10/2015 The Rate of Vitamin A Dimerization in Lipofuscinogenesis, Fundus Autofluorescence, Retinal Senescence and Degeneration
Ilyas Washington, Leonide Saad
Retinal Degenerative Diseases - Adv Exp Med Biol. 2016;854:347-53
One of the earliest events preceding several forms of retinal degeneration is the formation and accumulation of vitamin A dimers in the retinal pigment epithelium (RPE) and underlying Bruch's membrane (BM). Such degenerations include Stargardt disease, Best disease, forms of retinitis pigmentosa, and age-related macular degeneration (AMD). Since their discovery in the 1990's, dimers of vitamin A, have been postulated as chemical triggers driving retinal senescence and degeneration. There is evidence to suggest that the rate at which vitamin A dimerizes and the eye's response to the dimerization products may dictate the retina's lifespan. Here, we present outstanding questions, finding the answers to which may help to elucidate the role of vitamin A dimerization in retinal degeneration.
10/2015 Can Vitamin A be Improved to Prevent Blindness due to Age-Related Macular Degeneration, Stargardt Disease and Other Retinal Dystrophies?
Leonide Saad, Ilyas Washington
Retinal Degenerative Diseases - Adv Exp Med Biol., 2016;854:355-61
We discuss how an imperfect visual cycle results in the formation of vitamin A dimers, thought to be involved in the pathogenesis of various retinal diseases, and summarize how slowing vitamin A dimerization has been a therapeutic target of interest to prevent blindness. To elucidate the molecular mechanism of vitamin A dimerization, an alternative form of vitamin A, one that forms dimers more slowly yet maneuvers effortlessly through the visual cycle, was developed. Such a vitamin A, reinforced with deuterium (C20-D3-vitamin A), can be used as a non-disruptive tool to understand the contribution of vitamin A dimers to vision loss. Eventually, C20-D3-vitamin A could become a disease-modifying therapy to slow or stop vision loss associated with dry age-related macular degeneration (AMD), Stargardt disease and retinal diseases marked by such vitamin A dimers. Human clinical trials of C20-D3-vitamin A (ALK-001) are underway.
08/2015 Can deuterated vitamin A be used to prevent blindness? The case of ALK-001
Presentation by Leonide Saad
American Chemical Society Annual Meeting, August 2015
06/2015 Rescue of the Stargardt phenotype in Abca4 knockout mice through inhibition of vitamin A dimerization
Charbel Issa, Peter; Barnard, Alun; Herrmann, Philipp; Washington, Ilyas; MacLaren, Robert.
PNAS 06/22/2015
Stargardt disease, an ATP-binding cassette, subfamily A, member 4 (ABCA4)-related retinopathy, is a genetic condition characterized by the accelerated accumulation of lipofuscin in the retinal pigment epithelium, degeneration of the neuroretina, and loss of vision. No approved treatment exists. Here, using a murine model of Stargardt disease, we show that the propensity of vitamin A to dimerize is responsible for triggering the formation of the majority of lipofuscin and transcriptional dysregulation of genes associated with inflammation. Data further demonstrate that replacing vitamin A with vitamin A deuterated at the carbon 20 position (C20- D3-vitamin A) impedes the dimerization rate of vitamin Aby approximately fivefold for the vitamin A dimer A2Eand subsequent lipofuscinogenesis and normalizes the aberrant transcription of complement genes without impairing retinal function. Phenotypic rescue by C20-D3-vitamin A was also observed noninvasively by quantitative autofluorescence, an imaging technique used clinically, in as little as 3 months after the initiation of treatment, whereas upon interruption of treatment, the age-related increase in autofluorescence resumed. Data suggest that C20-D3-vitamin A is a clinically amiable tool to inhibit vitamin A dimerization, which can be used to determine whether slowing the dimerization of vitamin A can prevent vision loss caused by Stargardt disease and other retinopathies associated with the accumulation of lipofuscin in the retina.
05/2014 C20-D3-Vitamin A (ALK-001) rescues the phenotype of an Abca4-/- mouse model of Stargardt disease
Charbel Issa, Peter; Barnard, Alun; Washington, Ilyas; MacLaren, Robert.
