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Effects of emixustat hydrochloride in patients with proliferative diabetic retinopathy: a randomized, placebo-controlled phase 2 study. Graefes Arch Clin Exp Ophthalmol 2021; 259:369-378. [PMID: 32852613 PMCID: PMC7843479 DOI: 10.1007/s00417-020-04899-y] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/12/2020] [Revised: 07/29/2020] [Accepted: 08/16/2020] [Indexed: 01/18/2023] Open
Abstract
PURPOSE To evaluate the effects of oral emixustat hydrochloride on pro-angiogenic and inflammatory cytokines in the aqueous humor, as well as other ophthalmic parameters, in subjects with proliferative diabetic retinopathy (PDR). METHODS Twenty-three patients with PDR, with or without diabetic macular edema (DME), were assigned to emixustat or placebo in daily oral doses ranging from 5 to 40 mg over a step-up titration period, for 84 days. The main outcome measures included levels of IL-1β, IL-6, IL-8, TGFβ-1, and VEGF in the aqueous humor. RESULTS Seven of 12 subjects (58%) who were randomized to emixustat and 11 of 12 subjects (92%) who were randomized to placebo completed the study. No statistically significant differences between treatment groups were observed for changes in any of the aqueous humor cytokines tested. However, median VEGF levels were slightly reduced in the emixustat but not the placebo group (- 70.0 pg/mL versus + 42.7 pg/mL, or - 11.8% versus + 6.7%). In a post hoc analysis of all subjects (with or without DME), statistically significant differences between treatment arms in mean changes from baseline in central subfield thickness (CST; emixustat - 11.9 μm, placebo + 36.2 μm; P = 0.076) and total macular volume (TMV; emixustat - 0.13 mm3, placebo + 0.23 mm3; P = 0.026) were observed, both favoring emixustat. Emixustat's safety profile was consistent with prior studies (i.e., the adverse events of delayed dark adaptation and visual impairment were more common in subjects treated with emixustat). CONCLUSION Although this pilot study did not demonstrate statistically significant differences in changes in aqueous humor cytokine levels between the emixustat and placebo groups, VEGF levels were slightly reduced in the emixustat but not in the placebo group. In addition, statistically significant differences favoring the emixustat group were observed in CST and TMV among all subjects. These data warrant further investigation of emixustat's potential therapeutic effects in diabetic retinopathy. TRIAL REGISTRATION ClinicalTrials.gov identifier: NCT02753400 (April 2016).
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Kubota R, Calkins DJ, Henry SH, Linsenmeier RA. Emixustat Reduces Metabolic Demand of Dark Activity in the Retina. Invest Ophthalmol Vis Sci 2020; 60:4924-4930. [PMID: 31770432 DOI: 10.1167/iovs.19-28194] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
Abstract
Purpose In the dark, photoreceptor outer segments contain high levels of cyclic guanosine 3'-5' monophosphate (cGMP), which binds to ion channels, holding them open and allowing an influx of cations. Ion pumping activity, which balances cation influx, uses considerable amounts of adenosine triphosphate (ATP) and oxygen. Light reduces cation influx and thereby lowers metabolic demand. Blood vessels are compromised in the diabetic retina and may not be able to meet the higher metabolic demand in darkness. Emixustat is a visual cycle modulator (VCM) that reduces chromophore levels and, therefore, may mimic light conditions. We evaluated the effect of emixustat on oxygen consumption and cation influx in dark conditions. Methods Cation influx was measured in rats using Mn2+-magnetic resonance imaging (MEMRI). Retinal oxygen profiles were recorded to evaluate oxygen consumption. In the MEMRI protocol, animals were treated with either emixustat or vehicle. In the oxygen protocol, animals were untreated or treated with emixustat. Results In vehicle-treated animals, cation channel activity increased in the dark. Emixustat treatment reduced cation channel activity; activity was comparable to vehicle-treated controls in light conditions. In vehicle-treated animals, minimum retinal oxygen tension decreased as the retina recovered from a photobleach, indicating that more oxygen was being consumed. Emixustat treatment prevented the decrease in oxygen pressure after photobleach. Conclusions Emixustat reduced the cation influx and retinal oxygen consumption associated with dark conditions. VCMs are a promising potential treatment for ischemic retinal neovascularization, such as that in diabetic retinopathy.
