Positively Charged Retinoids Are Potent and Selective Inhibitors of the Trans-Cis Isomerization in the Retinoid (Visual) Cycle

• Published in: Proceedings of the National Academy of Sciences - PNAS 2005-06, Vol.102 (23), p.8162-8167
• Main Authors: Golczak, Marcin, Kuksa, Vladimir, Maeda, Tadao, Moise, Alexander R., Palczewski, Krzysztof, Dryja, Thaddeus P.
• Format: Article
• Language: English
• Subjects: Amides; Animals; Biological Sciences; Bleaching; Chromatography, Gel; Chromophores; cis-trans-Isomerases - antagonists & inhibitors; cis-trans-Isomerases - metabolism; Cytochrome P-450 Enzyme System - metabolism; Diterpenes - chemistry; Diterpenes - pharmacology; Enzymes; Esters; Inhibitor drugs; Isomerism; Isomerization; Isomers; Mice; Oximes; Photoreceptor Cells, Vertebrate - drug effects; Photoreceptor Cells, Vertebrate - metabolism; Photoreceptors; Receptors, Retinoic Acid - metabolism; Retina; Retinoic Acid 4-Hydroxylase; Retinoid X Receptors - metabolism; Retinoids; Retinoids - chemistry; Retinoids - pharmacology; Sensitivity and Specificity; Static Electricity; Substrate Specificity; Vertebrates; Vision, Ocular - drug effects; Vitamin A - analogs & derivatives; Vitamin A - chemistry; Vitamin A - metabolism
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.0503318102

In vertebrate retinal photoreceptors, photoisomerization of opsin-bound visual chromophore 11-cis-retinal to all-trans-retinal triggers phototransduction events. Regeneration of the chromophore is a critical step in restoring photoreceptors to their dark-adapted state. This regeneration process, called the retinoid cycle, takes place in the photoreceptor outer segments and in the retinal pigmented epithelium (RPE). We have suggested that the regeneration of the chromophore might occur through a retinyl carbocation intermediate. Here, we provide evidence that isomerization is inhibited by positively charged retinoids, which could act as transition state analogs of the isomerization process. We demonstrate that retinylamine ( Ret- NH2) potently and selectively inhibits the isomerization step of the retinoid cycle in vitro and in vivo. Ret- NH2binds a protein(s) in the RPE microsomes, but it does not bind RPE65, a protein implicated in the isomerization reaction. Although Ret- NH2inhibits the regeneration of visual chromophore in rods and, in turn, severely attenuates rod responses, it has a much smaller effect on cone function in mice. Ret- NH2interacts only at micromolar concentrations with retinoic acid receptor, does not activate retinoid-X receptor, and is not a substrate for CYP26s, the retinoic acid-metabolizing cytochrome P450 enzymes. Ret- NH2can be a significant investigational tool to study the mechanism of regeneration of visual chromophore.