In today's digital age, our eyes are constantly facing challenges, and the health of the retina is a top priority. In our last blog post, we learned that retinitis pigmentosa can be prevented/delayed through dietary supplementation. Among them, there is a magical nutrient-beta-carotene, which is gradually entering people's vision, bringing hope for the prevention and improvement of retinitis pigmentosa.
Rhodopsin synthesis pathway
The synthesis of rhodopsin is the oxidation of vitamin A to complete trans-retinal, after which all-trans-retinal is oxidized to 11-cis retinal and opsin to form rhodopsin, where the conversion between vitamin A and retinal is reversible, but part of the retinal is consumed during the reaction and needs to rely on the supply of vitamin A in the blood. Vitamin A cannot be synthesized by the body and needs to be supplemented from food.
The main source of vitamin A dietary supplements on the market is all-trans carotene. However, in some patients with retinitis pigmentosa, the RPE65 enzyme gene in the all-trans retinaldehyde synthesis 11-cis-retinal pathway is mutated, which leads to the blockage of 11-cis-retinal synthesis.
9-Cis-beta-carotene improves retinopathy
Mechanism
Studies have shown that 9-cis-beta-carotene is oxidized to form 9-cis-retinal after entering the human body, which can replace 11-cis-retinal and free opsin to form heterorhodopsin, thereby preserving the structure and function of the photoreceptor. RPE65 participation is not required in this process.
Clinical research
Experiments showed that mice fed Dunaliella salina powder rich in 9-cis-beta-carotene showed higher dark adaptation and light adaptation, and the number of M-cone photoreceptor cells in the retina increased[1].
In addition to patients with RPE65 gene mutation, other patients with retinitis pigmentosa can also delay retinal function by oral administration of 9-cis-beta-carotene. Studies have shown that after oral administration of 9-cis-beta-carotene in patients with retinitis pigmentosa, the mean change in dark adaptive B-wave amplitude and percentage change in photoadaptive B-wave response relative to initial baseline was +8.4uV and +17.8uV respectively. Patients showed significant improvement in retinal function compared to placebo [2]. In addition, 9-cis-beta-carotene can improve vision and retinal function in patients with leukofundus night blindness.
In addition, 9-cis-beta-carotene has strong antioxidant capacity. Retina in the daily metabolism and light exposure process, will produce a large number of free radicals, these free radicals like a group of "little devils", wantonly destroy the structure and function of retinal cells, and 9-cis-beta-carotene by its own powerful antioxidant properties, neutralize free radicals, reduce oxidative damage, Thus to create a relatively stable and healthy environment for retinal cells, effectively prevent the occurrence of retinitis pigmentosa.
Reference：
[1]. Edelshtain V ,Peled A ,Tzameret A , et al. Long-term treatment with 9-cis-β-carotene rich alga Dunaliella bardawil ameliorates photoreceptor degeneration in a mouse model of retinoid cycle defect[J]. Algal Research,2019,43101607-101607.
[2]. Reuchamps M, Baudewyns P, Dandoy R, et al. Treatment With 9- cis β-Carotene–Rich Powder in Patients With Retinitis Pigmentosa: A Randomized Crossover Trial[J]. JAMA Ophthalmology, 2013, 131(8). PP1-8.