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Affiliation(s)
- Ryo Kubota
- Acucela, Inc., Seattle, Washington, United States
| | - David J Calkins
- Department of Ophthalmology and Visual Sciences, Vanderbilt University Medical Center, Nashville, Tennessee, United States
| | | | - Robert A Linsenmeier
- Department of Biomedical Engineering, Northwestern University, Evanston, Illinois, United States.,Department of Neurobiology, Northwestern University, Evanston, Illinois, United States
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Chu B, Liu CH, Sengupta S, Gupta A, Raghu P, Hardie RC. Common mechanisms regulating dark noise and quantum bump amplification in Drosophila photoreceptors. J Neurophysiol 2013; 109:2044-55. [PMID: 23365183 DOI: 10.1152/jn.00001.2013] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Absolute visual thresholds are limited by "dark noise," which in Drosophila photoreceptors is dominated by brief (∼10 ms), small (∼2 pA) inward current events, occurring at ∼2/s, believed to reflect spontaneous G protein activations. These dark events were increased in rate and amplitude by a point mutation in myosin III (NINAC), which disrupts its interaction with the scaffolding protein, INAD. This phenotype mimics that previously described in null mutants of ninaC (no inactivation no afterpotential; encoding myosin III) and an associated protein, retinophilin (rtp). Dark noise was similarly increased in heterozygote mutants of diacylglycerol kinase (rdgA/+). Dark noise in ninaC, rtp, and rdgA/+ mutants was greatly suppressed by mutations of the Gq α-subunit (Gαq) and the major light-sensitive channel (trp) but not rhodopsin. ninaC, rtp, and rdgA/+ mutations also all facilitated residual light responses in Gαq and PLC hypomorphs. Raising cytosolic Ca(2+) in the submicromolar range increased dark noise, facilitated activation of transient receptor potential (TRP) channels by exogenous agonist, and again facilitated light responses in Gαq hypomorphs. Our results indicate that RTP, NINAC, INAD, and diacylglycerol kinase, together with a Ca(2+)-dependent threshold, share common roles in suppressing dark noise and regulating quantum bump generation; consequently, most spontaneous G protein activations fail to generate dark events under normal conditions. By contrast, quantum bump generation is reliable but delayed until sufficient G proteins and PLC are activated to overcome threshold, thereby ensuring generation of full-size bumps with high quantum efficiency.
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Affiliation(s)
- Brian Chu
- Department of Physiology, Development and Neuroscience, University of Cambridge, Cambridge, United Kingdom
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Bedolla DE, Torre V. A component of retinal light adaptation mediated by the thyroid hormone cascade. PLoS One 2011; 6:e26334. [PMID: 22039463 PMCID: PMC3200322 DOI: 10.1371/journal.pone.0026334] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/12/2011] [Accepted: 09/25/2011] [Indexed: 11/18/2022] Open
Abstract
Analysis with DNA-microrrays and real time PCR show that several genes involved in the thyroid hormone cascade, such as deiodinase 2 and 3 (Dio2 and Dio3) are differentially regulated by the circadian clock and by changes of the ambient light. The expression level of Dio2 in adult rats (2-3 months of age) kept continuously in darkness is modulated by the circadian clock and is up-regulated by 2 fold at midday. When the diurnal ambient light was on, the expression level of Dio2 increased by 4-8 fold and a consequent increase of the related protein was detected around the nuclei of retinal photoreceptors and of neurons in inner and outer nuclear layers. The expression level of Dio3 had a different temporal pattern and was down-regulated by diurnal light. Our results suggest that DIO2 and DIO3 have a role not only in the developing retina but also in the adult retina and are powerfully regulated by light. As the thyroid hormone is a ligand-inducible transcription factor controlling the expression of several target genes, the transcriptional activation of Dio2 could be a novel genomic component of light adaptation.
