Lea D. Marchette

Retinol dehydrogenase 12 detoxifies 4-hydroxynonenal in photoreceptor cells

Mutations of the photoreceptor retinol dehydrogenase 12 (RDH12) gene cause the early onset retinal dystrophy Leber congenital amaurosis (LCA) by mechanisms not completely resolved. Determining the physiological role of RDH12 in photoreceptors is the focus of this study. Previous studies showed that RDH12, and the closely related retinol dehydrogenase RDH11, can enzymatically reduce toxic lipid peroxidation products such as 4-hydroxynonenal (4-HNE), in vitro. To explore the significance of this activity, we investigated the ability of RDH11 and RDH12 to protect stably transfected HEK-293 cells against the toxicity of 4-HNE. Both enzymes protected against 4-HNE modification of proteins and 4-HNE-induced apoptosis in HEK-293 cells. In the retina, exposure to bright light induced lipid peroxidation, 4-HNE production, and 4-HNE modification of proteins in photoreceptor inner segments, where RDH11 and RDH12 are located. In mouse retina, RDH12-but not RDH11-protected against adduct formation, suggesting that 4-HNE is a physiological substrate of RDH12. RDH12-but not RDH11-also protected against light-induced apoptosis of photoreceptors. We conclude that in mouse retina RDH12 reduces 4-HNE to a nontoxic alcohol, protecting cellular macromolecules against oxidative modification and protecting photoreceptors from light-induced apoptosis. This activity is of particular significance to the understanding of the molecular mechanisms of RDH12-induced LCA.

Carcinine Has 4-Hydroxynonenal Scavenging Property and Neuroprotective Effect in Mouse Retina

PURPOSE Oxidative stress induces retinal damage and contributes to vision loss in progressive retinopathies. Carcinine (β-alanyl-histamine) is a natural imidazole-containing peptide derivative with antioxidant activity. It is predicted to scavenge 4-hydroxynonenal (4-HNE), a toxic product of lipid oxidation. The aim of this study was to confirm the 4-HNE scavenging effect and evaluate the neuroprotective effect of carcinine in mouse retina subjected to oxidative stress. METHODS HPLC coupled with mass spectrometry was used to analyze carcinine and 4-HNE-carcinine adduct. Protection of retinal proteins from modification by 4-HNE was tested by incubating carcinine with retinal protein extract and 4-HNE. Modified retinal proteins were quantified by dot-blot analysis. Mice were treated with carcinine (intravitreal injection and gavage) and exposed to bright light to induce oxidative damage in the retina. Photoreceptor degeneration was measured by histology and electroretinography. Retinal levels of retinol dehydrogenase 12 (RDH12) were measured by immunoblot analysis, after exposure to bright light and in retinal explants after exposure to 4-HNE. RESULTS The ability of carcinine to form an adduct with 4-HNE, as well as to prevent and even reverse the adduction of retinal proteins by the toxic aldehyde was demonstrated in vitro. Carcinine, administered by intravitreal injection or gavage, strongly protected mouse retina against light-induced photoreceptor degeneration and had a protective effect on RHD12, a protein found specifically in photoreceptor cells. CONCLUSIONS This study suggests that carcinine can be administered noninvasively to efficiently protect photoreceptor cells from oxidative damage. Carcinine could be administered daily to prevent vision loss in progressive retinopathies.

Mechanisms of RDH12-Induced Leber Congenital Amaurosis and Therapeutic Approaches

Retinal dystrophies are characterized by the degeneration of vision-supporting photoreceptor cells of the retina, leading to irreversible blindness. It is a heterogeneous group of diseases that can be caused by mutations on more than 150 identified genes with diverse functions (http://www.sph.uth.tmc.edu/Retnet/home.htm). Retinal dystrophies can be classified based on whether the rod or the cone photoreceptor cells are affected first, and based on the onset and progression of vision loss [1]. Leber congenital amaurosis (LCA) is in clear contrast with other inherited retinal dystrophies in that both rod and cone photoreceptor cells are affected from the onset of the disease [1]. The second major characteristic of LCA is that the progression to complete blindness is fast, making it the most devastating form of inherited retinal dystrophies [1]. In most cases, visual handicap is diagnosed before one year of age and progresses to legal blindness in early adulthood [2]. Other signs of the disease are an extinguished or severely reduced scotopic and photopic electroretinogram, absent or diminished pupillary response to light, and nystagmus (roaming eye movements) [3]. It is a rare disease, affecting approximately 1:30,000 people worldwide but it is the first cause of inherited blindness in children [2].