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Gennadiy P Moiseyev, Younghwa Shin, Yusuke Takahashi, Jian-Xing (Jay) Ma; Fenofibrate is a competitive inhibitor of the RPE65 isomerase. Invest. Ophthalmol. Vis. Sci. 2016;57(12):1749.
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© 2017 Association for Research in Vision and Ophthalmology.
Fenofibrate, a drug originally developed to treat high cholesterol and triglycerides, has recently attracted a major attention as a novel medical treatment for diabetic retinopathy (DR). The mechanism for the benefits of fenofibrate in DR is not known. Recently, it has been shown that retinyl amine, retinoid visual cycle inhibitor, delayed the development of early DR lesions in diabetic mice. We hypothesized that fenofibrate may inhibit the visual cycle. To this end, we studied the effect of fenofibrate on the RPE65 isomerase activity.
All-trans-[3H]-retinol was used as a substrate to measure the activities of lecithin:retinol acyltransferase (LRAT) and isomerase in bovine RPE microsomes. Fenofibrate dissolved in dimethylformamide was added in a small volume (less than 2%) from the stock solution into the reaction mixture. The generated retinoids were extracted and analyzed by HPLC with a Radiomatic flow scintillation analyzer. To determine the inhibition mode of the fenofibrate, an adenoviral expression vector was used to express chicken RPE65 in 293A cells, and inhibition of RPE65 was measured in a liposome-based isomerase assay.
Fenofibrate showed a concentration-dependent inhibition of the isomerase activity as measured in bovine microsomes, with an IC50 of 90 µM. In the same reaction system, LRAT activity was not affected by fenofibrate at a concentration as high as 500 µM. To analyze the inhibition type, all-trans retinyl palmitate was incorporated in liposomes and used as a substrate for recombinant RPE65. The concentration dependence of the RPE65 reaction was measured in the absence and presence of fenofibrate. The Lineweaver-Burk plot demonstrated two lines crossing Y-axis at the same point suggesting that fenofibrate inhibits the retinoid isomerase reaction in a competitive manner. Analysis of these results yielded Ki = 42 ± 4 µM.
Fenofibrate potently and selectively inhibited conversion of all-trans-retinyl ester to 11-cis-retinol catalyzed by RPE65 isomerase. The competitive mode of the fenofibrate inhibition suggests that it is likely bound to the RPE65 active site. This inhibition may be used to slow down the visual cycle and to decrease the accumulation of A2E in the RPE indicating its therapeutic potential in Stargardt’s disease and age-related macular degeneration.
This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.
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