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Affiliation(s)
- Diana E. Bedolla
- Neurobiology Sector, International School for Advanced Studies (SISSA), Trieste, Italy
| | - Vincent Torre
- Neurobiology Sector, International School for Advanced Studies (SISSA), Trieste, Italy
- Italian Institute of Technology (IIT), SISSA-Unit, Trieste, Italy
- * E-mail:
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Sun H. Membrane receptors and transporters involved in the function and transport of vitamin A and its derivatives. Biochim Biophys Acta Mol Cell Biol Lipids 2011; 1821:99-112. [PMID: 21704730 DOI: 10.1016/j.bbalip.2011.06.010] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/04/2011] [Revised: 06/01/2011] [Accepted: 06/10/2011] [Indexed: 12/12/2022]
Abstract
The eye is the human organ most sensitive to vitamin A deficiency because of vision's absolute and heavy dependence on vitamin A for light perception. Studies of the molecular basis of vision have provided important insights into the intricate mechanistic details of the function, transport and recycling of vitamin A and its derivatives (retinoid). This review focuses on retinoid-related membrane receptors and transporters. Three kinds of mammalian membrane receptors and transporters are discussed: opsins, best known as vitamin A-based light sensors in vision; ABCA4, an ATP-dependent transporter specializes in the transport of vitamin A derivative; and STRA6, a recently identified membrane receptor that mediates cellular uptake of vitamin A. The evolutionary driving forces for their existence and the wide spectrum of human diseases associated with these proteins are discussed. Lessons learned from the study of the visual system might be useful for understanding retinoid biology and retinoid-related diseases in other organ systems as well. This article is part of a Special Issue entitled Retinoid and Lipid Metabolism.
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Affiliation(s)
- Hui Sun
- Department of Physiology, Jules Stein Eye Institute, Brian Research Institute, and Howard Hughes Medical Institute, David Geffen School of Medicine, University of California, Los Angeles, CA, USA.
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Maeda A, Maeda T, Imanishi Y, Sun W, Jastrzebska B, Hatala DA, Winkens HJ, Hofmann KP, Janssen JJ, Baehr W, Driessen CA, Palczewski K. Retinol dehydrogenase (RDH12) protects photoreceptors from light-induced degeneration in mice. J Biol Chem 2006; 281:37697-704. [PMID: 17032653 PMCID: PMC4124513 DOI: 10.1074/jbc.m608375200] [Citation(s) in RCA: 86] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
RDH12 has been suggested to be one of the retinol dehydrogenases (RDH) involved in the vitamin A recycling system (visual cycle) in the eye. Loss of function mutations in the RDH12 gene were recently reported to be associated with autosomal recessive childhood-onset severe retinal dystrophy. Here we show that RDH12 localizes to the photoreceptor inner segments and that deletion of this gene in mice slows the kinetics of all-trans-retinal reduction, delaying dark adaptation. However, accelerated 11-cis-retinal production and increased susceptibility to light-induced photoreceptor apoptosis were also observed in Rdh12(-/-) mice, suggesting that RDH12 plays a unique, nonredundant role in the photoreceptor inner segments to regulate the flow of retinoids in the eye. Thus, severe visual impairments of individuals with null mutations in RDH12 may likely be caused by light damage(1).
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Affiliation(s)
- Akiko Maeda
- Department of Pharmacology, Case Western Reserve University, Cleveland, Ohio 44106
| | - Tadao Maeda
- Department of Pharmacology, Case Western Reserve University, Cleveland, Ohio 44106
| | - Yoshikazu Imanishi
- Department of Pharmacology, Case Western Reserve University, Cleveland, Ohio 44106
| | - Wenyu Sun
- Department of Pharmacology, Case Western Reserve University, Cleveland, Ohio 44106
| | - Beata Jastrzebska
- Department of Pharmacology, Case Western Reserve University, Cleveland, Ohio 44106
| | - Denise A. Hatala
- Department of Ophthalmology, Case Western Reserve University, Cleveland, Ohio 44106
| | - Huub J. Winkens
- Department of Ophthalmology, University of Nijmegen, 6525 EX Nijmegen, The Netherlands
| | - Klaus Peter Hofmann
- Institut für Medizinische Physik und Biophysik, Universitätsklinikum Charité, Humboldt Universität zu Berlin, 10098 Berlin, Germany
| | - Jacques J. Janssen
- Department of Ophthalmology, University of Nijmegen, 6525 EX Nijmegen, The Netherlands
| | - Wolfgang Baehr
- Departments of Ophthalmology and Visual Sciences, Biology, and Neurobiology and Anatomy, University of Utah, Salt Lake City, Utah 84112
| | - Carola A. Driessen
- Department of Biochemistry, University of Nijmegen, 6525 EX Nijmegen, The Netherlands
| | - Krzysztof Palczewski
- Department of Pharmacology, Case Western Reserve University, Cleveland, Ohio 44106
