retinol-acetate and Optic-Atrophy--Hereditary--Leber

Inactivating mutations in the retinoid isomerase (RPE65) or lecithin:retinol acyltransferase (LRAT) genes cause Leber congenital amaurosis (LCA), a severe visual impairment in humans. Both enzymes participate in the retinoid (visual) cycle, the enzymatic pathway that continuously generates 11-cis-retinal, the chromophore of visual pigments in rod and cone photoreceptor cells needed for vision. We investigated human RPE65-LCA patients and mice with visual cycle abnormalities to determine the impact of chronic chromophore deprivation on cones. Young patients with RPE65 mutations showed foveal cone loss along with shortened inner and outer segments of remaining cones; cone cell loss also was dramatic in young mice lacking Rpe65 or Lrat gene function. To selectively evaluate cone pathophysiology, we eliminated the rod contribution to electroretinographic (ERG) responses by generating double knockout mice lacking Lrat or Rpe65 together with an inactivated rod-specific G protein transducin gene (Gnat1-/-). Cone ERG responses were absent in Gnat1-/-Lrat-/- mice which also showed progressive degeneration of cones. Cone ERG responses in Gnat1-/-Rpe65-/- mice were markedly reduced and declined over weeks. Treatment of these mice with the artificial chromophore pro-drug, 9-cis-retinyl acetate, partially protected inferior retinal cones as evidenced by improved ERGs and retinal histochemistry. Gnat1-/- mice chronically treated with retinylamine, a selective inhibitor of RPE65, also showed a decline in the number of cones that was ameliorated by 9-cis-retinyl acetate. These results suggest that chronic lack of chromophore leads to progressive loss of cones in mice and humans. Therapy for LCA patients should be geared toward early adequate delivery of chromophore to cone photoreceptors.

Topics: Adaptor Proteins, Signal Transducing; Animals; Carrier Proteins; cis-trans-Isomerases; Diterpenes; Eye Proteins; GTP-Binding Protein alpha Subunits; Humans; Mice; Mice, Knockout; Optic Atrophy, Hereditary, Leber; Prodrugs; Retinal Cone Photoreceptor Cells; Retinaldehyde; Retinyl Esters; Transducin; Vitamin A

Leber congenital amaurosis (LCA), a heterogeneous early-onset retinal dystrophy, accounts for approximately 15% of inherited congenital blindness. One cause of LCA is loss of the enzyme lecithin:retinol acyl transferase (LRAT), which is required for regeneration of the visual photopigment in the retina.. An animal model of LCA, the Lrat-/- mouse, recapitulates clinical features of the human disease. Here, we report that two interventions--intraocular gene therapy and oral pharmacologic treatment with novel retinoid compounds--each restore retinal function to Lrat-/- mice. Gene therapy using intraocular injection of recombinant adeno-associated virus carrying the Lrat gene successfully restored electroretinographic responses to approximately 50% of wild-type levels (p < 0.05 versus wild-type and knockout controls), and pupillary light responses (PLRs) of Lrat-/- mice increased approximately 2.5 log units (p < 0.05). Pharmacological intervention with orally administered pro-drugs 9-cis-retinyl acetate and 9-cis-retinyl succinate (which chemically bypass the LRAT-catalyzed step in chromophore regeneration) also caused long-lasting restoration of retinal function in LRAT-deficient mice and increased ERG response from approximately 5% of wild-type levels in Lrat-/- mice to approximately 50% of wild-type levels in treated Lrat-/- mice (p < 0.05 versus wild-type and knockout controls). The interventions produced markedly increased levels of visual pigment from undetectable levels to 600 pmoles per eye in retinoid treated mice, and approximately 1,000-fold improvements in PLR and electroretinogram sensitivity. The techniques were complementary when combined.. Intraocular gene therapy and pharmacologic bypass provide highly effective and complementary means for restoring retinal function in this animal model of human hereditary blindness. These complementary methods offer hope of developing treatment to restore vision in humans with certain forms of hereditary congenital blindness.

Topics: Acyltransferases; Adenoviridae; Administration, Oral; Animals; Blindness; Disease Models, Animal; Diterpenes; Genetic Therapy; Genetic Vectors; Mice; Mice, Knockout; Molecular Sequence Data; Optic Atrophy, Hereditary, Leber; Prodrugs; Pupil; Retinal Pigments; Retinyl Esters; Vitamin A