Norbixin Protects Retinal Pigmented Epithelium Cells and Photoreceptors against A2E-Mediated Phototoxicity In Vitro and In Vivo

Abstract

The accumulation of N-retinylidene-N-retinylethanolamine (A2E, a toxic by-product of the visual pigment cycle) in the retinal pigment epithelium (RPE) is a major cause of visual impairment in the elderly. Photooxidation of A2E results in retinal pigment epithelium degeneration followed by that of associated photoreceptors. Present treatments rely on nutrient supplementation with antioxidants. 9’-cis-Norbixin (a natural diapocarotenoid, 97% purity) was prepared from Bixa orellana seeds. It was first evaluated in primary cultures of porcine retinal pigment epithelium cells challenged with A2E and illuminated with blue light, and it provided an improved photo-protection as compared with lutein or zeaxanthin. In Abca4-/- Rdh8-/- mice (a model of dry AMD), intravitreally-injected norbixin maintained the electroretinogram and protected photoreceptors against light damage. In a standard rat blue-light model of photodamage, norbixin was at least equally as active as phenyl-N-tert-butylnitrone, a free radical spin-trap. Chronic experiments performed with Abca4-/- Rdh8-/- mice treated orally for 3 months with norbixin showed a reduced A2E accumulation in the retina. Norbixin appears promising for developing an oral treatment of macular degeneration. A drug candidate (BIO201) with 9’-cis-norbixin as the active principle ingredient is under development, and its potential will be assessed in a forthcoming clinical trial.

A2E induces the transactivation of RARs, PPARs and RXRs and its effects are counteracted by norbixin in retinal pigment epithelium cellsin vitro

“…Firstly, we confirmed our previously published results (24) showing approximately 80% photoprotection of RPE cells by 20 µM of norbixin following blue light exposure in presence of A2E ( Fig. 4A).…”

“…Since A2-PE and other A2E precursors, which are present in photoreceptor outer segments, are internalized during the same process, it could be hypothesized that LXRs may also play a role in the metabolism of A2E by RPE cells. We have shown previously that norbixin reduces A2E accumulation in vitro (24). The reduction of intracellular concentrations of A2E may affect the level of transactivation of RARs, RXRs and PPARs.…”

“…9'-cis-norbixin was prepared from 9'-cisbixin (AICABIX P, purity 92%) purchased from Aica-Color (Cusco, Peru) upon alkaline hydrolysis as previously described (24) and according to Santos et al (58). The obtained product (the 9'-cis isomer) showed an HPLC purity of 97% as confirmed by 1 H-nuclear magnetic resonance (using malonic acid as internal standard).…”

“…9'-cis-Norbixin (norbixin) is a 6,6'-diapo-carotenoid extracted from annatto (Bixa orellana) seeds (23). We have previously demonstrated that norbixin protects primary porcine RPE cells from phototoxicity induced by blue light illumination coupled with A2Eexposure in vitro (24). Moreover, norbixin reduces accumulation of A2E in RPE cells in vitro (24).…”

“…We have previously demonstrated that norbixin protects primary porcine RPE cells from phototoxicity induced by blue light illumination coupled with A2Eexposure in vitro (24). Moreover, norbixin reduces accumulation of A2E in RPE cells in vitro (24). Recently, it has been reported that norbixin is a PPAR-g ligand with agonist activity (25).…”