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Liu C, Varnum MD. Functional consequences of progressive cone dystrophy-associated mutations in the human cone photoreceptor cyclic nucleotide-gated channel CNGA3 subunit. Am J Physiol Cell Physiol 2005; 289:C187-98. [PMID: 15743887 DOI: 10.1152/ajpcell.00490.2004] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Progressive cone dystrophies are a genetically heterogeneous group of disorders characterized by early deterioration of visual acuity and color vision, together with psychophysical and electrophysiological evidence of abnormal cone function and cone degeneration. Recently, three mutations in the gene encoding the CNGA3 subunit of cone photoreceptor cyclic nucleotide-gated (CNG) channels have been linked to progressive cone dystrophy in humans. To investigate the functional consequences of these mutations, we expressed mutant human CNGA3 subunits in Xenopus oocytes, alone or together with human CNGB3, and studied these channels using patch-clamp recording. Compared with wild-type channels, homomeric and heteromeric channels containing CNGA3-N471S or CNGA3-R563H subunits exhibited an increase in apparent affinity for cGMP and an increase in the relative agonist efficacy of cAMP compared with cGMP. In contrast, R277C subunits did not form functional homomeric or heteromeric channels. Cell surface expression levels, determined using confocal microscopy of green fluorescent protein-tagged subunits and patch-clamp recording, were significantly reduced for both R563H and R277C but unchanged for N471S. Overall, these results suggest that the plasma membrane localization and gating properties of cone CNG channels are altered by progressive cone dystrophy-associated mutations, providing evidence that supports the pathogenicity of these mutations.
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Affiliation(s)
- Chunming Liu
- Department of Veterinary and Comparative Anatomy, Pharmacology, and Physiology and Program in Neuroscience, Washington State University, PO Box 646520, Pullman, Washington 99164-6520, USA
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Hong S, Grossberg S. A neuromorphic model for achromatic and chromatic surface representation of natural images. Neural Netw 2004; 17:787-808. [PMID: 15288898 DOI: 10.1016/j.neunet.2004.02.007] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/13/2004] [Accepted: 02/13/2004] [Indexed: 12/01/2022]
Abstract
This study develops a neuromorphic model of human lightness perception that is inspired by how the mammalian visual system is designed for this function. It is known that biological visual representations can adapt to a billion-fold change in luminance. How such a system determines absolute lightness under varying illumination conditions to generate a consistent interpretation of surface lightness remains an unsolved problem. Such a process, called 'anchoring' of lightness, has properties including articulation, insulation, configuration, and area effects. The model quantitatively simulates such psychophysical lightness data, as well as other data such as discounting the illuminant, and lightness constancy and contrast effects. The model retina embodies gain control at retinal photoreceptors, and spatial contrast adaptation at the negative feedback circuit between mechanisms that model the inner segment of photoreceptors and interacting horizontal cells. The model can thereby adjust its sensitivity to input intensities ranging from dim moonlight to dazzling sunlight. A new anchoring mechanism, called the Blurred-Highest-Luminance-As-White rule, helps simulate how surface lightness becomes sensitive to the spatial scale of objects in a scene. The model is also able to process natural color images under variable lighting conditions, and is compared with the popular RETINEX model.
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Affiliation(s)
- Simon Hong
- Department of Cognitive and Neural Systems, Center for Adaptive Systems, Boston University, 677 Beacon Street, Boston, MA 02215, USA
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Abstract
"Bleaching desensitization" in rod photoreceptors refers to the prolonged depression of phototransduction sensitivity exhibited by rods after their exposure to bright light, i.e., after photolysis (bleaching) of a substantial fraction of rhodopsin in the outer segments. Rod recovery from bleaching desensitization depends critically on operation of the retinoid visual cycle: in particular, on the removal of all-trans retinal bleaching product from opsin and on the delivery of 11-cis retinal to opsin's chromophore binding site. The present paper summarizes representative findings that address the mechanism of bleaching desensitization.
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Affiliation(s)
- David R Pepperberg
- Department of Ophthalmology and Visual Sciences, Lions of Illinois Eye Research Institute, University of Illinois at Chicago, College of Medicine, 1855 W. Taylor Street, Chicago, IL 60612, USA.
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