ARVO Podium Presentation, Orlando, May 7, 2014. Program #5015
Purpose: To investigate the effect of C20-D3-Vitamin A (ALK-001) on the phenotype of the Abca4-/- mouse Methods: Abca4-/- mice treated with ALK-001 for various amounts of time (3, 6, 7.5 and 9 months) were compared to untreated Abca4-/- mice and wild type (WT) controls reared on chow containing normal amounts of vitamin A. Quantitative fundus autofluorescence (AF) imaging and electroretinography (ERG) were assessed in vivo (n=10 per group) and assessment of bisretinoid (A2E) accumulation was then performed postmortem. Results: In all Abca4-/- mice that received ALK-001, lipofuscin-related fundus AF levels were significantly lower than in untreated Abca4-/- controls, in which AF levels were about twice those of WT controls at 9 months.The longer animals had stayed on ALK-001, the lower their AF signals. The most significant effect was observed in Abca4-/- mice maintained on ALK-001 for 9 months, with AF signals similar to those of untreated WT controls. When animals were crossed over from ALK-001 to normal chow, AF signals increased steeply. Absence of diet-related changes on scotopic and photopic ERG recordings between the same groups of 9 month-old animals indicated that ALK-001 was safe to the retina. Post-mortem analyses of eye cups revealed an about 8-fold increase of A2E in 9-month old Abca4-/- mice compared to WT controls, while treatment with ALK-001 from birth reduced bisretinoid concentration in eyes of Abca4-/- mice down to the levels measured in WT controls. Conclusions: These experiments confirm that an increase in the concentration of ocular A2E levels is paralleled by an increase in fundus AF intensity, and that treatment effects of C20-D3-vitamin A (ALK-001) in mice can be monitored with measurement of A2E and AF intensity. Finally, the results demonstrate that ALK-001 can be administered safely in mice and rescues the phenotype of a mouse model of Stargardt disease by reducing the rate of formation of autofluorescent materials in the eyes, without negatively affecting the ERG recordings.
07/2013 The retina rapidly incorporates ingested C20-D3-vitamin A in a swine model.
Doina M. Mihai, Hongfeng Jiang, William S. Blaner, Alexander Romanov, Ilyas Washington.
Molecular Vision 2013; 19:1677-1683.
Purpose: To determine how the retina uses vitamin A for vision, we studied the flux of oral vitamin A into and out of the swine retina. Methods: We administered labeled vitamin A to swine daily for 30 days and measured the percent of the labeled vitamin A to native unlabeled vitamin A in the retinal epithelium, neuroretina, plasma, liver, lung, and kidney. Results: We show that during normal vitamin A homeostasis, the retina rapidly assimilates newly ingested dietary vitamin A, which replaces native vitamin A. Retinal vitamin A is turned over faster than previously thought. Provitamin A carotenoids do not significantly contribute to retinal vitamin A pools when consuming diets adequate in vitamin A. Conclusions: Fast vitamin A turnover in the retina has direct implications for emerging therapies to prevent major forms of blindness based on controlling the concentrations of retinal vitamin A.
03/2011 Deuterium Enrichment of Vitamin A at the C20 Position Slows the Formation of Detrimental Vitamin A Dimers in Wild-type Rodents.
Kaufman Y, Ma L, Washington I.
Journal of Biological Chemistry 2011 Mar 11;286(10):7958-65.
Degenerative eye diseases are the most common causes of untreatable blindness. Accumulation of lipofuscin (granular deposits) in the retinal pigment epithelium (RPE) is a hallmark of major degenerative eye diseases such as Stargardt disease, Best disease, and age-related macular degeneration. The intrinsic reactivity of vitamin A leads to its dimerization and to the formation of pigments such as A2E, and is believed to play a key role in the formation of ocular lipofuscin. We sought a clinically pragmatic method to slow vitamin A dimerization as a means to elucidate the pathogenesis of macular degenerations and to develop a therapeutic intervention. We prepared vitamin A enriched with the stable isotope deuterium at carbon twenty (C20-D(3)-vitamin A). Results showed that dimerization of deuterium-enriched vitamin A was considerably slower than that of vitamin A at natural abundance as measured in vitro. Administration of C20-D(3)-vitamin A to wild-type rodents with no obvious genetic defects in vitamin A processing, slowed A2E biosynthesis. This study elucidates the mechanism of A2E biosynthesis and suggests that administration of C20-D(3)-vitamin A may be a viable, long-term approach to retard vitamin A dimerization and by extension, may slow lipofuscin deposition and the progression of common degenerative eye diseases.
03/2011 C20-D3-vitamin A Slows Lipofuscin Accumulation and Electrophysiological Retinal Degeneration in a Mouse Model of Stargardt Disease.
Ma L, Kaufman Y, Zhang J, Washington I.
Journal of Biological Chemistry 2011 Mar 11;286(10):7966-74. Epub 2010 Dec 14.
Stargardt disease, also known as juvenile macular degeneration, occurs in approximately one in 10,000 people and results from genetic defects in the ABCA4 gene. The disease is characterized by premature accumulation of lipofuscin in the retinal pigment epithelium (RPE) of the eye and by vision loss. No cure or treatment is available. Although lipofuscin is considered a hallmark of Stargardt disease, its mechanism of formation and its role in disease pathogenesis are poorly understood. In this work we investigated the effects of long-term administration of deuterium-enriched vitamin A, C20-D(3)-vitamin A, on RPE lipofuscin deposition and eye function in a mouse model of Stargardt disease. Results support the notion that lipofuscin forms partly as a result of the aberrant reactivity of vitamin A through the formation of vitamin A dimers, provide evidence that preventing vitamin A dimerization may slow disease related, retinal physiological changes and perhaps vision loss and suggest that administration of C20-D(3)-vitamin A may be a potential clinical strategy to ameliorate clinical symptoms resulting from ABCA4 genetic defects.