to initiate a clinical trial with AMD patients using a once-weekly glatiramer administration protocol. The effect of glatiramer on drusen was examined during a prospective, randomized, double-blind, placebo-controlled pilot trial. The study profile was approved by the Institutional Review Board of the Kaplan Medical Center in Rehovot, Israel. Patients over 50 years old with intermediate dry AMD in both eyes were included. All patients were randomly treated with subcutaneous injections of either 20 mg glatiramer or placebo (ratio 2:1) on a weekly basis for a 12 weeks.
Visual acuity examinations, fundus photography, fluorescein angiography, and ocular coherence tomography were performed at baseline and at 6- and 12-week visits. The natural course of drusen accumulation was investigated using archival fundus photographs of consecutive untreated dry AMD patients who comprised the observational group. The primary outcome measure was the change in total drusen area, measured using Image-Pro software (MediaCybernetics, Bethesda, MD) by a masked analyzer. Analysis of 17 untreated eyes of dry AMD patients from the observational group showed an average increase of 25.2% in total drusen area over 6 months. In no case was regression of drusen area observed. At week 12, 6 eyes treated with glatiramer showed a reduction in total drusen area from a baseline of 53.6% (range 5% to 89%). Two eyes receiving placebo injections demonstrated reduction of 0.6% (range 0.2% to 1.0%) in total drusen area. In terms of safety, there have been no severe adverse events, no evidence of atrophy in the areas of drusen disappearance, and no evidence of choroidal neovascularization in any of the treated patients so far during the follow-up.
These results, with historical controls collected from 17 patients showing drusen accumulation after 6 months, make the study very encouraging. Due to the limited number of eyes tested, no statistical analysis was possible. In light of the underlying mechanism of weekly glatiramer treatment in animal models of neurodegenerative diseases, its effect in AMD might also go beyond drusen elimination to protecting photoreceptors and promoting repair.
This study is in progress at the Department of Ophthalmology at the Kaplan Medical Center in Rehovot, and a larger trial is currently taking place at the New York Eye and Ear Infirmary, which includes measurements of drusen volume change using the drusen-analysis technique of the spectral scanning laser ophthalmoscopy/optical coherence tomography system. RP
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Retinal Physician, Issue: June 2008